WorldWideScience

Sample records for symbiotic n2 fixation

  1. A single evolutionary innovation drives the deep evolution of symbiotic N2-fixation in angiosperms

    Science.gov (United States)

    Werner, Gijsbert D. A.; Cornwell, William K.; Sprent, Janet I.; Kattge, Jens; Kiers, E. Toby

    2014-01-01

    Symbiotic associations occur in every habitat on earth, but we know very little about their evolutionary histories. Current models of trait evolution cannot adequately reconstruct the deep history of symbiotic innovation, because they assume homogenous evolutionary processes across millions of years. Here we use a recently developed, heterogeneous and quantitative phylogenetic framework to study the origin of the symbiosis between angiosperms and nitrogen-fixing (N2) bacterial symbionts housed in nodules. We compile the largest database of global nodulating plant species and reconstruct the symbiosis’ evolution. We identify a single, cryptic evolutionary innovation driving symbiotic N2-fixation evolution, followed by multiple gains and losses of the symbiosis, and the subsequent emergence of ‘stable fixers’ (clades extremely unlikely to lose the symbiosis). Originating over 100 MYA, this innovation suggests deep homology in symbiotic N2-fixation. Identifying cryptic innovations on the tree of life is key to understanding the evolution of complex traits, including symbiotic partnerships. PMID:24912610

  2. Malic Enzyme Cofactor and Domain Requirements for Symbiotic N2 Fixation by Sinorhizobium meliloti▿ †

    Science.gov (United States)

    Mitsch, Michael J.; Cowie, Alison; Finan, Turlough M.

    2007-01-01

    The NAD+-dependent malic enzyme (DME) and the NADP+-dependent malic enzyme (TME) of Sinorhizobium meliloti are representatives of a distinct class of malic enzymes that contain a 440-amino-acid N-terminal region homologous to other malic enzymes and a 330-amino-acid C-terminal region with similarity to phosphotransacetylase enzymes (PTA). We have shown previously that dme mutants of S. meliloti fail to fix N2 (Fix−) in alfalfa root nodules, whereas tme mutants are unimpaired in their N2-fixing ability (Fix+). Here we report that the amount of DME protein in bacteroids is 10 times greater than that of TME. We therefore investigated whether increased TME activity in nodules would allow TME to function in place of DME. The tme gene was placed under the control of the dme promoter, and despite elevated levels of TME within bacteroids, no symbiotic nitrogen fixation occurred in dme mutant strains. Conversely, expression of dme from the tme promoter resulted in a large reduction in DME activity and symbiotic N2 fixation. Hence, TME cannot replace the symbiotic requirement for DME. In further experiments we investigated the DME PTA-like domain and showed that it is not required for N2 fixation. Thus, expression of a DME C-terminal deletion derivative or the Escherichia coli NAD+-dependent malic enzyme (sfcA), both of which lack the PTA-like region, restored wild-type N2 fixation to a dme mutant. Our results have defined the symbiotic requirements for malic enzyme and raise the possibility that a constant high ratio of NADPH + H+ to NADP in nitrogen-fixing bacteroids prevents TME from functioning in N2-fixing bacteroids. PMID:17071765

  3. Malic enzyme cofactor and domain requirements for symbiotic N2 fixation by Sinorhizobium meliloti.

    Science.gov (United States)

    Mitsch, Michael J; Cowie, Alison; Finan, Turlough M

    2007-01-01

    The NAD(+)-dependent malic enzyme (DME) and the NADP(+)-dependent malic enzyme (TME) of Sinorhizobium meliloti are representatives of a distinct class of malic enzymes that contain a 440-amino-acid N-terminal region homologous to other malic enzymes and a 330-amino-acid C-terminal region with similarity to phosphotransacetylase enzymes (PTA). We have shown previously that dme mutants of S. meliloti fail to fix N(2) (Fix(-)) in alfalfa root nodules, whereas tme mutants are unimpaired in their N(2)-fixing ability (Fix(+)). Here we report that the amount of DME protein in bacteroids is 10 times greater than that of TME. We therefore investigated whether increased TME activity in nodules would allow TME to function in place of DME. The tme gene was placed under the control of the dme promoter, and despite elevated levels of TME within bacteroids, no symbiotic nitrogen fixation occurred in dme mutant strains. Conversely, expression of dme from the tme promoter resulted in a large reduction in DME activity and symbiotic N(2) fixation. Hence, TME cannot replace the symbiotic requirement for DME. In further experiments we investigated the DME PTA-like domain and showed that it is not required for N(2) fixation. Thus, expression of a DME C-terminal deletion derivative or the Escherichia coli NAD(+)-dependent malic enzyme (sfcA), both of which lack the PTA-like region, restored wild-type N(2) fixation to a dme mutant. Our results have defined the symbiotic requirements for malic enzyme and raise the possibility that a constant high ratio of NADPH + H(+) to NADP in nitrogen-fixing bacteroids prevents TME from functioning in N(2)-fixing bacteroids.

  4. Use of low enriched 15N2 for symbiotic fixation tests

    International Nuclear Information System (INIS)

    Victoria, R.L.

    1975-01-01

    Gaseous atmospheres containing 15 N 2 with low enrichment were used to test symbiotic nitrogen fixation in beans (Phaseolus vulgari, L.). The tests of fixation in nodulated roots and the tests of fixation in the whole plant, in which the plants were placed inside a specially constructed growth chamber, gave positive results and suggest that the methodology used can be very helpfull in more detailed studies on symbiotic fixation. Samples of atmospheric air were purified by absorption of O 2 and CO 2 by two methods. The purified N 2 obtained was analysed and the results were compared. Samples of bean plant material were collected in natural conditions and analysed for 15 N natural variation. Several samples were prepared for 15 N isotopic analysis by two methods. The results obtained were compared. All samples were analysed in an Atlas-Varian Ch-4 model mass spectrometer, and the results were given in delta 15 N 0 / 00 variation in relation to a standard gas

  5. Grain yield, symbiotic N2 fixation and interspecific competition for inorganic N in pea-barley intercrops

    DEFF Research Database (Denmark)

    Jensen, E.S.

    1996-01-01

    g N-15-labeled N m(-2). The effect of intercropping on the dry matter and N yields, competition for inorganic N among the intercrop components, symbiotic fixation in pea and N transfer from pea to barley were determined. As an average of four years the grain yields were similar in monocropped pea...... only 9% of total fertilizer-N recovery in the intercrop. The amount of symbiotic N-2 fixation in the intercrop was less than expected from its composition and the fixation in monocrop. This indicates that the competition from barley had a negative effect on the fixation, perhaps via shading...... by the intercrop components, resulting in reduced competition for inorganic N, rather than a facilitative effect, in which symbiotically fixed N-2 is made available to barley....

  6. Genetic Factors in Rhizobium Affecting the Symbiotic Carbon Costs of N2 Fixation and Host Plant Biomass Production

    DEFF Research Database (Denmark)

    Skøt, L.; Hirsch, P. R.; Witty, J. F.

    1986-01-01

    The effect of genetic factors in Rhizobium on host plant biomass production and on the carbon costs of N2 fixation in pea root nodules was studied. Nine strains of Rhizobium leguminosarum were constructed, each containing one of three symbiotic plasmids in combination with one of three different...

  7. Short-range spatial variability of soil δ15N natural abundance – effects on symbiotic N2-fixation estimates in pea

    DEFF Research Database (Denmark)

    Holdensen, Lars; Hauggaard-Nielsen, Henrik; Jensen, Erik Steen

    2007-01-01

    abundance in spring barley and N2-fixing pea was measured within the 0.15-4 m scale at flowering and at maturity. The short-range spatial variability of soil δ15N natural abundance and symbiotic nitrogen fixation were high at both growth stages. Along a 4-m row, the δ15N natural abundance in barley......-abundance are that estimates of symbiotic N2-fixation can be obtained from the natural abundance method if at least half a square meter of crop and reference plants is sampled for the isotopic analysis. In fields with small amounts of representative reference crops (weeds) it might be necessary to sow in reference crop...

  8. NAD(P)+-malic enzyme mutants of Sinorhizobium sp. strain NGR234, but not Azorhizobium caulinodans ORS571, maintain symbiotic N2 fixation capabilities.

    Science.gov (United States)

    Zhang, Ye; Aono, Toshihiro; Poole, Phillip; Finan, Turlough M

    2012-04-01

    C(4)-dicarboxylic acids appear to be metabolized via the tricarboxylic acid (TCA) cycle in N(2)-fixing bacteria (bacteroids) within legume nodules. In Sinorhizobium meliloti bacteroids from alfalfa, NAD(+)-malic enzyme (DME) is required for N(2) fixation, and this activity is thought to be required for the anaplerotic synthesis of pyruvate. In contrast, in the pea symbiont Rhizobium leguminosarum, pyruvate synthesis occurs via either DME or a pathway catalyzed by phosphoenolpyruvate carboxykinase (PCK) and pyruvate kinase (PYK). Here we report that dme mutants of the broad-host-range Sinorhizobium sp. strain NGR234 formed nodules whose level of N(2) fixation varied from 27 to 83% (plant dry weight) of the wild-type level, depending on the host plant inoculated. NGR234 bacteroids had significant PCK activity, and while single pckA and single dme mutants fixed N(2) at reduced rates, a pckA dme double mutant had no N(2)-fixing activity (Fix(-)). Thus, NGR234 bacteroids appear to synthesize pyruvate from TCA cycle intermediates via DME or PCK pathways. These NGR234 data, together with other reports, suggested that the completely Fix(-) phenotype of S. meliloti dme mutants may be specific to the alfalfa-S. meliloti symbiosis. We therefore examined the ME-like genes azc3656 and azc0119 from Azorhizobium caulinodans, as azc3656 mutants were previously shown to form Fix(-) nodules on the tropical legume Sesbania rostrata. We found that purified AZC3656 protein is an NAD(P)(+)-malic enzyme whose activity is inhibited by acetyl-coenzyme A (acetyl-CoA) and stimulated by succinate and fumarate. Thus, whereas DME is required for symbiotic N(2) fixation in A. caulinodans and S. meliloti, in other rhizobia this activity can be bypassed via another pathway(s).

  9. Symbiotic N2 fixation in pea and field bean estimated by 15N fertilizer dilution in field experiments with barley as a reference crop

    DEFF Research Database (Denmark)

    Jensen, Erik Steen

    1986-01-01

    The total amount of nitrogen derived from symbiotic nitrogen fixation in two pea and one field bean cultivar, supplied with 50 kg N ha−1 at sowing (‘starter’-N), was estimated to 165, 136, and 186 kg N ha−1, respectively (three-year means). However, estimates varied considerably between the three...

  10. Pea-barley intercropping for efficient symbiotic N-2-fixation, soil N acquisition and use of other nutrients in European organic cropping systems

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Henrik; Gooding, M.; Ambus, Per

    2009-01-01

    Complementarity in acquisition of nitrogen (N) from soil and N-2-fixation within pea and barley intercrops was studied in organic field experiments across Western Europe (Denmark, United Kingdom, France, Germany and Italy). Spring pea and barley were sown either as sole crops, at the recommended...... recovery was greater in the pea-barley intercrops than in the sole Crops Suggesting a high degree of complementarity over a wide range of growing conditions. Complementarity was partly attributed to greater soil mineral N acquisition by barley, forcing pea to rely more on N-2-fixation. At all sites...

  11. Symbiotic N2-Fixation Estimated by the 15N Tracer Technique and Growth of Pueraria phaseoloides (Roxb.) Benth. Inoculated with Bradyrhizobium Strain in Field Conditions

    Science.gov (United States)

    Sarr, Papa Saliou; Okon, Judith Wase; Begoude, Didier Aime Boyogueno; Araki, Shigeru; Ambang, Zachée; Shibata, Makoto; Funakawa, Shinya

    2016-01-01

    This field experiment was established in Eastern Cameroon to examine the effect of selected rhizobial inoculation on N2-fixation and growth of Pueraria phaseoloides. Treatments consisted of noninoculated and Bradyrhizobium yuanmingense S3-4-inoculated Pueraria with three replications each. Ipomoea batatas as a non-N2-fixing reference was interspersed in each Pueraria plot. All the twelve plots received 2 gN/m2 of 15N ammonium sulfate 10% atom excess. At harvest, dry matter yields and the nitrogen derived from atmospheric N2-fixation (%Ndfa) of inoculated Pueraria were significantly (P < 0.05) higher (81% and 10.83%, resp.) than those of noninoculated Pueraria. The inoculation enhanced nodule dry weight 2.44-fold. Consequently, the harvested N significantly (P < 0.05) increased by 83% in inoculated Pueraria, resulting from the increase in N2-fixation and soil N uptake. A loss of 55 to 60% of the N fertilizer was reported, and 36 to 40% of it was immobilized in soil. Here, we demonstrated that both N2-fixing potential of P. phaseoloides and soil N uptake are improved through field inoculations using efficient bradyrhizobial species. In practice, the inoculation contributes to maximize N input in soils by the cover crop's biomass and represent a good strategy to improve soil fertility for subsequent cultivation. PMID:26904363

  12. Free atmospheric CO2 enrichment increased above ground biomass but did not affect symbiotic N2-fixation and soil carbon dynamics in a mixed deciduous stand in Wales

    Directory of Open Access Journals (Sweden)

    A. R. Smith

    2011-02-01

    Full Text Available Through increases in net primary production (NPP, elevated CO2 is hypothesized to increase the amount of plant litter entering the soil. The fate of this extra carbon on the forest floor or in mineral soil is currently not clear. Moreover, increased rates of NPP can be maintained only if forests can escape nitrogen limitation. In a Free atmospheric CO2 Enrichment (FACE experiment near Bangor, Wales, 4 ambient and 4 elevated [CO2] plots were planted with patches of Betula pendula, Alnus glutinosa and Fagus sylvatica on a former arable field. After 4 years, biomass averaged for the 3 species was 5497 (se 270 g m−2 in ambient and 6450 (se 130 g m−2 in elevated [CO2] plots, a significant increase of 17% (P = 0.018. During that time, only a shallow L forest floor litter layer had formed due to intensive bioturbation. Total soil C and N contents increased irrespective of treatment and species as a result of afforestation. We could not detect an additional C sink in the soil, nor were soil C stabilization processes affected by elevated [CO2]. We observed a decrease of leaf N content in Betula and Alnus under elevated [CO2], while the soil C/N ratio decreased regardless of CO2 treatment. The ratio of N taken up from the soil and by N2-fixation in Alnus was not affected by elevated [CO2]. We infer that increased nitrogen use efficiency is the mechanism by which increased NPP is sustained under elevated [CO2] at this site.

  13. Symbiosis revisited : Phosphorus and acid buffering stimulate N2 fixation but not Sphagnum growth

    NARCIS (Netherlands)

    Van Den Elzen, Eva; Kox, Martine A R; Harpenslager, Sarah F.; Hensgens, Geert; Fritz, Christian; Jetten, Mike S M; Ettwig, Katharina F.; Lamers, Leon P M

    2017-01-01

    In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands,

  14. Exploring the Boundaries of N2-Fixation in Cereals and Grasses: A Hypothetical and Experimental Framework

    NARCIS (Netherlands)

    Giller, K.E.; Merckx, R.

    2003-01-01

    Despite more than 40 years of research on free-living and endophytic bacteria associated with cereals and grasses, conclusive examples of impacts of non-symbiotic N2-fixation in agriculture are lacking. All available methods for measurement of N2-fixation associated with cereals and grasses have

  15. Symbiotic nitrogen fixation and nitrate uptake by the pea crop

    International Nuclear Information System (INIS)

    Jensen, E.S.

    1986-08-01

    Symbiotic nitrogen fixation and nitrate uptake by pea plants (Pisum sativum L.) were studied in field and pot experiments using the 15 N isotope dilution technique and spring barley as a non-fixing reference crop. Barley, although not ideal, seemed to be a suitable reference for pea in the 15 N-technique. Maximum N 2 fixation activity of 10 kg N fixed per ha per day was reached around the flat pod growth stage, and the activity decreased rapidly during pod-filling. The pea crop fixed between 100 and 250 kg N ha -1 , corresponding to from 45 to 80 per cent of total crop N. The amount of symbiotically fixed N 2 depended on the climatic conditions in the experimental year, the level of soil mineral N and the pea cultivar. Field-grown pea took up 60 to 70 per cent of the N-fertilizer supplied. The supply of 50 kg NO 3 -N ha -1 inhibited the N 2 fixation approximately 15 per cent. Small amounts of fertilizer N, supplied at sowing (starter-N), slightly stimulated the vegetative growth of pea, but the yields of seed dry matter and protein were not significantly influenced. In the present field experiments the environmental conditions, especially the distribution of rainfall during the growth season, seemed to be more important in determining the protein and dry matter yield of the dry pea crop, than the ability of pea to fix nitrogen symbiotically. However, fertilizer N supplied to pot-grown pea plants at the flat pod growth stage or as split applications significantly increased the yield of seed dry matter and protein. (author)

  16. Evaluation of the symbiotic nitrogen fixation in soybean by labelling of soil organic matter

    International Nuclear Information System (INIS)

    Ruschel, A.P.; Freitas, J.R. de; Vose, P.B.

    1982-01-01

    An experiment was carried out using the isotopic dilution method to evaluate symbiotic nitrogen fixation in soybean grown in soil labelled with 15 N enriched organic matter. Symbiotic N 2 -fixed was 71-76% of total N in the plant. Non nodulated soybean utilized 56-59% N from organic matter and 40% from soil. Roots of nodulated plants had lower NdN 2 than aereal plant parts. The advantage of using labelled organic matter as compared with 15 N-fertilizer addition in evaluating N 2 -fixation is discussed. (Author) [pt

  17. Eco-physiological responses and symbiotic nitrogen fixation ...

    African Journals Online (AJOL)

    Administrator

    2010-11-01

    Nov 1, 2010 ... Nitrogen nutrition of Hedysarum carnosum, a pastoral legume common in Tunisian central and southern rangelands ... Despite the fact that Na+ accumulation decreased plant growth, both nodulation and symbiotic nitrogen fixation capacity of H. ... of the symbiotic interaction as well as nodule development.

  18. Nitrogen cycling in summer active perennial grass systems in South Australia: Non-symbiotic nitrogen fixation

    NARCIS (Netherlands)

    Gupta, V.V.S.R.; Kroker, S.J.; Hicks, M.; Davoren, W.; Descheemaeker, K.K.E.; Llewellyn, R.

    2014-01-01

    Non-symbiotic nitrogen (N2) fixation by diazotrophic bacteria is a potential source for biological N inputs in non-leguminous crops and pastures. Perennial grasses generally add larger quantities of above- and belowground plant residues to soil, and so can support higher levels of soil biological

  19. N2 Fixation by Grain Legume Varieties as Affected By Rhizobia ...

    African Journals Online (AJOL)

    acer

    ABSTRACT: Rhizobium – legume symbiotic association contributes considerable amount of N in tropical soils. However, low rainfall and high temperature in Sudano-Sahelian region of Northeastern. Nigeria may affect the Rhizobial population in the soil. Therefore, the influence of Rhizobia inoculation on N2 fixation by ...

  20. Evaluation of natural 15N abundance method in estimating symbiotic dinitrogen fixation by leguminous grasses

    International Nuclear Information System (INIS)

    Yao Yunyin; Cheng Ming; Ma Changlin; Wang Zhidong; Hou Jinqin; Zhang Lihong; Luo Yongyun

    1991-01-01

    Natural 15 N abundance method was used to estimate contribution of symbiotic dinitrogen fixation by leguminous grasses. With the method the expensive 15 N fertilizer did not need to be applied to the soil and the normal ecosystem was not disturbed. Collecting samples of shoots of leguminous grasses and measuring the content of 15 N in them wee all to do for estimating potential of symbiotically fixed N 2 . Isotopic fractionation associated with N 2 fixation by legumes was studied. Values for 7 cultivars of alfalfa were ranged between 1.0000 ∼ 1.0015 (δ 15 N values were -0.05 ∼ 1.47 per mille); and the values for white clover, mung bean and whitepopinac lead tree were 0.0079, 0.9983 and 1.0018 (δ 15 N values: 2.15, 1.74 and -1.81 per mille) respectively. According to the δ 15 N values of grasses tested, the potential of N 2 fixation for 6 cultivars of alfalfa was estimated. Glory and rambler had higher potential of N 2 fixation; Baoding, Aigonquin and Minto had lower potential, and Peru was the lowest.N 2 fixing activity of alfalfa varied with different periods. The peak was found between June and July. Effects of non-N 2 -fixing references and different methods on estimates of %Ndfa of leguminous grasses were also discussed

  1. Role of symbiotic nitrogen fixation in the improvement of legume ...

    African Journals Online (AJOL)

    Role of symbiotic nitrogen fixation in the improvement of legume productivity under stressed environments. R Serraj, J Adu-Gyamfi. Abstract. No Abstract. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · http://dx.doi.org/10.4314/wajae.v6i1.45613.

  2. Symbiotic nitrogen fixation in a tropical rainforest: 15N natural abundance measurements supported by experimental isotopic enrichment.

    Science.gov (United States)

    Pons, Thijs L; Perreijn, Kristel; van Kessel, Chris; Werger, Marinus J A

    2007-01-01

    * Leguminous trees are very common in the tropical rainforests of Guyana. Here, species-specific differences in N(2) fixation capability among nodulating legumes growing on different soils and a possible limitation of N(2) fixation by a relatively high nitrogen (N) and low phosphorus (P) availability in the forest were investigated. * Leaves of 17 nodulating species and 17 non-nodulating reference trees were sampled and their delta(15)N values measured. Estimates of N(2) fixation rates were calculated using the (15)N natural abundance method. Pot experiments were conducted on the effect of N and P availability on N(2) fixation using the (15)N-enriched isotope dilution method. * Nine species showed estimates of > 33% leaf N derived from N(2) fixation, while the others had low or undetectable N(2) fixation rates. High N and low P availability reduced N(2) fixation substantially. * The results suggest that a high N and low P availability in the forest limit N(2) fixation. At the forest ecosystem level, N(2) fixation was estimated at c. 6% of total N uptake by the tree community. We conclude that symbiotic N(2) fixation plays an important role in maintaining high amounts of soil available N in undisturbed forest.

  3. Symbiotic N fixation of several soybean varieties and mutants

    International Nuclear Information System (INIS)

    Gandanegara, S.; Hendratno, K.

    1988-01-01

    Symbiotic N fixation of several soybean varieties and mutants. Research activities comprising of three experiments were carried out to screen several soybean varieties and mutants for symbiotic N fixation potential. Depending on the medium used, plant response to strains was different. In sterile medium, Rhizobium strain USDA 136, 142 and TAL 102 showed a high nitrogen potential. In soil only Rhizobium strain USDA 110 had better performance and proved to be competitive to the native strains. Nitrogen-15 dilution method was used to screen nitrogen fixing ability of several soybean varieties and mutants. Guntur variety showed a better response to high dose of N fertilizer without disturbance in its fixing ability. This variety then was considered good to be introduced in the cropping system. (author). 8 refs

  4. Screening with nuclear techniques for yield and N2 fixation in mung bean in Thailand

    International Nuclear Information System (INIS)

    Boonkerd, N.; Wadisrisuk, P.; Siripin, S.; Murakami, T.; Danso, S.K.A.

    1998-01-01

    For a farmer to reap benefit from mung bean's (Vigna radiata) capacity to fix N 2 , the crop's requirement for N must come mainly from the atmosphere through symbiotic fixation in the root nodules. The aim of this study was to evaluate recommended mung-bean cultivars and advanced breeding lines, and identify high fixers. Preliminary investigations with the 15 N natural-abundance method indicated its utility for measuring N 2 fixation, and the examination of five recommended cultivars and two advanced breeding lines of mung using the 15 N-dilution method showed diversity in N 2 fixation and yield. More than 400 lines of mung bean were screened in soil in cement containers for growth, nodulation, N accumulation and N 2 fixation at 35 days after planting, with the natural-abundance method used to determine N 2 fixation. Genetic variability was observed for all characteristics. Estimates of fixed N ranged from 0-300 mg N/plant. Whereas some lines obtained N mainly from fixation, recommended cultivars apparently obtained their N mainly from soil. The data are discussed in terms of reliability of the 15 N natural-abundance method

  5. Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

    Science.gov (United States)

    Batterman, Sarah A.; Hedin, Lars O.; van Breugel, Michiel; Ransijn, Johannes; Craven, Dylan J.; Hall, Jefferson S.

    2013-10-01

    Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2 may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N2), but it is unclear whether this functional group can supply the nitrogen needed as forests recover from disturbance or previous land use, or expand in response to rising CO2 (refs 6, 8). Here we identify a powerful feedback mechanism in which N2 fixation can overcome ecosystem-scale deficiencies in nitrogen that emerge during periods of rapid biomass accumulation in tropical forests. Over a 300-year chronosequence in Panama, N2-fixing tree species accumulated carbon up to nine times faster per individual than their non-fixing neighbours (greatest difference in youngest forests), and showed species-specific differences in the amount and timing of fixation. As a result of fast growth and high fixation, fixers provided a large fraction of the nitrogen needed to support net forest growth (50,000kg carbon per hectare) in the first 12years. A key element of ecosystem functional diversity was ensured by the presence of different N2-fixing tree species across the entire forest age sequence. These findings show that symbiotic N2 fixation can have a central role in nitrogen cycling during tropical forest stand development, with potentially important implications for the ability of tropical forests to sequester CO2.

  6. Plant densities and modulation of symbiotic nitrogen fixation in soybean

    Directory of Open Access Journals (Sweden)

    Marcos Javier de Luca

    2014-06-01

    Full Text Available Soybean nitrogen (N demands can be supplied to a large extent via biological nitrogen fixation, but the mechanisms of source/sink regulating photosynthesis/nitrogen fixation in high yielding cultivars and current crop management arrangements need to be investigated. We investigated the modulation of symbiotic nitrogen fixation in soybean [Glycine max (L. Merrill] at different plant densities. A field trial was performed in southern Brazil with six treatments, including non-inoculated controls without and with N-fertilizer, both at a density of 320,000 plants ha−1, and plants inoculated with Bradyrhizobium elkanii at four densities, ranging from 40,000 to 320,000 plants ha−1. Differences in nodulation, biomass production, N accumulation and partition were observed at stage R5, but not at stage V4, indicating that quantitative and qualitative factors (such as sunlight infrared/red ratio assume increasing importance during the later stages of plant growth. Decreases in density in the inoculated treatments stimulated photosynthesis and nitrogen fixation per plant. Similar yields were obtained at the different plant densities, with decreases only at the very low density level of 40,000 plants ha−1, which was also the only treatment to show differences in seed protein and oil contents. Results confirm a fine tuning of the mechanisms of source/sink, photosynthesis/nitrogen fixation under lower plant densities. Higher photosynthesis and nitrogen fixation rates are capable of sustaining increased plant growth.

  7. N-2 fixation by non-heterocystous cyanobacteria

    NARCIS (Netherlands)

    Bergman, B.; Gallon, J.R.; Rai, A.N.; Stal, L.J.

    1997-01-01

    Many, though not all, non-heterocystous cyanobacteria can fix N-2. However, very few strains can fix N-2 aerobically. Nevertheless, these organisms may make a substantial contribution to the global nitrogen cycle. In this general review, N-2 fixation by laboratory cultures and natural populations of

  8. Asparagine: an amide of particular distinction in the regulation of symbiotic nitrogen fixation of legumes.

    Science.gov (United States)

    Sulieman, Saad; Tran, Lam-Son Phan

    2013-09-01

    Symbiotic nitrogen fixation is tightly regulated by a range of fine processes at the nodule level, over which the host plant has overall control through the whole life of the plant. The operation of this control at the nodule level is not yet fully understood, but greater knowledge will ultimately lead to a better improvement of N2 fixation through the use of crop legumes and genetic engineering of crop plants for higher performance. It has been suggested that, nodule responses to the nutritional complexity of the rhizosphere environment involve a great deal of coordination of sensing and signal transduction. This regulation can be achieved through several mechanisms, including changes in carbon metabolism, oxygen supply and/or overproduction of reactive oxygen and nitrogen species. Recently, the cycling of amino acids observed between the plant and bacteroid fractions suggests a new and important regulatory mechanism involved in nodule responses. Most of the recent transcriptional findings are consistent with the earlier biochemical and physiological reports. Current research revealed unique advances for nodule metabolism, especially on the regulation of asparagine synthetase gene expression and the control of asparagine (ASN) to N2 fixing activity. A large amount of ASN is found accumulating in the root nodules of the symbiotic plants under restricted environments, such as drought, salinity and nutrient deficiency. Exceptionally, ASN phloem feeding has resulted in an increased concentration of the ASN amide in nodules followed by a remarkable decrease in nodule activity. In this review, recent progress concerning the possible role of ASN in whole-plant-based down-regulation of symbiotic N2 fixation will be reviewed.

  9. Nodulation and N2 fixation effectiveness of Bradyrhizobium strains in symbiosis with Adzuki Bean, Vigna angularis

    Directory of Open Access Journals (Sweden)

    Dušica Delić

    2010-04-01

    Full Text Available In pot experiment, one isolate Knj from a Serbian soil, four strains of Bradyrhizobium japonicum and three strains of Bradyrhizobium spp. were examined for the effect on adzuki bean nodulation and effectiveness in symbiotic N2 fixation. All the tested strains produced root nodules in adzuki bean. Strains of B. japonicum showed high potential of N2 fixation, particularly 525 and 542. B. japonicum strains resulted 65-71% shoot dry weight and 99-138% total N content of uninoculated control with full N content (100%. No significant difference was found between the plants inoculated with Bradyrhizobium spp. strains and uninoculated control plants without N (40-42 and 42% shoot dry weight, respectively, which indicated symbiotic N2 fixation inactivity of the Bradyrhizobium spp. strains. Knj strain had the middle position (56% shoot dry weight. These data showed that B. japonicum 525 and 542 strains could be used in further investigations in order to apply them as inoculants in microbiological N fertilizers.

  10. Drought enhances symbiotic dinitrogen fixation and competitive ability of a temperate forest tree.

    Science.gov (United States)

    Wurzburger, Nina; Miniat, Chelcy Ford

    2014-04-01

    General circulation models project more intense and frequent droughts over the next century, but many questions remain about how terrestrial ecosystems will respond. Of particular importance, is to understand how drought will alter the species composition of regenerating temperate forests wherein symbiotic dinitrogen (N2)-fixing plants play a critical role. In experimental mesocosms we manipulated soil moisture to study the effect of drought on the physiology, growth and competitive interactions of four co-occurring North American tree species, one of which (Robinia pseudoacacia) is a symbiotic N2-fixer. We hypothesized that drought would reduce growth by decreasing stomatal conductance, hydraulic conductance and increasing the water use efficiency of species with larger diameter xylem vessel elements (Quercus rubra, R. pseudoacacia) relative to those with smaller elements (Acer rubrum and Liriodendron tulipifera). We further hypothesized that N2 fixation by R. pseudoacacia would decline with drought, reducing its competitive ability. Under drought, growth declined across all species; but, growth and physiological responses did not correspond to species' hydraulic architecture. Drought triggered an 80% increase in nodule biomass and N accrual for R. pseudoacacia, improving its growth relative to other species. These results suggest that drought intensified soil N deficiency and that R. pseudoacacia's ability to fix N2 facilitated competition with non-fixing species when both water and N were limiting. Under scenarios of moderate drought, N2 fixation may alleviate the N constraints resulting from low soil moisture and improve competitive ability of N2-fixing species, and as a result, supply more new N to the ecosystem.

  11. Assessing N2 fixation in estuarine mangrove soils

    Science.gov (United States)

    Shiau, Yo-Jin; Lin, Ming-Fen; Tan, Chen-Chung; Tian, Guanglong; Chiu, Chih-Yu

    2017-04-01

    Nitrogen (N) limited mangrove forest may have a high potential for microbial N2 fixation. Previous research has focused on soil nitrogenase activity in pristine mangrove forests with little anthropogenic impact. This research was designed to evaluate the magnitude of nitrogenase activity of mangrove soils in a high anthropogenic N-loading environment and the way in which soil N2 fixation in mangrove forest may be related to organic carbon and salinity. The test involved an acetylene reduction method under controlled laboratory conditions. The mangrove forests with high anthropogenic N loading may have high nitrogenase activity in the soils. The diazotrophs in these mangrove soils were mostly heterotrophs and the sulfate-reducing bacteria were the major N2-fixing bacteria. The nitrogenase activity was little affected by the soil salinity, which suggests that these groups of N2 fixation bacteria adapted well to saline conditions in the estuary.

  12. Biological N2 fixation mainly controlled by Sphagnum tissue N:P ratio in ombrotrophic bogs

    Science.gov (United States)

    Zivkovic, Tatjana; Moore, Tim R.

    2017-04-01

    Most of the 18 Pg nitrogen (N) accumulated in northern nutrient-poor and Sphagnum-dominated peatlands (bogs and fens) can be attributed to N2-fixation by diazotrophs either associated with the live Sphagnum or non-symbiotically in the deeper peat such as through methane consumption close to the water table. Where atmospheric N deposition is low (Sphagnum, suggested by the increase in tissue N:P to >16. It is unclear how Sphagnum-hosted diazotrophic activity may be affected by N deposition and thus changes in N:P ratio. First, we investigated the effects of long-term addition of different sources of nitrogen (0, 1.6, 3.2 and 6.4 g N m-2 y-1as NH4Cl and NaNO3), and phosphorus (5 g P m-2 y-1as KH2PO4) on Sphagnum nutrient status (N, P and N:P ratio), net primary productivity (NPP) and Sphagnum-associated N2fixation at Mer Bleue, a temperate ombrotrophic bog. We show that N concentration in Sphagnum tissue increased with larger rates of N addition, with a stronger effect on Sphagnum from NH4 than NO3. The addition of P created a 3.5 fold increase in Sphagnum P content compared to controls. Sphagnum NPP decreased linearly with the rise in N:P ratio, while linear growth declined exponentially with increase in Sphagnum N content. Rates of N2-fixation determined in the laboratory significantly decreased in response to even the smallest addition of both N species. In contrast, the addition of P increased N2 fixation by up to 100 times compared to N treatments and up to 5-30 times compared to controls. The change in N2-fixation was best modeled by the N:P ratio, across all experimental treatments. Secondly, to test the role of N:P ratio on N2-fixation across a range of bogs, eight study sites along the latitudinal gradient from temperate, boreal to subarctic zone in eastern Canada were selected. From each bog, two predominant microptopographies, hummocks and hollows, were tested for both N2-fixation activity in the laboratory and Sphagnum tissue concentrations of N, P and N

  13. Symbiosis revisited: phosphorus and acid buffering stimulate N2 fixation but not Sphagnum growth

    Science.gov (United States)

    van den Elzen, Eva; Kox, Martine A. R.; Harpenslager, Sarah F.; Hensgens, Geert; Fritz, Christian; Jetten, Mike S. M.; Ettwig, Katharina F.; Lamers, Leon P. M.

    2017-03-01

    In pristine Sphagnum-dominated peatlands, (di)nitrogen (N2) fixing (diazotrophic) microbial communities associated with Sphagnum mosses contribute substantially to the total nitrogen input, increasing carbon sequestration. The rates of symbiotic nitrogen fixation reported for Sphagnum peatlands, are, however, highly variable, and experimental work on regulating factors that can mechanistically explain this variation is largely lacking. For two common fen species (Sphagnum palustre and S. squarrosum) from a high nitrogen deposition area (25 kg N ha-1 yr-1), we found that diazotrophic activity (as measured by 15 - 15N2 labeling) was still present at a rate of 40 nmol N gDW-1 h-1. This was surprising, given that nitrogen fixation is a costly process. We tested the effects of phosphorus availability and buffering capacity by bicarbonate-rich water, mimicking a field situation in fens with stronger groundwater or surface water influence, as potential regulators of nitrogen fixation rates and Sphagnum performance. We expected that the addition of phosphorus, being a limiting nutrient, would stimulate both diazotrophic activity and Sphagnum growth. We indeed found that nitrogen fixation rates were doubled. Plant performance, in contrast, did not increase. Raised bicarbonate levels also enhanced nitrogen fixation, but had a strong negative impact on Sphagnum performance. These results explain the higher nitrogen fixation rates reported for minerotrophic and more nutrient-rich peatlands. In addition, nitrogen fixation was found to strongly depend on light, with rates 10 times higher in light conditions suggesting high reliance on phototrophic organisms for carbon. The contrasting effects of phosphorus and bicarbonate on Sphagnum spp. and their diazotrophic communities reveal strong differences in the optimal niche for both partners with respect to conditions and resources. This suggests a trade-off for the symbiosis of nitrogen fixing microorganisms with their Sphagnum

  14. Benthic N2 fixation in coral reefs and the potential effects of human-induced environmental change

    Science.gov (United States)

    Cardini, Ulisse; Bednarz, Vanessa N; Foster, Rachel A; Wild, Christian

    2014-01-01

    Tropical coral reefs are among the most productive and diverse ecosystems, despite being surrounded by ocean waters where nutrients are in short supply. Benthic dinitrogen (N2) fixation is a significant internal source of “new” nitrogen (N) in reef ecosystems, but related information appears to be sparse. Here, we review the current state (and gaps) of knowledge on N2 fixation associated with coral reef organisms and their ecosystems. By summarizing the existing literature, we show that benthic N2 fixation is an omnipresent process in tropical reef environments. Highest N2 fixation rates are detected in reef-associated cyanobacterial mats and sea grass meadows, clearly showing the significance of these functional groups, if present, to the input of new N in reef ecosystems. Nonetheless, key benthic organisms such as hard corals also importantly contribute to benthic N2 fixation in the reef. Given the usually high coral coverage of healthy reef systems, these results indicate that benthic symbiotic associations may be more important than previously thought. In fact, mutualisms between carbon (C) and N2 fixers have likely evolved that may enable reef communities to mitigate N limitation. We then explore the potential effects of the increasing human interferences on the process of benthic reef N2 fixation via changes in diazotrophic populations, enzymatic activities, or availability of benthic substrates favorable to these microorganisms. Current knowledge indicates positive effects of ocean acidification, warming, and deoxygenation and negative effects of increased ultraviolet radiation on the amount of N fixed in coral reefs. Eutrophication may either boost or suppress N2 fixation, depending on the nutrient becoming limiting. As N2 fixation appears to play a fundamental role in nutrient-limited reef ecosystems, these assumptions need to be expanded and confirmed by future research efforts addressing the knowledge gaps identified in this review. PMID:24967086

  15. Novel Lipid Biomarkers for Past Oceanic N2 Fixation

    Science.gov (United States)

    Bale, N. J.; Hopmans, E. C.; Villareal, T. A.; Zell, C. I.; Sinninghe Damsté, , J.; Schouten, S.

    2014-12-01

    Nitrogen-fixing cyanobacteria play important roles in the biogeochemical cycles of aquatic systems. Both heterocystous and non-heterocystous N2-fixing cyanobacteria are symbiotic with marine diatoms and thrive in low nutrient environments. These associations are significant exporters of carbon to the deep-sea, but suitable tracers for reconstructing their importance in past environments are lacking. We recently analyzed the heterocyst glycolipids (HGs) of the heterocystous Richelia intracellularis symbiont of the marine diatoms Hemiaulus hauckii and H. membranaceus and found unique C5 glycolipids with C30-32 carbon chains, a structure different from the C6 glycolipids detected in freshwater heterocystous cyanobacteria. We developed a high performance liquid chromatography/ multiple reaction monitoring mass spectrometry (HPLC/MS) method specific for trace analysis of long chain C5 HGs and applied it to suspended particulate matter (SPM) and surface sediment from the Amazon plume, a region known to harbor marine diatoms carrying heterocystous cyanobacteria as endosymbionts. C5 HGs were detected in both SPM and sediments demonstrating their biomarker potential. They were not detected in SPM or sediment from freshwater settings in the region. Rather, limnetic SPM and sediments contained C6 HGs which are established biomarkers for free-living heterocystous cyanobacteria. Glycolipids have been found preserved in sediments of up to 49 Ma old. Our development of the C5 biomarkers has the potential to improve our knowledge of the contribution of symbiotic cyanobacteria to the paleo-N-cycle.

  16. Breeding for high N2 fixation in groundnut and soybean in Viet Nam

    International Nuclear Information System (INIS)

    Nguyen Xuan Hong

    1998-01-01

    Groundnut (Arachis hypogaea L.) and soybean (Glycine max (L.) Mer.) are grown mainly on two types of soil in Viet Nam: coastal-sandy and upland-degraded soils. These soils are deficient in N, and considering that fertilizer N is not only costly to farmers but also a threat to the environment, it is important to maximize productivity by exploiting the ability of these legumes to fix N 2 symbiotically in their root nodules. We initiated programmes of breeding and selection to combine high N 2 fixation and high grain-yielding capacity. In the spring of 1992, breeding lines of groundnut and soybean were tested under greenhouse conditions for varietal differences in the capacity to fix N 2 using the acetylene reduction assay and the 15 N-dilution technique, with upland rice as reference plants. Varietal differences were found in nitrogenase activity, and percent N derived from fixation (%Ndfa) ranged from 11 to 63% for groundnut and from 9 to 79% for soybean. Field experiments in the autumn-winter season of 1992 again revealed significant varietal differences; %Ndfa ranged from 36 to 56% for groundnut and from 28 to 58% for soybean. Gamma-irradiated seeds of soybean were propagated in bulk from M 1 to M 4 . Five high-yielding mutant lines of both species were selected from the M 5 populations, and N 2 fixation was estimated using the 15 N-dilution technique. The average values for %Ndfa of the mutants were 55 and 57%, significant improvements over the parent-cultivar values of 25 and 29% for soybean and groundnut, respectively

  17. Fixating on metals: new insights into the role of metals in nodulation and symbiotic nitrogen fixation.

    Science.gov (United States)

    González-Guerrero, Manuel; Matthiadis, Anna; Sáez, Ángela; Long, Terri A

    2014-01-01

    Symbiotic nitrogen fixation is one of the most promising and immediate alternatives to the overuse of polluting nitrogen fertilizers for improving plant nutrition. At the core of this process are a number of metalloproteins that catalyze and provide energy for the conversion of atmospheric nitrogen to ammonia, eliminate free radicals produced by this process, and create the microaerobic conditions required by these reactions. In legumes, metal cofactors are provided to endosymbiotic rhizobia within root nodule cortical cells. However, low metal bioavailability is prevalent in most soils types, resulting in widespread plant metal deficiency and decreased nitrogen fixation capabilities. As a result, renewed efforts have been undertaken to identify the mechanisms governing metal delivery from soil to the rhizobia, and to determine how metals are used in the nodule and how they are recycled once the nodule is no longer functional. This effort is being aided by improved legume molecular biology tools (genome projects, mutant collections, and transformation methods), in addition to state-of-the-art metal visualization systems.

  18. The effect of soil carbon on symbiotic nitrogen fixation and symbiotic ...

    African Journals Online (AJOL)

    Soil organic carbon (SOC) is the main attribute of high-quality soil. The amount of nitrogen fixed by Rhizobium symbiotically with Trifolium repens (white clover) is ultimately determined by the quality of the soil environment. The effect of SOC on the total number of symbiotic and saprophytic rhizobia was determined.

  19. Measurement of symbiotic nitrogen-fixation in leguminous host-plants grown in heavy metal-contaminated soils amended with sewage sludge.

    Science.gov (United States)

    Obbard, J P; Jones, K C

    2001-01-01

    Rates of nitrogen fixation by Rhizobium in symbiosis with leguminous host-plants including white clover, broad bean and peas have been established in soils that have been amended experimentally with heavy metal-contaminated sewage sludges. Results from 15N-dilution experiments for the measurement of N2 fixation have shown that adverse heavy metal effects are apparent on symbiotic N2 fixation rates for white clover grown in inter-specific competition with ryegrass under mixed sward conditions, compared to white clover grown in pure sward. Further experiments on broad bean and pea indicated a significant, but minor-inhibitory metal-related effect on the rate of N2 fixation compared to untreated soils and soils amended with a relatively uncontaminated sludge. The implications of the results with respect to sludge utilisation in agriculture are discussed.

  20. Genotypic Variation for N2-FIXATION in Voandzou (vigna Subterranea) Under P Deficiency and P Sufficiency

    Science.gov (United States)

    Andry, A.; Mahamadou, M.; Lilia, R.; Laurie, A.; Hélène, V.; Dominique, M.; Christian, M.; Jean-Jacques, D.

    2011-12-01

    Genetic variation associated with N2 fixation exists in numerous legume species (Graham, 2004). High symbiotic N2 fixation under P deficiency is related closely to nodulation which was used in legume selection for N2 fixation (Herridge and Rose, 2000). Until now, study of genetic potential of neglected crops like Vigna subterranea (bambara groundnut or voandzou) is often limited while its agronomic properties is interesting for the farmers of Africa. In order to assess the genotypic variation of voandzou for tolerance to phosphorus deficiency, a physiological approach of cultivar selection was performed with 54 cultivars from Madagascar, Niger and Mali in hydroponic culture under P deficiency and P sufficiency and inoculated with the reference strain of Bradyrhizobium sp. Vigna CB756. The results of nodulation and plant biomass, which are closely related, showed a large dispersion between cultivars (0.05-0.43 g nodule dry weight per plant and 0.50-5.51 g shoot dry weight per plant). The cultivars which presented the maximum growth during the experiment presented a high efficiency in use of the rhizobial symbiosis calculated as the slope of plant biomass regression as a function of nodulation. A large increase in nodulated-root O2 consumption under P deficiency was observed for the two most tolerant cultivars. The microscopic analysis with in situ RT-PCR of the nodule sections showed an increase of a phytase gene expression with tolerance of cultivars to P deficiency. From two most contrasting cultivars, an isotopic exchange method 32P was carried out on rhizosphere soil in rhizotron culture in order to assess the direct effect induced by the roots in terms of phosphorus mobilization. The rhizospheric effect was observed under P deficiency marked by a strong re-supplying capacity of soil solution in the diffusive phosphate ion between solid phase and soil solution leading to great phosphorus nutrition. These results highlight the genotypic variability among voandzou

  1. Efectos del fósforo y carbono lábiles en la fijación no simbiótica de N2 en hojarasca de bosques siempreverdes manejados y no manejados de la Isla de Chiloé, Chile Effects of labile phosphorous and carbón on non-symbiotic N2 fixation in logged and unlogged evergreen forests in Chiloé Island, Chile

    Directory of Open Access Journals (Sweden)

    SANDRA E PÉREZ

    2008-06-01

    Full Text Available El flujo de entrada de nitrógeno (N en ecosistemas de bosques templados de la Isla de Chiloé puede ocurrir en una proporción importante vía fijación no simbiótica (FNS. Debido a que este proceso es llevado a cabo por bacterias (diazótrofas está regulado, además del efecto de factores climáticos (temperatura y humedad, por la disponibilidad de nutrientes, en particular fósforo y carbono como fuentes de energía. Nuestra hipótesis es que si el fósforo y el carbono son limitantes para la FNS, esta limitación se acentuaría en bosques manejados, en donde adición experimental de P y C deberían estimular la actividad microbiana. En este trabajo se determinó los efectos de la adición de cuatro niveles de fósforo inorgánico (0 mmol P/L, 0,645 mmol P/L, 3,23 mmol P/L y 6,45 mmol P/L y cuatro niveles de carbono lábil como glucosa (0 mmol P/L, 23,3 mmol C/L, 46,6 mmol C/L y 70 mmol C/L, en la FNS de N2 de hojarasca homogenizada de cada bosque, en condiciones controladas de temperatura y humedad, en experimentos de laboratorio. Se estudiaron bosques de zonas bajas (100-200 m de altitud ubicados en la comuna de Chonchi, Isla de Chiloé. De estos bosques, dos habían sido manejados, uno por corta selectiva y otro por floreo, y el tercero (control era un bosque antiguo no intervenido. La FNS del nitrógeno se estimó mediante la "técnica de reducción de acetileno". Análisis de varianzas de dos vías mostraron que las adiciones de fósforo no afectaron en forma significativa las tasas de reducción de acetileno (TRA de la hojarasca en ninguno de los tres bosques, pero la adición de carbono lábil en forma de glucosa afectó negativamente la TRA en el máximo nivel aplicado, en la hojarasca del bosque no manejado. Solo el factor bosque, relacionado a la práctica silvicultural, dio cuenta de las diferencias observadas en las TRA, siendo mayores en el bosque no manejado. Estas diferencias no fueron explicadas por las variables manipuladas

  2. Characterization of a symbiotic, heterocystous, N2-fixing cyanobacterium fromCycas coralloid roots.

    Science.gov (United States)

    Sharma, A; Mishra, D P; Kumar, A

    1992-09-01

    A symbiotic, heterocystous, N2-fixing blue-green alga, isolated from the coralloid roots of a xerophytic plant,Cycas revoluta, grew best in liquid medium supplemented with 4 mM NO 3 (-) . Morphologically, the isolated alga was identical to that of the natural endophyte but the cell size had decreased markedly. The alga was heterotrophic. Intact coralloid roots had nearly 4 to 5 times more nitrogenase activity compared with natural- and laboratory-grown agla but nitrate reductase was inducible in both the forms. Plasmid(s) were found in both algal forms.

  3. Effects of macro nutrient concentration on biological N2 fixation by Azotobacter vinelandii ATCC 12837

    International Nuclear Information System (INIS)

    Liew Pauline Woan Ying; Nazalan Najimudin; Jong Bor Chyan; Latiffah Noordin; Khairuddin Abdul Rahim; Amir Hamzah Ahmad Ghazali

    2010-01-01

    The dynamic changes of biological N 2 fixation by Azotobacter vinelandii ATCC 12837 under the influence of various macro nutrients, specifically phosphorus (P) and potassium (K), was investigated. In this attempt, Oryza sativa L. var. MR 219 was used as the model plant. Results obtained showed changes in the biological N 2 fixation activities with different macro nutrient(s) manipulations. The research activity enables optimisation of macro nutrients concentration for optimal/ enhanced biological N 2 fixation by A. vinelandii ATCC 12837. (author)

  4. Symbiotic relationships between soil fungi and plants reduce N2O emissions from soil.

    Science.gov (United States)

    Bender, S Franz; Plantenga, Faline; Neftel, Albrecht; Jocher, Markus; Oberholzer, Hans-Rudolf; Köhl, Luise; Giles, Madeline; Daniell, Tim J; van der Heijden, Marcel Ga

    2014-06-01

    N2O is a potent greenhouse gas involved in the destruction of the protective ozone layer in the stratosphere and contributing to global warming. The ecological processes regulating its emissions from soil are still poorly understood. Here, we show that the presence of arbuscular mycorrhizal fungi (AMF), a dominant group of soil fungi, which form symbiotic associations with the majority of land plants and which influence a range of important ecosystem functions, can induce a reduction in N2O emissions from soil. To test for a functional relationship between AMF and N2O emissions, we manipulated the abundance of AMF in two independent greenhouse experiments using two different approaches (sterilized and re-inoculated soil and non-mycorrhizal tomato mutants) and two different soils. N2O emissions were increased by 42 and 33% in microcosms with reduced AMF abundance compared to microcosms with a well-established AMF community, suggesting that AMF regulate N2O emissions. This could partly be explained by increased N immobilization into microbial or plant biomass, reduced concentrations of mineral soil N as a substrate for N2O emission and altered water relations. Moreover, the abundance of key genes responsible for N2O production (nirK) was negatively and for N2O consumption (nosZ) positively correlated to AMF abundance, indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the soil microbial community. Our results suggest that the disruption of the AMF symbiosis through intensification of agricultural practices may further contribute to increased N2O emissions.

  5. Symbiotic nitrogen fixation in an arid ecosystem measured by sup 15 N natural abundance

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, G.V. (Univ. of New Mexico, Albuquerque (USA))

    1990-05-01

    Plants dependent on nitrogen fixation have an {sup 15}N abundance similar to the atmosphere, while non-nitrogen fixing plants usually are enriched in {sup 15}N and are similar to soil nitrogen values. The natural abundance of {sup 15}N in leaf tissues and soils was determined to evaluate symbiotic nitrogen fixation by several legumes and actinorhizal species in the Sevilleta Long-term Ecological Research area in central New Mexico. Comparison of {delta}{sup 15}N values for the legume Prosopis glandulosa (mesquite) to adjacent Atriplex canascens (fourwing saltbush) indicated that P. glandulosa obtained 66% of its nitrogen by fixation. The legume Hoffmanseggia jamesii was found to be utilizing soil nitrogen. The {delta}{sup 15}N values for the actinorhizal plants, Elaeagnus angustifolia and Cercocarpus montanus, while below values for soil nitrogen, did not differ from associated non-fixing plants.

  6. Tropical Dominance of N2 Fixation in the North Atlantic Ocean

    Science.gov (United States)

    Marconi, Dario; Sigman, Daniel M.; Casciotti, Karen L.; Campbell, Ethan C.; Alexandra Weigand, M.; Fawcett, Sarah E.; Knapp, Angela N.; Rafter, Patrick A.; Ward, Bess B.; Haug, Gerald H.

    2017-10-01

    To investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.1 ± 4.3 Tg N/yr and 3.0 ± 0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, 90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron-rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P-bearing, N-poor conditions. We estimate a N2 fixation rate of 30.5 ± 4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P-bearing, N-poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in Pacific basins.

  7. Environmental and biogeochemical controls on N2 fixation in ombrotrophic peatlands

    Science.gov (United States)

    Zivkovic, T.; Moore, T. R.

    2017-12-01

    Northern peatlands have low atmospheric nitrogen (N) inputs and acquire N mostly via biological, microbially-driven N2-fixation. Little is known about rates and controls on N2-fixation in ombrotrophic bogs. We conducted two studies to test environmental and biogeochemical controls on N2-fixation. First, we used acetylene reduction assay (ARA) calibrated with 15N2 tracer to measure N2-fixation rates in three species of Sphagnum mosses along a hydrological gradient (beaver pond, hollow and hummock in bog margin and in bog) at Mer Bleue bog from June-October 2013 and May - November 2014. We tested the following controls: moisture availability, temperature, and PAR. The largest ARA rates throughout both seasons occurred in the pond in floating Sphagnum cuspidatum mats (50.3 ± 12.9 μmol m-2 d-1 Mean ± SE), which were up to 2.5 times larger than the rates found in the driest hummock site. There was a significant seasonal peak in both years in July and early August that coincided with the peak of the air temperature. In fact, 45% of the variance of N2 fixation rates over the two field seasons was explained by rain events, water table fluctuations and the surface peat temperature (multiple regression analysis, n = 539). Our results highlight the potential impact of climate change, namely negative effects due to potential droughts and positive effect of warming, on N2 fixation patterns in ombrotrophic peatlands. Secondly, we tested stoichiometric controls (Sphagnum tissue N and phosphorous (P) ratio) of N2-fixation. In a controlled environment, we selected eight study sites along a latitudinal gradient from temperate, boreal to subarctic zone in eastern Canada. We found that decreasing N:P ratio corresponded to increasing N2-fixation. N:P explained 65% of the variance in N2-fixation in hollows but only 20% in hummocks. Changes in neither N or P concentration alone explained the increase in N2-fixation better than N:P ratio. We interpret that the difference between

  8. A Medicago truncatula tobacco retrotransposon insertion mutant collection with defects in nodule development and symbiotic nitrogen fixation.

    Science.gov (United States)

    Pislariu, Catalina I; Murray, Jeremy D; Wen, JiangQi; Cosson, Viviane; Muni, RajaSekhara Reddy Duvvuru; Wang, Mingyi; Benedito, Vagner A; Andriankaja, Andry; Cheng, Xiaofei; Jerez, Ivone Torres; Mondy, Samuel; Zhang, Shulan; Taylor, Mark E; Tadege, Million; Ratet, Pascal; Mysore, Kirankumar S; Chen, Rujin; Udvardi, Michael K

    2012-08-01

    A Tnt1-insertion mutant population of Medicago truncatula ecotype R108 was screened for defects in nodulation and symbiotic nitrogen fixation. Primary screening of 9,300 mutant lines yielded 317 lines with putative defects in nodule development and/or nitrogen fixation. Of these, 230 lines were rescreened, and 156 lines were confirmed with defective symbiotic nitrogen fixation. Mutants were sorted into six distinct phenotypic categories: 72 nonnodulating mutants (Nod-), 51 mutants with totally ineffective nodules (Nod+ Fix-), 17 mutants with partially ineffective nodules (Nod+ Fix+/-), 27 mutants defective in nodule emergence, elongation, and nitrogen fixation (Nod+/- Fix-), one mutant with delayed and reduced nodulation but effective in nitrogen fixation (dNod+/- Fix+), and 11 supernodulating mutants (Nod++Fix+/-). A total of 2,801 flanking sequence tags were generated from the 156 symbiotic mutant lines. Analysis of flanking sequence tags revealed 14 insertion alleles of the following known symbiotic genes: NODULE INCEPTION (NIN), DOESN'T MAKE INFECTIONS3 (DMI3/CCaMK), ERF REQUIRED FOR NODULATION, and SUPERNUMERARY NODULES (SUNN). In parallel, a polymerase chain reaction-based strategy was used to identify Tnt1 insertions in known symbiotic genes, which revealed 25 additional insertion alleles in the following genes: DMI1, DMI2, DMI3, NIN, NODULATION SIGNALING PATHWAY1 (NSP1), NSP2, SUNN, and SICKLE. Thirty-nine Nod- lines were also screened for arbuscular mycorrhizal symbiosis phenotypes, and 30 mutants exhibited defects in arbuscular mycorrhizal symbiosis. Morphological and developmental features of several new symbiotic mutants are reported. The collection of mutants described here is a source of novel alleles of known symbiotic genes and a resource for cloning novel symbiotic genes via Tnt1 tagging.

  9. Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand ...

    Indian Academy of Sciences (India)

    To estimate the N2 fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction method in an 18-year-old stand naturally regenerated after disturbance by road construction in Japan. To evaluate the contribution of N2 ...

  10. The sensitivity of marine N2 fixation to dissolved inorganic nitrogen

    Directory of Open Access Journals (Sweden)

    Angela eKnapp

    2012-10-01

    Full Text Available The dominant process adding nitrogen (N to the ocean, di-nitrogen (N2 fixation, is mediated by prokaryotes (diazotrophs sensitive to a variety of environmental factors. In particular, it is often assumed that consequential rates of marine N2 fixation do not occur where concentrations of nitrate (NO3- and/or ammonium (NH4+ exceed 1 µM because of the additional energetic cost associated with assimilating N2 gas relative to NO3- or NH4+. However, an examination of culturing studies and in situ N2 fixation rate measurements from marine euphotic, mesopelagic, and benthic environments indicates that while elevated concentrations of NO3- and/or NH4+ can depress N2 fixation rates, the process can continue at substantial rates in the presence of as much as 30 µM NO3- and/or 200 µM NH4+. These findings challenge expectations of the degree to which inorganic N inhibits this process. The high rates of N2 fixation measured in some benthic environments suggest that certain benthic diazotrophs may be less sensitive to prolonged exposure to NO3- and/or NH4+ than cyanobacterial diazotrophs. Additionally, recent work indicates that cyanobacterial diazotrophs may have mechanisms for mitigating NO3- inhibition of N2 fixation. In particular, it has been recently shown that increasing phosphorus (P availability increases diazotroph abundance, thus compensating for lower per-cell rates of N2 fixation that result from NO3- inhibition. Consequently, low ambient surface ocean N:P ratios such as those generated by the increasing rates of N loss thought to occur during the last glacial to interglacial transition may create conditions favorable for N2 fixation and thus help to stabilize the marine N inventory on relevant time scales. These findings suggest that restricting measurements of marine N2 fixation to oligotrophic surface waters may underestimate global rates of this process and contribute to uncertainties in the marine N budget.

  11. In silico insights into the symbiotic nitrogen fixation in Sinorhizobium meliloti via metabolic reconstruction.

    Science.gov (United States)

    Zhao, Hansheng; Li, Mao; Fang, Kechi; Chen, Wenfeng; Wang, Jing

    2012-01-01

    Sinorhizobium meliloti is a soil bacterium, known for its capability to establish symbiotic nitrogen fixation (SNF) with leguminous plants such as alfalfa. S. meliloti 1021 is the most extensively studied strain to understand the mechanism of SNF and further to study the legume-microbe interaction. In order to provide insight into the metabolic characteristics underlying the SNF mechanism of S. meliloti 1021, there is an increasing demand to reconstruct a metabolic network for the stage of SNF in S. meliloti 1021. Through an iterative reconstruction process, a metabolic network during the stage of SNF in S. meliloti 1021 was presented, named as iHZ565, which accounts for 565 genes, 503 internal reactions, and 522 metabolites. Subjected to a novelly defined objective function, the in silico predicted flux distribution was highly consistent with the in vivo evidences reported previously, which proves the robustness of the model. Based on the model, refinement of genome annotation of S. meliloti 1021 was performed and 15 genes were re-annotated properly. There were 19.8% (112) of the 565 metabolic genes included in iHZ565 predicted to be essential for efficient SNF in bacteroids under the in silico microaerobic and nutrient sharing condition. As the first metabolic network during the stage of SNF in S. meliloti 1021, the manually curated model iHZ565 provides an overview of the major metabolic properties of the SNF bioprocess in S. meliloti 1021. The predicted SNF-required essential genes will facilitate understanding of the key functions in SNF and help identify key genes and design experiments for further validation. The model iHZ565 can be used as a knowledge-based framework for better understanding the symbiotic relationship between rhizobia and legumes, ultimately, uncovering the mechanism of nitrogen fixation in bacteroids and providing new strategies to efficiently improve biological nitrogen fixation.

  12. Bacterial N2-fixation in mangrove ecosystems: insights from a diazotroph-mangrove interaction.

    Science.gov (United States)

    Alfaro-Espinoza, Gabriela; Ullrich, Matthias S

    2015-01-01

    Mangrove forests are highly productive ecosystems but represent low nutrient environments. Nitrogen availability is one of the main factors limiting mangrove growth. Diazotrophs have been identified as key organisms that provide nitrogen to these environments. N2-fixation by such organisms was found to be higher in the mangrove roots than in surrounding rhizosphere. Moreover, previous studies showed that mangroves grew better in the presence of N2-fixers indicating a potentially mutualistic relationship. However, the molecular signals and mechanisms that govern these interactions are still poorly understood. Here we present novel insights in the interaction of a diazotroph with a mangrove species to improve our understanding of the molecular and ecophysiological relationship between these two organisms under controlled conditions. Our results showed that Marinobacterium mangrovicola is a versatile organism capable of competing with other organisms to survive for long periods in mangrove soils. N2-fixation by this bacterium was up-regulated in the presence of mangrove roots, indicating a possible beneficial interaction. The increase in N2-fixation was limited to cells of the exponential growth phase suggesting that N2-fixation differs over the bacterial growth cycle. Bacterial transformants harboring a transcriptional nifH::gusA fusion showed that M. mangrovicola successfully colonized mangrove roots and simultaneously conducted N2-fixation. The colonization process was stimulated by the lack of an external carbon source suggesting a possible mutualistic relationship. M. mangrovicola represents an interesting genetically accessible diazotroph, which colonize mangrove roots and exhibit higher N2-fixation in the presence of mangrove roots. Consequently, we propose this microorganism as a tool to study molecular interactions between N2-fixers and mangrove plants and to better understand how changes in the environment could impact these important and relatively unknown

  13. Five decades of N2 fixation research in the North Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    Mar eBenavides

    2015-06-01

    Full Text Available Dinitrogen (N2 fixation (the reduction of atmospheric N2 to ammonium by specialized prokaryotic microbes, represents an important input of fixed nitrogen and contributes significantly to primary productivity in the oceans. Marine N2 fixation was discovered in the North Atlantic Ocean (NA in the 1960s. Ever since, the NA has been subject to numerous studies that have looked into the diversity and abundance of N2-fixing microbes (diazotrophs, the spatial and temporal variability of N2 fixation rates, and the range of physical and chemical variables that control them. The NA provides 10-25% of the globally fixed N2, ranking as the third basin with the largest N2 fixation inputs in the world’s oceans. This basin suffers a chronic depletion in phosphorus availability, more aeolian dust deposition than any other basin in the world’s oceans, and significant nutrient inputs from important rivers like the Amazon and the Congo. These characteristics make it unique in comparison with other oceanic basins. After five decades of intensive research, here we present a comprehensive review of our current understanding of diazotrophic activity in the NA from both a geochemical and biological perspective. We discuss the advantages and disadvantages of current methods, future perspectives, and questions which remain to be answered.

  14. Expression of drought-tolerant N2 fixation in heterogeneous inbred families derived from PI 471938 and Hutcheson soybean

    Science.gov (United States)

    Nitrogen fixation of soybean is particularly vulnerable to drought, since, in most genotypes, N2 fixation activity decreases very early in the soil drying cycle. Although a few soybean genotypes, including ‘PI 471938’, have been identified that express N2 fixation tolerance of drought, it is unknown...

  15. Field evaluation of N2 fixation by seventeen mung bean genotypes in the Philippines

    International Nuclear Information System (INIS)

    Rosales, C.M.; Rivera, F.; Hautia, R.A.; Del Rosario, E.

    1994-12-01

    Seventeen mung bean genotypes were screened for biological nitrogen fixation (BNF) during the late dry (March-May) and early dry (October-December) seasons of 1992 in the Philippines. The 15 N isotope dilution method was used to measure N 2 fixation. Performances were quantified based on both indirect and direct measurements of N 2 fixation. Genetic variation was observed among varieties tested for some BNF characteristic. However, genetic variability for percent N derived from fixation (%Ndfa) was not evident. PAEC 3 mutant, Taiwan Green, Acc 687 and Pagasa 7 were the best performers. Whereas Acc 2041 consistently performed poorly for most of the BNF characters tested. (author). 14 refs., 1 fig., 2 tabs

  16. Symbiotic leghemoglobins are crucial for nitrogen fixation in legume root nodules but not for general plant growth and development

    DEFF Research Database (Denmark)

    Ott, Thomas; van Dongen, Joost T; Günther, Catrin

    2005-01-01

    Hemoglobins are ubiquitous in nature and among the best-characterized proteins. Genetics has revealed crucial roles for human hemoglobins, but similar data are lacking for plants. Plants contain symbiotic and nonsymbiotic hemoglobins; the former are thought to be important for symbiotic nitrogen...... accumulate to millimolar concentrations in the cytoplasm of infected plant cells prior to nitrogen fixation and are thought to buffer free oxygen in the nanomolar range, avoiding inactivation of oxygen-labile nitrogenase while maintaining high oxygen flux for respiration. Although widely accepted......RNAi plants grew normally when fertilized with mineral nitrogen. These data indicate roles for leghemoglobins in oxygen transport and buffering and prove for the first time that plant hemoglobins are crucial for symbiotic nitrogen fixation. Udgivelsesdato: 2005-Mar-29...

  17. Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand in Japan.

    Science.gov (United States)

    Tobita, Hiroyuki; Hasegawa, Shigeaki F; Yazaki, Kenichi; Komatsu, Masabumi; Kitao, Mitsutoshi

    2013-11-01

    To estimate the N2 fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction method in an 18-year-old stand naturally regenerated after disturbance by road construction in Japan. To evaluate the contribution of N2 fixation to the nitrogen (N) economy in this alder stand, we also measured the phenology of the alder, the litterfall, the decomposition rate of the leaf litter, and N accumulation in the soil. The acetylene reduction activity per unit nodule mass (ARA) under field conditions appeared after bud break, peaked the maximum in midsummer after full expansion of the leaves, and disappeared after all leaves had fallen. There was no consistent correlation between ARA and tree size (dbh). The amount of N2 fixed in this alder stand was estimated at 56.4 kg ha-1 year-1 when a theoretical molar ratio of 3 was used to convert the amount of reduced acetylene to the amount of fixed N2. This amount of N2 fixation corresponded to the 66.4 percent of N in the leaf litter produced in a year. These results suggested that N2 fixation still contributed to the large portion of N economy in this alder stand.

  18. Does N2 fixation amplify the temperature dependence of ecosystem metabolism?

    Science.gov (United States)

    Welter, Jill R; Benstead, Jonathan P; Cross, Wyatt F; Hood, James M; Huryn, Alexander D; Johnson, Philip W; Williamson, Tanner J

    2015-03-01

    Variation in resource supply can cause variation in temperature dependences of metabolic processes (e.g., photosynthesis and respiration). Understanding such divergence is particularly important when using metabolic theory to predict ecosystem responses to climate warming. Few studies, however, have assessed the effect of temperature-resource interactions on metabolic processes, particularly in cases where the supply of limiting resources exhibits temperature dependence. We investigated the responses of biomass accrual, gross primary production (GPP), community respiration (CR), and N2 fixation to warming during biofilm development in a streamside channel experiment. Areal rates of GPP, CR, biomass accrual, and N2 fixation scaled positively with temperature, showing a 32- to 71-fold range across the temperature gradient (approximately 7 degrees-24 degrees C). Areal N2-fixation rates exhibited apparent activation energies (1.5-2.0 eV; 1 eV = approximately 1.6 x 10(-19) J) approximating the activation energy of the nitrogenase reaction. In contrast, mean apparent activation energies for areal rates of GPP (2.1-2.2 eV) and CR (1.6-1.9 eV) were 6.5- and 2.7-fold higher than estimates based on metabolic theory predictions (i.e., 0.32 and 0.65 eV, respectively) and did not significantly differ from the apparent activation energy observed for N2 fixation. Mass-specific activation energies for N2 fixation (1.4-1.6 eV), GPP (0.3-0.5 eV), and CR (no observed temperature relationship) were near or lower than theoretical predictions. We attribute the divergence of areal activation energies from those predicted by metabolic theory to increases in N2 fixation with temperature, leading to amplified temperature dependences of biomass accrual and areal rates of GPP and R. Such interactions between temperature dependences must be incorporated into metabolic models to improve predictions of ecosystem responses to climate change.

  19. Global changes in transcription orchestrate metabolic differentiation during symbiotic nitrogen fixation in Lotus japonicus

    DEFF Research Database (Denmark)

    Colebatch, Gillian; Desbrosses, Guilhem; Ott, Thomas

    2004-01-01

    from specific sets of induced genes. In addition to the expected signs of hypoxia, numerous indications were obtained that nodule cells also experience P-limitation and osmotic stress. Several potential regulators of these stress responses were identified. Metabolite profiling by gas chromatography......Research on legume nodule metabolism has contributed greatly to our knowledge of primary carbon and nitrogen metabolism in plants in general, and in symbiotic nitrogen fixation in particular. However, most previous studies focused on one or a few genes/enzymes involved in selected metabolic...... pathways in many different legume species. We utilized the tools of transcriptomics and metabolomics to obtain an unprecedented overview of the metabolic differentiation that results from nodule development in the model legume, Lotus japonicus. Using an array of more than 5000 nodule cDNA clones...

  20. Field evaluation of N2 fixation by mung bean in the Philippines, and residual effects on maize

    International Nuclear Information System (INIS)

    Rosales, C.M.; Rivera, F.G.; Hautea, R.A.; Del Rosario, E.

    1998-01-01

    Seventeen genotypes of mung bean (Vigna radiata) were screened for growth, yield, and symbiotic N 2 fixation during the late-dry (March-May) and early-dry (October-December) seasons of 1992 at the University of the Philippines at Los Banos (UPLB). The 15 N-dilution method was used to determine amounts of N fixed. Soil mineral N availability was higher (average 22 kg N/ha) in the late- than in the early-dry season (9.2 kg N/ha), and, possibly in consequence, vegetative growth was better in the late- than in the early-dry season; however, in contrast, seed yields were better in the latter. Cultivar Pagasa 5 had the highest value (52 kg N/ha) for fixed N in the late-dry season, whereas PAEC 3 had the highest value (70 kg N/ha) in the early-dry season; Accession 2041 had the lowest values in both seasons (33 and 26 kg N/ha, respectively). Genetic variability, albeit slight, was observed for total N fixed, but not for percent N derived from fixation (%Ndfa). Further field work at UPLB and at the Philippine Nuclear Research Institute (PNRI), Quezon City, investigated five mung genotypes, including three from the previous trials, for yield N 2 fixation and residual effects on subsequent maize (Zea mays). Estimates for %Ndfa and for amounts of N fixed ranged from 64 to 87% and 43 to 85 kg N/ha, respectively, at PNRI, and from 37 to 72% and 21 to 85 kg N/ha, respectively, at UPLB. The highest mung-bean seed yields obtained were 1.99 t/ha at PNRI and 0.86 t/ha at UPLB in the two locations. When maize was planted after mung, dry matter, seed yields and total N were consistently higher than when planted after maize or cotton, although most of the differences fell short of statistical significance. The data are discussed in terms of genetic diversity for yield and N 2 fixation in these soils, and potential to exploit mung-fixed N to improve cereal yields

  1. The value of biodiversity in legume symbiotic nitrogen fixation and nodulation for biofuel and food production.

    Science.gov (United States)

    Gresshoff, Peter M; Hayashi, Satomi; Biswas, Bandana; Mirzaei, Saeid; Indrasumunar, Arief; Reid, Dugald; Samuel, Sharon; Tollenaere, Alina; van Hameren, Bethany; Hastwell, April; Scott, Paul; Ferguson, Brett J

    2015-01-01

    Much of modern agriculture is based on immense populations of genetically identical or near-identical varieties, called cultivars. However, advancement of knowledge, and thus experimental utility, is found through biodiversity, whether naturally-found or induced by the experimenter. Globally we are confronted by ever-growing food and energy challenges. Here we demonstrate how such biodiversity from the food legume crop soybean (Glycine max L. Merr) and the bioenergy legume tree Pongamia (Millettia) pinnata is a great value. Legume plants are diverse and are represented by over 18,000 species on this planet. Some, such as soybean, pea and medics are used as food and animal feed crops. Others serve as ornamental (e.g., wisteria), timber (e.g., acacia/wattle) or biofuel (e.g., Pongamia pinnata) resources. Most legumes develop root organs (nodules) after microsymbiont induction that serve as their habitat for biological nitrogen fixation. Through this, nitrogen fertiliser demand is reduced by the efficient symbiosis between soil Rhizobium-type bacteria and the appropriate legume partner. Mechanistic research into the genetics, biochemistry and physiology of legumes is thus strategically essential for future global agriculture. Here we demonstrate how molecular plant science analysis of the genetics of an established food crop (soybean) and an emerging biofuel P. pinnata feedstock contributes to their utility by sustainable production aided by symbiotic nitrogen fixation. Crown Copyright © 2014. Published by Elsevier GmbH. All rights reserved.

  2. Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand ...

    Indian Academy of Sciences (India)

    2013-10-01

    Oct 1, 2013 ... Previous address: Laboratory of Forest Ecology, Graduate School of Agriculture,. Kyoto University, Kyoto 606-8502, Japan. To estimate the N2 fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction ...

  3. Low concentrations of nitrate and ammonium stimulate nodulation and N-2 fixation while inhibiting specific nodulation (nodule DW g(-1) root dry weight) and specific N-2 fixation (N-2 fixed g(-1) root dry weight) in soybean

    NARCIS (Netherlands)

    Gan, YB; Stulen, [No Value; van Keulen, H; Kuiper, PJC

    Nitrate N is a major inhibitor of the soybean/Bradyrhizobium symbiosis in legumes and although this inhibition has been studied for many years, as yet no consensus has been reached on the specific and quantitative interactions between nitrate and ammonium supply and N-2 fixation. The effect of

  4. Nitrate reductase and nitrogenase activities in relation to N-uptake from soil, 15N-fertilizer and symbiotic fixation in soybean (Glycine max)

    International Nuclear Information System (INIS)

    Ruschel, A.P.; Saito, S.M.T.; Vose, P.B.

    1980-01-01

    Nitrate reductase (NRA) and nitrogenase (ARA) activities were evaluated in relation to nitrogen in the plant from soil (NFS), fertilizer (NFF) and symbiotic fixation (NFN 2 ) to study the pattern of utilization of nitrogen in nodulated and non nodulated soybean, 35, 55 and 75 days after planting. Three levels of ( 15 NH 4 ) 2 SO 4 - added to soil were used (0 - 25 and 50 kg N/ha), being the experiment conducted in the greenhouse, with a split plot statistical design and 4 replications. Maximum levels of RNA and ARA occurred 55 days after planting. Addition of 50 kg N/ha decreased NRA at all harvesting time studied; and nodule ARA only 75 days after planting. By that time the nodulated isoline showed higher NRA than the non nodulated one, the NFS and NFF of the isolines were not different 35 and 55 days after planting, but decreased at the last harvest, especially in nodulated soybean. Symbiotic N 2 -fixation increased plant-N after 55 days growth, contribution about 65% of plant-N in the period between 55 and 75 days after planting. Nodulated plant showed higher N than non nodulated, a sinergistic effect of the three sources of N studied on N increase of nodulated plants was observed. (Author) [pt

  5. N2 production and fixation in deep-tier burrows of Squilla empusa in muddy sediments of Great Peconic Bay

    Science.gov (United States)

    Waugh, Stuart; Aller, Robert C.

    2017-11-01

    Global marine N budgets often show deficits due to dominance of benthic N2 production relative to pelagic N2 fixation. Recent studies have argued that benthic N2 fixation in shallow water environments has been underestimated. In particular, N2 fixation associated with animal burrows may be significant as indicated by high rates of N2 fixation reported in muddy sands populated by the ghost shrimp, Neotrypaea californiensis (Bertics et al., 2010). We investigated whether N2 fixation occurs at higher rates in the burrow-walls of the deep-burrowing ( 0.5-4 m) mantis shrimp, Squilla empusa, compared to ambient, estuarine muds and measured seasonal in-situ N2 concentrations in burrow-water relative to bottom-water. Acetylene reduction assays showed lower N2 fixation in burrow-walls than in un-populated sediments, likely due to inhibitory effects of O2 on ethylene production. Dissolved N2 was higher in burrow-water than proximate bottom-water at all seasons, demonstrating a consistent balance of net N2 production relative to fixation in deep-tier biogenic structures.

  6. Selection and breeding of grain legumes in Australia for enhanced nodulation and N2 fixation

    International Nuclear Information System (INIS)

    Herridge, D.F.; Holland, J.F.; Rose, I.A.; Redden, R.J.

    1998-01-01

    During the period 1980-87, the areas sown to grain legumes in Australia increased dramatically, from 0.25 Mha to 1.65 Mha. These increases occurred in the western and southern cereal belts, but not in the north which N continued to be supplied by the mineralization of soil organic matter. Therefore, there was a need to promote the use of N 2 -fixing legumes in the cereal-dominated northern cropping belt. Certain problems had to be addressed before farmers would accept legumes and change established patterns of cropping. Here we describe our efforts to improve N 2 fixation by soybean, common bean and pigeon pea. Selection and breeding for enhanced N 2 fixation of soybean commenced at Tamworth in 1980 after surveys of commercial crops indicated that nodulation was sometimes inadequate, particularly on new land, and that the levels of fixed-N inputs were variable and often low. Similar programmes were established in 1985 (common bean) and 1988 (pigeon bean). Progress was made in increasing N 2 fixation by these legumes towards obtaining economic yields without fertilizer N and contributing organic N for the benefit of subsequent cereal crops

  7. Soybean nodulation and symbiotic nitrogen fixation in response to soil compaction and mulching

    Science.gov (United States)

    Siczek, A.; Lipiec, J.

    2009-04-01

    Symbiotic nitrogen fixation by legume crops such as soybean plays a key role in supplying nitrogen for agricultural systems. In symbiotic associations with Bradyrhizobium japonicum soybean can fix up to 200 kg N ha-1 yr-1. This reduces the need for expensive and often environmentally harmful because of leaching nitrogen fertilization. However both soybean nodulation and nitrogen fixation are sensitive to soil conditions. One of the critical soil constraints is soil compaction. Increasing use of heavy equipment and intensive cropping in modern agriculture leads to excessive soil compaction. Compaction often is found as a result of field operations that have to be performed in a very short period of time and when soils are wet and more susceptible to compaction. This results in unfavourable water content, temperature, aeration, pore size distribution, strength for plant growth and microbial activity. The surface mulching can alleviate the adverse effect of the environmental factors on soil by decreasing fluctuation of soil temperature, increasing moisture by controlling evaporation from the soil surface, decreasing bulk density, preventing soil crusting. The effect of mulch on soil conditions largely depends on soil compaction and weather conditions during growing season. The positive effect of the straw mulch on soil moisture has been seen under seasons with insufficient rainfalls. However thicker layers of mulch can act as diffusion barrier, especially when the mulch is wet. Additionally, low soil temperature prevalent during early spring under mulch can impede development of nodule, nodule size and delay onset of nodulation. The aim of this study was to determine the effect of the straw mulch on nodulation and nitrogen fixation of soybean in variously compacted soil. The experimental field was 192 m2and was divided into three parts composed of 6 micro-plots with area 7 m2. Three degrees of soil compaction obtained in each field part through tractor passes were

  8. Uptake rate of nitrogen from soil and fertilizer, and N derived from symbiotic fixation in cowpea (Vigna unguiculata (L.) Walp.) and common bean (Phaseolus vulgaris L.) determined using the 15N isotope

    International Nuclear Information System (INIS)

    Brito, Marciano de Medeiros Pereira; Muraoka, Takashi; Silva, Edson Cabral da

    2009-01-01

    Common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata (L.) Walp.) are among the main sources of plant protein for a large part of the world population, mainly that of low income, and nitrogen is the main constituent of these proteins. The objectives of this study were to evaluate, through the 15 N-dilution technique and using rice and non-nodulating soybean as control plants, the relative contributions of nitrogen sources (symbiotically fixed N, soil native N and fertilizer N) on the growth of common bean and cowpea and to compare the isotopic technique (ID) with the difference methods (DM) for the evaluation of symbiotic N 2 fixation. The study was carried out in a greenhouse of the Center for Nuclear Energy in Agriculture - CENA/USP, Sao Paulo State, Brazil, using 5 kg pots with a Typic Haplustox (Dystrophic Red-Yellow Latosol). The experiment was arranged in completely randomized blocks, with 16 treatments and three replications, in an 8 x 2 factorial design. The treatments were eight sampling times: 7, 24, 31, 38, 47, 58, 68 and 78 days after sowing (DAS) and two crops: common bean and cowpea. An N rate of 10 mg kg -1 soil was used, as urea, enriched with an excess of 10 % of 15 N atoms. Symbiotic N fixation supplied the bean and cowpea plants with the greatest amount of accumulated N, followed, in decreasing order, by soil and fertilizer. The highest rate of N symbiotic fixation was observed at the pre-flowering growth stage of the bean and cowpea plants. After the initial growth stage, 24 DAS, rice and non nodulating soybean were appropriate control plants to evaluate symbiotic N fixation. There was a good agreement between ID and DM, except in the initial growth stage of the crops. (author)

  9. Determination of N2 -fixation ability of legume trees using the 15N method

    International Nuclear Information System (INIS)

    Wemay, Johannis; Syaukat, Sriharti; Sisworo, Elsje L

    1998-01-01

    A sequence field experiment has been conducted for determining the capability of N 2 -fixation by several legume trees. The experiment was designed using a randomize design with 4 replicates. Each replicate was planted with 100 legume trees and 100 non legume trees. The isotope plot, where 15 N was applied with 18 legume trees and 18 non legume trees. The planting distance was 1m x 1m. For the calculation of N 2 -fixation each legume and standard tree (Eucalypthus alba) was applied with 12.52g in the from of ammonium sulfate with 10.12% 15 N. The 15 N AS was applied in three splits 11 month earlier. Data obtained from this experiment showed that percentage of N derived from fixation (%N-dfF) of all legume trees was reasonable high. The legume trees used in this experiment were, Leucaena leucocephala, Acacia mangium, Caliandra tetragona, Flemengia congesta and Gliriciadia sepium with potential fixation from 62.31% to 90,68%. (author)

  10. Biological N2O fixation in the Eastern South Pacific Ocean and marine cyanobacterial cultures.

    Directory of Open Access Journals (Sweden)

    Laura Farías

    Full Text Available Despite the importance of nitrous oxide (N2O in the global radiative balance and atmospheric ozone chemistry, its sources and sinks within the Earth's system are still poorly understood. In the ocean, N2O is produced by microbiological processes such as nitrification and partial denitrification, which account for about a third of global emissions. Conversely, complete denitrification (the dissimilative reduction of N2O to N2 under suboxic/anoxic conditions is the only known pathway accountable for N2O consumption in the ocean. In this work, it is demonstrated that the biological assimilation of N2O could be a significant pathway capable of directly transforming this gas into particulate organic nitrogen (PON. N2O is shown to be biologically fixed within the subtropical and tropical waters of the eastern South Pacific Ocean, under a wide range of oceanographic conditions and at rates ranging from 2 pmol N L(-1 d(- to 14.8 nmol N L(-1 d(-1 (mean ± SE of 0.522 ± 1.06 nmol N L(-1 d(-1, n = 93. Additional assays revealed that cultured cyanobacterial strains of Trichodesmium (H-9 and IMS 101, and Crocosphaera (W-8501 have the capacity to directly fix N2O under laboratory conditions; suggesting that marine photoautotrophic diazotrophs could be using N2O as a substrate. This metabolic capacity however was absent in Synechococcus (RCC 1029. The findings presented here indicate that assimilative N2O fixation takes place under extreme environmental conditions (i.e., light, nutrient, oxygen where both autotrophic (including cyanobacteria and heterotrophic microbes appear to be involved. This process could provide a globally significant sink for atmospheric N2O which in turn affects the oceanic N2O inventory and may also represent a yet unexplored global oceanic source of fixed N.

  11. N2-fixation and seedling growth promotion of lodgepole pine by endophytic Paenibacillus polymyxa.

    Science.gov (United States)

    Anand, Richa; Grayston, Susan; Chanway, Christopher

    2013-08-01

    We inoculated lodgepole pine (Pinus contorta var. latifolia (Dougl.) Engelm.) with Paenibacillus polymyxa P2b-2R, a diazotrophic bacterium previously isolated from internal stem tissue of a naturally regenerating pine seedling to evaluate biological nitrogen fixation and seedling growth promotion by this microorganism. Seedlings generated from pine seed inoculated with strain P2b-2R were grown for up to 13 months in a N-limited soil mix containing 0.7 mM available N labeled as Ca((15)NO3)2 to facilitate detection of N2-fixation. Strain P2b-2R developed a persistent endophytic population comprising 10(2)-10(6) cfu g(-1) plant tissue inside pine roots, stems, and needles during the experiment. At the end of the growth period, P2b-2R had reduced seedling mortality by 14 % and (15)N foliar N abundance 79 % and doubled foliar N concentration and seedling biomass compared to controls. Our results suggest that N2-fixation by P. polymyxa enhanced growth of pine seedlings and support the hypothesis that plant-associated diazotrophs capable of endophytic colonization can satisfy a significant proportion of the N required by tree seedlings growing under N-limited conditions.

  12. Symbiotic nitrogen fixation in the alpine community of a lichen heath of the Northwestern Caucasus Region (the Teberda Reserve)

    Science.gov (United States)

    Makarov, M. I.; Malysheva, T. I.; Ermak, A. A.; Onipchenko, V. G.; Stepanov, A. L.; Menyailo, O. V.

    2011-12-01

    The symbiotic fixation of atmospheric nitrogen by leguminous plants in the alpine community of a lichen heath at the Teberda State Biosphere Reserve is well adapted to low soil temperature characteristic for the altitude of 2800 m a.s.l. For the determination of the N fixation by isotopic methods (the method of the natural 15N abundance and the method of isotopic 15N dilution), Trifolium polyphyllum was taken as the control plant. This plant was used as it does not form symbiosis with the nitrogen-fixing bacteria in the highlands of the Northern Caucasus Region. The contribution of the N fixation to the N nutrition of different leguminous plant species as determined by the natural 15N abundance method amounted to 28-73% at δ15N0 = 0‰ and 46-117% at δ15N0 = -1‰; for the determination of the N fixation by the method of the isotopic label's dilution, it was 34-97%. The best correlation of the results obtained by these two isotopic methods was observed for the natural fractionation of the N isotopes in the course of the N fixation in the range of -0.5 to -0.7‰. The determination of the nitrogenase activity of the roots by the acetylene method confirmed the absence of N fixation in T. polyphyllum and its different contribution to the N nutrition of different species of leguminous plants.

  13. Oxygen-Poor Microzones as Potential Sites of Microbial N2 Fixation in Nitrogen-Depleted Aerobic Marine Waters

    Science.gov (United States)

    Paerl, Hans W.; Prufert, Leslie E.

    1987-01-01

    The nitrogen-deficient coastal waters of North Carolina contain suspended bacteria potentially able to fix N2. Bioassays aimed at identifying environmental factors controlling the development and proliferation of N2 fixation showed that dissolved organic carbon (as simple sugars and sugar alcohols) and particulate organic carbon (derived from Spartina alterniflora) additions elicited and enhanced N2 fixation (nitrogenase activity) in these waters. Nitrogenase activity occurred in samples containing flocculent, mucilage-covered bacterial aggregates. Cyanobacterium-bacterium aggregates also revealed N2 fixation. In all cases bacterial N2 fixation occurred in association with surficial microenvironments or microzones. Since nitrogenase is oxygen labile, we hypothesized that the aggregates themselves protected their constituent microbes from O2. Microelectrode O2 profiles revealed that aggregates had lower internal O2 tensions than surrounding waters. Tetrazolium salt (2,3,5-triphenyl-3-tetrazolium chloride) reduction revealed that patchy zones existed both within microbes and extracellularly in the mucilage surrounding microbes where free O2 was excluded. Triphenyltetrazolium chloride reduction also strongly inhibited nitrogenase activity. These findings suggest that N2 fixation is mediated by the availability of the appropriate types of reduced microzones. Organic carbon enrichment appears to serve as an energy and structural source for aggregate formation, both of which were required for eliciting N2 fixation responses of these waters. Images PMID:16347337

  14. Heterogeneous fixation of N2: Investigation of a novel mechanism for formation of NO

    DEFF Research Database (Denmark)

    Zheng, Ying; Jensen, Anker Degn; Glarborg, Peter

    2009-01-01

    Formation of NO initiated by heterogeneous fixation of N2 during pyrolysis is investigated experimentally and theoretically. The experiments were conducted with beech wood as well as with the pure biomass components cellulose, xylan, and lignin. The NO formation during char oxidation was recorded...... as function of pyrolysis atmosphere (N2 or Ar), pyrolysis temperature (700–1050 °C), and oxidizing atmosphere (O2 in N2 or Ar). The results confirm earlier reports that biomass char may be enriched in N during pyrolysis at 900 °C and above. The N-uptake involves re-capture of N-volatiles as well as uptake...... of N2. During char oxidation, the captured N is partly oxidized to NO, resulting in increased NO formation. The NO yield from oxidation of beech wood char made in N2 increases with pyrolysis temperature, and is about a factor of two higher at 1050 °C than the corresponding yield from chars made in Ar...

  15. Effects of ultraviolet radiation on photosynthetic performance and N2 fixation in Trichodesmium erythraeum IMS 101

    Science.gov (United States)

    Cai, Xiaoni; Hutchins, David A.; Fu, Feixue; Gao, Kunshan

    2017-10-01

    Biological effects of ultraviolet radiation (UVR; 280-400 nm) on marine primary producers are of general concern, as oceanic carbon fixers that contribute to the marine biological CO2 pump are being exposed to increasing UV irradiance due to global change and ozone depletion. We investigated the effects of UV-B (280-320 nm) and UV-A (320-400 nm) on the biogeochemically critical filamentous marine N2-fixing cyanobacterium Trichodesmium (strain IMS101) using a solar simulator as well as under natural solar radiation. Short exposure to UV-B, UV-A, or integrated total UVR significantly reduced the effective quantum yield of photosystem II (PSII) and photosynthetic carbon and N2 fixation rates. Cells acclimated to low light were more sensitive to UV exposure compared to high-light-grown ones, which had more UV-absorbing compounds, most likely mycosporine-like amino acids (MAAs). After acclimation under natural sunlight, the specific growth rate was lower (by up to 44 %), MAA content was higher, and average trichome length was shorter (by up to 22 %) in the full spectrum of solar radiation with UVR, than under a photosynthetically active radiation (PAR) alone treatment (400-700 nm). These results suggest that prior shipboard experiments in UV-opaque containers may have substantially overestimated in situ nitrogen fixation rates by Trichodesmium, and that natural and anthropogenic elevation of UV radiation intensity could significantly inhibit this vital source of new nitrogen to the current and future oligotrophic oceans.

  16. N resource of grasses and N2-fixation of alfalfa in mono-culture and mixture

    International Nuclear Information System (INIS)

    Zhu Shuxiu

    1992-01-01

    The N behavior in alfalfa and gramineous forage grasses, tall fescue, siberian wild rye, wheat grass and awnless brome were studied in potting and pasture experiments in 1986-1988 by using 15 N isotope dilution technique. Comparison was made between the mixed culture and mono-culture. The % Ndff and %Ndfs of grasses were decreased by 14.19% and 20.76% respectively, while %Ndfa of alfalfa was increased by 20.22% in mixed culture as compared with mono-culture. The 15 N and soil N uptake data revealed that this enhancement was largely due to a lower competitive ability for soil N by alfalfa than by grass in mixed stands, causing the alfalfa to depend more on atmospheric N 2 fixation. 20.62%of N of grasses in mixed culture was from the N 2 -fixation by alfalfa, causing N level in root-sphere of alfalfa decreasing, which was considered to be one of the reasons that %Ndfa increased in mixed culture. N transfer may be carried out by the decomposition of roots and nodules of alfalfa plants

  17. SYMBIOTIC N2 FIXATION IN ALPINE TUNDRA: ECOSYSTEM INPUT AND VARIATION IN FIXATION RATES AMONG PLANT COMMUNITIES (R823442)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  18. Evaluation of yield and N2 fixation of mutant lines of groundnut in Malaysia

    International Nuclear Information System (INIS)

    Rusli, I.; Harun, A.R.; Rahman, K.A.; Shamsuddin, S.; Rahim, K.A.; Danso, S.K.A.

    1998-01-01

    The 15 N-dilution technique was used to evaluate N 2 fixation in groundnut (Arachis hypogaea L.) in three field trials of cultivars Matjan and V-13 (parents), their selected mutant lines, and a other local and foreign genotypes. Matjan mutant MJ/40/42 consistently produced the highest pod yields, at above 4 t ha -1 , 14-22% higher yields than the parent. In contrast, none of the V-13 mutants had consistently better yields than the parent. The mutant lines did not show consistent agronomic performance from year to year. Total dry matter yield did not correlate with pod yield, and pod yield did not correlate with amount of N fixed

  19. Effects of ultraviolet radiation on photosynthetic performance and N2 fixation in Trichodesmium erythraeum IMS 101

    Directory of Open Access Journals (Sweden)

    X. Cai

    2017-10-01

    Full Text Available Biological effects of ultraviolet radiation (UVR; 280–400 nm on marine primary producers are of general concern, as oceanic carbon fixers that contribute to the marine biological CO2 pump are being exposed to increasing UV irradiance due to global change and ozone depletion. We investigated the effects of UV-B (280–320 nm and UV-A (320–400 nm on the biogeochemically critical filamentous marine N2-fixing cyanobacterium Trichodesmium (strain IMS101 using a solar simulator as well as under natural solar radiation. Short exposure to UV-B, UV-A, or integrated total UVR significantly reduced the effective quantum yield of photosystem II (PSII and photosynthetic carbon and N2 fixation rates. Cells acclimated to low light were more sensitive to UV exposure compared to high-light-grown ones, which had more UV-absorbing compounds, most likely mycosporine-like amino acids (MAAs. After acclimation under natural sunlight, the specific growth rate was lower (by up to 44 %, MAA content was higher, and average trichome length was shorter (by up to 22 % in the full spectrum of solar radiation with UVR, than under a photosynthetically active radiation (PAR alone treatment (400–700 nm. These results suggest that prior shipboard experiments in UV-opaque containers may have substantially overestimated in situ nitrogen fixation rates by Trichodesmium, and that natural and anthropogenic elevation of UV radiation intensity could significantly inhibit this vital source of new nitrogen to the current and future oligotrophic oceans.

  20. Evaluation of chickpea and groundnut for N2 fixation and yield in Bangladesh

    International Nuclear Information System (INIS)

    Sattar, M.A.; Podder, A.K.; Das, M.L.; Shaikh, M.A.Q.; Danso, S.K.A.

    1998-01-01

    Field experiments on chickpea and groundnut were variously carried out at four locations in Bangladesh. Generally consistent trends were obtained in terms of positive effects of inoculation with rhizobia, and genotypic diversity for components of N 2 fixation and yield. Inoculation of groundnut increased average nodule number by 77% at Rajshahi, 99% at Mymensingh and 148% at Jamalput. The increases in nodule dry weight, plant dry weight, pod and stover yields due to inoculation ranged from 93 to 146%, 55 to 77%, 43 to 50% and 29 to 80%, respectively. At all three locations, significant differences were found amongst the genotypes for nodulation, dry matter production and yield. Mutant genotype 62-30 was superior for most components, and statistically better than the present variety Dacca-1 for all characteristics investigated. Inoculant application to chickpea resulted in at least a doubling of nodule number at Ishurdi and Mymensingh; on average, there was a three-fold increase in nodule mass as a result of inoculation. Seed-yield increases due to inoculation ranged from 24 to 50%. Inoculated cv. G-97 recorded a seed yield of about 1.5 t/ha at Ishurdi, 47% higher than that produced by Nabin, a variety widely cultivated in Bangladesh. Total-N yield and the amount of N fixed by G-97 with inoculant were also higher than for Hyprosola, which is known for high yield and protein content. In a screening trial at Mymensingh the commercial chickpea Nabin and Hyprosola were consistently inferior to advanced lines produced by mutation breeding. Of 12 mutant groundnut genotypes tested, D1-15KR/62-30 maintained superiority for almost all components. Most of the mutants performed better than the commercial variety Dacca-1. The data show the potential for increasing chickpea and groundnut yields in Bangladesh by improving N 2 fixation via selection of superior genotype in conjunction with compatible rhizobia

  1. Molybdenum isotope fractionation by cyanobacterial assimilation during nitrate utilization and N2fixation

    Science.gov (United States)

    Zerkle, A L; Scheiderich, K; Maresca, J A; Liermann, L J; Brantley, S L

    2011-01-01

    We measured the δ98Mo of cells and media from molybdenum (Mo) assimilation experiments with the freshwater cyanobacterium Anabaena variabilis, grown with nitrate as a nitrogen (N) source or fixing atmospheric N2. This organism uses a Mo-based nitrate reductase during nitrate utilization and a Mo-based dinitrogenase during N2 fixation under culture conditions here. We also demonstrate that it has a high-affinity Mo uptake system (ModABC) similar to other cyanobacteria, including marine N2-fixing strains. Anabaena variabilis preferentially assimilated light isotopes of Mo in all experiments, resulting in fractionations of −0.2‰ to −1.0‰ ± 0.2‰ between cells and media (εcells–media), extending the range of biological Mo fractionations previously reported. The fractionations were internally consistent within experiments, but varied with the N source utilized and for different growth phases sampled. During growth on nitrate, A. variabilis consistently produced fractionations of −0.3 ± 0.1‰ (mean ± standard deviation between experiments). When fixing N2, A. variabilis produced fractionations of −0.9 ± 0.1‰ during exponential growth, and −0.5 ± 0.1‰ during stationary phase. This pattern is inconsistent with a simple kinetic isotope effect associated with Mo transport, because Mo is likely transported through the ModABC uptake system under all conditions studied. We present a reaction network model for Mo isotope fractionation that demonstrates how Mo transport and storage, coordination changes during enzymatic incorporation, and the distribution of Mo inside the cell could all contribute to the total biological fractionations. Additionally, we discuss the potential importance of biologically incorporated Mo to organic matter-bound Mo in marine sediments. PMID:21092069

  2. Pea mutant risnod27 as reference line for field assessment of impact of symbiotic nitrogen fixation

    Czech Academy of Sciences Publication Activity Database

    Biedermannová, E.; Novák, Karel; Vondrys, J.

    2002-01-01

    Roč. 25, č. 9 (2002), s. 2051-2066 ISSN 0190-4167 R&D Projects: GA ČR GA521/00/0937 Institutional research plan: CEZ:AV0Z5020903 Keywords : pea mutant * symbiotic nodules Subject RIV: EE - Microbiology, Virology Impact factor: 0.593, year: 2002

  3. Determination of symbiotic nitrogen fixation by labelling the soil atmosphere with sup(15)N sub(2) at low isotope enrichment

    International Nuclear Information System (INIS)

    Trivelin, P.C.O.

    1982-01-01

    A direct method to determine the total symbiotic nitrogen fixation during the leguminous plants cycles has been, developed, by labelling the soil atmosphere with sup(15)N sub(2) at low isotope enrichment, of about 1 atom % excess. The soil explored by the root system of leguminous plants was confined by means of a chamber in the field and by sealed pots in greenhouse experiments in order to maintain the soil air labelled with sup(15)N sub(2). The average sup(15)N concentration in the soil atmosphere, necessary to calculate dinitrogen fixation, was obtained by integration of the exponential functions of isotope dilution. Those functions were obtained by periodic sampling and analysis of the N sub(2) in the soil atmosphere. The field experiment with labelled atmosphere was carried out from the 22 sup(nd) to the 31 sup(st) day of the bean crop cycle and 5.5 mg N/plant (24% of total plant N) was derived from fixation. In pot experiments, under greenhouse conditions, integrated determination of fixation was made in Phaseolus beans (from the 19 sup(th) to the 67 sup(th) day from planting) and in soybeans (from the 24 sup(th) to the 70 sup(th) day from planting). The soil atmosphere was labelled with sup(15)N sub(2) in both cases. Average fixation obtained for Phaseolus beans was 80 mg N/plant (65% of total plant N) and for soybeans 265 mg N/plant (71% of total plant N). Evaluation of the basic concept of the isotope dilution method to determine nitrogen fixation in pots experiments, as proposed by Fried and Middelboe (1977) has also been made in the present paper. Simultaneous determinations of fixation in soybeans, using the isotope dilution method of Fried and Middelboe, natural variation of the sup(15)N/ sup(14)N ratios, and total-N differences, indicated the same results for pot experiments, harvested at the end of the plant cycle. (author)

  4. Diversity of Nitrogen Fixation Genes in the Symbiotic Intestinal Microflora of the Termite Reticulitermes speratus

    OpenAIRE

    Ohkuma, M.; Noda, S.; Usami, R.; Horikoshi, K.; Kudo, T.

    1996-01-01

    The diversity of nitrogen-fixing organisms in the symbiotic intestinal microflora of a lower termite, Reticulitermes speratus, was investigated without culturing the resident microorganisms. Fragments of the nifH gene, which encodes the dinitrogenase reductase, were directly amplified from the DNA of the mixed microbial population in the termite gut and were clonally isolated. The phylogenetic analysis of the nifH product amino acid sequences showed that there was a remarkable diversity of ni...

  5. Co-optimization of diesel fuel biodegradation and N2 fixation through the addition of particulate organic carbon

    International Nuclear Information System (INIS)

    Piehler, M.; Swistak, J.; Paerl, H.

    1995-01-01

    Petroleum hydrocarbon pollution in the marine environment is widespread and current bioremedial techniques are often not cost effective for small spills. The formulation of simple and inexpensive bioremedial methods could help reduce the impacts of frequent low volume spills in areas like marinas and ports. Particulate organic carbon (POC) was added to diesel fuel amended samples from inshore marine waters in the form of corn-slash (post-harvest leaves and stems), with and without inorganic nutrients (nitrate and phosphate). Biodegradation of diesel fuel ( 14 C hexadecane mineralization) and N 2 fixation were measured in response to the additions, The addition of POC was necessary for N 2 fixation and diesel fuel biodegradation to co-occur. The effects of diesel fuel and inorganic nutrient additions on N 2 fixation rates were not consistent, with both inhibitory and stimulatory responses to each addition observed. The highest observed diesel fuel biodegradation levels were in response to treatments that included inorganic nutrients. The addition of POC alone increased diesel fuel degradation levels above that observed in the control. In an attempt to determine the effect of the POC on the microbial community, the corn particles were observed microscopically using scanning electron microscopy and light microscopy with tetrazolium salt additions. The corn particles were found to have abundant attached bacterial communities and microscale oxygen concentration gradients occurring on individual particles. The formation of oxygen replete microzones may be essential for the co-occurrence of aerobic diesel fuel biodegradation and oxygen inhibited N2 fixation. Mesocosm experiments are currently underway to further examine the structure and function of this primarily heterotrophic system and to explore the potential contribution of N 2 fixation to the N requirements of diesel fuel biodegradation

  6. Forage production and N2 fixation in mixed cropping of saltbush and shrubby medic grown on a salt affected soil

    International Nuclear Information System (INIS)

    Kurdali, F.

    2008-11-01

    Two experiments were conducted to evaluate dry matter, nitrogen yield, N 2 fixation (Ndfa) and soil N uptake in saltbush (Atriplex halimus) and shrubby medic (Medicago arborea) grown either solely or in mixture on a salt affected soil, using 15 N tracer techniques. In a pot experiment, the combined dry matter yield of both species was considerably higher than that of solely grown shrubs. The inclusion of saltbush in the mixed cropping system decreased soil N uptake by shrubby medic and enhanced %Ndfa without affecting amounts of N 2 fixed. Under field conditions, estimated values of %Ndfa via δ 15 N natural abundance were relatively similar to those of the pot experiment using 15 N enrichment method. It can be concluded that the use of mixed cropping system of shrubby medic and saltbush could be a promising bio-saline agricultural approach to utilize salt affected soils in terms of forage yield and N 2 -fixation. (Author)

  7. Highly productive forage legume stands show no positive biodiversity effect on yield and N2-fixation

    DEFF Research Database (Denmark)

    Dhamala, Nawa Raj; Eriksen, Jørgen; Carlsson, Georg

    2017-01-01

    Background and aims While N fixation in diversified grasslands including forage legumes and non-legumes has been widely studied, N fixation in swards containing only forage legumes remains unclear. In this study, we investigated N fixation in pure stands and mixtures of three forage legumes....... Methodology N fixation, dry matter (DM) and nitrogen (N) yields were quantified in a field experiment for red clover (Trifolium pratense L.), white clover (Trifolium repens L.) and lucerne (Medicago sativa L.) pure stands and mixtures using the isotope dilution method. Results All three forage legume species...... derived most (around 85%) of their N from atmospheric N fixation (%Ndfa). However, no positive effect of species diversity was found in any of the mixtures. Species composition of the forage legume mixtures affected the amount of N from N fixation by affecting DM production and N accumulation...

  8. Rates and Controls of N2 Fixation in Sphagnum spp. along the Hydrological Gradient - Beaver Pond to Bog Transition at Mer Bleue, Ontario, Canada

    Science.gov (United States)

    Zivkovic, T.; Moore, T. R.

    2014-12-01

    Many northern bogs with low atmospheric N inputs acquire N only via N2-fixation. Little is known about rates and controls on N2-fixation in bogs. The aim of this study was to: 1) test the important ecological drivers for N2-fixation, 2) investigate seasonal and temporal patterns of N2 fixation, and 3) to estimate current N2-fixation rates at Mer Bleue bog. We used acetylene reduction assay (ARA) to measure N2-fixation from June-October 2013 and 2014 (currently ongoing field season) along a hydrological gradient (beaver pond, hollows and hummocks). The highest ARA rates in 2013 growing season occurred in the pond in floating Sphagnum cuspidatum mats (50.3 ± 12.9 μmol m-2 d-1 Mean ± Std Err) which were up to 2.5 times latger than the rates found in the hummock with the lowest water table depth throughout the season. Two rain events during the summer 2013 increased ARA rates in all plots by 1 to 4 times, suggesting that moisture availability may play a crucial role on N2 fixation potential in the field. We are currently investigating the role of moisture, temperature, PAR and nutrient content (N, phosphorous and metals) on ARA along the gradient. In addition, we are using 15N2 enrichment method to estimate N2 fixation rates and compare them to ARA method at Mer Bleue bog.

  9. Increased genetic variability for symbiotic nitrogen fixation in green gram (Vigna radiata L.)

    International Nuclear Information System (INIS)

    Rosaiah, G.; Kumari, D.S.; Satyanarayana, A.; Seenaiah, P.

    1989-01-01

    Full text: When green gram is planted after rice in Andhra Pradesh, its nitrogen fixation relies upon local rhizobia that have been able to survive the stress of 5-6 months submergence. No rhizobia strain isolated elsewhere was found superior to native rhizobia. Thus improvement of the host may be the only practicable way to improve nitrogen fixation. 15 mutants obtained from gamma irradiated green gram variety 'LGG 127' were tested along with the parent and the cultivar 'Pant Mung 2'. Nodule no. per plant was higher in the mutants. There was also considerable variation in dry weight of nodules per plant and in seed yield. However the number of nodules per plant showed no correlation with seed yield, nodule size may be more relevant. The N content of the shoots at anthesis was positively correlated with dry weight of nodules, seed protein % and seed yield per plant. (author)

  10. Assessment of N 2 fixation in 32 cowpea ( Vigna unguiculata L ...

    African Journals Online (AJOL)

    ... 3.1 and 2.9 t/ha, respectively) in 2006. In general, these data show that genotypes that fixed more N also produced more biomass and grain yield and are therefore, the best candidates for inclusion in cropping systems as biofertilizers. Key words: Symbiotic performance, N nutrition, biomass, N-fixed, cowpea varieties.

  11. Electrochemical Reduction of N2 under Ambient Conditions for Artificial N2 Fixation and Renewable Energy Storage Using N2 /NH3 Cycle.

    Science.gov (United States)

    Bao, Di; Zhang, Qi; Meng, Fan-Lu; Zhong, Hai-Xia; Shi, Miao-Miao; Zhang, Yu; Yan, Jun-Min; Jiang, Qing; Zhang, Xin-Bo

    2017-01-01

    Using tetrahexahedral gold nanorods as a heterogeneous electrocatalyst, an electrocatalytic N 2 reduction reaction is shown to be possible at room temperature and atmospheric pressure, with a high Faradic efficiency up to 4.02% at -0.2 V vs reversible hydrogen electrode (1.648 µg h -1 cm -2 and 0.102 µg h -1 cm -2 for NH 3 and N 2 H 4 ·H 2 O, respectively). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Effect of saline water on growth, yield and N2 fixation by faba bean and lentil plants using nitrogen-15

    International Nuclear Information System (INIS)

    Gadalla, A.M.; Galal, Y.G.M.; Elakel, E.A.; Ismail, H.; Hamdy, A.

    2003-01-01

    This work had been carried out under greenhouse conditions through joint research project between international agronomic mediterranean (IAM, Bari), italy and soils and water dept., Egyptian atomic energy authority. The aim of this dy was to assess the effect of saline water irrigation on growth, yield and nitrogen fixation (% Ndfa) by faba bean and lentil plants inoculated with selected rhizobium strains. Four saline irrigation water levels (fresh water, 3.6 and ds/m) were used. 20 kg N/ha as ammonium sulfate contained 10% N-15 atom excess was applied for quantification of biological N-fixation N-portions derived from fertilizer (Ndff). Results showed that high levels of salinity negatively affected seed yield and N accumulated in tissue of faba bean. Similar trend was noticed with dry matter of lentil while shoot-N was increased at 6 and 9 ds/m. Both leguminous crops were mainly dependent on N 2 fixation as an important source of nitrogen nutrition. Under adverse conditions salinity, the plants gained some of their N requirements from the other two N sources (Ndff and Ndfs). Application of the suitable Rhizobium bacteria strains could be beneficial for both the plant growth and soil fertility via N 2 fixation

  13. Biological N2 Fixation by Chickpea in inter cropping System on Sand Soil

    International Nuclear Information System (INIS)

    Ismail, M. M.; Moursy, A. A. A.; Kotb, E. A.; Farid, I. M.

    2012-12-01

    A field experiment was carried out at the plant Nutrition and Fertilization Unit, Soils and Water Research Department, Nuclear Research Center, Atomic Energy Authority, Inshas, Egypt on wheat and chickpea inter cropping. The benefits of N 2 fixation by legumes to cereals growing in inter crops or to grasses growing in mixed swards are high clear. in cases the benefit to the N status of cereals has bee seen when they are inter cropped with legumes , where benefit is found ,it is mainly due to sparing of soil N rather than direct transfer from the legume. inter cropped wheat has a high grains yield as compared to those recorded under sole crop. The application of inter cropping system induced an increase of wheat grain yield against the sole system. regardless the cultivation system, the over all means of fertilizer rates indicated (50% MF + 50% OM) treatment was superiority (100% OM) and (75% MF + 25% OM) or those recorded with either un fertilizer when wheat grain yield considered. Comparison heed between organic sources reflected the superiority of under sole cultivation, while chickpea straw was the best under inter cropping. Inter cropped has a high grain N uptake compared to soil system. While totally organic materials had accumulates more N in grain than those of underrated treated control. In the same time, the overall mean indicated the superiority of compost treatment combined with 50% mineral fertilizer under inter cropping system over those of either only organic materials treatment or those combined with 75% mineral fertilizer. Plants treated of chickpea straw and compost, achieved the best value of straw weight. Among the organic manure treatments, chickpea straw and compost seem to be the best ones. Nitrogen derived from air (% Ndfa) shoots and seeds of chickpea plant: In case of cow manure and maize stalk, the best value of nitrogen derived from air was detected followed by compost, while the lowest value was recorded with wheat straw. In general

  14. Biological N2 fixation by chickpea in inter cropping system on sand soil

    International Nuclear Information System (INIS)

    Ismail, M. M.; Moursy, A. A. A.; Kotb, E. A.; Farid, I. M.

    2012-12-01

    A field experiment was carried out at the plant nutrition and fertilization unit, Soils and Water Research Department, Nuclear Research Center, Atomic Energy Authority, Inshas, Egypt on wheat and chickpea incorporating. The benefits of N 2 fixation by legumes to cereals growing in inter crops or to grasses growing in mixed swards are high clear. In cases the benefit to the N status of cereals has bee seen when they are inter cropped with legumes, where benefit is found, it is mainly due to sparing of soil N rather than direct transfer from the legume. Inter cropped wheat, has a high grains yield as compared to those recorded under sole crop. The application of inter cropping system an increase of wheat grain yield against the sole system, regardless the cultivation system, the over all means of fertilizer rates indicated (50% MF + 50% OM) treatment was superiority (100% OM) and (75% MF + 25% OM) or those recorded with either un fertilizer when wheat grain yield considered. Comparison heed between or gain sources reflected the superiority of compost under sole cultivation, while chickpea straw was the best under inter cropping. Inter cropped has a high grain N uptake compared to soil systems. While totally organic materials had accumulates more N in grains than those of untreated treated control. In the some time, the overall mean indicated the superiority of compost treatment combined with 50% mineral fertilizer under inter cropping system over those of either only organic materials treatment or those combined with 75% mineral fertilizer. Plants treated of chickpea straw and compost, achieved the best value of straw weight. A mong the organic manure treatments, chickpea straw and compost seem to be the best ones. Nitrogen derived from air (%Ndfa) shoots and seeds of chickpea plants: In case of cow manure and maize stalk, the best value of nitrogen derived from air was detected followed by compost, while the lowest value was recorded with wheat straw. In general

  15. Mesopelagic N2 Fixation Related to Organic Matter Composition in the Solomon and Bismarck Seas (Southwest Pacific.

    Directory of Open Access Journals (Sweden)

    Mar Benavides

    Full Text Available Dinitrogen (N2 fixation was investigated together with organic matter composition in the mesopelagic zone of the Bismarck (Transect 1 and Solomon (Transect 2 Seas (Southwest Pacific. Transparent exopolymer particles (TEP and the presence of compounds sharing molecular formulae with saturated fatty acids and sugars, as well as dissolved organic matter (DOM compounds containing nitrogen (N and phosphorus (P were higher on Transect 1 than on Transect 2, while oxygen concentrations showed an opposite pattern. N2 fixation rates (up to ~1 nmol N L-1 d-1 were higher in Transect 1 than in Transect 2, and correlated positively with TEP, suggesting a dependence of diazotroph activity on organic matter. The scores of the multivariate ordination of DOM molecular formulae and their relative abundance correlated negatively with bacterial abundances and positively with N2 fixation rates, suggesting an active bacterial exploitation of DOM and its use to sustain diazotrophic activity. Sequences of the nifH gene clustered with Alpha-, Beta-, Gamma- and Deltaproteobacteria, and included representatives from Clusters I, III and IV. A third of the clone library included sequences close to the potentially anaerobic Cluster III, suggesting that N2 fixation was partially supported by presumably particle-attached diazotrophs. Quantitative polymerase chain reaction (qPCR primer-probe sets were designed for three phylotypes and showed low abundances, with a phylotype within Cluster III at up to 103 nifH gene copies L-1. These results provide new insights into the ecology of non-cyanobacterial diazotrophs and suggest that organic matter sustains their activity in the mesopelagic ocean.

  16. Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

    DEFF Research Database (Denmark)

    Batterman, Sarah A.; Hedin, Lars O.; Van Breugel, Michiel

    2013-01-01

    Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO 2 may be constrained by nitrogen, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N 2), but it is unclear whether this function...

  17. Key role of symbiotic dinitrogen fixation in tropical forest secondary succession

    NARCIS (Netherlands)

    Batterman, S.A.; Hedin, L.O.; Breugel, van M.; Ransijn, J.; Craven, D.J.; Hall, J.S.

    2013-01-01

    Forests contribute a significant portion of the land carbon sink, but their ability to sequester CO2 may be constrained by nitrogen1, 2, 3, 4, 5, 6, a major plant-limiting nutrient. Many tropical forests possess tree species capable of fixing atmospheric dinitrogen (N2)7, but it is unclear whether

  18. [Factor analysis of interactions between alfalfa nodule bacteria (Sinorhizobium meliloti) genes that regulate symbiotic nitrogen fixation].

    Science.gov (United States)

    Provorov, N A; Chuklina, E; Vorob'ev, N I; Onishchuk, O P; Simarov, B V

    2013-04-01

    Factor analysis has been conducted for the data on the interaction between the genes of the root nodule bacteria (rhizobia), which influence the efficiency of symbiosis with leguminous plants, including dctA (encoding succinate permease), dctBD (activating the dctA gene due to binding its enhancer in the presence of succinate), rpoN (activating the promoters of dctA and nitrogenase genes nifHDK), and nifA (activating the nitrogenase genes due to binding their enhancers). The analysis of the alfalfa rhizobia (Sinorhizobium meliloti) recombinants that contain additional copies ofthese genes suggested the antagonistic (epistatic) interaction between nifA and rpoN. It may be associated either with the competition for C compounds imported into the nodules between the energy production and nitrogen assimilation processes or with the competition for redox potentials between the oxidative phosphorylation and nitrogen fixation processes. Since the phenotypic effects of the studied genes depend on the activity of nitrogen export into the aerial parts of plants, we suppose that its accumulation in bacteroids impairs the activation of the nifHDK genes by the NifA protein due to its interaction with the GlnB protein (the nitrogen metabolism regulator) or with the FixLJ and ActSR proteins (the redox potential regulators).

  19. Highly productive forage legume stands show no positive biodiversity effect on yield and N2-fixation

    DEFF Research Database (Denmark)

    Dhamala, Nawa Raj; Eriksen, Jørgen; Carlsson, Georg

    2017-01-01

    . Methodology N fixation, dry matter (DM) and nitrogen (N) yields were quantified in a field experiment for red clover (Trifolium pratense L.), white clover (Trifolium repens L.) and lucerne (Medicago sativa L.) pure stands and mixtures using the isotope dilution method. Results All three forage legume species...

  20. Free-air CO2 enrichment (FACE) reduces the inhibitory effect of soil nitrate on N2 fixation of Pisum sativum.

    Science.gov (United States)

    Butterly, Clayton R; Armstrong, Roger; Chen, Deli; Tang, Caixian

    2016-01-01

    Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen (N) fixation in legumes. This study examined the interactive effects of atmospheric CO2 and nitrate (NO3(-)) concentration on the growth, nodulation and N fixation of field pea (Pisum sativum) in a semi-arid cropping system. Field pea was grown for 15 weeks in a Vertosol containing 5, 25, 50 or 90 mg NO3(-)-N kg(-1) under either ambient CO2 (aCO2; 390 ppm) or elevated CO2 (eCO2; 550 ppm) using free-air CO2 enrichment (SoilFACE). Under aCO2, field pea biomass was significantly lower at 5 mg NO3(-)-N kg(-1) than at 90 mg NO3(-)-N kg(-1) soil. However, increasing the soil N level significantly reduced nodulation of lateral roots but not the primary root, and nodules were significantly smaller, with 85% less nodule mass in the 90 NO3(-)-N kg(-1) than in the 5 mg NO3(-)-N kg(-1) treatment, highlighting the inhibitory effects of NO3(-). Field pea grown under eCO2 had greater biomass (approx. 30%) than those grown under aCO2, and was not affected by N level. Overall, the inhibitory effects of NO3(-) on nodulation and nodule mass appeared to be reduced under eCO2 compared with aCO2, although the effects of CO2 on root growth were not significant. Elevated CO2 alleviated the inhibitory effect of soil NO3(-) on nodulation and N2 fixation and is likely to lead to greater total N content of field pea growing under future elevated CO2 environments. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  1. 15N2 Fixation and H2 Evolution by Six Species of Tropical Leguminous Trees 1

    Science.gov (United States)

    van Kessel, Christopher; Roskoski, Joann P.; Wood, Timothy; Montano, Jorge

    1983-01-01

    The C2H4/15N2 and H2/15N2 ratios for six species of tropical leguminous trees are reported. C2H4/15N2 ratios ranged from 2.4 to 4.7; values for the H2/15N2 ratios were between 0.6 and 1.4. Relative efficiency values, based on C2H2 reduction, 15N incorporation, and H2 evolution during 15N incorporation varied between 0.68 and 0.84 for the six species. Overall, approximately 30% of the electron flow through nitrogenase was used for H2 evolution. PMID:16663109

  2. Development of a new biofertilizer with a high capacity for N2 fixation, phosphate and potassium solubilization and auxin production.

    Science.gov (United States)

    Leaungvutiviroj, Chaveevan; Ruangphisarn, Pimtida; Hansanimitkul, Pikul; Shinkawa, Hidenori; Sasaki, Ken

    2010-01-01

    Biofertilizers that possess a high capacity for N(2) fixation (Azotobacter tropicalis), and consist of phosphate solubilizing bacteria (Burkhoderia unamae), and potassium solubilizing bacteria (Bacillus subtilis) and produce auxin (KJB9/2 strain), have a high potential for growth and yield enhancement of corn and vegetables (Chinese kale). For vegetables, the addition of biofertilizer alone enhanced growth 4 times. Moreover, an enhancement of growth by 7 times was observed due to the addition of rock phosphate and K-feldspar, natural mineral fertilizers, in combination with the biofertilizer.

  3. The evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes may involve a loss of nitrate responsiveness of the NIN transcription factor.

    Science.gov (United States)

    Suzuki, Wataru; Konishi, Mineko; Yanagisawa, Shuichi

    2013-10-01

    NODULE INCEPTION (NIN) is a key regulator of the symbiotic nitrogen fixation pathway in legumes including Lotus japonicus. NIN-like proteins (NLPs), which are presumably present in all land plants, were recently identified as key transcription factors in nitrate signaling and responses in Arabidopsis thaliana, a non-leguminous plant. Here we show that both NIN and NLP1 of L. japonicus (LjNLP1) can bind to the nitrate-responsive cis-element (NRE) and promote transcription from an NRE-containing promoter as did the NLPs of A. thaliana (AtNLPs). However, differing from LjNLP1 and the AtNLPs that are activated by nitrate signaling through their N-terminal regions, the N-terminal region of NIN did not respond to nitrate. Thus, in the course of the evolution of NIN into a transcription factor that functions in nodulation in legumes, some mutations might arise that converted it to a nitrate-insensitive transcription factor. Because nodule formation is induced under nitrogen-deficient conditions, we speculate that the loss of the nitrate-responsiveness of NIN may be one of the evolutionary events necessary for the emergence of symbiotic nitrogen fixation in legumes.

  4. Symbiotic N2-fixation by the cover crop Pueraria phaseoloides as influenced by litter mineralization

    DEFF Research Database (Denmark)

    Vesterager, J.M.; Østerby, S.; Jensen, E.S.

    1995-01-01

    ) and litter N (Ndfl) to total plant N in P phaseoloides was determined in a pot experiment using a N-15 cross-labeling technique. For determination of N-2-fixation the non-fixing plant Axonopus compressus was used as a reference. The experiment was carried out in a growth chamber during 9 weeks with a sandy...... soil and 4 rates of ground litter (C/N=16, 2.8% N). P. phaseoloides plants supplied with the highest amount of litter produced 26% more dry matter and fixed 23% more N than plants grown in soil with no litter application, but the percentage of Ndfa decreased slightly, but significantly, from 87 to 84...... (shoot + root) and was not affected by the quantity added. A parallel incubation experiment also showed that, as an average of all litter levels, 26% of the litter N was present in the inorganic N pool. The amounts of fertilizer and soil N taken up by plants decreased with litter application, probably...

  5. Stimulation of biological N2-fixation to accelerate the microbial remediation of soil contaminated by petroleum hydrocarbons

    International Nuclear Information System (INIS)

    Tereshenko, N.N.; Lushnikov, S.V.

    2005-01-01

    All remediation projects are comprised at least in accelerating the processes of the self-cleaning and self-restoration of biocenose which is led to increasing the functional activity of hydrocarbon-oxidizing microflora (HOM). Some of experts are carefully relate to introducing the commercial cultures of active hydrocarbon-consuming microbes into soils. They are afraid of unpredictable behavior of the cultures in soils. That why the stimulation of metabolic activity of indigenous soil microflora seems to be most preferable. In fact, contamination of soil with low nitrogen capacity by oil spills leads to significant deficient of nitrogen for HOM. Nitrogen content limits the soil self-restoration. Inorganic nitrogen fertilizers are supplied to recover the balance. The study of the microbial destruction of petroleum-hydrocarbons in association with biochemical transformation of nitrogen was carried out in lab and field experiments during 2000-2004. Study showed the activity of HOM correlates with rate of microbial fixing atmospheric nitrogen. Activity of biological N 2 -fixation significantly depends on supplying fertilizers (dose, date and kind). General practice of remediation of hydrocarbon-contaminated soils applies high initial doses of nitrogen-fertilizers (0.5-1 t per ha). Such practice leads to inhibition of N 2 -fixation processes, decreasing rate of oil destruction and loosing nitrogen due to activation of microbial denitrification. In opposition to that, the fractioned and advanced supplying mineral nitrogen fertilizers with aluminosilicate is the cost-effective approach to remediation of hydrocarbon-contaminated soils. Field experiments showed that the approach allows to increase efficiency of treatment up to 70-75% and to decrease operational expenses 2-3 times at least. (authors)

  6. Simple approach for the preparation of 15-15N2-enriched water for nitrogen fixation assessments: Evaluation, application and recommendations

    Directory of Open Access Journals (Sweden)

    Isabell eKlawonn

    2015-08-01

    Full Text Available Recent findings revealed that the commonly used 15N2 tracer assay for the determination of dinitrogen (N2 fixation can underestimate the activity of aquatic N2-fixing organisms. Therefore, a modification to the method using pre-prepared 15-15N2-enriched water was proposed. Here, we present a rigorous assessment and outline a simple procedure for the preparation of 15-15N2-enriched water. We recommend to fill sterile-filtered water into serum bottles and to add 15-15N2 gas to the water in amounts exceeding the standard N2 solubility, followed by vigorous agitation (vortex mixing ≥5 min. Optionally, water can be degassed at low-pressure (≥950 mbar for ten minutes prior to the 15-15N2 gas addition to indirectly facilitate the 15-15N2 dissolution. This preparation of 15-15N2-enriched water can be done within one hour using standard laboratory equipment. The final 15N-atom% excess was 5% after replacing 2–5% of the incubation volume with 15-15N2-enriched water. Notably, the addition of 15-15N2-enriched water can alter levels of trace elements in the incubation water due to the contact of 15-15N2-enriched water with glass, plastic and rubber ware during its preparation. In our tests, levels of trace elements (Fe, P, Mn, Mo, Cu, Zn increased by up to 0.1 nmol L-1 in the final incubation volume, which may bias rate measurements in regions where N2 fixation is limited by trace elements. For these regions, we tested an alternative way to enrich water with 15-15N2. The 15-15N2 was injected as a bubble directly to the incubation water, followed by gentle shaking. Immediately thereafter, the bubble was replaced with water to stop the 15-15N2 equilibration. This method achieved a 15N-atom excess of 6.6±1.7% when adding 2 mL 15-15N2 per liter of incubation water. The herein presented methodological tests offer guidelines for the 15N2 tracer assay and thus, are crucial to circumvent methodological draw-backs for future N2 fixation assessments.

  7. Estimation of N2 fixation in winter and spring sown chickpea and in lentil grown under rainfed conditions using 15 N

    International Nuclear Information System (INIS)

    Kurdali, F.; Khalifa, Kh.; Al-Asfari, F.

    1996-03-01

    A field experiment was conducted under rainfed conditions to asses N 2 fixation in one cultivar of lentil and in two cultivars of chickpea (Gab 1 for winter and spring sowing, and Baladi for spring sowing). Moreover, the effect of P fertilizer on dry matter production, percentages and amounts of different N sources was studied using 15 N isotope dilution method. Wheat was used as a reference crop. The rate of N 2 fixation affected by several factors such as plant species, cultivar, date of sowing, P-fertilizer and the growing season. The highest amount of N 2 fixation obtained in winter sown chickpea was 126 Kg N ha -1 . Whereas, that of spring sowing for the same cultivar was 30 Kg N ha -1 . For Baladi cultivar, the highest amount of N-fixed was 55 Kg N ha -1 . While it was 104 Kg N ha -1 in lentil. Generally, N 2 -fixation affected positively by P-application. In the first growing season, N 2 -fixation increased from 33 to %58 by P application in spring sown chickpea (Baladi), and from 20 to %35 in spring sown chickpea (Gab 1). Whereas, no significant differences were observed upon P application in winter sown chickpea and in lentil. In the second growing season, P-fertilizer increased the percentage of N 2 fixation from 54 to %64 in winter sown chickpea, and from 45 to %64 in spring sown chickpea (Gab 1), and from 49 to %60 in spring sown chickpea (Baladi). While, in lentil it was from 66 to %72. The rate of N 2 fixation in winter sown chickpea was clearly higher than that of spring sowings. Moreover, this last one absorbed more N from the soil. Our results indicate the importance of winter sown chickpea in terms of N 2 fixation, seed yield and the reduction of soil N-uptake, besides a positive P-fertilizer response, especially when suitable rain fall occurs during the season. Moreover, the importance of these results from agronomical point of view was discussed. (author). 24 refs., 6 figs., 7 tabs

  8. Short-term effects of a dung pat on N2 fixation and total N uptake in a perennial ryegrass/white clover mixture

    DEFF Research Database (Denmark)

    Jørgensen, F.V.; Jensen, E.S.

    1997-01-01

    The short-term effects of a simulated cattle dung pat on N-2 fixation and total uptake of N in a perennial ryegrass/white clover mixture was studied in a container experiment using sheep faeces mixed with water to a DM content of 13%. We used a new N-15 cross-labelling technique to determine...... the influence of dung-pat N on N-2 fixation in a grass/clover mixture and the uptake of dung N in grass and clover. The proportion of N in clover derived from N-2 fixation (%Ndfa) varied between 88-99% during the 16 weeks following application of the dung. There was no effect of dung on the %Ndfa in clover...... herbage, 78% was recovered from the soil and the residual dung, and 18% was not accounted for. It is concluded that N-2 fixation in the dung patch border area in grass/clover mixtures is not influenced directly by the release of N from dung pats in the short term. However the amount of N-2 fixed may...

  9. Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

    Science.gov (United States)

    Lu, Yangyang; Wen, Zuozhu; Shi, Dalin; Chen, Mingming; Zhang, Yao; Bonnet, Sophie; Li, Yuhang; Tian, Jiwei; Kao, Shuh-Ji

    2018-01-01

    Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotroph-derived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient) range of 193 to 315 µE m-2 s-1, with light saturation at around 400 µE m-2 s-1. The proportion of DDN net release ranged from ˜ 6 to ˜ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF / NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m-2 s-1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term ( metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

  10. Theoretical implications for the estimation of dinitrogen fixation by large perennial plant species using isotope dilution

    Science.gov (United States)

    Dwight D. Baker; Maurice Fried; John A. Parrotta

    1995-01-01

    Estimation of symbiotic N2 fixation associated with large perennial plant species, especially trees, poses special problems because the process must be followed over a potentially long period of time to integrate the total amount of fixation. Estimations using isotope dilution methodology have begun to be used for trees in field studies. Because...

  11. Photosynthesis, N(2) fixation and taproot reserves during the cutting regrowth cycle of alfalfa under elevated CO(2) and temperature.

    Science.gov (United States)

    Erice, G; Sanz-Sáez, A; Aranjuelo, I; Irigoyen, J J; Aguirreolea, J; Avice, J-C; Sánchez-Díaz, M

    2011-11-15

    Future climatic conditions, including rising atmospheric CO(2) and temperature may increase photosynthesis and, consequently, plant production. A larger knowledge of legume performance under the predicted growth conditions will be crucial for safeguarding crop management and extending the area under cultivation with these plants in the near future. N(2) fixation is a key process conditioning plant responsiveness to varying growth conditions. Moreover, it is likely to increase under future environments, due to the higher photosynthate availability, as a consequence of the higher growth rate under elevated CO(2). However, as described in the literature, photosynthesis performance is frequently down-regulated (acclimated) under long-term exposure to CO(2), especially when affected by stressful temperature and water availability conditions. As growth responses to elevated CO(2) are dependent on sink-source status, it is generally accepted that down-regulation occurs in situations with insufficient plant C sink capacity. Alfalfa management involves the cutting of shoots, which alters the source-sink relationship and thus the photosynthetic behaviour. As the growth rate decreases at the end of the pre-cut vegetative growth period, nodulated alfalfa plants show photosynthetic down-regulation, but during regrowth following defoliation, acclimation to elevated CO(2) disappears. The shoot harvest also leads to a drop in mineral N uptake and C translocation to the roots, resulting in a reduction in N(2) fixation due to the dependence on photosynthate supply to support nodule function. Therefore, the production of new shoots during the first days following cutting requires the utilization of reduced C and N compounds that have been stored previously in reserve organs. The stored reserves are mediated by phytohormones such as methyl jasmonate and abscisic acid and in situations where water stress reduces shoot production this potentially enables the enhancement of taproot

  12. Regulation of respiration and the oxygen diffusion barrier in soybean protect symbiotic nitrogen fixation from chilling-induced inhibition and shoots from premature senescence.

    Science.gov (United States)

    van Heerden, Philippus D R; Kiddle, Guy; Pellny, Till K; Mokwala, Phatlane W; Jordaan, Anine; Strauss, Abram J; de Beer, Misha; Schlüter, Urte; Kunert, Karl J; Foyer, Christine H

    2008-09-01

    Symbiotic nitrogen fixation is sensitive to dark chilling (7 degrees C-15 degrees C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT.

  13. Metabolic adaptation, a specialized leaf organ structure and vascular responses to diurnal N2 fixation by nostoc azollae sustain the astonishing productivity of azolla ferns without nitrogen fertilizer

    NARCIS (Netherlands)

    Brouwer, Paul; Bräutigam, Andrea; Buijs, Valerie A.; Tazelaar, Anne O.E.; van der Werf, Adrie; Schlüter, Urte; Reichart, Gert-Jan; Bolger, Anthony; Usadel, Björn; Weber, Andreas P.M.; Schluepmann, Henriette

    2017-01-01

    Sustainable agriculture demands reduced input of man-made nitrogen (N) fertilizer, yet N2 fixation limits the productivity of crops with heterotrophic diazotrophic bacterial symbionts. We investigated floating ferns from the genus Azolla that host phototrophic diazotrophic Nostoc azollae in leaf

  14. Effect of N fertilizer top-dressing at various reproductive stages on growth, N-2 fixation and yield of three soybean (Glycine max (L.) Merr.) genotypes

    NARCIS (Netherlands)

    Gan, YB; Stulen, [No Value; van Keulen, H; Kuiper, PJC

    2003-01-01

    Soybean (Glycine max (L.) Merr.) is one of the most important food and cash crops in China and a key protein source for the farmers in northern China. Previous experiments in both the field and greenhouse have shown that N-2 fixation alone cannot meet the N requirement for maximizing soybean yield,

  15. Effect of N fertilizer top-dressing at various reproductive stages on growth, N2 fixation and yield of three soybean (Glycine max (L.) Merr.) genotypes

    NARCIS (Netherlands)

    Gan, Y.B.; Stulen, I.; Kuiper, P.J.C.; Keulen, van H.

    2003-01-01

    Soybean (Glycine max (L.) Merr.) is one of the most important food and cash crops in China and a key protein source for the farmers in northern China. Previous experiments in both the field and greenhouse have shown that N2 fixation alone cannot meet the N requirement for maximizing soybean yield,

  16. Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

    Directory of Open Access Journals (Sweden)

    Y. Lu

    2018-01-01

    Full Text Available Dinitrogen fixation (NF by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve of NF rate and the effect of light on diazotroph-derived nitrogen (DDN net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15N2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF was measured in parallel using the 13C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a Ik (light saturation coefficient range of 193 to 315 µE m−2 s−1, with light saturation at around 400 µE m−2 s−1. The proportion of DDN net release ranged from  ∼  6 to  ∼  50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF ∕ NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m−2 s−1. Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that short-term ( <  24 h light change modulates the physiological state, which subsequently determined the C ∕ N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle

  17. Natural abundances of 15Nitrogen and 13Carbon indicative of growth and N2 fixation in potassium fed lentil grown under water stress

    International Nuclear Information System (INIS)

    Kurdali, F.; Alshmmaa, M.

    2010-01-01

    Dual natural abundance analysis of 15 N and 13 C isotopes in lentil plants subjected to different soil moisture levels and rates of potassium fertilizer (K) were determined to assess crop performance variability in terms of growth and N 2 -fixation (Ndfa). δ 15 N values in lentils ranged from +0.67 to +1.36%; whereas, those of the N 2 -fixed and reference plant were -0.45 and +2.94%, respectively. Consequently, the Ndfa% ranged from 45 and 65% of total plant N uptake. Water stress reduced Δ 13 C values. However, K fertilization enhanced whole plant Δ 13 C along with dry matter yield and N 2 -fixation. The water stressed plants amended with K fertilizer seemed to be the best treatment because of its highest pod yield, high N balance and N 2 -fixation with low consumption of irrigation water. This illustrates the ecological and economical importance of K fertilizer in alleviating water stress occurring during the post-flowering period of lentil. (author)

  18. Symbiotic nitrogen fixation and yield of Pachyrhizus Erosus (L) urban cultivars and Pachyrhizus Ahipa (WEDD) parodi landraces as affected by flower pruning

    DEFF Research Database (Denmark)

    Castellanos, J.Z.; Zapata, F.; Badillo, V.

    1997-01-01

    as reference crops. In the second experiment N-15 isotopic dilution methodology was used to determine N-2 fixation in the same cultivars as in Experiment 1, using the same reference crops, but tuber legumes were only grown with pruning of flowers. In the first experiment the amounts of nitrogen fixed ranged...... biomass without N fertiliser application. In some climatic regions P. erosus is reproductively pruned in order to obtain economic yields, but little is known about how the pruning influences the capacity of these tuber legumes to fix nitrogen. Two experiments were carried out to investigate the effect...

  19. The use of N-15 in the measurement of symbiotic nitrogen fixation by legumes under field condition

    International Nuclear Information System (INIS)

    Impithuksa, Viroj

    1982-01-01

    The amount of N fixation by legume crop in field condition by using 15 N can determine by the addition of labelled 15 N fertilizer into the soil and measuring the amount of labelled 15 N, soil N, and fixed N taken up by legume crop. This requires a standard crop (reference crop) as a control to determine labelled 15 N and soil N taken up by this crop. In case the same rate of labelled 15 N fertilizer is added to the legume crop and a standard crop

  20. Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat.

    Science.gov (United States)

    Steunou, Anne-Soisig; Jensen, Sheila I; Brecht, Eric; Becraft, Eric D; Bateson, Mary M; Kilian, Oliver; Bhaya, Devaki; Ward, David M; Peters, John W; Grossman, Arthur R; Kühl, Michael

    2008-04-01

    Nitrogen fixation, a prokaryotic, O2-inhibited process that reduces N2 gas to biomass, is of paramount importance in biogeochemical cycling of nitrogen. We analyzed the levels of nif transcripts of Synechococcus ecotypes, NifH subunit and nitrogenase activity over the diel cycle in the microbial mat of an alkaline hot spring in Yellowstone National Park. The results showed a rise in nif transcripts in the evening, with a subsequent decline over the course of the night. In contrast, immunological data demonstrated that the level of the NifH polypeptide remained stable during the night, and only declined when the mat became oxic in the morning. Nitrogenase activity was low throughout the night; however, it exhibited two peaks, a small one in the evening and a large one in the early morning, when light began to stimulate cyanobacterial photosynthetic activity, but O2 consumption by respiration still exceeded the rate of O2 evolution. Once the irradiance increased to the point at which the mat became oxic, the nitrogenase activity was strongly inhibited. Transcripts for proteins associated with energy-producing metabolisms in the cell also followed diel patterns, with fermentation-related transcripts accumulating at night, photosynthesis- and respiration-related transcripts accumulating during the day and late afternoon, respectively. These results are discussed with respect to the energetics and regulation of N2 fixation in hot spring mats and factors that can markedly influence the extent of N2 fixation over the diel cycle.

  1. Investigating patterns of symbiotic nitrogen fixation during vegetation change from grassland to woodland using fine scale δ(15) N measurements.

    Science.gov (United States)

    Soper, Fiona M; Boutton, Thomas W; Sparks, Jed P

    2015-01-01

    Biological nitrogen fixation (BNF) in woody plants is often investigated using foliar measurements of δ(15) N and is of particular interest in ecosystems experiencing increases in BNF due to woody plant encroachment. We sampled δ(15) N along the entire N uptake pathway including soil solution, xylem sap and foliage to (1) test assumptions inherent to the use of foliar δ(15) N as a proxy for BNF; (2) determine whether seasonal divergences occur between δ(15) Nxylem sap and δ(15) Nsoil inorganic N that could be used to infer variation in BNF; and (3) assess patterns of δ(15) N with tree age as indicators of shifting BNF or N cycling. Measurements of woody N-fixing Prosopis glandulosa and paired reference non-fixing Zanthoxylum fagara at three seasonal time points showed that δ(15) Nsoil inorganic N varied temporally and spatially between species. Fractionation between xylem and foliar δ(15) N was consistently opposite in direction between species and varied on average by 2.4‰. Accounting for these sources of variation caused percent nitrogen derived from fixation values for Prosopis to vary by up to ∼70%. Soil-xylem δ(15) N separation varied temporally and increased with Prosopis age, suggesting seasonal variation in N cycling and BNF and potential long-term increases in BNF not apparent through foliar sampling alone. © 2014 John Wiley & Sons Ltd.

  2. Symbiotic Nitrogen Fixation in Alfalfa (Medicago Sativa L.) by Sinorhizobium Meliloti at Al-Qassim Regions, Saudi Arabia

    International Nuclear Information System (INIS)

    Al-Barakah, F. N.; Mridha, M. A. U.

    2016-01-01

    The nodulation status in alfalfa (Medicago sativa L.) plants by Sinorhizobium meliloti under Saudi field condition was assessed in some selected farms in four seasons for two years. In the present study, we also monitored the introduced S. meliloti strains activity under Saudi soil conditions. The samples were collected at regular seasonal intervals from the selected farms. The total number of nodules, morphology of the nodules and the effectiveness of N/sub 2/-fixation was assessed. In general, it was revealed that soils in the selected areas in Saudi Arabia have sufficient bacteria of the proper types to nodulate the alfalfa plants. These nodules are high in number, small in size and white in color. The nodules obtained from most of the selected farms are ineffective for nitrogen fixation. Inoculation of alfalfa seeds with imported S. meliloti strains failed to fix the atmospheric nitrogen sufficiently and also the growth improvement of alfalfa plants. There was a wide variation in the occurrence of number of nodules among the four seasons in two years. It was also observed that summer season severely affected the nodulation making it nearly zero. This low number of nodules exerts a very slow recovery of nodule formation in the next year. The introduced strains were always over competing with the native strains but they did not survive because of hot and dry summer. Nitrogenase activity of the nodules collected from both the inoculated and non-inoculated farms were always very low in all the collected samples, which indicates that the ability of fixing nitrogen by S. meliloti strains in alfalfa under Saudi soils conditions is very low. (author)

  3. Termites create spatial structure and govern ecosystem function by affecting N2 fixation in an East African savanna.

    Science.gov (United States)

    Fox-Dobbs, Kena; Doak, Daniel F; Brody, Alison K; Palmer, Todd M

    2010-05-01

    The mechanisms by which even the clearest of keystone or dominant species exert community-wide effects are only partially understood in most ecosystems. This is especially true when a species or guild influences community-wide interactions via changes in the abiotic landscape. Using stable isotope analyses, we show that subterranean termites in an East African savanna strongly influence a key ecosystem process: atmospheric nitrogen fixation by a monodominant tree species and its bacterial symbionts. Specifically, we applied the 15N natural abundance method in combination with other biogeochemical analyses to assess levels of nitrogen fixation by Acacia drepanolobium and its effects on co-occurring grasses and forbs in areas near and far from mounds and where ungulates were or were not excluded. We find that termites exert far stronger effects than do herbivores on nitrogen fixation. The percentage of nitrogen derived from fixation in Acacia drepanolobium trees is higher (55-80%) away from mounds vs. near mounds (40-50%). Mound soils have higher levels of plant available nitrogen, and Acacia drepanolobium may preferentially utilize soil-based nitrogen sources in lieu of fixed nitrogen when these sources are readily available near termite mounds. At the scale of the landscape, our models predict that termite/soil derived nitrogen sources influence >50% of the Acacia drepanolobium trees in our system. Further, the spatial extent of these effects combine with the spacing of termite mounds to create highly regular patterning in nitrogen fixation rates, resulting in marked habitat heterogeneity in an otherwise uniform landscape. In summary, we show that termite-associated effects on nitrogen processes are not only stronger than those of more apparent large herbivores in the same system, but also occur in a highly regular spatial pattern, potentially adding to their importance as drivers of community and ecosystem structure.

  4. Inhibition of nitrogen fixation in symbiotic Medicago truncatula upon Cd exposure is a local process involving leghaemoglobin.

    Science.gov (United States)

    Marino, Daniel; Damiani, Isabelle; Gucciardo, Sébastien; Mijangos, Iker; Pauly, Nicolas; Puppo, Alain

    2013-12-01

    Leguminous biological nitrogen fixation (BNF) is very sensitive to environmental fluctuations. It is still contentious how BNF is regulated under stress conditions. The local or systemic control of BNF and the role played by reactive oxygen species (ROS) in such regulation have still not been elucidated completely. Cadmium, which belongs to the so-called heavy metals, is one of the most toxic substances released into the environment. The mechanisms involved in Cd toxicity are still not completely understood but the overproduction of ROS is one of its characteristic symptoms. In this work, we used a split-root system approach to study nodule BNF and the antioxidant machinery's response to the application of a mild Cd treatment on one side of a nodulated Medicago truncatula root system. Cd induced the majority of nodule antioxidants without generating any oxidative damage. Cd treatment also provoked BNF inhibition exclusively in nodules directly exposed to Cd, without provoking any effect on plant shoot biomass or chlorophyll content. The overall data suggest that the decline in BNF was not due to a generalized breakdown of the plant but to control exerted through leghaemoglobin/oxygen availability, affecting nitrogenase function.

  5. A Biosensor-Based Leaf Punch Assay for Glutamine Correlates to Symbiotic Nitrogen Fixation Measurements in Legumes to Permit Rapid Screening of Rhizobia Inoculants under Controlled Conditions.

    Science.gov (United States)

    Thilakarathna, Malinda S; Moroz, Nicholas; Raizada, Manish N

    2017-01-01

    Legumes are protein sources for billions of humans and livestock. These traits are enabled by symbiotic nitrogen fixation (SNF), whereby root nodule-inhabiting rhizobia bacteria convert atmospheric nitrogen (N) into usable N. Unfortunately, SNF rates in legume crops suffer from undiagnosed incompatible/suboptimal interactions between crop varieties and rhizobia strains. There are opportunities to test much large numbers of rhizobia strains if cost/labor-effective diagnostic tests become available which may especially benefit researchers in developing countries. Inside root nodules, fixed N from rhizobia is assimilated into amino acids including glutamine (Gln) for export to shoots as the major fraction (amide-exporting legumes) or as the minor fraction (ureide-exporting legumes). Here, we have developed a new leaf punch based technique to screen rhizobia inoculants for SNF activity following inoculation of both amide exporting and ureide exporting legumes. The assay is based on measuring Gln output using the GlnLux biosensor, which consists of Escherichia coli cells auxotrophic for Gln and expressing a constitutive lux operon. Subsistence farmer varieties of an amide exporter (lentil) and two ureide exporters (cowpea and soybean) were inoculated with different strains of rhizobia under controlled conditions, then extracts of single leaf punches were incubated with GlnLux cells, and light-output was measured using a 96-well luminometer. In the absence of external N and under controlled conditions, the results from the leaf punch assay correlated with 15 N-based measurements, shoot N percentage, and shoot total fixed N in all three crops. The technology is rapid, inexpensive, high-throughput, requires minimum technical expertise and very little tissue, and hence is relatively non-destructive. We compared and contrasted the benefits and limitations of this novel diagnostic assay to methods.

  6. A Biosensor-Based Leaf Punch Assay for Glutamine Correlates to Symbiotic Nitrogen Fixation Measurements in Legumes to Permit Rapid Screening of Rhizobia Inoculants under Controlled Conditions

    Directory of Open Access Journals (Sweden)

    Malinda S. Thilakarathna

    2017-10-01

    Full Text Available Legumes are protein sources for billions of humans and livestock. These traits are enabled by symbiotic nitrogen fixation (SNF, whereby root nodule-inhabiting rhizobia bacteria convert atmospheric nitrogen (N into usable N. Unfortunately, SNF rates in legume crops suffer from undiagnosed incompatible/suboptimal interactions between crop varieties and rhizobia strains. There are opportunities to test much large numbers of rhizobia strains if cost/labor-effective diagnostic tests become available which may especially benefit researchers in developing countries. Inside root nodules, fixed N from rhizobia is assimilated into amino acids including glutamine (Gln for export to shoots as the major fraction (amide-exporting legumes or as the minor fraction (ureide-exporting legumes. Here, we have developed a new leaf punch based technique to screen rhizobia inoculants for SNF activity following inoculation of both amide exporting and ureide exporting legumes. The assay is based on measuring Gln output using the GlnLux biosensor, which consists of Escherichia coli cells auxotrophic for Gln and expressing a constitutive lux operon. Subsistence farmer varieties of an amide exporter (lentil and two ureide exporters (cowpea and soybean were inoculated with different strains of rhizobia under controlled conditions, then extracts of single leaf punches were incubated with GlnLux cells, and light-output was measured using a 96-well luminometer. In the absence of external N and under controlled conditions, the results from the leaf punch assay correlated with 15N-based measurements, shoot N percentage, and shoot total fixed N in all three crops. The technology is rapid, inexpensive, high-throughput, requires minimum technical expertise and very little tissue, and hence is relatively non-destructive. We compared and contrasted the benefits and limitations of this novel diagnostic assay to methods.

  7. Mechanisms of physiological adjustment of N2 fixation in Cicer arietinum L. (chickpea) during early stages of water deficit: single or multi-factor controls.

    Science.gov (United States)

    Nasr Esfahani, Maryam; Sulieman, Saad; Schulze, Joachim; Yamaguchi-Shinozaki, Kazuko; Shinozaki, Kazuo; Tran, Lam-Son Phan

    2014-09-01

    Drought negatively impacts symbiotic nitrogen fixation (SNF) in Cicer arietinum L. (chickpea), thereby limiting yield potential. Understanding how drought affects chickpea nodulation will enable the development of strategies to biotechnologically engineer chickpea varieties with enhanced SNF under drought conditions. By analyzing carbon and nitrogen metabolism, we studied the mechanisms of physiological adjustment of nitrogen fixation in chickpea plants nodulated with Mesorhizobium ciceri during both drought stress and subsequent recovery. The nitrogenase activity, levels of several key carbon (in nodules) and nitrogen (in both nodules and leaves) metabolites and antioxidant compounds, as well as the activity of related nodule enzymes were examined in M. ciceri-inoculated chickpea plants under early drought stress and subsequent recovery. Results indicated that drought reduced nitrogenase activity, and that this was associated with a reduced expression of the nifK gene. Furthermore, drought stress promoted an accumulation of amino acids, mainly asparagine in nodules (but not in leaves), and caused a cell redox imbalance in nodules. An accumulation of organic acids, especially malate, in nodules, which coincided with the decline of nodulated root respiration, was also observed under drought stress. Taken together, our findings indicate that reduced nitrogenase activity occurring at early stages of drought stress involves, at least, the inhibition of respiration, nitrogen accumulation and an imbalance in cell redox status in nodules. The results of this study demonstrate the potential that the genetic engineering-based improvement of SNF efficiency could be applied to reduce the impact of drought on the productivity of chickpea, and perhaps other legume crops. © 2014 The Authors The Plant Journal © 2014 John Wiley & Sons Ltd.

  8. Growth and N2-fixation of dhaincha (Sesbania aculata) and sunflower (Helianthus annuus) in an inter cropping system using natural abundances of 15N and 13C

    International Nuclear Information System (INIS)

    Kurdali, F.

    2010-06-01

    A field experiment on dhaincha (Sesbania aculata) and sunflower (Helianthus annuus) plants grown in mono cropping and inter cropping systems was conducted to evaluate seed yield , oil content, dry matter production (DM), land equivalent ratio (LER), N- yield, competition for soil N uptake and N 2 -fixation using 13 C and 15 N natural abundance techniques. Three different combinations of sesbania (ses) and sunflower (sun) were investigated in the inter cropping system (1ses:1sun; 1ses:2sun, and 2ses:1sun, row ratio). The results showed that: From productivity standpoint, the 1ses:1sun surpassed the other treatments in terms of N and DM yields and exhibited a similar distribution of total DM and N uptake in the sesbania and sunflower plant species. The 1ses:2sun was next in order in terms of DM and N uptake showing also a similar distribution of total N in both plant species. On the other hand, the 1ses:2sun gave the greatest seed and oil production and together with 1ses:1sun treatment were satisfactory in terms of LER for DM in both species having almost similar values. However, the former treatment was more appropriate than the latter because of its higher LER value for seed and oil yield of sunflower plants. Nevertheless, 2ses:1sun treatment seemed not to be an appropriate treatment due to the divergence of LER values in both species, where sunflower plants had a low value as compared to sesbania. From ecological standpoint, the best treatment was 1ses:2sun which showed the greatest N 2 -fixation. Sesbania plants fixed almost identical amounts of atmospheric N 2 in both the mono cropping and inter cropping systems although the density of these plants in the latter was only 1/3 that of the former system. Moreover, soil N-uptake in the 1ses:2sun was the lowest among other treatments. These results give an advantage to the 1ses:2sun treatment over other treatments in terms of soil N consumption and N 2 fixation to meet sesbania's N requirements. %Δ 13 C in the

  9. Estimation of N2-fixation in cowpea grown in monoculture or in mixture with maize using 15 N

    International Nuclear Information System (INIS)

    Shammaa, Mouhammad; Kurd Ali, Fawaz

    1994-01-01

    A pot experiment was carried out under natural climatic conditions to determine the proportion of different nitrogen sources (air, soil, fertilizer) in cowpea and maize grown alone or in mixture using 15 N isotope dilution technique. On average, the proportion of N derived from fixation by cowpea grown in mixed culture was 55% lower than that derived by the sole cropped cowpea (77%). Dry matter produced by one plant of maize grown in mixed culture was twice as much as that produced by a plant grown in mono culture. Moreover, total nitrogen content in one maize plant grown in mixed culture was 213 mg higher than that determined by two plant of maize grown in mono culture (171 mg). However, the amount of nitrogen derived from soil by maize grown in mixed culture was equal or even higher than that taken up by two plants of maize grown in mono culture. This indicates a better utilization of soil N by the maize in mixed culture. This data emphasize the crucial role of interspecific competition in soil N uptake. Data from this study do not support the hypothesis of N transfer from the legume to the cereal because no significant differences were found between mixed and pure maize in terms of 15 N in excess content. (author). 9 refs., 1 tab

  10. Evaluation of symbiotic performance of some mutant lines of soybean inoculated with two bradyrhizobium japonicum strains using 15N technique

    International Nuclear Information System (INIS)

    Kurdali, F.; Mir-Ali, N.; Al-Nabulsi, I.

    2002-11-01

    A pot experiment was conducted to study the symbiotic performance of two soybean varieties and some of their mutants (that were obtained as a result of a previous mutation breeding program) with two bradyrhizobium japonicum strains (RG and FA3) using 15 N isotopic dilution method. Random amplified polymorphic DNA technique (RAPD) was used to study the genetic relationships among the soybean genotypes and to make sure that the two rhizobial strains are different. The 25 random primers used discriminated the different soybean genotypes and the dendrogram resultants from shared polymorphic fragments put each variety and its mutants in two separate clusters asserting that the mutants and their mother lines are different. Both strains of B. japonicum were able to form effective nodules on all soybean plants. However, number of nodules, dry matter yield and N-uptake from the available sources by soybeans were affected by both plant genotype and rhizobial strains. N 2 -fixation was affected to a large extent by different strain and plant genotype combinations. Percentage of fixed N 2 (N dfa) ranged between 35 and 49%; whereas, the actual amounts of fixed N 2 were between 105 and 210 mg N/pot. Amounts of N 2 -fixed by FA3 strain were higher than of RG in both soybean varieties, whereas, the latter strain showed higher performance in the mutant lines. The results showed that total plant N estimation may not be a sufficient indicator for high N 2 -fixation. the results also showed that it is very important to determine both the amount of nitrogen derived from N 2 -fixation and N derived from soil for evaluating the symbiotic performance ability. Moreover, the performance of symbiotic N 2 -fixation in soybean was shown to depend on both plant genotype and rhizobial strain and the amount of N 2 -fixation can be increased by combining the best plant genotypes and the most adapted strain. (author)

  11. Spatial variation of N-2-fixation in field pea (Pisum sativum L.) at the field scale determined by the N-15 natural abundance method

    DEFF Research Database (Denmark)

    Hauggaard-Nielsen, Henrik; Holdensen, Lars; Wulfsohn, D.

    2010-01-01

    variability could be explained by the variability in selected abiotic soil properties. All measured soil variables showed substantial variability across the field and the pea dry matter production ranged between 4.9 and 13.8 Mg ha−1 at maturity. The percent of total N derived from the atmosphere (%Ndfa...... pea dry matter production and humus content, potassium content (collinear with humus) and total N in the 0–25 cm topsoil. No correlation was found between any individual soil property and %Ndfa or kg N fixed ha−1. It was not possible to create a satisfactory global multi-regression model for the field...... dry matter production and N2-fixation. A number of other models were tested, but the best was only able to explain less than 40% of the variance in %Ndfa using seven soil properties. Together with the use of interpolated soil data, high spatial variation of soil 15N natural abundance, a mean increase...

  12. Impact of increased ultraviolet-B radiation stress due to stratospheric ozone depletion on N2 fixation in traditional African commercial legumes

    International Nuclear Information System (INIS)

    Chimphango, S.B.M.; Musil, C.F.; Dakora, F.D.

    2004-01-01

    Reports of diminished nodule formation and nitroge-nase activity in some Asian tropical legumes exposed to above-ambient levels of ultraviolet-B (UV-B: 280-315nm) radiation have raised concerns as to the impact of stratospheric ozone depletion on generally poorly developed traditional African farming systems confronted by the high cost and limited availability of chemical fertilisers. These rely on N 2 -fixing legumes as the cheapest source of N for maintaining soil fertility and sustainable yields in the intrinsically infertile and heterogeneous African soils. In view of this, we examined the effects of supplemental UV-B radiation approximating 15% and 25% depletions in the total ozone column on N 2 fixation in eight traditional African commercial legume species representing crop, forest, medicinal, ornamental and pasture categories. In all categories examined, except medicinal, supplemental UV-B had no effect on root non-structural carbohydrates, antho-cyanins and flavonoids, known to signal Rhizobiaceae micro-symbionts and promote nodule formation, or on nodule mass, activity and quantities of N fixed in different plant organs and whole plants. In contrast, in the medicinal category Cyclopia maculata (Honeybush) a slow growing commercially important herbal beverage with naturally high flavonoid concentrations, displayed decreased nodule activity and quantities of N fixed in different plant organs and whole plants with increased UV-B. This study's findings conclude negligible impacts of ozone depletion on nitrogen fixation and soil fertility in most traditional African farming systems, these limited to occasional inhibition of nodule induction in some crops. (author)

  13. Biological N2-FIXATION and Mineral N-Fertilization Effects on Soybean (Glicine max L. Merr.) Yield Under Temperate Climate Conditions

    Science.gov (United States)

    László Phd, M., ,, Dr.

    2009-04-01

    Summary In a nitrogen fertilization experiment set up on slightly calcareous Ramann sandy- loam brown forest soil studies were made on the effect of nitrogen (N) x Rhizobium japonicum inoculation (I) x variety (V) interactions on soybean yield in Hungary. The agrochemical parameters of the ploughed layer of soil were as follows: humus 1.3%, CaCO3 2.1%, silty clay 27%, pH (H2O) 7.2, pH (KCl) 7.0. The experiment involved 4N x 3I x 3V = combinations in 4 replications, giving a total of 144 plots. The most important results can be summarized as follows: (a.) 0, (b.) 100, (c.) 150 and (d.) 200 kg ha-1 year-1 of nitrogen application (a.) inoculation effect was maximum at 1 kg t-1 Nitrofix, (b.) yields were linearly and inversely related to the rate of Nitrofix, (c.) presence of any amount of Nitrofix has been a negative effect on yield and (d.) Nitrofix 1 kg t-1 was showed the best results. Both biological N2 fixation (BNF) and nitrate (NO3-) utilization by mineral nitrogen fertilizer (MNF) input were essential for maximum soybean yield. Introduction Nitrogen is the most frequently deficient nutrient in crop production therefore, most cropping system require N- inputs (Johnston 2000, Márton 2000, 2001). Many soursces are available for use in supplying N to crops (Kováts et al. 1985). In addition to from N2 fixation by leguminous crops can supply sufficient N for optimum crop production (Wilcox 1987, Kádár & Márton 1999, Márton & Kádár 1998, László & Jose 2001, László et al. 2001). Understanding the behaviour of N in the soil is essential for maximizing agricultural productivity and profitability while reducing the impacts of N fertilization on the environment. Managing the delicate balance in the soil N- supply in order to meet this goals. Nowadays there is an essential need to use nitrogen to achieve both economic yields and to produce enough food. Because the only way for agriculture to keep pace with population (world's population now exceeds 6 billion and

  14. Phylogeny of nodulation genes and symbiotic diversity of Acacia senegal (L.) Willd. and A. seyal (Del.) Mesorhizobium strains from different regions of Senegal.

    Science.gov (United States)

    Bakhoum, Niokhor; Galiana, Antoine; Le Roux, Christine; Kane, Aboubacry; Duponnois, Robin; Ndoye, Fatou; Fall, Dioumacor; Noba, Kandioura; Sylla, Samba Ndao; Diouf, Diégane

    2015-04-01

    Acacia senegal and Acacia seyal are small, deciduous legume trees, most highly valued for nitrogen fixation and for the production of gum arabic, a commodity of international trade since ancient times. Symbiotic nitrogen fixation by legumes represents the main natural input of atmospheric N2 into ecosystems which may ultimately benefit all organisms. We analyzed the nod and nif symbiotic genes and symbiotic properties of root-nodulating bacteria isolated from A. senegal and A. seyal in Senegal. The symbiotic genes of rhizobial strains from the two Acacia species were closed to those of Mesorhizobium plurifarium and grouped separately in the phylogenetic trees. Phylogeny of rhizobial nitrogen fixation gene nifH was similar to those of nodulation genes (nodA and nodC). All A. senegal rhizobial strains showed identical nodA, nodC, and nifH gene sequences. By contrast, A. seyal rhizobial strains exhibited different symbiotic gene sequences. Efficiency tests demonstrated that inoculation of both Acacia species significantly affected nodulation, total dry weight, acetylene reduction activity (ARA), and specific acetylene reduction activity (SARA) of plants. However, these cross-inoculation tests did not show any specificity of Mesorhizobium strains toward a given Acacia host species in terms of infectivity and efficiency as stated by principal component analysis (PCA). This study demonstrates that large-scale inoculation of A. senegal and A. seyal in the framework of reafforestation programs requires a preliminary step of rhizobial strain selection for both Acacia species.

  15. Stable symbiotic nitrogen fixation under water-deficit field conditions by a stress-tolerant alfalfa microsymbiont and its complete genome sequence.

    Science.gov (United States)

    Jozefkowicz, Cintia; Brambilla, Silvina; Frare, Romina; Stritzler, Margarita; Piccinetti, Carlos; Puente, Mariana; Berini, Carolina Andrea; Pérez, Pedro Reyes; Soto, Gabriela; Ayub, Nicolás

    2017-12-10

    We here characterized the stress-tolerant alfalfa microsymbiont Sinorhizobium meliloti B401. B401-treated plants showed high nitrogen fixation rates under humid and semiarid environments. The production of glycine betaine in isolated bacteroids positively correlated with low precipitation levels, suggesting that this compound acts as a critical osmoprotectant under field conditions. Genome analysis revealed that strain B401 contains alternative pathways for the biosynthesis and uptake of glycine betaine and its precursors. Such genomic information will offer substantial insight into the environmental physiology of this biotechnologically valuable nitrogen-fixing bacterium. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. Comparison of inhibition of N2 fixation and ureide accumulation under water deficit in four common bean genotypes of contrasting drought tolerance.

    Science.gov (United States)

    Coleto, I; Pineda, M; Rodiño, A P; De Ron, A M; Alamillo, J M

    2014-05-01

    Drought is the principal constraint on world production of legume crops. There is considerable variability among genotypes in sensitivity of nitrogen fixation to drought, which has been related to accumulation of ureides in soybean. The aim of this study was to search for genotypic differences in drought sensitivity and ureide accumulation in common bean (Phaseolus vulgaris) germplasm that may be useful in the improvement of tolerance to water deficit in common bean. Changes in response to water deficit of nitrogen fixation rates, ureide content and the expression and activity of key enzymes for ureide metabolism were measured in four P. vulgaris genotypes differing in drought tolerance. A variable degree of drought-induced nitrogen fixation inhibition was found among the bean genotypes. In addition to inhibition of nitrogen fixation, there was accumulation of ureides in stems and leaves of sensitive and tolerant genotypes, although this was higher in the leaves of the most sensitive ones. In contrast, there was no accumulation of ureides in the nodules or roots of stressed plants. In addition, the level of ureides in the most sensitive genotype increased after inhibition of nitrogen fixation, suggesting that ureides originate in vegetative tissues as a response to water stress, probably mediated by the induction of allantoinase. Variability of drought-induced inhibition of nitrogen fixation among the P. vulgaris genotypes was accompanied by subsequent accumulation of ureides in stems and leaves, but not in nodules. The results indicate that shoot ureide accumulation after prolonged exposure to drought could not be the cause of inhibition of nitrogen fixation, as has been suggested in soybean. Instead, ureides seem to be produced as part of a general response to stress, and therefore higher accumulation might correspond to higher sensitivity to the stressful conditions.

  17. Influence of tree canopy on N₂ fixation by pasture legumes and soil rhizobial abundance in Mediterranean oak woodlands.

    Science.gov (United States)

    Carranca, C; Castro, I V; Figueiredo, N; Redondo, R; Rodrigues, A R F; Saraiva, I; Maricato, R; Madeira, M A V

    2015-02-15

    Symbiotic N2 fixation is of primordial significance in sustainable agro-forestry management as it allows reducing the use of mineral N in the production of mixed stands and by protecting the soils from degradation. Thereby, on a 2-year basis, N2 fixation was evaluated in four oak woodlands under Mediterranean conditions using a split-plot design and three replicates. (15)N technique was used for determination of N2 fixation rate. Variations in environmental conditions (temperature, rainfall, radiation) by the cork tree canopy as well as the age of stands and pasture management can cause great differences in vegetation growth, legume N2 fixation, and soil rhizobial abundance. In the present study, non-legumes dominated the swards, in particular beneath the tree canopy, and legumes represented only 42% of total herbage. A 2-fold biomass reduction was observed in the oldest sown pasture in relation to the medium-age sward (6 t DW ha(-1)yr(-1)). Overall, competition of pasture growth for light was negligible, but soil rhizobial abundance and symbiotic N2 fixation capacity were highly favored by this environmental factor in the spring and outside the influence of tree canopy. Nitrogen derived from the atmosphere was moderate to high (54-72%) in unsown and sown swards. Inputs of fixed N2 increased from winter to spring due to more favorable climatic conditions (temperature and light intensity) for both rhizobia and vegetation growths. Assuming a constant fixation rate at each seasonal period, N2 fixation capacity increased from about 0.10 kg N ha(-1) per day in the autumn-winter period to 0.15 kg N ha(-1) per day in spring. Belowground plant material contributed to 11% of accumulated N in pasture legumes and was not affected by canopy. Size of soil fixing bacteria contributed little to explain pasture legumes N. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Marcha de absorção do nitrogênio do solo, do fertilizante e da fixação simbiótica em feijão-caupi (Vigna unguiculata (L. walp. e feijão-comum (Phaseolus vulgaris L. determinada com uso de 15N Uptake rate of nitrogen from soil and fertilizer, and n derived from symbiotic fixation in cowpea (Vigna unguiculata (L. walp. and common bean (Phaseolus vulgaris L. determined using the 15N isotope

    Directory of Open Access Journals (Sweden)

    Marciano de Medeiros Pereira Brito

    2009-08-01

    , through the 15N-dilution technique and using rice and non-nodulating soybean as control plants, the relative contributions of nitrogen sources (symbiotically fixed N, soil native N and fertilizer N on the growth of common bean and cowpea and to compare the isotopic technique (ID with the difference methods (DM for the evaluation of symbiotic N2 fixation. The study was carried out in a greenhouse of the Center for Nuclear Energy in Agriculture - CENA/USP, Sao Paulo State, Brazil, using 5 kg pots with a Typic Haplustox (Dystrophic Red-Yellow Latosol. The experiment was arranged in completely randomized blocks, with 16 treatments and three replications, in an 8 x 2 factorial design. The treatments were eight sampling times: 7, 24, 31, 38, 47, 58, 68 and 78 days after sowing (DAS and two crops: common bean and cowpea. An N rate of 10 mg kg-1 soil was used, as urea, enriched with an excess of 10 % of 15N atoms. Symbiotic N fixation supplied the bean and cowpea plants with the greatest amount of accumulated N, followed, in decreasing order, by soil and fertilizer. The highest rate of N symbiotic fixation was observed at the pre-flowering growth stage of the bean and cowpea plants. After the initial growth stage, 24 DAS, rice and non nodulating soybean were appropriate control plants to evaluate symbiotic N fixation. There was a good agreement between ID and DM, except in the initial growth stage of the crops.

  19. Fixação do nitrogênio do ar pelas bactérias que vivem em simbiose com as raízes da centrosema Fixation of the atmospheric nitrogen by bacteria which live symbiotically on centrosema

    Directory of Open Access Journals (Sweden)

    J. Casado Montojos

    1963-01-01

    Full Text Available Continuando a série de trabalhos sôbre a quantidade de nitrogênio atmosférico fixada por bactérias que vivem em simbiose com raízes de leguminosas, são relatados os resultados encontrados em centrosema (Centrosema pubescens Benth. Foram utilizados vasos de Mitscherlich, com terra-roxa-misturada. A colheita das plantas foi efetuada por ocasião do florescimento. A parte aérea foi pesada para cálculo da quantidade de massa verde produzida, e, em seguida, juntamente com as raízes, sêca a 60°C até pêso constante. Determinaram-se os teores de nitrogênio na parte aérea e subterrânea das plantas, assim como da terra dos vasos. Os resultados mostraram elevada capacidade de fixação simbiótica de nitrogênio pela centrosema correspondente a cêrca de 204 quilogramas de nitrogênio por hectare.Following a series of research work with the purpose of verifying the amount of atmospheric nitrogen fixed by symbiotic bacteria, the authors report in this paper the results on their research with the leguminous plant Centrosema pubescens Benth. This experiment was conducted in Mitscherlich pots containing terra-roxa-misturada obtained from a 20 cm deep layer of soil taken from the Central Experiment Station "Theodureto de Camargo", in Campinas. The plants were cut in the blooming period, as this is the proper season for turning over green manure crops. The aerial portion of the plants was weighed so as to determine the total production of green matter and then it was dried together with the roots at 60°C. Thus, nitrogen of the total plant was determined and the same analysis was done at the end of the experiment for the soil removed from the pots. According to the results of this experiment, it was found that 204 kilograms of nitrogen per hectare were fixed, showing therefore that centrosema has a high capacity of symbiotic nitrogen fixation.

  20. The value of symbiotic nitrogen fixation by grain legumes in comparison to the cost of nitrogen fertilizer used in developing countries

    International Nuclear Information System (INIS)

    Hardarson, G.; Bunning, S.; Montanez, A.; Roy, R.; MacMillan, A.

    2001-01-01

    A great challenge lies in devising more sustainable farming systems without compromising food production levels and food security. Obviously, increasing productivity is necessary to accommodate growth in the global population. World wide, the environmental factors that most severely restrict plant growth are the availability of water and nitrogen. The challenges in developing countries are to find ways of meeting this additional nitrogen demand without concomitant degrading natural productivity. Widespread adoption of biological nitrogen fixation (BNF) would contribute to this goal. BNF, together with adequate N management in the ecosystem, appears to be the most promising alternative to increasing the use of inorganic fertiliser nitrogen. BNF technologies represent economic, sustainable and environmentally friendly means of ensuring the nitrogen requirement of an agro-ecosystem. Here we investigate the value of BNF by grain legumes and compares it to the cost of nitrogen fertilizer used in developing countries. Our data show that major grain legumes fix approximately 11.1 million metric tons of nitrogen per annum in developing countries. If this N was supplied by inorganic fertiliser one would have to apply at least double that amount to achieve the same yields, and this would cost approximately 6.7 billion US dollars. As the eight major grain legumes grown in developing countries contribute 30 - 40% of the annual N requirement the contribution of BNF is of great economic and environmental importance. (author)

  1. Update: Biological Nitrogen Fixation.

    Science.gov (United States)

    Wiseman, Alan; And Others

    1985-01-01

    Updates knowledge on nitrogen fixation, indicating that investigation of free-living nitrogen-fixing organisms is proving useful in understanding bacterial partners and is expected to lead to development of more effective symbioses. Specific areas considered include biochemistry/genetics, synthesis control, proteins and enzymes, symbiotic systems,…

  2. Identifying abnormalities in symbiotic development between Trifolium spp. and Rhizobium leguminosarum bv. trifolii leading to sub-optimal and ineffective nodule phenotypes

    Science.gov (United States)

    Melino, V. J.; Drew, E. A.; Ballard, R. A.; Reeve, W. G.; Thomson, G.; White, R. G.; O'Hara, G. W.

    2012-01-01

    Background and Aims Legumes overcome nitrogen limitations by entering into a mutualistic symbiosis with N2-fixing bacteria (rhizobia). Fully compatible associations (effective) between Trifolium spp. and Rhizobium leguminosarum bv. trifolii result from successful recognition of symbiotic partners in the rhizosphere, root hair infection and the formation of nodules where N2-fixing bacteroids reside. Poorly compatible associations can result in root nodule formation with minimal (sub-optimal) or no (ineffective) N2-fixation. Despite the abundance and persistence of strains in agricultural soils which are poorly compatible with the commercially grown clover species, little is known of how and why they fail symbiotically. The aims of this research were to determine the morphological aberrations occurring in sub-optimal and ineffective clover nodules and to determine whether reduced bacteroid numbers or reduced N2-fixing activity is the main cause for the Sub-optimal phenotype. Methods Symbiotic effectiveness of four Trifolium hosts with each of four R. leguminosarum bv. trifolii strains was assessed by analysis of plant yields and nitrogen content; nodule yields, abundance, morphology and internal structure; and bacteroid cytology, quantity and activity. Key Results Effective nodules (Nodule Function 83–100 %) contained four developmental zones and N2-fixing bacteroids. In contrast, Sub-optimal nodules of the same age (Nodule Function 24–57 %) carried prematurely senescing bacteroids and a small bacteroid pool resulting in reduced shoot N. Ineffective-differentiated nodules carried bacteroids aborted at stage 2 or 3 in differentiation. In contrast, bacteroids were not observed in Ineffective-vegetative nodules despite the presence of bacteria within infection threads. Conclusions Three major responses to N2-fixation incompatibility between Trifolium spp. and R. l. trifolii strains were found: failed bacterial endocytosis from infection threads into plant cortical

  3. Growth and N2-fixation of Dhaincha C-3/Sorghum C-4 and Dhaincha C-3/Sunflower C-3 intercropping systems using the 15N and 13C natural abundance method technique

    International Nuclear Information System (INIS)

    Kurdali, F.

    2007-06-01

    A field experiment on dhaincha C 3 (Sesbania aculeata Pers), sunflower C 3 (Helianthus annuus L.) and sorghum C 4 (Sorghum bicolor L.) plants grown in monocropping and intercropping systems was conducted to evaluate seed yield, dry matter production, total N yield, land equivalent ratio (LER), intraspecific competition for soil N uptake, water use efficiency (WUE) and N 2 -fixation using the 15 N natural abundance technique (δ 15 N ). Moreover, carbon isotope discrimination (Δ13 C ) was determined to assess factors responsible for crop performance variability in the different cropping systems. Intercropping of sesbania/sorghum showed greater efficiency over monocropping in producing dry matter, during the entire growth period, as indicated by the LERs (>1); whereas, the efficiency of producing dry matter in the sesbania /sunflower intercropping was similar to that in the monocropping system (LER=1). Moreover, sorghum plants (C 4 ) was more competitive than sesbania (C 3 ) for soil N uptake; whereas, sesbania seemed to be more competitive than its associated sunflower (C 3 ). N uptake in the mixed stand of sesbania/sorghum was improved due to the increase in soil N uptake by the component sorghum and the higher root nodule activity of component sesbania without affecting the amount of N 2 fixed. In both cropping systems, sesbania plants fixed almost the same amount of N 2 (an average of 105 kg N/ha) although the number of rows in the mixed stand was 2/3 of that in the pure stand. This gives an advantage of the intercropping over sole cropping system with regards to N 2 -fixation. 13 C discrimination in plant materials was found to be affected by plant species and the cropping system. Factors affected Δ13 C in plants grown in the mixed stand relative to solely grown crops are discussed.(author)

  4. Uptake rate of nitrogen from soil and fertilizer, and N derived from symbiotic fixation in cowpea (Vigna unguiculata (L.) Walp.) and common bean (Phaseolus vulgaris L.) determined using the {sup 15}N isotope; Marcha de absorcao do nitrogenio do solo, do fertilizante e da fixacao simbiotica em feijao-caupi (Vigna unguiculata (L.) Walp.) e feijao-comum (Phaseolus vulgaris L.) determinada com uso de {sup 15}N

    Energy Technology Data Exchange (ETDEWEB)

    Brito, Marciano de Medeiros Pereira; Muraoka, Takashi; Silva, Edson Cabral da [Centro de Energia Nuclear na Agricultura (CENA/USP), Piracicaba SP (Brazil)], e-mail: marcianobrito@hotmail.com, e-mail: muraoka@cena.usp.br, e-mail: ecsilva@cena.usp.br

    2009-07-15

    Common bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata (L.) Walp.) are among the main sources of plant protein for a large part of the world population, mainly that of low income, and nitrogen is the main constituent of these proteins. The objectives of this study were to evaluate, through the {sup 15}N-dilution technique and using rice and non-nodulating soybean as control plants, the relative contributions of nitrogen sources (symbiotically fixed N, soil native N and fertilizer N) on the growth of common bean and cowpea and to compare the isotopic technique (ID) with the difference methods (DM) for the evaluation of symbiotic N{sub 2} fixation. The study was carried out in a greenhouse of the Center for Nuclear Energy in Agriculture - CENA/USP, Sao Paulo State, Brazil, using 5 kg pots with a Typic Haplustox (Dystrophic Red-Yellow Latosol). The experiment was arranged in completely randomized blocks, with 16 treatments and three replications, in an 8 x 2 factorial design. The treatments were eight sampling times: 7, 24, 31, 38, 47, 58, 68 and 78 days after sowing (DAS) and two crops: common bean and cowpea. An N rate of 10 mg kg{sup -1} soil was used, as urea, enriched with an excess of 10 % of {sup 15}N atoms. Symbiotic N fixation supplied the bean and cowpea plants with the greatest amount of accumulated N, followed, in decreasing order, by soil and fertilizer. The highest rate of N symbiotic fixation was observed at the pre-flowering growth stage of the bean and cowpea plants. After the initial growth stage, 24 DAS, rice and non nodulating soybean were appropriate control plants to evaluate symbiotic N fixation. There was a good agreement between ID and DM, except in the initial growth stage of the crops. (author)

  5. Discussion on the planting patterns of alfalfa and meadow fescue in mixed culture and evaluation for their contribution from N2 fixation

    International Nuclear Information System (INIS)

    Yao Yunyin; Zhang Xizhong; Chen Ming

    1996-01-01

    Effects of planting patterns on dry weight, N yield and dinitrogen fixation in alfalfa-meadow fescue pasture are studied by using split plot design in the field for two successive years. The results show that the pattern of row seeding in mixture (RM) is superior to the pattern of broadcasting in mixture (BM) and intercropping (TC), and advantageous to develop the superiority of legume-grass mixed pasture. The annual average of dry weight for RM, BM and TC is 1535.9 g/m 2 , 1208.8 g/m 2 and 1249.3 g/m 2 respectively. The annual average of N yield of them is 50.83 g(N)/m 2 , 36.65 g(N)/m 2 and 36.86 g(N)/m 2 . The annual average Ndfa is 42.37 g(N)/m 2 , 28.21 g(N)/m 2 and 28.42 g(N)/m 2 , and %Ndfa is 83.4%, 77.0% and 77.1% for RM, BM and TC respectively. The comparison of 15 N isotope dilution method, natural 15 N abundance method and total N difference method to measure %Ndfa of herbage for all the treatments are made

  6. Expression of the N2 fixation gene operon of Paenibacillus sp. WLY78 under the control of the T7 promoter in Escherichia coli BL21.

    Science.gov (United States)

    Zhang, Lihong; Liu, Xiaomeng; Li, Xinxin; Chen, Sanfeng

    2015-10-01

    To investigate the transcription and translation and nitrogenase activity of the nine N2-fixing-gene (nif) operon (nifBHDKENXhesAnifX) of Paenibacillus sp. WLY78 under the control of the T7 promoter in Escherichia coli BL21 under different conditions. The Paenibacillus nif operon under the control of the T7 promoter is significantly transcribed and effectively translated in E. coli BL21 when grown in medium containing organic N compounds (yeast extract and Tryptone) or NH4+ by using RT-PCR and Western blot analysis. Transcription and translation of foreign nif genes in E. coli are not inhibited by environmental organic or inorganic N compounds or O2. However, contrary to transcription and translation, nitrogenase activity is 4% lower in the recombinant E. coli 78-32 compared to the native Paenibacillus sp. WLY78. The Paenibacillus nif operon under the control of T7 promoter enables E. coli BL21 to synthesize active nitrogenase. This study shows how the nif gene operon can be transferred to non-N2-fixing bacteria or to eukaryotic organelles.

  7. Evaluation of the biological nitrogen fixation (N2) contribution in several forage legumes and the transfer of N to associated grasses

    International Nuclear Information System (INIS)

    Vargas, M.S.V.

    1991-12-01

    The objective of experiment 1 was to compare two different techniques for labelling the soil mineral nitrogen with 15 N, for studies to quantify the contribution of biological nitrogen fixation (BNF) to forage legumes using the 15 N isotope dilution technique. The two techniques for labelling the soil were: incorporation a 15 N labelled organic compost (slow release treatment), and split applications of 15 N labelled ammonium sulphate. The evaluation of the techniques was through the quantification of BNF in the Itaguai Hybrid of Centrosema using two non-Na- fixing control plants (P. maximum K K-16 and Sorghum bicolor). The objective of experiment 2 was to quantify the contribution of BNF to forage legumes and the transfer of fixed nitrogen to associated grasses in mixed swards again using the 15 N isotope dilution technique. This study was conducted on a red podzolic soil (Typic Hapludult), with 7 forage legumes and 3 grasses in monoculture, and 3 mixed swards of Brachiaria brizantha with the Centrosema hybrid, Galactia striata and Desmodium ovalifolium, respectively, with varying ratios of grass to legume (4:1 to 1:4). In order to quantify the BNF contributions to the legumes and the transfer of fixed N to the B. brizantha, the plots were amended 8 times with doses of 0.01 g 15 N m -2 of 15 N labelled ammonium sulphate (12.5 atom % 15 N) each 14 days, giving a total of 0.08 g 15 N m -2 of 15 N during the 97 days of the experiment. In monoculture the different forage legumes obtained the equivalent of between 43 and 100 kg N ha -1 from BNF. Stylosanthes guianensis showed the greatest contributions from BNF at 100 Kg N ha -1 . In mixed swards with Brachiaria brizantha the proportion of N derived from BNF in the three legumes studied (Centrosema hybrid, G. striata and D. ovalifolium) was significantly greater than when they were grown in monoculture. (author). 197 refs, 9 figs, 19 tabs

  8. Symbiotic nitrogen-fixing bacterial populations trapped from soils under agroforestry systems in the Western Amazon

    Directory of Open Access Journals (Sweden)

    Paula Marcela Duque Jaramillo

    2013-12-01

    Full Text Available Cowpea (Vigna unguiculata is an important grain-producing legume that can forego nitrogen fertilization by establishing an efficient symbiosis with nitrogen-fixing bacteria. Although inoculating strains have already been selected for this species, little is known about the genotypic and symbiotic diversity of native rhizobia. Recently, Bradyrhizobium has been shown to be the genus most frequently trapped by cowpea in agricultural soils of the Amazon region. We investigated the genetic and symbiotic diversity of 148 bacterial strains with different phenotypic and cultural properties isolated from the nodules of the trap species cowpea, which was inoculated with samples from soils under agroforestry systems from the western Amazon. Sixty non-nodulating strains indicated a high frequency of endophytic strains in the nodules. The 88 authenticated strains had varying symbiotic efficiency. The SPAD (Soil Plant Analysis Development index (indirect measurement of chlorophyll content was more efficient at evaluating the contribution of symbiotic N2-fixation than shoot dry matter under axenic conditions. Cowpea-nodulating bacteria exhibited a high level of genetic diversity, with 68 genotypes identified by BOX-PCR. Sequencing of the 16S rRNA gene showed a predominance of the genus Bradyrhizobium, which accounted for 70 % of all strains sequenced. Other genera identified were Rhizobium, Ochrobactrum, Paenibacillus, Bosea, Bacillus, Enterobacter, and Stenotrophomonas. These results support the promiscuity of cowpea and demonstrate the high genetic and symbiotic diversity of rhizobia in soils under agroforestry systems, with some strains exhibiting potential for use as inoculants. The predominance of Bradyrhizobium in land uses with different plant communities and soil characteristics reflects the adaptation of this genus to the Amazon region.

  9. Nitrate levels and stages of growth in hypernodulating mutants of Lupinus albus. I. N2 fixation potential Influência dos diferentes níveis de nitrato e estágio de crescimento em mutantes hipernodulantes de Lupinus albus I. potencial de fixação de N2

    Directory of Open Access Journals (Sweden)

    Hélio Almeida Burity

    1999-04-01

    Full Text Available This work aimed to evaluate physiological parameters, nodulation response and N2 fixation rate in mutants of Lupinus albus in comparison with the standard Multolupa cultivar. Two nitrate levels (0 and 5mM and two evaluation periods (7 and 10 weeks were used. Significant differences were observed among genotypes, in relation to fresh nodule weight, nitrate levels and growth stages. The overall average for nitrate level differed between them where 5mM severely inhibited the number of nodules, reaching a 49.5% reduction in relation to treatment without nitrate. There were no behaviour differences among genotypes, nor among evaluation periods. Although the level of nitrate did not influence the production of shoot dry matter in relation to the average among levels applied, the L-135 genotype, being an inefficient mutant, reached very low values. There were no significant differences in electron allocation coefficient (EAC among nitrate levels, nor among genotypes studied. However, the evaluation periods revealed differences, where the EAC for the seventh week had a higher value than that for the tenth week, when a 5mM aplication was evaluated. The N2 fixation rate (N2 FIX showed the existence of the nitrate interference in fixation, given that the application of 5mM severely reduced. However, there were no differences among the genotypes and it was noted that the fixation rate was much higher in those that received nitrate. The L-88 and L-62 genotypes were the ones that have shown best adaptability in this experiment, thus being able to be recommended for new studies with higher nitrate levels and different evaluation periods. The nitrate (5mM interferes in the nitrogen fixation rate, given that all the genotypes were affected by the level applied.Este trabalho teve como objetivo avaliar parâmetros fisiológicos, resposta da nodulação e a taxa de fixação de N2 em mutantes de Lupinus albus comparando com a cultivar padrão Multolupa. Foram

  10. Potential N2O emissions from leguminous tree plantation soils in the humid tropics

    Science.gov (United States)

    Arai, Seiko; Ishizuka, Shigehiro; Ohta, Seiichi; Ansori, Saifuddin; Tokuchi, Naoko; Tanaka, Nagaharu; Hardjono, Arisman

    2008-06-01

    We compared nitrous oxide (N2O) emissions over 1 year from soils of plantations growing acacia, which is a leguminous plant capable of symbiotic nitrogen fixation in root nodules, and secondary forests in Sumatra, Indonesia. N2O emissions from acacia plantation soils fluctuated seasonally, from high in the wetter season to low in the drier season, whereas N2O emissions from secondary forest soils were low throughout the year. Water-filled-pore-space data showed that denitrification contributed substantially to N2O emissions from soils at acacia sites. The average annual N2O flux in acacia plantations was 2.56 kg N ha-1 a-1, which was eight times higher than that from secondary forest soils (0.33 kg N ha-1 a-1). In secondary forests, NH4+ was the dominant form of inorganic nitrogen. However, in acacia plantations, the NH4+: NO3- ratio was relatively lower than that in secondary forests. These results suggest that secondary forests were nitrogen limited, but acacia plantations were less nitrogen limited. Leguminous tree plantations may increase nitrogen cycling, resulting in greater N2O emissions from the soil. However, on a global warming potential basis, N2O emissions from acacia plantation soils accounted for less than 10% of the carbon uptake by plants. Nevertheless, because of the spread of leguminous tree plantations in Asia, the importance of N2O emissions from leguminous tree stands will increase in the coming decades.

  11. The role of nitrogen fixation in neotropical dry forests: insights from ecosystem modeling and field data

    Science.gov (United States)

    Trierweiler, A.; Xu, X.; Gei, M. G.; Powers, J. S.; Medvigy, D.

    2016-12-01

    Tropical dry forests (TDFs) have immense functional diversity and face multiple resource constraints (both water and nutrients). Legumes are abundant and exhibit a wide diversity of N2-fixing strategies in TDFs. The abundance and diversity of legumes and their interaction with N2-fixing bacteria may strongly control the coupled carbon-nitrogen cycle in the biome and influence whether TDFs will be particularly vulnerable or uniquely adapted to projected global change. However, the importance of N2-fixation in TDFs and the carbon cost of acquiring N through symbiotic relationships are not fully understood. Here, we use models along with field measurements to examine the role of legumes, nitrogen fixation, and plant-symbiont nutrient exchanges in TDFs. We use a new version of the Ecosystem Demography (ED2) model that has been recently parameterized for TDFs. The new version incorporates plant-mycorrhizae interactions and multiple resource constraints (carbon, nitrogen, phosphorus, and water). We represent legumes and other functional groups found in TDFs with a range of resource acquisition strategies. In the model, plants then can dynamically adjust their carbon allocation and nutrient acquisition strategies (e.g. N2-fixing bacteria and mycorrhizal fungi) according to the nutrient limitation status. We test (i) the model's performance against a nutrient gradient of field sites in Costa Rica and (ii) the model's sensitivity to the carbon cost to acquire N through fixation and mycorrhizal relationships. We also report on simulated tree community responses to ongoing field nutrient fertilization experiments. We found that the inclusion of the N2-fixation legume plant functional traits were critical to reproducing community dynamics of Costa Rican field TDF sites and have a large impact on forest biomass. Simulated ecosystem fixation rates matched the magnitude and temporal patterns of field measured fixation. Our results show that symbiotic nitrogen fixation plays an

  12. Woody encroachment impacts on ecosystem nitrogen cycling: fixation, storage and gas loss

    Science.gov (United States)

    Soper, F.; Sparks, J. P.

    2016-12-01

    Woody encroachment is a pervasive land cover change throughout the tropics and subtropics. Encroachment is frequently catalyzed by nitrogen (N)-fixing trees and the resulting N inputs have the potential to alter whole-ecosystem N cycling, accumulation and loss. In the southern US, widespread encroachment by legume Prosopis glandulosa is associated with increased soil total N storage, inorganic N concentrations, and net mineralization and nitrification rates. To better understand the effects of this process on ecosystem N cycling, we investigated patterns of symbiotic N fixation, N accrual and soil N trace gas and N2 emissions during Prosopis encroachment into the southern Rio Grande Plains. Analyses of d15N in foliage, xylem sap and plant-available soil N suggested that N fixation rates vary seasonally, inter-annually and as a function of plant age and abiotic conditions. Applying a small-scale mass balance model to soil N accrual around individual trees (accounting for atmospheric inputs, and gas and hydrologic losses) generated current fixation estimates of 11 kg N ha-1 yr-1, making symbiotic fixation the largest input of N to the ecosystem. However, soil N accrual and increased cycling rates did not translate into increased N gas losses. Two years of field measurements of a complete suite of N trace gases (ammonia, nitrous oxide, nitric oxide and other oxidized N compounds) found no difference in flux between upland Prosopis groves and adjacent unencroached grasslands. Total emissions average 0.56-0.65 kg N ha-1 yr-1, comparable to other southern US grasslands. Lab incubations suggested that N2 losses are likely to be low, with field oxygen conditions not usually conducive to denitrification. Taken together, results suggest that this ecosystem is currently experiencing a period of significant net N accrual, driven by fixation under ongoing encroachment. Given the large scale of woody legume encroachment in the USA, this process is likely to contribute

  13. Ocorrência do processo de fixação biológica de N2 atmosférico na fermentação de fécula de mandioca Biological fixation of atmospheric N2 in the initial phase of cassava starch fermentation

    Directory of Open Access Journals (Sweden)

    Luiz Ermindo Cavallet

    2006-09-01

    Full Text Available A fase inicial do processo de fermentação natural de fécula de mandioca apresenta a ocorrência de fermentação vigorosa em apenas 24 h, mesmo com o meio tendo uma relação carbono/nitrogênio muito alta. Assim, o nitrogênio necessário à formação da biomassa nos primeiros estágios da fermentação seria originário de fora do sistema via fixação biológica de N2 atmosférico, já que o teor protéico disponível na fécula de mandioca é muito baixo. Para verificar tal hipótese, foram feitos dois experimentos fundamentados no balanço de nitrogênio na suspensão com grânulos de fécula durante as primeiras 120 h do processo fermentativo, conduzido sob temperatura ambiente e sob temperatura controlada a 28 °C. Não foram detectados aumentos de nitrogênio na fase estudada, o que sugere a não existência do processo de fixação biológica de N2 atmosférico. Os resultados sugerem que a origem do nitrogênio para o processo fermentativo é a própria fécula, que, quando na forma de polvilho apresenta alta relação C/N, porém, quando em suspensão essa relação abaixa propiciando uma fermentação vigorosa em apenas 24 h.The initial phase of natural fermentation of cassava starch presents vigorous fermentation within the first 24 h and is characterized by a high ration of carbon/nitrogen. Consequently, the necessary nitrogen to the formation of biomass would be originated from outside of the system because the available protein content from cassava starch is very low and depending on biological fixation of atmospheric N2. To verify that hypothesis two essays were conducted with the nitrogen balance in the starch granule suspension during the initial 120 h of the fermentation process. The essays were set at room temperature and at the controlled temperature of 28 °C. No increase in the nitrogen content was detected suggesting that no involvement of atmospheric N2. Results suggest that the origin of the nitrogen to the

  14. Population genomics of the symbiotic plasmids of sympatric nitrogen-fixing Rhizobium species associated with Phaseolus vulgaris.

    Science.gov (United States)

    Pérez Carrascal, Olga M; VanInsberghe, David; Juárez, Soledad; Polz, Martin F; Vinuesa, Pablo; González, Víctor

    2016-09-01

    Cultivated common beans are the primary protein source for millions of people around the world who subsist on low-input agriculture, enabled by the symbiotic N2 -fixation these legumes perform in association with rhizobia. Within a single agricultural plot, multiple Rhizobium species can nodulate bean roots, but it is unclear how genetically isolated these species remain in sympatry. To better understand this issue, we sequenced and compared the genomes of 33 strains isolated from the rhizosphere and root nodules of a particular bean variety grown in the same agricultural plot. We found that the Rhizobium species we observed coexist with low genetic recombination across their core genomes. Accessory plasmids thought to be necessary for the saprophytic lifestyle in soil show similar levels of genetic isolation, but with higher rates of recombination than the chromosomes. However, the symbiotic plasmids are extremely similar, with high rates of recombination and do not appear to have co-evolved with the chromosome or accessory plasmids. Therefore, while Rhizobium species are genetically isolated units within the microbial community, a common symbiotic plasmid allows all Rhizobium species to engage in symbiosis with the same host in a single agricultural plot. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

  15. Outbursts in Symbiotic Binaries

    Science.gov (United States)

    Sonneborn, George (Technical Monitor); Kenyon, Scott J.

    2004-01-01

    Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

  16. Dark CO/sub 2/ fixation and amino acid metabolism in symbiotic N/sub 2/-fixing systems. Labeling studies with /sup 14/C and /sup 13/N-labeled tracers. [Roots of soybean plants and alders

    Energy Technology Data Exchange (ETDEWEB)

    Coker, G.T. III

    1982-01-01

    Amino acid metabolism was examined by monitoring the amino acids labeled with (/sup 14/C) incorporated during dark CO/sub 2/ fixation and with (/sup 13/N) incorporated from /sup 13/NH/sub 4/+, /sup 13/NO/sub 3/- or (/sup 13/N)N/sub 2/. Label from /sup 14/CO/sub 2/ was directly incorporated in soybean roots and the N/sub 2/-fixing root nodules of soybeans and alders. The products of dark CO/sub 2/ fixation were primarily amino and organic acids. The distribution of label incorporated from /sup 14/CO/sub 2/ into amino acids depended on the plant species and the nitrigen source. The major labeled amino acids in roots and nodules of soybean plants dependent on N/sub 2/ were aspartate and glutamate; in alder nodules, citrulline; in roots of soybean plants treated with NO/sub 3/-, asparagine; and in roots of soybean plants treated with NH/sub 4/+, asparagine and glutamine. Asparagine was the major amino acid transported out of the soybean root system. Experiments indicated that asparagine was synthesized directly from aspartate. After exposure to /sup 14/CO/sub 2/, the specific activity of glutamine was consistently higher than that of glutamate in soybean nodules and roots of plants treated with NO/sub 3/-. This was taken as evidence that there were two pools of glutamate, only one of which was associated with glutamine synthesis. Alder and soybean nodules and roots were incubated with /sup 13/N-labeled tracers. Those tissues incubated with /sup 13/NH/sub 4/+ had a higher ratio of (/sup 13/N)glutamine to (/sup 13/N)glutamate that similar tissues exposed to /sup 13/NO/sub 3/- or (/sup 13/N)N/sub 2/. An explanation for these results based on the relative rates of glutamine and glutamate synthesis is discussed.

  17. Ecological consequences of the expansion of N2-fixing plants in cold biomes

    Science.gov (United States)

    Hiltbrunner, Erika; Aerts, Rien; Bühlmann, Tobias; Huss-Danell, Kerstin; Magnusson, Borgthor; Myrold, David D.; Reed, Sasha C.; Sigurdsson, Bjarni D.; Körner, Christian

    2014-01-01

    Research in warm-climate biomes has shown that invasion by symbiotic dinitrogen (N2)-fixing plants can transform ecosystems in ways analogous to the transformations observed as a consequence of anthropogenic, atmospheric nitrogen (N) deposition: declines in biodiversity, soil acidification, and alterations to carbon and nutrient cycling, including increased N losses through nitrate leaching and emissions of the powerful greenhouse gas nitrous oxide (N2O). Here, we used literature review and case study approaches to assess the evidence for similar transformations in cold-climate ecosystems of the boreal, subarctic and upper montane-temperate life zones. Our assessment focuses on the plant genera Lupinus and Alnus, which have become invasive largely as a consequence of deliberate introductions and/or reduced land management. These cold biomes are commonly located in remote areas with low anthropogenic N inputs, and the environmental impacts of N2-fixer invasion appear to be as severe as those from anthropogenic N deposition in highly N polluted areas. Hence, inputs of N from N2 fixation can affect ecosystems as dramatically or even more strongly than N inputs from atmospheric deposition, and biomes in cold climates represent no exception with regard to the risk of being invaded by N2-fixing species. In particular, the cold biomes studied here show both a strong potential to be transformed by N2-fixing plants and a rapid subsequent saturation in the ecosystem’s capacity to retain N. Therefore, analogous to increases in N deposition, N2-fixing plant invasions must be deemed significant threats to biodiversity and to environmental quality.

  18. CO2 fixation in alfalfa and birdsfoot trefoil root nodules and partitioning of 14C to the plant

    International Nuclear Information System (INIS)

    Maxwell, C.A.; Vance, C.P.; Heichel, G.H.; Stade, S.

    1984-01-01

    The objectives of this study were to determine if nonphotosynthetic CO 2 fixation by root nodules contributes carbon for the assimilation of fixed N 2 in alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) and if assimilation products are partitioned to different plant organs. Effective alfalfa nodules excised from or attached to roots had apparent 14 CO 2 fixation rates of 50 to 80 μg CO 2 kg -1 s -1 (dry weight) at 0.0012 to 0.0038 mole fraction CO 2 . Nodule CO 2 fixation rates increased six- to seven-fold as ambient CO 2 was raised from 0.0038 to 0.0663 mole fraction. Respiration rates of nodules (3 to 4 mg CO 2 kg -1 s -1 ) were 10 to 100-fold higher than 14 CO 2 fixation rates of nodules. Pulse chase experiments with 14 CO 2 combined with nodule and xylem sap analysis demonstrated the initial products of root and nodule CO 2 fixation were organic acids. However, the export of fixed 14 C from effective nodules was primarily in the form of amino acids. In contrast, nodule and/or root fixed 14 C in ineffectively nodulated alfalfa and denodulated effective alfalfa and birdsfoot trefoil was transported primarily as organic acids. Aspartate, asparagine, alanine, glutamate, and glutamine were the most heavily labeled compounds in the amino acid fraction of both effective alfalfa and birdsfoot trefoil nodules exposed to 14 CO 2 . By contrast, asparate, asparagine, and glutamine were the predominantly labeled amino acids in xylem sap collected from nodulated effective roots exposed to 14 CO 2 . The occurrence of nodule CO 2 fixation in alfalfa and birdsfoot trefoil and the export of fixed carbon as asparagine and aspartate to roots and shoots is consistent with a role for CO 2 fixation by nodules in providing carbon skeletons for assimilation and transport of symbiotically fixed N 2

  19. Outbursts of symbiotic novae

    International Nuclear Information System (INIS)

    Kenyon, S.J.; Truran, J.W.

    1983-01-01

    We discuss possible conditions under which thermonuclear burning episodes in the hydrogen-rich envelopes of accreting white dwarfs give rise to outbursts similar in nature to those observed in the symbiotic stars AG Peg, RT Ser, RR Tel, AS 239, V1016 Cyg, V1329 Cyg, and HM Sge. In principle, thermonuclear runaways involving low-luminosity white dwarfs accreting matter at low rates produce configurations that evolve into A--F supergiants at maximum visual light and which resemble the outbursts of RR Tel, RT Ser, and AG peg. Very weak, nondegenerage hydrogen shell flashes on white dwarfs accreting matter at high rates (M> or approx. =10 -8 M/sub sun/ yr -1 ) do not produce cool supergiants at maximum, and may explain the outbursts in V1016 Cyg, V1329 Cyg, and HM Sge. The low accretion rates demanded for systems developing strong hydrogen shell flashes on low-luminsoity white dwarfs are not compatible with observations of ''normal'' quiescent symbiotic stars. The extremely slow outbursts of symbiotic novae appear to be typical of accreting white dwarfs in wide binaries, which suggests that the outbursts of classical novae may be accelerated by the interaction of the expanding white dwarf envelope with its close binary companion

  20. Influence of tree canopy on N{sub 2} fixation by pasture legumes and soil rhizobial abundance in Mediterranean oak woodlands

    Energy Technology Data Exchange (ETDEWEB)

    Carranca, C., E-mail: corina.carranca@iniav.pt [INIAV, Qta Marquês, 2784-505 Oeiras (Portugal); Castro, I.V.; Figueiredo, N. [INIAV, Qta Marquês, 2784-505 Oeiras (Portugal); Redondo, R. [Laboratorio de Isotopos Estables, Universidade Autonoma, Madrid (Spain); Rodrigues, A.R.F. [Centro de Estudos Florestais, ISA/UL, Tapada Ajuda, 1349-017 Lisboa (Portugal); Saraiva, I.; Maricato, R. [INIAV, Qta Marquês, 2784-505 Oeiras (Portugal); Madeira, M.A.V. [Centro de Estudos Florestais, ISA/UL, Tapada Ajuda, 1349-017 Lisboa (Portugal)

    2015-02-15

    Symbiotic N{sub 2} fixation is of primordial significance in sustainable agro-forestry management as it allows reducing the use of mineral N in the production of mixed stands and by protecting the soils from degradation. Thereby, on a 2-year basis, N{sub 2} fixation was evaluated in four oak woodlands under Mediterranean conditions using a split-plot design and three replicates. {sup 15}N technique was used for determination of N{sub 2} fixation rate. Variations in environmental conditions (temperature, rainfall, radiation) by the cork tree canopy as well as the age of stands and pasture management can cause great differences in vegetation growth, legume N{sub 2} fixation, and soil rhizobial abundance. In the present study, non-legumes dominated the swards, in particular beneath the tree canopy, and legumes represented only 42% of total herbage. A 2-fold biomass reduction was observed in the oldest sown pasture in relation to the medium-age sward (6 t DW ha{sup −1} yr{sup −1}). Overall, competition of pasture growth for light was negligible, but soil rhizobial abundance and symbiotic N{sub 2} fixation capacity were highly favored by this environmental factor in the spring and outside the influence of tree canopy. Nitrogen derived from the atmosphere was moderate to high (54–72%) in unsown and sown swards. Inputs of fixed N2 increased from winter to spring due to more favorable climatic conditions (temperature and light intensity) for both rhizobia and vegetation growths. Assuming a constant fixation rate at each seasonal period, N{sub 2} fixation capacity increased from about 0.10 kg N ha{sup −1} per day in the autumn–winter period to 0.15 kg N ha{sup −1} per day in spring. Belowground plant material contributed to 11% of accumulated N in pasture legumes and was not affected by canopy. Size of soil fixing bacteria contributed little to explain pasture legumes N. - Highlights: • Legumes fixation in oak woodlands was quantified in terms of biomass and N

  1. Symbiotic functioning and bradyrhizobial biodiversity of cowpea (Vigna unguiculata L. Walp. in Africa

    Directory of Open Access Journals (Sweden)

    Dakora Felix D

    2010-03-01

    Full Text Available Abstract Background Cowpea is the most important food grain legume in Sub-Saharan Africa. However, no study has so far assessed rhizobial biodiversity and/or nodule functioning in relation to strain IGS types at the continent level. In this study, 9 cowpea genotypes were planted in field experiments in Botswana, South Africa and Ghana with the aim of i trapping indigenous cowpea root-nodule bacteria (cowpea "rhizobia" in the 3 countries for isolation, molecular characterisation using PCR-RFLP analysis, and sequencing of the 16S - 23S rDNA IGS gene, ii quantifying N-fixed in the cowpea genotypes using the 15N natural abundance technique, and iii relating the levels of nodule functioning (i.e. N-fixed to the IGS types found inside nodules. Results Field measurements of N2 fixation revealed significant differences in plant growth, δ15N values, %Ndfa and amounts of N-fixed between and among the 9 cowpea genotypes in Ghana and South Africa. Following DNA analysis of 270 nodules from the 9 genotypes, 18 strain IGS types were found. Relating nodule function to the 18 IGS types revealed significant differences in IGS type N2-fixing efficiencies. Sequencing the 16S - 23S rDNA gene also revealed 4 clusters, with cluster 2 forming a distinct group that may be a new Bradyrhizobium species. Taken together, our data indicated greater biodiversity of cowpea bradyrhizobia in South Africa relative to Botswana and Ghana. Conclusions We have shown that cowpea is strongly dependant on N2 fixation for its N nutrition in both South Africa and Ghana. Strain IGS type symbiotic efficiency was assessed for the first time in this study, and a positive correlation was discernible where there was sole nodule occupancy. The differences in IGS type diversity and symbiotic efficiency probably accounts for the genotype × environment interaction that makes it difficult to select superior genotypes for use across Africa. The root-nodule bacteria nodulating cowpea in this study

  2. Dinitrogen fixation in aphotic oxygenated marine environments

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    Eyal eRahav

    2013-08-01

    Full Text Available We measured N2 fixation rates from oceanic zones that have traditionally been ignored as sources of biological N2 fixation; the aphotic, fully oxygenated, nitrate (NO3--rich, waters of the oligotrophic Levantine Basin (LB and the Gulf of Aqaba (GA. N2 fixation rates measured from pelagic aphotic waters to depths up to 720 m, during the mixed and stratified periods, ranged from 0.01 nmol N L-1 d-1 to 0.38 nmol N L-1 d-1. N2 fixation rates correlated significantly with bacterial productivity and heterotrophic diazotrophs were identified from aphotic as well as photic depths. Dissolved free amino acid amendments to whole water from the GA enhanced bacterial productivity by 2to 3.5 and N2 fixation rates by ~ 2 fold in samples collected from aphotic depths while in amendments to water from photic depths bacterial productivity increased 2 to 6 fold while N2 fixation rates increased by a factor of 2 to 4 illustrating that both BP an heterotrophic N2 fixation are carbon limited. Experimental manipulations of aphotic waters from the LB demonstrated a significant positive correlation between transparent exopolymeric particles (TEP concentration and N2 fixation rates. This suggests that sinking organic material and high carbon (C: nitrogen (N micro-environments (such as TEP-based aggregates or marine snow could support high heterotrophic N2 fixation rates in oxygenated surface waters and in the aphotic zones. Indeed, our calculations show that aphotic N2 fixation accounted for 37 to 75 % of the total daily integrated N2 fixation rates at both locations in the Mediterranean and Red Seas with rates equal or greater to those measured from the photic layers. Moreover, our results indicate that that while N2 fixation may be limited in the surface waters, aphotic, pelagic N2 fixation may contribute significantly to new N inputs in other oligotrophic basins, yet it is currently not included in regional or global N budgets.

  3. Identification of an algal carbon fixation-enhancing factor extracted from Paramecium bursaria.

    Science.gov (United States)

    Kato, Yutaka; Imamura, Nobutaka

    2011-01-01

    The green ciliate Paramecium bursaria contains several hundred symbiotic Chlorella species. We previously reported that symbiotic algal carbon fixation is enhanced by P. bursaria extracts and that the enhancing factor is a heat-stable, low-molecular-weight, water-soluble compound. To identify the factor, further experiments were carried out. The enhancing activity remained even when organic compounds in the extract were completely combusted at 700 degrees C, suggesting that the factor is an inorganic substance. Measurement of the major cations, K+, Ca2+, and Mg2+, by an electrode and titration of the extract resulted in concentrations of 0.90 mM, 0.55 mM, and 0.21 mM, respectively. To evaluate the effect of these cations, a mixture of the cations at the measured concentrations was prepared, and symbiotic algal carbon fixation was measured in the solution. The results demonstrated that the fixation was enhanced to the same extent as with the P. bursaria extract, and thus this mixture of K+, Ca2+, and Mg2+ was concluded to be the carbon fixation-enhancing factor. There was no effect of the cation mixture on free-living C. vulgaris. Comparison of the cation concentrations of nonsymbiotic and symbiotic Paramecium extracts revealed that the concentrations of K+ and Mg2+ in nonsymbiotic Paramecium extracts were too low to enhance symbiotic algal carbon fixation, suggesting that symbiotic P. bursaria provide suitable cation conditions for photosynthesis to its symbiotic Chlorella.

  4. Interactions among nitrogen fixation and soil phosphorus acquisition strategies in lowland tropical rain forests.

    Science.gov (United States)

    Nasto, Megan K; Alvarez-Clare, Silvia; Lekberg, Ylva; Sullivan, Benjamin W; Townsend, Alan R; Cleveland, Cory C

    2014-10-01

    Paradoxically, symbiotic dinitrogen (N2 ) fixers are abundant in nitrogen (N)-rich, phosphorus (P)-poor lowland tropical rain forests. One hypothesis to explain this pattern states that N2 fixers have an advantage in acquiring soil P by producing more N-rich enzymes (phosphatases) that mineralise organic P than non-N2 fixers. We assessed soil and root phosphatase activity between fixers and non-fixers in two lowland tropical rain forest sites, but also addressed the hypothesis that arbuscular mycorrhizal (AM) colonisation (another P acquisition strategy) is greater on fixers than non-fixers. Root phosphatase activity and AM colonisation were higher for fixers than non-fixers, and strong correlations between AM colonisation and N2 fixation at both sites suggest that the N-P interactions mediated by fixers may generally apply across tropical forests. We suggest that phosphatase enzymes and AM fungi enhance the capacity of N2 fixers to acquire soil P, thus contributing to their high abundance in tropical forests. © 2014 John Wiley & Sons Ltd/CNRS.

  5. On the relationship between C and N fixation in nodulated alfalfa (Medicago sativa)

    OpenAIRE

    Molero Milán, Gemma; Tcherkez, G.; Araus Ortega, José Luis; Nogués Mestres, Salvador; Aranjuelo Michelena, Iker

    2014-01-01

    Legumes such as alfalfa (Medicago sativa L.) are vital N2-fixing crops accounting for a global N2 fixation of ~35 MtNyear-1. Although enzymatic and molecular mechanisms of nodule N2 fixation are now well documented, some uncertainty remains as to whether N2 fixation is strictly coupled with photosynthetic carbon fixation. That is, the metabolic origin and redistribution of carbon skeletons used to incorporate nitrogen are still relatively undefined. Here, we conducted isotopic labelling with ...

  6. Green symbiotic cloud communications

    CERN Document Server

    Mustafa, H D; Desai, Uday B; Baveja, Brij Mohan

    2017-01-01

    This book intends to change the perception of modern day telecommunications. Communication systems, usually perceived as “dumb pipes”, carrying information / data from one point to another, are evolved into intelligently communicating smart systems. The book introduces a new field of cloud communications. The concept, theory, and architecture of this new field of cloud communications are discussed. The book lays down nine design postulates that form the basis of the development of a first of its kind cloud communication paradigm entitled Green Symbiotic Cloud Communications or GSCC. The proposed design postulates are formulated in a generic way to form the backbone for development of systems and technologies of the future. The book can be used to develop courses that serve as an essential part of graduate curriculum in computer science and electrical engineering. Such courses can be independent or part of high-level research courses. The book will also be of interest to a wide range of readers including b...

  7. The effect of vesicular-arbuscular mycorrhiza isolated from Syrian soil on alfalfa growth and nitrogen fixation in saline soil

    International Nuclear Information System (INIS)

    El Atrash, F

    2001-01-01

    The influence of vesicular - arbuscular Mycorrhiza fungi (VAM) on symbiotic fixation of N 2 n alfalfa plants has been observed. Beneficial effects of study the effect of VAM or phosphorous fertilization on alfalfa (Medicago sativa L,) yields, umber of nodules and N 2 fixation by N 15 isotope dilution at different salinity levels. This experiment was realized in green house conditions, using soil of 2.3 dsm -1 conductivity mixed with sand (5: 2V) for alfalfa plants growing at various levels of phosphorus, or infected by Mycorrhiza fungi. Different conductivities (13.18, 22.2, 28.8, 43.5 dsm -1 ) were applied on these treatment by increasing concentrations of Nacl, CaCl 2 and MgCl 2 and MgCl 2 by salinity soil irrigation. Ten days after planting, soil was enriched with 2 ppm of (NH 4 15 ) 2 SO 4 . Plant were grown under greenhouse condition for ten weeks. Our results confirmed that increased salinity reduced nitrogen - fixation and the number of nodules. The negative effect with increasing salinity was less in Mycorrhiza plants than in plants fertilized with various levels of phosphorus, and only the higher levels of salinity reduced significantly, the percentage of Mycorrhiza colonization, However, at all levels of salinity, VAM stimulated plant growth and nutrient uptake. (author)

  8. Influence of arbuscular mycorrhizae on biomass production and nitrogen fixation of berseem clover plants subjected to water stress.

    Science.gov (United States)

    Saia, Sergio; Amato, Gaetano; Frenda, Alfonso Salvatore; Giambalvo, Dario; Ruisi, Paolo

    2014-01-01

    Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N) fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season) on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rain-fed conditions) or the crop was well-watered. Mycorrhization treatments consisted of inoculation of berseem clover seeds with arbuscular mycorrhizal spores or suppression of arbuscular mycorrhizal symbiosis by means of fungicide treatments. Nitrogen biological fixation was assessed using the 15N-isotope dilution technique. Arbuscular mycorrhizal symbiosis was able to mitigate the negative effect of water stress on berseem clover grown in a typical semiarid Mediterranean environment. In fact, under water stress conditions, arbuscular mycorrhizal symbiosis resulted in increases in total biomass, N content, and N fixation, whereas no effect of crop mycorrhization was observed in the well-watered treatment.

  9. Influence of arbuscular mycorrhizae on biomass production and nitrogen fixation of berseem clover plants subjected to water stress.

    Directory of Open Access Journals (Sweden)

    Sergio Saia

    Full Text Available Several studies, performed mainly in pots, have shown that arbuscular mycorrhizal symbiosis can mitigate the negative effects of water stress on plant growth. No information is available about the effects of arbuscular mycorrhizal symbiosis on berseem clover growth and nitrogen (N fixation under conditions of water shortage. A field experiment was conducted in a hilly area of inner Sicily, Italy, to determine whether symbiosis with AM fungi can mitigate the detrimental effects of drought stress (which in the Mediterranean often occurs during the late period of the growing season on forage yield and symbiotic N2 fixation of berseem clover. Soil was either left under water stress (i.e., rain-fed conditions or the crop was well-watered. Mycorrhization treatments consisted of inoculation of berseem clover seeds with arbuscular mycorrhizal spores or suppression of arbuscular mycorrhizal symbiosis by means of fungicide treatments. Nitrogen biological fixation was assessed using the 15N-isotope dilution technique. Arbuscular mycorrhizal symbiosis was able to mitigate the negative effect of water stress on berseem clover grown in a typical semiarid Mediterranean environment. In fact, under water stress conditions, arbuscular mycorrhizal symbiosis resulted in increases in total biomass, N content, and N fixation, whereas no effect of crop mycorrhization was observed in the well-watered treatment.

  10. Variable Nitrogen Fixation in Wild Populus.

    Directory of Open Access Journals (Sweden)

    Sharon L Doty

    Full Text Available The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees.

  11. Variable Nitrogen Fixation in Wild Populus.

    Science.gov (United States)

    Doty, Sharon L; Sher, Andrew W; Fleck, Neil D; Khorasani, Mahsa; Bumgarner, Roger E; Khan, Zareen; Ko, Andrew W K; Kim, Soo-Hyung; DeLuca, Thomas H

    2016-01-01

    The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N) is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees.

  12. Nitrogen supply of crops by biological nitrogen fixation. 2

    International Nuclear Information System (INIS)

    Jensen, E.S.; Andersen, A.J.; Soerensen, H.; Thomsen, J.D.

    1985-02-01

    In the present work the contributions from combined N-sources and symbiotic nitrogen fixation to the nitrogen supply of field-grown peas and field beans were evaluated by means of 15 N fertilizer dilution. The effect of N-fertilizer, supplied at sowing and at different stages of plant development, on nitrogen fixation, yield and protein production in peas, was studied in pot experiments. (author)

  13. Symbiotic nitrogen fixation in legumes: Perspectives for saline agriculture

    NARCIS (Netherlands)

    Bruning, B.; Rozema, J.

    2013-01-01

    Saline agriculture provides a solution for at least two environmental and social problems. It allows us to return to agricultural production areas that have been lost as a consequence of salinization and it can save valuable fresh water by using brackish or salt water to irrigate arable lands. Sea

  14. [Metabolic integration of organisms within symbiotic systems].

    Science.gov (United States)

    Provorov, N A; Dolgikh, E A

    2006-01-01

    Adaptation of organisms to coexisence in symbiotic systems is usually related to significant metabolic changes resulting in the integration of the biochemical pathways of the partners. In the symbioses between plants and nitrogen-fixing organisms, between heterotrophic and autotrophic organisms, as well as between animals and microorganisms providing the consumption of plant biomass, the systems of C- and N-metabolism, controlling the utilization of various sources of nitrogen (N2, organic and inorganic compounds, metabolic waste of the host) and carbon (CO2, plant polymers), of the partners are tightly integrated. Bilateral biochemical links between partners are typical to mutualistic symbioses (wherein biotrophic nutrition predominates, in some cases including necrotrophy of secondary origin). In antagonistic symbioses, unilateral links predominate, though active assimilation of the pathogen's secondary metabolites by the host is also possible. In most mutualistic symbioses, integrated metabolic ties have derived from trophic chains in biocenoses (syntrophic consortia, "predator-prey" systems), but not from the systems where the pathogens consume host metabolites. At the same time, molecular analysis of symbiotic interactions has shown that symbioses considerably differ from biocenoses, where the cycling of nutrients and energy implies no functional integration of the partner's genes.

  15. The NifA-RpoN Regulon of Mesorhizobium loti Strain R7A and Its Symbiotic Activation by a Novel LacI/GalR-Family Regulator

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan, John T.; Brown, Steven D.; Ronson, Clive W.; de Crécy-Lagard, Valerie

    2013-01-07

    Mesorhizobium loti is the microsymbiont of Lotus species, including the model legume L. japonicus. M. loti differs from other rhizobia in that it contains two copies of the key nitrogen fixation regulatory gene nifA, nifA1 and nifA2, both of which are located on the symbiosis island ICEMlSymR7A. M. loti R7A also contains two rpoN genes, rpoN1 located on the chromosome outside of ICEMlSymR7A and rpoN2 that is located on ICEMlSymR7A. The aims of the current work were to establish how nifA expression was activated in M. loti and to characterise the NifA-RpoN regulon. The nifA2 and rpoN2 genes were essential for nitrogen fixation whereas nifA1 and rpoN1 were dispensable. Expression of nifA2 was activated, possibly in response to an inositol derivative, by a novel regulator of the LacI/GalR family encoded by the fixV gene located upstream of nifA2. Other than the well-characterized nif/fix genes, most NifA2-regulated genes were not required for nitrogen fixation although they were strongly expressed in nodules. The NifA-regulated nifZ and fixU genes, along with nifQ which was not NifA-regulated, were required in M. loti for a fully effective symbiosis although they are not present in some other rhizobia. The NifA-regulated gene msi158 that encodes a porin was also required for a fully effective symbiosis. Several metabolic genes that lacked NifA-regulated promoters were strongly expressed in nodules in a NifA2-dependent manner but again mutants did not have an overt symbiotic phenotype. In summary, many genes encoded on ICEMlSymR7A were strongly expressed in nodules but not free-living rhizobia, but were not essential for symbiotic nitrogen fixation. It seems likely that some of these genes have functional homologues elsewhere in the genome and that bacteroid metabolism may be sufficiently plastic to adapt to loss of certain enzymatic functions.

  16. The NifA-RpoN regulon of Mesorhizobium loti strain R7A and its symbiotic activation by a novel LacI/GalR-family regulator.

    Directory of Open Access Journals (Sweden)

    John T Sullivan

    Full Text Available Mesorhizobium loti is the microsymbiont of Lotus species, including the model legume L. japonicus. M. loti differs from other rhizobia in that it contains two copies of the key nitrogen fixation regulatory gene nifA, nifA1 and nifA2, both of which are located on the symbiosis island ICEMlSym(R7A. M. loti R7A also contains two rpoN genes, rpoN1 located on the chromosome outside of ICEMlSym(R7A and rpoN2 that is located on ICEMlSym(R7A. The aims of the current work were to establish how nifA expression was activated in M. loti and to characterise the NifA-RpoN regulon. The nifA2 and rpoN2 genes were essential for nitrogen fixation whereas nifA1 and rpoN1 were dispensable. Expression of nifA2 was activated, possibly in response to an inositol derivative, by a novel regulator of the LacI/GalR family encoded by the fixV gene located upstream of nifA2. Other than the well-characterized nif/fix genes, most NifA2-regulated genes were not required for nitrogen fixation although they were strongly expressed in nodules. The NifA-regulated nifZ and fixU genes, along with nifQ which was not NifA-regulated, were required in M. loti for a fully effective symbiosis although they are not present in some other rhizobia. The NifA-regulated gene msi158 that encodes a porin was also required for a fully effective symbiosis. Several metabolic genes that lacked NifA-regulated promoters were strongly expressed in nodules in a NifA2-dependent manner but again mutants did not have an overt symbiotic phenotype. In summary, many genes encoded on ICEMlSym(R7A were strongly expressed in nodules but not free-living rhizobia, but were not essential for symbiotic nitrogen fixation. It seems likely that some of these genes have functional homologues elsewhere in the genome and that bacteroid metabolism may be sufficiently plastic to adapt to loss of certain enzymatic functions.

  17. Review on Association Between Corals and Their Symbiotic Microorganisms From the Ecology and Biotechnology Perspective

    Directory of Open Access Journals (Sweden)

    Zahra Amini Khoei

    2017-04-01

    Full Text Available Background: Corals have a diversity of prokaryotic communities as an internal or external symbiotic . This review will examine the association between corals and their symbiotic microorganisms from the ecology and biotechnology perspective. Material and Methods: In this study, articles were examined which indexed in Pubmed, Science Direct, Google Scholar and Scirus databases. Keywords we used included coral, symbiotic microorganisms, ecology, and biotechnology. Finally, overall of 120 articles and reports, 103 articles were evaluated by eliminating the same articles. Results: The Corals symbiotic microorganisms stay on in the ecological niches such as the surface mucus layer, tissue and their skeleton. They play role in the cycle of sulfur, nitrogen fixation, production of antimicrobial compounds and protect corals against pathogens. Many bioactive compounds which attributed to invertebrates such as sponges and corals in fact they are produced by symbiotic bacteria. Various metabolites produced by these microorganisms can be used as medicine. Five screening strategies including conventional screening, met genomics, genomics, combinatorial biosynthesis, and synthetic biology are used for marine microbial natural products discovery and development. Conclusion: According to the collected material we can be concluded that, the ecological studies about the natural association between corals and their symbiotic microorganisms were technological prerequisite for biomedical research and they make clear the road to attainment to bioactive compounds in fauna. Also, in the first step, it is recommended that modern technology and advanced screening methods used to identification of marine organisms and then to identify secondary metabolites among them.

  18. The influence of woody encroachment on the nitrogen cycle: fixation, storage and gas loss

    Science.gov (United States)

    Soper, F.; Sparks, J. P.

    2015-12-01

    Woody encroachment is a pervasive land cover change throughout the tropics and subtropics. Encroachment is frequently catalyzed by nitrogen (N)-fixing trees and the resulting N inputs potentially alter whole-ecosystem N cycling, accumulation and loss. In the southern US, widespread encroachment by legume Prosopis glandulosa is associated with increased soil total N storage, inorganic N concentrations, and net mineralization and nitrification rates. To better understand the effects of this process on ecosystem N cycling, we investigated patterns of symbiotic N fixation, N accrual and soil N trace gas and N2 emissions during Prosopis encroachment into the southern Rio Grande Plains. Analyses of d15N in foliage, xylem sap and plant-available soil N suggested that N fixation rates increase with tree age and are influenced by abiotic conditions. A model of soil N accrual around individual trees, accounting for atmospheric inputs and gas losses, generates lifetimes N fixation estimates of up to 9 kg for a 100-year-old tree and current rates of 7 kg N ha-1 yr-1. However, these N inputs and increased soil cycling rates do not translate into increased N gas losses. Two years of field measurements of a complete suite of N trace gases (ammonia, nitrous oxide, nitric oxide and other oxidized N compounds) found no difference in flux between upland Prosopis groves and adjacent unencroached grasslands. Total emissions for both land cover types average 0.56-0.65 kg N ha-1 yr-1, comparable to other southern US grasslands. Additional lab experiments suggested that N2 losses are low and that field oxygen conditions are not usually conducive to denitrification. Taken together, results suggest that this ecosystem is currently experiencing a period of net N accrual under ongoing encroachment.

  19. Use of 15N enriched plant material for labelling of soil nitrogen in legume dinitrogen fixation experiments

    International Nuclear Information System (INIS)

    Jensen, E.S.

    1989-06-01

    The soil nitrogen in a field plot was labelled with nitrogen-15 (15N) by incorporating labelled plant material derived from previous experiments. The plot was used the following 3 years for determination of the amount of N2 fixed by different leguminous plants. The atom % 15N excess in grains of cereals grown as reference crops was 0.20, 0.05 and 0.03 in the 3 years, respectively. In the first year the level of enrichment was adequate for estimating symbiotic nitrogen fixation. In the second and third year lack of precision in determination of the 15N/14N ratios of legume N, may have caused an error in estimates of nitrogen fixation. About 23% of the labelled N was taken up by plants during the 3 years of cropping; after 4 years about 44% of the labelled N was found still to be present in the top soil. The labelling of the soil nitrogen with organic bound 15N, compared to adding mineral 15N at sowing, is advantageous because the labelled N is released by mineralization so that the enrichment of the plant available soil N pool become more uniform during the growth season; and high levels of mineral N, which may depress the fixation process, is avoided. (author) 7 tabs., 1 ill., 30 refs

  20. Rapid synthesis and metabolism of glutamate in N2-fixing bacteroids

    International Nuclear Information System (INIS)

    Salminen, S.O.; Streeter, J.G.

    1987-01-01

    Symbiotic nodule bacteroids are thought to support N 2 fixation mainly by metabolizing dicarboxylic acids to CO 2 , generating reductant and ATP required by nitrogenase. Bradyrhizobium japonicum bacteroids were isolated anaerobically and incubated at 2% O 2 with 14 C-labeled succinate, malate, glutamate, or aspartate. 14 CO 2 was collected, and the bacteroid contents separated into neutral, organic acid, and amino acid fractions. The respiration of substrates, relative to their uptake, was malate > glutamate > succinate > aspartate. Analysis of the fractions revealed that will all substrates the radioactivity was found mostly in the amino acid fraction. The labeling of the neutral fraction was negligible and only a small amount of label was found in the organic acid fraction indicating a small pool size. TLC of the amino acid fraction showed the label to be principally in glutamate. Glutamate contained 67, 80, 97, and 88% of the 14 C in the amino acid fraction in bacteroids fed with succinate, malate, glutamate and aspartate, respectively. The data suggest that glutamate may play an important role in the bacteroid function

  1. Growth and Nitrogen Fixation in Silicon and/or Potassium Fed Chickpeas Grown under Drought and Well Watered Conditions

    Directory of Open Access Journals (Sweden)

    Fawaz Kurdali

    2013-08-01

    Full Text Available A pot experiment was conducted to study the effects of silicon (Si and/or potassium (K on plant growth, nitrogen uptake and N2-fixation in water stressed (FC1 and well watered (FC2 chickpea plants using 15N and 13C isotopes. Three fertilizer rates of Si (Si50, Si100 and Si200 and one fertilizer rate of K were used. For most of the growth parameters, it was found that Si either alone or in combination with K was more effective to alleviate water stress than K alone. Increasing soil water level from FC1 to FC2 often had a positive impact on values of almost all studied parameters. The Si100K+ (FC1 and Si50K+ (FC2 treatments gave high enough amounts of N2-fixation, higher dry matter production and greater nitrogen yield. The percent increments of total N2-fixed in the above mentioned treatments were 51 and 47% over their controls, respectively. On the other hand, increasing leave’s dry matter in response to the solely added Si (Si50K- and Si100K- is associated with lower Δ13C under both watering regimes. This may indicate that Si fertilization had a beneficial effect on water use efficiency (WUE. Hence, Δ13C could be an adequate indicator of WUE in response to the exogenous supply of silicon to chickpea plants. Our results highlight that Si is not only involved in amelioration of growth and in maintaining of water status but it can be also considered an important element for the symbiotic performance of chickpea plants. It can be concluded that the synergistic effect of silicon and potassium fertilization with adequate irrigation improves growth and nitrogen fixation in chickpea plants.

  2. Effect of systemic herbicides on N2-fixing and phosphate solubilizing microorganisms in relation to availability of nitrogen and phosphorus in paddy soils of West Bengal.

    Science.gov (United States)

    Das, Amal Chandra; Debnath, Anjan

    2006-11-01

    A field experiment has been conducted with four systemic herbicides viz., butachlor [N-(butoxymethyl)-2-chloro-2',6'-diethyl-acetanilide], fluchloralin [N-(2-chloroethyl)-(2,6-dinitro-N-propyl-4-trifluoromethyl) aniline], oxadiazon [5-terbutyl-3-(2,4-dichloro-5-isopro poxyphenyl)-1,3,4-oxadiazol-2-one] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenyl)-4-(trifluoromethyl) benzene] at their recommended field rates (2.0, 1.5, 0.4 and 0.12kga.i.ha(-1), respectively) to investigate their effects on growth and activities of aerobic non-symbiotic N(2)-fixing bacteria and phosphate solubilizing microorganisms in relation to availability of nitrogen and phosphorus in the rhizosphere soils as well as yield of the rice crop (Oryza sativa L cv. IR-36). Application of herbicides, in general, highly stimulated the population and activities of the target microorganisms, which resulted in a greater amount of atmospheric nitrogen fixation and phosphate solubilization in the rhizosphere soils of the test crop. The greater microbial activities subsequently augmented the mineralization and availability of nitrogen and phosphorus in the soil solution, which in turn increased the yield of the crop. Among the herbicides, oxyfluorfen was most stimulative followed by fluchloralin and oxadiazon in augmenting the microbial activities in soil. Butachlor also accentuated the mineralization and availability of nitrogen due to higher incitement of non-symbiotic N(2)-fixing bacteria in paddy soil. The grain and straw yields of the crop were also significantly increased due to the application of oxyfluorfen (20.2% and 21%) followed by fluchloralin (13.1% and 15.4%) and butachlor (9.1% and 10.2%), respectively.

  3. [Physiological and agrochemical properties of different symbiotic genotypes of pea (Pisum sativum L.)].

    Science.gov (United States)

    Nazariuk, V M; Sidorova, K K; Shumny, V K; Kallimullina, F R; Klenova M I

    2006-01-01

    Physiological characters of symbiotic mutants of pea were studied: nodulation, activities of nitrogenase and nitrate reductase, chlorophyll content in leaves and their water-holding capacity, biomass accumulation, and nitrogen forms. The parameters reflecting the genotype state of the macrosymbiont under soil conditions considerably varied. Supernodulation mutants stood out against symbiotic pea genotypes by high contents of chlorophyll and nonprotein nitrogen compounds, high nitrogenase activity, and low nitrate reductase activity. The efficiency of the legume-rhizobium symbiosis was largely mediated by the macrosymbiont genotype. The highest atmospheric nitrogen fixation (50-80%) was observed in the parental pea varieties. Despite the highest nitrogenase activity in the nodules, the supernodulation mutants were inferior to the parental varieties by the nitrogen fixation capacity (40-60%), which was due to their low productivity.

  4. The influence of rate and time of nitrate supply on nitrogen fixation and yield in pea (Pisum sativum L.)

    DEFF Research Database (Denmark)

    Jensen, Erik Steen

    1986-01-01

    The influence of nitrate N supply on dry matter production, N content and symbiotic nitrogen fixation in soil-grown pea (Pisum sativum L.) was studied in a pot experiment by means of15N fertilizer dilution. In pea receiving no fertilizer N symbiotic nitrogen fixation, soil and seed-borne N...... contributed with 82, 13 and 5% of total plant N, respectively. The supply of low rates of nitrate fertilizer at sowing (“starter N”) increased the vegetative dry matter production, but not the seed yield significantly. Nitrogen fixation was not significantly decreased by the lower rates of nitrate but higher...

  5. N = 2 string amplitudes

    International Nuclear Information System (INIS)

    Ooguri, H.

    1995-08-01

    In physics, solvable models have played very important roles. Understanding a simple model in detail teaches us a lot about more complicated models in generic situations. Five years ago, C. Vafa and I found that the closed N = 2 string theory, that is a string theory with the N = 2 local supersymmetry on the worldsheet, is classically equivalent to the self-dual Einstein gravity in four spacetime dimensions. Thus this string theory is solvable at the classical level. More recently, we have examined the N = 2 string partition function for spacial compactifications, and computed it to all order in the string perturbation expansion. The fact that such computation is possible at all suggests that the N = 2 string theory is solvable even quantum mechanically

  6. Exopolysaccharides produced by the symbiotic nitrogen-fixing bacteria of leguminosae

    OpenAIRE

    Bomfeti,Cleide Aparecida; Florentino,Ligiane Aparecida; Guimarães,Ana Paula; Cardoso,Patrícia Gomes; Guerreiro,Mário César; Moreira,Fatima Maria de Souza

    2011-01-01

    The process of biological nitrogen fixation (BNF), performed by symbiotic nitrogen fixing bacteria with legume species, commonly known as α and β rhizobia, provides high sustainability for the ecosystems. Its management as a biotechnology is well succeeded for improving crop yields. A remarkable example of this success is the inoculation of Brazilian soybeans with Bradyrhizobium strains. Rhizobia produce a wide diversity of chemical structures of exopolysaccharides (EPS). Although t...

  7. Rhizobial peptidase HrrP cleaves host-encoded signaling peptides and mediates symbiotic compatibility.

    Science.gov (United States)

    Price, Paul A; Tanner, Houston R; Dillon, Brett A; Shabab, Mohammed; Walker, Graham C; Griffitts, Joel S

    2015-12-08

    Legume-rhizobium pairs are often observed that produce symbiotic root nodules but fail to fix nitrogen. Using the Sinorhizobium meliloti and Medicago truncatula symbiotic system, we previously described several naturally occurring accessory plasmids capable of disrupting the late stages of nodule development while enhancing bacterial proliferation within the nodule. We report here that host range restriction peptidase (hrrP), a gene found on one of these plasmids, is capable of conferring both these properties. hrrP encodes an M16A family metallopeptidase whose catalytic activity is required for these symbiotic effects. The ability of hrrP to suppress nitrogen fixation is conditioned upon the genotypes of both the host plant and the hrrP-expressing rhizobial strain, suggesting its involvement in symbiotic communication. Purified HrrP protein is capable of degrading a range of nodule-specific cysteine-rich (NCR) peptides encoded by M. truncatula. NCR peptides are crucial signals used by M. truncatula for inducing and maintaining rhizobial differentiation within nodules, as demonstrated in the accompanying article [Horváth B, et al. (2015) Proc Natl Acad Sci USA, 10.1073/pnas.1500777112]. The expression pattern of hrrP and its effects on rhizobial morphology are consistent with the NCR peptide cleavage model. This work points to a symbiotic dialogue involving a complex ensemble of host-derived signaling peptides and bacterial modifier enzymes capable of adjusting signal strength, sometimes with exploitative outcomes.

  8. Biological Nitrogen Fixation In Tropical Dry Forests Of Costa Rica

    Science.gov (United States)

    Gei, M. G.; Powers, J. S.

    2012-12-01

    Evidence suggests that tropical dry forests (TDF) are not nitrogen (N) deficient. This evidence includes: high losses of gaseous nitrogen during the rainy season, high ecosystem soil N stocks and high N concentrations in leaves and litterfall. Its been commonly hypothesized that biological nitrogen fixation is responsible for the high availability of N in tropical soils. However, the magnitude of this flux has rarely if ever been measured in tropical dry forests. Because of the high cost of fixing N and the ubiquity of N fixing legume trees in the TDF, at the individual tree level symbiotic fixation should be a strategy down-regulated by the plant. Our main goal was to determine the rates of and controls over symbiotic N fixation. We hypothesized that legume tree species employ a facultative strategy of nitrogen fixation and that this process responds to changes in light availability, soil moisture and nutrient supply. We tested this hypothesis both on naturally established trees in a forest and under controlled conditions in a shade house by estimating the quantities of N fixed annually using the 15N natural abundance method, counting nodules, and quantifying (field) or manipulating (shade house) the variation in important environmental variables (soil nutrients, soil moisture, and light). We found that in both in our shade house experiment and in the forest, nodulation varied among different legume species. For both settings, the 15N natural abundance approach successfully detected differences in nitrogen fixation among species. The legume species that we studied were able to regulate fixation depending on the environmental conditions. They showed to have different strategies of nitrogen fixation that follow a gradient of facultative to obligate fixation. Our data suggest that there exists a continuum of nitrogen fixation strategies among species. Any efforts to define tropical legume trees as a functional group need to incorporate this variation.

  9. Efficiency of Nannochloropsis oculata and Bacillus polymyxa symbiotic composite at ammonium and phosphate removal from synthetic wastewater.

    Science.gov (United States)

    Wang, Sufeng; Liu, Jianxin; Li, Cui; Chung, Brian Michael

    2018-03-01

    Many issues, such as, DO accumulation, N 2 fixation obstacle, and carbon dioxide diffusion, hamper the application of microalgae-alginate immobilization in wastewater treatment. The objective of this study was to evaluate the effect of the microalgae Nannochloropsis oculata immobilized with the bacterium Bacillus polymyxa in alginate on ammonium and phosphate removal from synthetic wastewater. Results show that the co-immobilized Bacillus-Nannochloropsis can exploit ammonium and phosphate from wastewater more effectively than the immobilized Nannochloropsis, and immobilized Bacillus alone. A significantly higher ammonium and phosphate removal efficiency was found in co-immobilized Bacillus-Nannochloropsis (59.85%, 90.44%) than of that in immobilized Nannochloropsis (49.56%, 77.36%), and Bacillus immobilized (31.46%, 29.66%) alone. Additionally, the most effective co-immobilization mixture ratio for wastewater treatment was found to contain equal suspension (10 8 cell/ml) volume of the Nannochloropsis and Bacillus. Nannochloris and Bacillus can coexist harmoniously with the symbiotic and synergistic relationship, and the Nannochloropsis oculata- Bacillus polymyxa combination can be useful as a potential method to develop novel wastewater treatment.

  10. Enhanced N2-fixing ability of a deletion mutant of arctic rhizobia with sainfoin (Onobrychis viciifolia).

    Science.gov (United States)

    Jain, D K; Bordeleau, L M

    1990-12-01

    Mutagenesis provoked by exposure at elevated temperature of the cold-adapted, arctic Rhizobium strain N31 resulted in the generation of five deletion mutants, which exhibited loss of their smaller plasmid (200 kb), whereas the larger plasmid (> 500 kb) was still present in all mutants. Deletion mutants did not show differences from the wild type in the antibiotic resistance pattern, the carbohydrates and organic acids utilization, and the growth rate at low temperature. However, deletion mutants differed from the wild type and among themselves in the ex planta nitrogenase activity, the nodulation index, and the symbiotic effectiveness. The deletion mutant N31.6rif (r) showed higher nodulation index and exhibited higher nitrogenase activity and symbiotic efficiency than the other deletion mutants and the wild type. The process of deletion mutation resulted in the improvement of an arctic Rhizobium strain having an earlier and higher symbiotic nitrogen fixation efficiency than the wild type.

  11. Non-symbiotic Bradyrhizobium ecotypes dominate North American forest soils.

    Science.gov (United States)

    VanInsberghe, David; Maas, Kendra R; Cardenas, Erick; Strachan, Cameron R; Hallam, Steven J; Mohn, William W

    2015-11-01

    The genus Bradyrhizobium has served as a model system for studying host-microbe symbiotic interactions and nitrogen fixation due to its importance in agricultural productivity and global nitrogen cycling. In this study, we identify a bacterial group affiliated with this genus that dominates the microbial communities of coniferous forest soils from six distinct ecozones across North America. Representative isolates from this group were obtained and characterized. Using quantitative population genomics, we show that forest soil populations of Bradyrhizobium represent ecotypes incapable of nodulating legume root hairs or fixing atmospheric nitrogen. Instead, these populations appear to be free living and have a greater potential for metabolizing aromatic carbon sources than their close symbiotic relatives. In addition, we identify fine-scaled differentiation between populations inhabiting neighboring soil layers that illustrate how diversity within Bradyrhizobium is structured by habitat similarity. These findings reconcile incongruent observations about this widely studied and important group of bacteria and highlight the value of ecological context to interpretations of microbial diversity and taxonomy. These results further suggest that the influence of this genus likely extends well beyond facilitating agriculture, especially as forest ecosystems are large and integral components of the biosphere. In addition, this study demonstrates how focusing research on economically important microorganisms can bias our understanding of the natural world.

  12. Host range, symbiotic effectiveness and nodulation competitiveness ...

    African Journals Online (AJOL)

    SERVER

    2008-04-17

    Apr 17, 2008 ... This symbiotic interaction is of agronomic and ecological importance because of its significant amount of nitrogen to the total nitrogen budget in terrestrial ecosystems (Postgate,. 1998). An important characteristic of this symbiotic interaction is host specificity, where defined species of rhizobia forms nodules ...

  13. Latarjet Fixation

    Science.gov (United States)

    Alvi, Hasham M.; Monroe, Emily J.; Muriuki, Muturi; Verma, Rajat N.; Marra, Guido; Saltzman, Matthew D.

    2016-01-01

    Background: Attritional bone loss in patients with recurrent anterior instability has successfully been treated with a bone block procedure such as the Latarjet. It has not been previously demonstrated whether cortical or cancellous screws are superior when used for this procedure. Purpose: To assess the strength of stainless steel cortical screws versus stainless steel cannulated cancellous screws in the Latarjet procedure. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen matched-pair shoulder specimens were randomized into 2 separate fixation groups: (1) 3.5-mm stainless steel cortical screws and (2) 4.0-mm stainless steel partially threaded cannulated cancellous screws. Shoulder specimens were dissected free of all soft tissue and a 25% glenoid defect was created. The coracoid process was osteomized, placed at the site of the glenoid defect, and fixed in place with 2 parallel screws. Results: All 10 specimens failed by screw cutout. Nine of 10 specimens failed by progressive displacement with an increased number of cycles. One specimen in the 4.0-mm screw group failed by catastrophic failure on initiation of the testing protocol. The 3.5-mm screws had a mean of 274 cycles (SD, ±171 cycles; range, 10-443 cycles) to failure. The 4.0-mm screws had a mean of 135 cycles (SD, ±141 cycles; range, 0-284 cycles) to failure. There was no statistically significant difference between the 2 types of screws for cycles required to cause failure (P = .144). Conclusion: There was no statistically significant difference in energy or cycles to failure when comparing the stainless steel cortical screws versus partially threaded cannulated cancellous screws. Clinical Relevance: Latarjet may be performed using cortical or cancellous screws without a clear advantage of either option. PMID:27158630

  14. The Biology of Heterotrophic N2-fixing Bacteria in Marine and Estuarine Waters

    DEFF Research Database (Denmark)

    Bentzon-Tilia, Mikkel

    Biological nitrogen (N)2 fixation is of paramount importance for marine N cycling and for life in the oceans in general. It represents the sole mechanism by which microorganisms can channel inert atmospheric N2 gas into biomass and hence it may fuel a significant fraction of primary production...... cyanobacterial endosymbionts of diatoms, and recently also unicellular cyanobacteria, have been considered the dominant marine diazotrophs. However, phylogenetic analyses of the functional genes involved in N2 fixation seem to suggest that heterotrophic N2-fixing organisms are present and active in various...

  15. Molybdenum and phosphorus interact to constrain asymbiotic nitrogen fixation in tropical forests.

    Directory of Open Access Journals (Sweden)

    Nina Wurzburger

    Full Text Available Biological di-nitrogen fixation (N(2 is the dominant natural source of new nitrogen to land ecosystems. Phosphorus (P is thought to limit N(2 fixation in many tropical soils, yet both molybdenum (Mo and P are crucial for the nitrogenase reaction (which catalyzes N(2 conversion to ammonia and cell growth. We have limited understanding of how and when fixation is constrained by these nutrients in nature. Here we show in tropical forests of lowland Panama that the limiting element on asymbiotic N(2 fixation shifts along a broad landscape gradient in soil P, where Mo limits fixation in P-rich soils while Mo and P co-limit in P-poor soils. In no circumstance did P alone limit fixation. We provide and experimentally test a mechanism that explains how Mo and P can interact to constrain asymbiotic N(2 fixation. Fixation is uniformly favored in surface organic soil horizons--a niche characterized by exceedingly low levels of available Mo relative to P. We show that soil organic matter acts to reduce molybdate over phosphate bioavailability, which, in turn, promotes Mo limitation in sites where P is sufficient. Our findings show that asymbiotic N(2 fixation is constrained by the relative availability and dynamics of Mo and P in soils. This conceptual framework can explain shifts in limitation status across broad landscape gradients in soil fertility and implies that fixation depends on Mo and P in ways that are more complex than previously thought.

  16. Intrascleral IOL Fixation.

    Science.gov (United States)

    Jacob, Soosan

    2017-01-01

    Intrascleral sutureless intraocular lens (IOL) fixation utilizes direct haptic fixation within the sclera in eyes with deficient capsular support. This has advantages of long-term stability, good control of tilt and decentration, and lesser pseudophakodonesis. This review summarizes various techniques for intrascleral haptic fixation, results, complications, adaptations in special situations, modifications of the technique, combination surgeries, and intrascleral capsular bag fixation techniques (glued capsular hook). Copyright 2017 Asia-Pacific Academy of Ophthalmology.

  17. The Biology of Heterotrophic N2-fixing Bacteria in Marine and Estuarine Waters

    DEFF Research Database (Denmark)

    Bentzon-Tilia, Mikkel

    Biological nitrogen (N)2 fixation is of paramount importance for marine N cycling and for life in the oceans in general. It represents the sole mechanism by which microorganisms can channel inert atmospheric N2 gas into biomass and hence it may fuel a significant fraction of primary production...... cyanobacterial endosymbionts of diatoms, and recently also unicellular cyanobacteria, have been considered the dominant marine diazotrophs. However, phylogenetic analyses of the functional genes involved in N2 fixation seem to suggest that heterotrophic N2-fixing organisms are present and active in various...... marine systems as well. Their role and ecological significance is, however currently unknown. By combining in situ analyses of the distribution and activity of diazotrophs in various marine environments with culture-­based examinations of the potential of N2 fixation and its regulation in representative...

  18. Benthic dinitrogen fixation traversing the oxygen minimum zone off Mauritania (NW Africa)

    DEFF Research Database (Denmark)

    Gier, Jessica; Löscher, Carolin R.; Dale, Andrew W.

    2017-01-01

    Nespite its potential to provide new nitrogen (N) to the environment, knowledge on benthic dinitrogen (N2) fixation remains relatively sparse, and its contribution to the marine N budget is regarded as minor. Benthic N2 fixation is often observed in organic-rich sediments coupled to heterotrophic...

  19. Exploring the symbiotic pangenome of the nitrogen-fixing bacterium Sinorhizobium meliloti

    Energy Technology Data Exchange (ETDEWEB)

    Galardini, Marco [University of Florence; Mengoni, Alessio [University of Florence; Brilli, Matteo [Universite de Lyon, France; Pini, Francesco [University of Florence; Fioravanti, Antonella [University of Florence; Lucas, Susan [U.S. Department of Energy, Joint Genome Institute; Lapidus, Alla L. [U.S. Department of Energy, Joint Genome Institute; Cheng, Jan-Fang [U.S. Department of Energy, Joint Genome Institute; Goodwin, Lynne A. [Los Alamos National Laboratory (LANL); Pitluck, Sam [U.S. Department of Energy, Joint Genome Institute; Land, Miriam L [ORNL; Hauser, Loren John [ORNL; Woyke, Tanja [U.S. Department of Energy, Joint Genome Institute; Mikhailova, Natalia [U.S. Department of Energy, Joint Genome Institute; Ivanova, N [U.S. Department of Energy, Joint Genome Institute; Daligault, Hajnalka E. [Los Alamos National Laboratory (LANL); Bruce, David [Los Alamos National Laboratory (LANL); Detter, J. Chris [U.S. Department of Energy, Joint Genome Institute; Tapia, Roxanne [Los Alamos National Laboratory (LANL); Han, Cliff [Los Alamos National Laboratory (LANL); Teshima, Hazuki [Los Alamos National Laboratory (LANL); Mocali, Stefano [Agrobiol & Pedol Ctr ABP, Agr Res Council, I-50121 Florence, Italy; Bazzicalupo, Marco [University of Florence; Biondi, Emanuele [University of Florence

    2011-01-01

    Background: Sinorhizobium meliloti is a model system for the studies of symbiotic nitrogen fixation. An extensive polymorphism at the genetic and phenotypic level is present in natural populations of this species, especially in relation with symbiotic promotion of plant growth. AK83 and BL225C are two nodule-isolated strains with diverse symbiotic phenotypes; BL225C is more efficient in promoting growth of the Medicago sativa plants than strain AK83. In order to investigate the genetic determinants of the phenotypic diversification of S. meliloti strains AK83 and BL225C, we sequenced the complete genomes for these two strains. Results: With sizes of 7.14 Mbp and 6.97 Mbp, respectively, the genomes of AK83 and BL225C are larger than the laboratory strain Rm1021. The core genome of Rm1021, AK83, BL225C strains included 5124 orthologous groups, while the accessory genome was composed by 2700 orthologous groups. While Rm1021 and BL225C have only three replicons (Chromosome, pSymA and pSymB), AK83 has also two plasmids, 260 and 70 Kbp long. We found 65 interesting orthologous groups of genes that were present only in the accessory genome, consequently responsible for phenotypic diversity and putatively involved in plant-bacterium interaction. Notably, the symbiosis inefficient AK83 lacked several genes required for microaerophilic growth inside nodules, while several genes for accessory functions related to competition, plant invasion and bacteroid tropism were identified only in AK83 and BL225C strains. Presence and extent of polymorphism in regulons of transcription factors involved in symbiotic interaction were also analyzed. Our results indicate that regulons are flexible, with a large number of accessory genes, suggesting that regulons polymorphism could also be a key determinant in the variability of symbiotic performances among the analyzed strains.

  20. Biological dinitrogen fixation and its economical importance for agriculture

    International Nuclear Information System (INIS)

    Ozbek, N.; Halitligil, M.B.; Korkmaz, A.

    1985-01-01

    The measurement of biological N 2 fixation is of considerable importance and recently AN values of the legume and non-nodulating crop using 1 5N labelled fertilizer were used extensively to estimate the amount of N 2 fixed legume crop growing under field conditions. The objective of this research was to estimate biological N 2 fixation under field conditions using 1 5N labelled fertilizer and growing Calland soybean and corn as the test plants. A field experiment was conducted at Cukurova (Adana) using randomized block design and 4 replications for each treatment. For the both crops 4 nitrogen rates and for soybean 4 inoculation rates were applied. (author)

  1. CO2 and soil water potential as regulators of the growth and N fraction derived from fixation of a legume in tallgrass prairie communities

    Science.gov (United States)

    CO2 enrichment may increase N input to ecosystems by increasing N2 fixation, but the fixation-CO2 response depends on factors such as soil water availability that are influenced by both CO2 and soil properties. We used the d15N natural abundance method to determine N2 fixation by the legume Desmant...

  2. Does legume nitrogen fixation underpin host quality for the hemiparasitic plant Rhinanthus minor?

    Science.gov (United States)

    Jiang, Fan; Jeschke, W Dieter; Hartung, Wolfram; Cameron, Duncan D

    2008-01-01

    The high quality of leguminous hosts for the parasitic plant Rhinanthus minor (in terms of growth and fecundity), compared with forbs (non-leguminous dicots) has long been assumed to be a function of the legume's ability to fix atmospheric nitrogen (N) from the air and the potential for direct transfer of compatible amino compounds to the parasite. Using associations between Rhinanthus minor and Vicia faba (Fabaceae) that receive N either exclusively via symbiotic associations with rhizobia supplying organic N fixed from N(2) or exclusively through the supply of inorganic nitrate to the substrate, the underlying reasons for the quality of legumes as hosts for this parasite are unravelled. It is shown that sole dependence of the host, V. faba, on N fixation results in lower growth of the attached parasite than when the host is grown in a substrate supplied exclusively with inorganic N. In contrast, the host plants themselves achieved a similar biomass irrespective of their N source. The physiological basis for this is investigated in terms of N and abscisic acid (ABA) partitioning, haustorial penetration, and xylem sap amino acid profiles. It is concluded that legume N fixation does not underpin the quality of legumes as hosts for Rhinanthus but rather the well-developed haustorium formed by the parasite, coupled with the lack of defensive response of the host tissues to the invading haustorium and the presence of sufficient nitrogenous compounds in the xylem sap accessible to the parasite haustoria, would appear to be the primary factors influencing host quality of the legumes.

  3. Enhanced Symbiotic Performance by Rhizobium tropici Glycogen Synthase Mutants

    Science.gov (United States)

    Marroquí, Silvia; Zorreguieta, Angeles; Santamaría, Carmen; Temprano, Francisco; Soberón, Mario; Megías, Manuel; Downie, J. Allan

    2001-01-01

    We isolated a Tn5-induced Rhizobium tropici mutant that has enhanced capacity to oxidize N,N-dimethyl-p-phenylendiamine (DMPD) and therefore has enhanced respiration via cytochrome oxidase. The mutant had increased levels of the cytochromes c1 and CycM and a small increase in the amount of cytochrome aa3. In plant tests, the mutant increased the dry weight of Phaseolus vulgaris plants by 20 to 38% compared with the control strain, thus showing significantly enhanced symbiotic performance. The predicted product of the mutated gene is homologous to glycogen synthases from several bacteria, and the mutant lacked glycogen. The DNA sequence of the adjacent gene region revealed six genes predicted to encode products homologous to the following gene products from Escherichia coli: glycogen phosphorylase (glgP), glycogen branching enzyme (glgB), ADP glucose pyrophosphorylase (glgC), glycogen synthase (glgA), phosphoglucomutase (pgm), and glycogen debranching enzyme (glgX). All six genes are transcribed in the same direction, and analysis with lacZ gene fusions suggests that the first five genes are organized in one operon, although pgm appears to have an additional promoter; glgX is transcribed independently. Surprisingly, the glgA mutant had decreased levels of high-molecular-weight exopolysaccharide after growth on glucose, but levels were normal after growth on galactose. A deletion mutant was constructed in order to generate a nonpolar mutation in glgA. This mutant had a phenotype similar to that of the Tn5 mutant, indicating that the enhanced respiration and symbiotic nitrogen fixation and decreased exopolysaccharide were due to mutation of glgA and not to a polar effect on a downstream gene. PMID:11208782

  4. Symbiotic Stars in X-rays

    Science.gov (United States)

    Luna, G. J. M.; Sokoloski, J. L.; Mukai, K.; Nelson, T.

    2014-01-01

    Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with

  5. N2-fixing red alder indirectly accelerates ecosystem nitrogen cycling

    Science.gov (United States)

    Perakis, Steven S.; Matkins, Joselin J.; Hibbs, David E.

    2012-01-01

    Symbiotic N2-fixing tree species can accelerate ecosystem N dynamics through decomposition via direct pathways by producing readily decomposed leaf litter and increasing N supply to decomposers, as well as via indirect pathways by increasing tissue and detrital N in non-fixing vegetation. To evaluate the relative importance of these pathways, we compared three-year decomposition and N dynamics of N2-fixing red alder leaf litter (2.34 %N) to both low-N (0.68 %N) and high-N (1.21 %N) litter of non-fixing Douglas-fir, and decomposed each litter source in four forests dominated by either red alder or Douglas-fir. We also used experimental N fertilization of decomposition plots to assess elevated N availability as a potential mechanism of N2-fixer effects on litter mass loss and N dynamics. Direct effects of N2-fixing red alder on decomposition occurred primarily as faster N release from red alder than Douglas-fir litter, but direct increases in N supply to decomposers via fertilization did not stimulate decomposition of any litter. Fixed N indirectly influenced detrital dynamics by increasing Douglas-fir tissue and litter N concentrations, which accelerated litter N release without accelerating mass loss. By increasing soil N, tissue N, and the rate of N release from litter of non-fixers, we conclude that N2-fixing vegetation can indirectly foster plant-soil feedbacks that contribute to the persistence of elevated N availability in terrestrial ecosystems.

  6. Genetic Diversity and Symbiotic Efficiency of Indigenous Common Bean Rhizobia in Croatia

    Directory of Open Access Journals (Sweden)

    Ines Pohajda

    2016-01-01

    Full Text Available Nodule bacteria (rhizobia in symbiotic associations with legumes enable considerable entries of biologically fixed nitrogen into soil. Efforts are therefore made to intensify the natural process of symbiotic nitrogen fixation by legume inoculation. Studies of field populationsof rhizobia open up the possibility to preserve and probably exploit some indigenous strains with hidden symbiotic or ecological potentials. The main aim of the present study is to determine genetic diversity of common bean rhizobia isolated from different field sites in central Croatia and to evaluate their symbiotic efficiency and compatibility with host plants. The isolation procedure revealed that most soil samples contained no indigenous common bean rhizobia. The results indicate that the cropping history had a significant impact on the presence of indigenous strains. Although all isolates were found to belong to species Rhizobium leguminosarum, significant genetic diversity at the strain level was determined. Application of both random amplifi cation of polymorphic DNA (RAPD and enterobacterial repetitive intergenic consensus–polymerase chain reaction (ERIC-PCR methods resulted in similar grouping of strains. Symbiotic efficiency of indigenous rhizobia as well as their compatibility with two commonly grown bean varieties were tested in field experiments. Application of indigenous rhizobial strains as inoculants resulted in significantly different values of nodulation, seed yield as well as plant nitrogen and seed protein contents. The most abundant nodulation and the highest plant nitrogen and protein contents were determined in plants inoculated with R. leguminosarum strains S17/2 and S21/6. Although, in general, the inoculation had a positive impact on seed yield, differences depending on the applied strain were not determined. The overall results show the high degree of symbiotic efficiency of the specific indigenous strain S21/6. These results indicate different

  7. Production of N2O in grass-clover pastures

    International Nuclear Information System (INIS)

    Carter, M.S.

    2005-09-01

    Agricultural soils are known to be a considerable source of the strong greenhouse gas nitrous oxide (N 2 O), and in soil N 2 O is mainly produced by nitrifying and denitrifying bacteria. In Denmark, grass-clover pastures are an important component of the cropping system in organic as well as conventional dairy farming, and on a European scale grass-clover mixtures represent a large part of the grazed grasslands. Biological dinitrogen (N 2 ) fixation in clover provides a major N input to these systems, but knowledge is sparse regarding the amount of fixed N 2 lost from the grasslands as N2O. Furthermore, urine patches deposited by grazing cattle are known to be hot-spots of N 2 O emission, but the mechanisms involved in the N 2 O production in urine-affected soil are very complex and not well understood. The aim of this Ph.D. project was to increase the knowledge of the biological and physical-chemical mechanisms, which control the production of N2O in grazed grass-clover pastures. Three experimental studies were conducted with the objectives of: 1: assessing the contribution of recently fixed N 2 as a source of N 2 O. 2: examining the link between N 2 O emission and carbon mineralization in urine patches. 3: investigating the effect of urine on the rates and N 2 O loss ratios of nitrification and denitrification, and evaluating the impact of the chemical conditions that arise in urine affected soil. The results revealed that only 3.2 ± 0.5 ppm of the recently fixed N 2 was emitted as N2O on a daily basis. Thus, recently fixed N released via easily degradable clover residues appears to be a minor source of N2O. Furthermore, increased N 2 O emission following urine application at rates up to 5.5 g N m -2 was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots. Finally, the increase of soil pH and ammonium following urine application led to raised nitrification rate, which appeared to be the most important factor

  8. Symbiots: Conceptual Interventions Into Urban Energy Systems

    DEFF Research Database (Denmark)

    Bergström, Jenny; Mazé, Ramia; Redströmand, Johan

    2009-01-01

    Symbiots set out to examine values such as ease-of-use, comfort, and rationality assumed within conventions of ‘good design’, in order to expose issues related to energy consumption and current human- (versus eco-) centered design paradigms. Exploring re-interpretations of graphical patterns......, architectural configura- tions and electrical infrastructure typical in Swedish cities, Symbiots takes the form of a photo series in the genre of contemporary hy- per-real art photography. Painting a vivid pic- ture of alternatives to current local priorities around energy consumption, the three design concepts...

  9. Nitrogen fixation improvement in Faidherbia albida

    International Nuclear Information System (INIS)

    Toure, O.; Dasilva, M.C.; Badji, S.; Dianda, M.; Ndoye, I.; Gueye, M.

    1998-01-01

    A greenhouse experiment investigated growth, N accumulation and N 2 fixation (using the 15 N-dilution method) by Faidherbia albida in comparison with three species of Acacia, with Parkia biglobosa and Tamarindus indica as non-fixing reference plants. Faidherbia albida was mediocre in comparison with A. seyel, therefore seven provenances of the former were examined in a second pot experiment to investigate within-species variability for the same performance components; a provenance from Kabrousse, Senegal, showed particular promise in terms of dry weight and N accumulation, and fixation of N. This promise was confirmed with a 15-month field experiment, but revealed that there is opportunity for further improvement in N 2 -fixing ability. Faidherbia albida is a slow-growing tree, therefore further field experiments with provenance Kabrousse should be longer term in scope. The data indicate that trenching of the 15 N-labelled area may not be necessary. (author)

  10. Phenotypic, Molecular and Symbiotic Characterization of the Rhizobial Symbionts of Desmanthus paspalaceus (Lindm.) Burkart That Grow in the Province of Santa Fe, Argentina

    Science.gov (United States)

    Fornasero, Laura Viviana; Del Papa, María Florencia; López, José Luis; Albicoro, Francisco Javier; Zabala, Juan Marcelo; Toniutti, María Antonieta; Pensiero, José Francisco; Lagares, Antonio

    2014-01-01

    Desmanthus paspalaceus (Lindm.) Burkart belongs to the D. virgatus complex, subfamily Mimosoidae. The known potential as livestock fodder of several of these legumes prompted us to undertake a phenotypic, molecular, and symbiotic characterization of the D. paspalaceus symbionts in the Santa Fe province, Argentina. The rhizobia collected—containing isolates with different abiotic-stress tolerances—showed a remarkable genetic diversity by PCR fingerprinting, with 11 different amplification profiles present among 20 isolates. In selected isolates 16S-rDNA sequencing detected mesorhizobia (60%) and rhizobia (40%) within the collection, in contrast to the genus of the original inoculant strain CB3126—previously isolated from Leucaena leucocephala—that we typified here through its 16S rDNA as Sinorhizobium terangae. The results revealed the establishment by diverse bacterial genera -rhizobia, sinorhizobia, and mesorhizobia- of full N2-fixing symbiotic associations with D. paspalaceus. This diversity was paralleled by the presence of at least two different nodC allelic variants. The identical nodC alleles of the Mesorhizobia sp. 10.L.4.2 and 10.L.5.3 notably failed to group within any of the currently described rhizo-/brady-/azorhizobial nodC clades. Interestingly, the nodC from S. terangae CB3126 clustered close to homologs from common bean nodulating rhizobia, but not with the nodC from S. terangae WSM1721 that nodulates Acacia. No previous data were available on nod-gene phylogeny for Desmanthus symbionts. A field assay indicated that inoculation of D. paspalaceus with the local Rhizobium sp. 10L.11.4 produced higher aerial-plant dry weights compared to S. teranga CB3126–inoculated plants. Neither the mesorhizobia 10.L.4.2 or 10.L.5.3 nor the rhizobium 10L.11.4 induced root nodules in L. leucocephala or P. vulgaris. The results show that some of the local isolates have remarkable tolerances to several abiotic stresses including acidity, salt, and temperature

  11. Guide to radiation fixatives

    International Nuclear Information System (INIS)

    Tawil, J.J.; Bold, F.C.

    1983-11-01

    This report identifies and then characterizes a variety of substances available in the market place for potential effectiveness as a fixative on radiologically contaminated surfaces. The substances include both generic chemicals and proprietary products. In selecting a fixative for a particular application, several attributes of the fixative may be relevant to the choice. These attributes include: toxicity, durability, and cleanliness and removability. In addition to the attributes of the fixative, one should also take into account certain characteristics of the site to be treated. These characteristics relate to climate, nature of the surface, use to which the treated surface will be put, subsequent cleanup operations, and type of neighboring surfaces. Finally, costs and potential environmental effects may influence the decision. A variety of fixatives are evaluated with respect to these various attributes and summarized in a reference table

  12. Guide to radiation fixatives

    Energy Technology Data Exchange (ETDEWEB)

    Tawil, J.J.; Bold, F.C.

    1983-11-01

    This report identifies and then characterizes a variety of substances available in the market place for potential effectiveness as a fixative on radiologically contaminated surfaces. The substances include both generic chemicals and proprietary products. In selecting a fixative for a particular application, several attributes of the fixative may be relevant to the choice. These attributes include: toxicity, durability, and cleanliness and removability. In addition to the attributes of the fixative, one should also take into account certain characteristics of the site to be treated. These characteristics relate to climate, nature of the surface, use to which the treated surface will be put, subsequent cleanup operations, and type of neighboring surfaces. Finally, costs and potential environmental effects may influence the decision. A variety of fixatives are evaluated with respect to these various attributes and summarized in a reference table.

  13. Benthic Dinitrogen Fixation Traversing the Oxygen Minimum Zone Off Mauritania (NW Africa

    Directory of Open Access Journals (Sweden)

    Jessica Gier

    2017-12-01

    Full Text Available Despite its potential to provide new nitrogen (N to the environment, knowledge on benthic dinitrogen (N2 fixation remains relatively sparse, and its contribution to the marine N budget is regarded as minor. Benthic N2 fixation is often observed in organic-rich sediments coupled to heterotrophic metabolisms, such as sulfate reduction. In the present study, benthic N2 fixation together with sulfate reduction and other heterotrophic metabolisms were investigated at six station between 47 and 1,108 m water depth along the 18°N transect traversing the highly productive upwelling region known as Mauritanian oxygen minimum zone (OMZ. Bottom water oxygen concentrations ranged between 30 and 138 μM. Benthic N2 fixation determined by the acetylene reduction assay was detected at all stations with highest rates (0.15 mmol m−2 d−1 on the shelf (47 and 90 m water depth and lowest rates (0.08 mmol m−2 d−1 below 412 m water depth. The biogeochemical data suggest that part of the N2 fixation could be linked to sulfate- and iron-reducing bacteria. Molecular analysis of the key functional marker gene for N2 fixation, nifH, confirmed the presence of sulfate- and iron-reducing diazotrophs. High N2 fixation further coincided with bioirrigation activity caused by burrowing macrofauna, both of which showed high rates at the shelf sites and low rates in deeper waters. However, statistical analyses proved that none of these processes and environmental variables were significantly correlated with benthic diazotrophy, which lead to the conclusion that either the key parameter controlling benthic N2 fixation in Mauritanian sediments remains unidentified or that a more complex interaction of control mechanisms exists. N2 fixation rates in Mauritanian sediments were 2.7 times lower than those from the anoxic Peruvian OMZ.

  14. DAILY BUDGETS OF PHOTOSYNTHETICALLY FIXED CARBON IN SYMBIOTIC ZOANTHIDS.

    Science.gov (United States)

    Steen, R Grant; Muscatine, L

    1984-10-01

    We tested the hypothesis that some zoanthids are able to meet a portion of their daily respiratory carbon requirement with photosynthetic carbon from symbiotic algal cells (= zooxanthellae). A daily budget was constructed for carbon (C) photosynthetically fixed by zooxanthellae of the Bermuda zoanthids Zoanthus sociatus and Palythoa variabilis. Zooxanthellae have an average net photosynthetic C fixation of 7.48 and 15.56 µgC·polyp -1 ·day -1 for Z. sociatus and P. variabilis respectively. The C-specific growth rate (µ c ) was 0.215·day -1 for Z. sociatus and 0.152·day -1 for P. variabilis. The specific growth rate (µ) of zooxanthellae in the zoanthids was measured to be 0.011 and 0.017·day -1 for Z. sociatus and P. variabilis zooxanthellae respectively. Z. sociatus zooxanthellae translocated 95.1% of the C assimilated in photosynthesis, while P. variabilis zooxanthellae translocated 88.8% of their fixed C. As the animal tissue of a polyp of Z. sociatus required 14.75 µgC·day -1 for respiration, and one of P. variabiis required 105.54 µgC·day -1 , the contribution of zooxanthellae to animal respiration (CZAR) was 48.2% for Z. sociatus and 13.1% for P. variabilis.

  15. Functional ecology of free-living nitrogen fixation: A contemporary perspective

    Science.gov (United States)

    Reed, Sasha C.; Cleveland, Cory C.; Townsend, Alan R.

    2011-01-01

    Nitrogen (N) availability is thought to frequently limit terrestrial ecosystem processes, and explicit consideration of N biogeochemistry, including biological N2 fixation, is central to understanding ecosystem responses to environmental change. Yet, the importance of free-living N2 fixation—a process that occurs on a wide variety of substrates, is nearly ubiquitous in terrestrial ecosystems, and may often represent the dominant pathway for acquiring newly available N—is often underappreciated. Here, we draw from studies that investigate free-living N2 fixation from functional, physiological, genetic, and ecological perspectives. We show that recent research and analytical advances have generated a wealth of new information that provides novel insight into the ecology of N2 fixation as well as raises new questions and priorities for future work. These priorities include a need to better integrate free-living N2 fixation into conceptual and analytical evaluations of the N cycle's role in a variety of global change scenarios.

  16. Learning fair play in industrial symbiotic relations

    NARCIS (Netherlands)

    Yazan, Devrim Murat; Yazdanpanah, Vahid; Fraccascia, Luca; Mancuso, Erika; Fantin, Valentina

    2017-01-01

    In this paper, we provide practical decision support to managers in firms involved in Industrial Symbiotic Relations (ISRs) in terms of strategy development and test the hypothesis that in the long-term, playing a fair strategy for sharing obtainable ISR-related benefits is dominant. We employ

  17. A report of symbiotic Siphonostomatoida (Copepoda) infecting ...

    African Journals Online (AJOL)

    Collected copepod specimens were fixed and preserved in 70% ethanol and studied with the stereo- and light microscopes. Most of the examined hosts (38) were infected with symbiotic siphonostomatoids. Ten different species representing five families were identified. Of these, seven represent new host records while four ...

  18. Screening for symbiotically effective and ecologically competitive ...

    African Journals Online (AJOL)

    This study was initiated to isolate and characterize chickpea rhizobia for their symbiotic effectiveness adapted to local environmental conditions. A total of seventy root nodule bacteria were isolated from different sampling sites in central and northern Ethiopia of which only 52% were rhizobia and the remaining were ...

  19. Clade identification of symbiotic zooxanthellae of dominant ...

    African Journals Online (AJOL)

    Tidal pools have harsh conditions due to lack of nutrients, food and pronounced changes in physical conditions such as pH, salinity and temperature, hence the study of symbiotic zooxanthellae on coral reefs of tidal pool seems to be necessary. Samples of five coral species that include Siderastrea savignyana, ...

  20. Screening soybean genotypes for promiscuous symbiotic ...

    African Journals Online (AJOL)

    A greenhouse experiment was conducted at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) with the aim of screening of soybean germplasm for promiscuous symbiotic association with Bradyrhizobium sp. in order to identify genotypes with potential to be used as parents to initiate a breeding ...

  1. Potential for nitrogen fixation in fungus-growing termite symbiosis

    DEFF Research Database (Denmark)

    Sapountzis, Panagiotis; de Verges, Jane; Rousk, Kathrin

    2016-01-01

    Termites host a gut microbiota of diverse and essential symbionts that enable specialization on dead plant material; an abundant, but nutritionally imbalanced food source. To supplement the severe shortage of dietary nitrogen (N), some termite species make use of diazotrophic bacteria to fix...... atmospheric nitrogen (N2). Fungus-growing termites (subfamily Macrotermitinae) host a fungal exosymbiont (genus Termitomyces) that provides digestive services and the main food source for the termites. This has been thought to obviate the need for N2-fixation by bacterial symbionts. Here, we challenge...... this notion by performing acetylene reduction assays of live colony material to show that N2 fixation is present in two major genera (Macrotermes and Odontotermes) of fungus-growing termites. We compare and discuss fixation rates in relation to those obtained from other termites, and suggest avenues...

  2. New nilpotent N =2 superfields

    Science.gov (United States)

    Kuzenko, Sergei M.; Tartaglino-Mazzucchelli, Gabriele

    2018-01-01

    We propose new off-shell models for spontaneously broken local N =2 supersymmetry, in which the supergravity multiplet couples to nilpotent Goldstino superfields that contain either a gauge one-form or a gauge two-form in addition to spin-1 /2 Goldstone fermions and auxiliary fields. In the case of N =2 Poincaré supersymmetry, we elaborate on the concept of twisted chiral superfields and present a nilpotent N =2 superfield that underlies the cubic nilpotency conditions given in J. High Energy Phys. 08 (2017) 109., 10.1007/JHEP08(2017)109 in terms of constrained N =1 superfields.

  3. Rates of Dinitrogen Fixation and the Abundance of Diazotrophs in North American Coastal Waters Between Cape Hatteras and Georges Bank

    Science.gov (United States)

    Mulholland, M.R.; Bernhardt, P. W.; Blanco-Garcia, J. L.; Mannino, A.; Hyde, K.; Mondragon, E.; Turk, K.; Moisander, P. H.; Zehr, J. P.

    2012-01-01

    We coupled dinitrogen (N2) fixation rate estimates with molecular biological methods to determine the activity and abundance of diazotrophs in coastal waters along the temperate North American Mid-Atlantic continental shelf during multiple seasons and cruises. Volumetric rates of N2 fixation were as high as 49.8 nmol N L(sup -1) d(sup -1) and areal rates as high as 837.9 micromol N m(sup -2) d(sup -1) in our study area. Our results suggest that N2 fixation occurs at high rates in coastal shelf waters that were previously thought to be unimportant sites of N2 fixation and so were excluded from calculations of pelagic marine N2 fixation. Unicellular N2-fixing group A cyanobacteria were the most abundant diazotrophs in the Atlantic coastal waters and their abundance was comparable to, or higher than, that measured in oceanic regimes where they were discovered. High rates of N2 fixation and the high abundance of diazotrophs along the North American Mid-Atlantic continental shelf highlight the need to revise marine N budgets to include coastal N2 fixation. Integrating areal rates of N2 fixation over the continental shelf area between Cape Hatteras and Nova Scotia, the estimated N2 fixation in this temperate shelf system is about 0.02 Tmol N yr(sup -1), the amount previously calculated for the entire North Atlantic continental shelf. Additional studies should provide spatially, temporally, and seasonally resolved rate estimates from coastal systems to better constrain N inputs via N2 fixation from the neritic zone.

  4. Exploring the symbiotic pangenome of the nitrogen-fixing bacterium Sinorhizobium meliloti

    Directory of Open Access Journals (Sweden)

    Daligault Hajnalka

    2011-05-01

    Full Text Available Abstract Background Sinorhizobium meliloti is a model system for the studies of symbiotic nitrogen fixation. An extensive polymorphism at the genetic and phenotypic level is present in natural populations of this species, especially in relation with symbiotic promotion of plant growth. AK83 and BL225C are two nodule-isolated strains with diverse symbiotic phenotypes; BL225C is more efficient in promoting growth of the Medicago sativa plants than strain AK83. In order to investigate the genetic determinants of the phenotypic diversification of S. meliloti strains AK83 and BL225C, we sequenced the complete genomes for these two strains. Results With sizes of 7.14 Mbp and 6.97 Mbp, respectively, the genomes of AK83 and BL225C are larger than the laboratory strain Rm1021. The core genome of Rm1021, AK83, BL225C strains included 5124 orthologous groups, while the accessory genome was composed by 2700 orthologous groups. While Rm1021 and BL225C have only three replicons (Chromosome, pSymA and pSymB, AK83 has also two plasmids, 260 and 70 Kbp long. We found 65 interesting orthologous groups of genes that were present only in the accessory genome, consequently responsible for phenotypic diversity and putatively involved in plant-bacterium interaction. Notably, the symbiosis inefficient AK83 lacked several genes required for microaerophilic growth inside nodules, while several genes for accessory functions related to competition, plant invasion and bacteroid tropism were identified only in AK83 and BL225C strains. Presence and extent of polymorphism in regulons of transcription factors involved in symbiotic interaction were also analyzed. Our results indicate that regulons are flexible, with a large number of accessory genes, suggesting that regulons polymorphism could also be a key determinant in the variability of symbiotic performances among the analyzed strains. Conclusions In conclusions, the extended comparative genomics approach revealed a

  5. CSF coccidioides complement fixation

    Science.gov (United States)

    Skip navigation U.S. National Library of Medicine The navigation menu has been collapsed. ... of this page: //medlineplus.gov/ency/article/003526.htm CSF coccidioides complement fixation test To use the sharing features ...

  6. Histoplasma complement fixation

    Science.gov (United States)

    Skip navigation U.S. National Library of Medicine The navigation menu has been collapsed. ... this page: //medlineplus.gov/ency/article/003527.htm Histoplasma complement fixation To use the sharing features on this page, ...

  7. Eficiência simbiótica de estirpes de Bradyrhizobium isoladas de solo do Cerrado em caupi Symbiotic efficiency of cowpea Bradyrhizobium strains in Cerrado soils

    Directory of Open Access Journals (Sweden)

    Jerri Édson Zilli

    2006-05-01

    Full Text Available O objetivo deste trabalho foi avaliar as relações filogenéticas de estirpes de Bradyrhizobium e a contribuição destas estirpes para a fixação biológica de nitrogênio em caupi, em solos do Cerrado. Na avaliação da relação filogenética, o gene 16S rDNA de cada uma das estirpes foi amplificado e seqüenciado, e para a análise da eficiência simbiótica, determinou-se: N total, matéria seca das plantas, massa de nódulos e redução de acetileno, em casa de vegetação, e ocupação nodular, em experimento de campo. A maioria das estirpes estudadas pertence a B. elkanii e, pelo menos dez das estirpes, independentemente da espécie, apresentaram bom desempenho quanto à fixação biológica de N2. As estirpes BR3262, BR3280 (caracterizadas como B. elkanii e BR3267, BR3287 e BR3288 (Bradyrhizobium sp. mostram-se como inoculantes potenciais para o caupi, em razão do bom desempenho tanto na eficiência simbiótica quanto na ocupação nodular.The obejctive of this study was to evaluate the phylogenetic relationships of Bradyrhizobium strains, and the contribution of these strains to cowpea biological nitrogen fixation in Cerrado soils. To elucidate the phylogenetic relationships among strains, their 16S rDNA gene was extracted, amplified and sequenced. In order to evaluate the symbiotic efficiency, total N, plant dry matter, nodular mass and acetylene reduction in a greenhouse experiment, and nodular occupation, in a field experiment, were determined. Most part of the strains belonge to B. elkanii, and at least ten of the analyzed strains, independently of the species, presented high capacity to fix N2. The strains BR3262, BR3280 (characterized as B. elkanii, BR3267, BR3287 and BR3288 (Bradyrhizobium sp. exhibit a potential as inoculant for cowpea, due to their high biological nitrogen fixation.

  8. Symbiotic options for the conquest of land.

    Science.gov (United States)

    Field, Katie J; Pressel, Silvia; Duckett, Jeffrey G; Rimington, William R; Bidartondo, Martin I

    2015-08-01

    The domination of the landmasses of Earth by plants starting during the Ordovician Period drastically altered the development of the biosphere and the composition of the atmosphere, with far-reaching consequences for all life ever since. It is widely thought that symbiotic soil fungi facilitated the colonization of the terrestrial environment by plants. However, recent discoveries in molecular ecology, physiology, cytology, and paleontology have brought into question the hitherto-assumed identity and biology of the fungi engaged in symbiosis with the earliest-diverging lineages of extant land plants. Here, we reconsider the existing paradigm and show that the symbiotic options available to the first plants emerging onto the land were more varied than previously thought. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. Symbiotic options for the conquest of land

    OpenAIRE

    Field, KJ; Pressel, S; Duckett, JG; Rimington, WR; Bidartondo, MI

    2015-01-01

    The domination of the landmasses of Earth by plants starting during the Ordovician Period drastically altered the development of the biosphere and the composition of the atmosphere, with far-reaching consequences for all life ever since. It is widely thought that symbiotic soil fungi facilitated the colonization of the terrestrial environment by plants. However, recent discoveries in molecular ecology, physiology, cytology, and paleontology have brought into question the hitherto-assumed iden...

  10. Nitrogen fixation in eukaryotes – New models for symbiosis

    Directory of Open Access Journals (Sweden)

    Lockhart Peter

    2007-04-01

    Full Text Available Abstract Background Nitrogen, a component of many bio-molecules, is essential for growth and development of all organisms. Most nitrogen exists in the atmosphere, and utilisation of this source is important as a means of avoiding nitrogen starvation. However, the ability to fix atmospheric nitrogen via the nitrogenase enzyme complex is restricted to some bacteria. Eukaryotic organisms are only able to obtain fixed nitrogen through their symbiotic interactions with nitrogen-fixing prokaryotes. These symbioses involve a variety of host organisms, including animals, plants, fungi and protists. Results We have compared the morphological, physiological and molecular characteristics of nitrogen fixing symbiotic associations of bacteria and their diverse hosts. Special features of the interaction, e.g. vertical transmission of symbionts, grade of dependency of partners and physiological modifications have been considered in terms of extent of co-evolution and adaptation. Our findings are that, despite many adaptations enabling a beneficial partnership, most symbioses for molecular nitrogen fixation involve facultative interactions. However, some interactions, among them endosymbioses between cyanobacteria and diatoms, show characteristics that reveal a more obligate status of co-evolution. Conclusion Our review emphasises that molecular nitrogen fixation, a driving force for interactions and co-evolution of different species, is a widespread phenomenon involving many different organisms and ecosystems. The diverse grades of symbioses, ranging from loose associations to highly specific intracellular interactions, might themselves reflect the range of potential evolutionary fates for symbiotic partnerships. These include the extreme evolutionary modifications and adaptations that have accompanied the formation of organelles in eukaryotic cells: plastids and mitochondria. However, age and extensive adaptation of plastids and mitochondria complicate the

  11. NAD1 Controls Defense-Like Responses in Medicago truncatula Symbiotic Nitrogen Fixing Nodules Following Rhizobial Colonization in a BacA-Independent Manner.

    Science.gov (United States)

    Domonkos, Ágota; Kovács, Szilárd; Gombár, Anikó; Kiss, Ernő; Horváth, Beatrix; Kováts, Gyöngyi Z; Farkas, Attila; Tóth, Mónika T; Ayaydin, Ferhan; Bóka, Károly; Fodor, Lili; Ratet, Pascal; Kereszt, Attila; Endre, Gabriella; Kaló, Péter

    2017-12-14

    Legumes form endosymbiotic interaction with host compatible rhizobia, resulting in the development of nitrogen-fixing root nodules. Within symbiotic nodules, rhizobia are intracellularly accommodated in plant-derived membrane compartments, termed symbiosomes. In mature nodule, the massively colonized cells tolerate the existence of rhizobia without manifestation of visible defense responses, indicating the suppression of plant immunity in the nodule in the favur of the symbiotic partner. Medicago truncatula DNF2 (defective in nitrogen fixation 2) and NAD1 (nodules with activated defense 1) genes are essential for the control of plant defense during the colonization of the nitrogen-fixing nodule and are required for bacteroid persistence. The previously identified nodule-specific NAD1 gene encodes a protein of unknown function. Herein, we present the analysis of novel NAD1 mutant alleles to better understand the function of NAD1 in the repression of immune responses in symbiotic nodules. By exploiting the advantage of plant double and rhizobial mutants defective in establishing nitrogen-fixing symbiotic interaction, we show that NAD1 functions following the release of rhizobia from the infection threads and colonization of nodule cells. The suppression of plant defense is self-dependent of the differentiation status of the rhizobia. The corresponding phenotype of nad1 and dnf2 mutants and the similarity in the induction of defense-associated genes in both mutants suggest that NAD1 and DNF2 operate close together in the same pathway controlling defense responses in symbiotic nodules.

  12. Physical Structure of Four Symbiotic Binaries

    Science.gov (United States)

    Kenyon, Scott J. (Principal Investigator)

    1997-01-01

    Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the

  13. Effects of symbiotic bacteria on chemical sensitivity of Daphnia magna.

    Science.gov (United States)

    Manakul, Patcharaporn; Peerakietkhajorn, Saranya; Matsuura, Tomoaki; Kato, Yasuhiko; Watanabe, Hajime

    2017-07-01

    The crustacean zooplankton Daphnia magna has been widely used for chemical toxicity tests. Although abiotic factors have been well documented in ecotoxicological test protocols, biotic factors that may affect the sensitivity to chemical compounds remain limited. Recently, we identified symbiotic bacteria that are critical for the growth and reproduction of D. magna. The presence of symbiotic bacteria on Daphnia raised the question as to whether these bacteria have a positive or negative effect on toxicity tests. In order to evaluate the effects of symbiotic bacteria on toxicity tests, bacteria-free Daphnia were prepared, and their chemical sensitivities were compared with that of Daphnia with symbiotic bacteria based on an acute immobilization test. The Daphnia with symbiotic bacteria showed higher chemical resistance to nonylphenol, fenoxycarb, and pentachlorophenol than bacteria-free Daphnia. These results suggested potential roles of symbiotic bacteria in the chemical resistance of its host Daphnia. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. N2O and NOy

    Science.gov (United States)

    Kawa, S. R.; Jackman, C. H.; Douglass, A. R.; Strahan, S. E.

    2003-01-01

    The principal loss processes for ozone in the stratosphere are either directly or indirectly closely coupled to the abundance and distribution of reactive oxides of nitrogen (NOy). The main source of NOy in the stratosphere is N2O, a trace gas that is changing significantly as a result of anthropogenic forcing. Thus diagnosis of the distributions of N2O, NOy, and their coupling is required to evaluate any chemistry-climate model aspiring to accurately simulate ozone change. In the NASA Assessment of the Effects of High-speed Aircraft in the Stratosphere: 1998 we found that the sensitivity of various models ozone to perturbation did correspond consistently with their background NOy distribution. Coordinated NOy and N2O mixing ratio distributions are available from observations: ER-2 aircraft in the lower stratosphere and ATMOS and balloon profiles to higher altitudes at a subset of latitudes and seasons. Although close comparison to these diagnostics is crucial, unfortunately the distributions are due to a combination of transport and chemical processes, and isolating the source of differences is not always simple. However, in combination with other transport and photochemical diagnostics, comparison with N2O and NOy can be very instructive in evaluation of model processes and performance.

  15. Direct and indirect costs of dinitrogen fixation in Crocosphaera watsonii WH8501 and possible implications for the nitrogen cycle

    Directory of Open Access Journals (Sweden)

    Tobias eGroßkopf

    2012-07-01

    Full Text Available The recent detection of heterotrophic nitrogen (N2 fixation in deep waters of the southern Californian and Peruvian OMZ questions our current understanding of marine N2 fixation as a process confined to oligotrophic surface waters of the oceans. In experiments with Crocosphaera watsonii WH8501, a marine unicellular diazotrophic (N2-fixing cyanobacterium, we demonstrated that the presence of high nitrate concentrations (up to 800 µM had no inhibitory effect on growth and N2 fixation over a period of two weeks. In contrast, the environmental oxygen concentration significantly influenced rates of N2 fixation and respiration, as well as carbon and nitrogen cellular content of C. watsonii over a 24 hour period. Cells grown under lowered oxygen atmosphere (5% had a higher nitrogenase activity and respired less carbon during the dark cycle than under normal oxygen atmosphere (20%. Respiratory oxygen drawdown during the dark period could be fully explained (104% by energetic needs due to basal metabolism and N2 fixation at low oxygen, while at normal oxygen these two processes could only account for 40% of the measured respiration rate. Our results revealed that under normal oxygen concentration most of the energetic costs during N2 fixation (~60% are not derived from the process of N2 fixation per se but rather from the indirect costs incurred for the removal of intracellular oxygen or by the reversal of oxidative damage (e.g. nitrogenase de novo synthesis. Theoretical calculations suggest a slight energetic advantage of N2 fixation relative to assimilatory nitrate uptake for heterotrophic and phototrophic growth, when oxygen supply is in balance with the oxygen requirement for cellular respiration (i.e. energy generation for basal metabolism and N2 fixation. Taken together our results imply the existence of a niche for diazotrophic organisms inside oxygen minimum zones, which are predicted to further expand in the future ocean.

  16. Proteome Insights into the Symbiotic Relationship Between a Captive Colony of Nasutitermes corniger and its Hindgut Microbiome

    Energy Technology Data Exchange (ETDEWEB)

    Burnum, Kristin E.; Callister, Stephen J.; Nicora, Carrie D.; Purvine, Samuel O.; Hugenholtz, Philip; Warnecke, Falk; Scheffrahn, Rudolf H.; Smith, Richard D.; Lipton, Mary S.

    2011-01-01

    Termites degrade and thrive on lignocellulose with help from the bacterial microbiome harbored within their guts. Because most of the diverse microorganisms within the gut microcobial community have yet to be cultivated, the proteomics details of the symbiotic mechanism remain unclear. In a metaproteomics study, we analyzed the bacterial community resident in the hindgut paunch of the wood-feeding ‘higher’ Nasutitermes species and identified 886 proteins, 197 of which have known enzymatic function. Using these enzymes, we reconstructed known metabolic pathways to gain a better understanding of carbohydrate transport and metabolism, nitrogen fixation and assimilation, energy production, and amino acid synthesis in these bacterial microbiomes.

  17. Estimates of biological nitrogen fixation by Pterocarpus lucens in a ...

    African Journals Online (AJOL)

    Nitrogen (N2) fixation by Pterocarpus lucens in a natural semi arid ecosystem, in Ferlo, Senegal was estimated using 15N natural abundance (15N) procedure. Other non-fixing trees accompanying P. lucens in the same area were also investigated as control. Results showed an important variation of 15N in leaves between ...

  18. Biological nitrogen fixation and habitat of running buffalo clover

    Science.gov (United States)

    D.R. Morris; V.S. Baligar; T.M. Schuler; P.J. Harmon

    2002-01-01

    Running buffalo clover (RBC) [Trifolium stoloniferum (Muhl. ex Eat.)] is an endangered species whose survival is uncertain. An experiment was conducted on extant RBC sites to investigate biological nitrogen (N2) fixation, associated plant species, and soil conditions under natural mountain settings. Isotope (15...

  19. Effect of Phosphorus Fertilizer on Nitrogen Fixation by Some Grain ...

    African Journals Online (AJOL)

    acer

    made by Weber (1996) that in the Northern. Guinea Savanna of Nigeria, legumes require about 30 kgPha-1 for optimal growth and N2- fixation. However, higher rate of the P (40 kgha-1) was used in this study because of the lower P level in the Sudan Savannah soils than that of Guinea Savannah coupled with continuous ...

  20. Use of 15N methodology to assess biological nitrogen fixation

    International Nuclear Information System (INIS)

    Hardarson, G.

    1990-01-01

    One of the most important characteristics of legumes are their ability in symbiosis with Rhizobium bacteria to fix atmospheric nitrogen for growth. For proper management and a full realization of the benefits of this plant-microbial association, it is necessary to estimate how much nitrogen is fixed under different conditions in the field. It is only after this is known that various factors can be manipulated so as to increase the amount and proportion of N a plant derives from biological fixation. A suitable method for accurately measuring the amount of N crops derive from fixation is therefore an important requirement in any programme aimed at maximizing biological nitrogen fixation. There are several methods available to measure N 2 fixation (Bergersen, 1980) based on (1) increment in N yield and plant growth, (2) nitrogen balance (3) acetylene reduction and (4) the use of isotopes of N. Only isotopic methods will be illustrated here. 20 refs, 2 figs, 9 tabs

  1. Orientifolding in N=2 superspace

    Energy Technology Data Exchange (ETDEWEB)

    Robles-Llana, D.; Saueressig, F.; Vandoren, S. [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, Utrecht (Netherlands); Rocek, M. [C.N. Yang Institute for Theoretical Physics, Stony Brook University, NY 11794-3840 (United States); Theis, U. [Institute for Theoretical Physics, Friedrich-Schiller-University Jena, 07743 Jena (Germany)

    2007-05-15

    We discuss orientifold projections on superspace effective actions for hypermultiplets. We present a simple and new mechanism that allows one to find the Kaehler potential and complex structure for the N=1 theory directly in terms of the parent N=2 theory. As an application, we demonstrate our method for Calabi-Yau orientifold compactifications of type IIB superstrings. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

  2. Improving carbon fixation pathways

    Energy Technology Data Exchange (ETDEWEB)

    Ducat, DC; Silver, PA

    2012-08-01

    A recent resurgence in basic and applied research on photosynthesis has been driven in part by recognition that fulfilling future food and energy requirements will necessitate improvements in crop carbon-fixation efficiencies. Photosynthesis in traditional terrestrial crops is being reexamined in light of molecular strategies employed by photosynthetic microbes to enhance the activity of the Calvin cycle. Synthetic biology is well-situated to provide original approaches for compartmentalizing and enhancing photosynthetic reactions in a species independent manner. Furthermore, the elucidation of alternative carbon-fixation routes distinct from the Calvin cycle raises possibilities that novel pathways and organisms can be utilized to fix atmospheric carbon dioxide into useful materials.

  3. Nitrogen fixation, denitrification, and ecosystem nitrogen pools in relation to vegetation development in the Subarctic

    DEFF Research Database (Denmark)

    Sørensen, Pernille Lærkedal; Jonasson, Sven Evert; Michelsen, Anders

    2006-01-01

    Nitrogen (N) fixation, denitrification, and ecosystem pools of nitrogen were measured in three subarctic ecosystem types differing in soil frost-heaving activity and vegetation cover. N2-fixation was measured by the acetylene reduction assay and converted to absolute N ecosystem input by estimates...... of conversion factors between acetylene reduction and 15N incorporation. One aim was to relate nitrogen fluxes and nitrogen pools to the mosaic of ecosystem types of different stability common in areas of soil frost movements. A second aim was to identify abiotic controls on N2-fixation by simultaneous...

  4. Investigating Tactile Stimulation in Symbiotic Systems

    DEFF Research Database (Denmark)

    Orso, Valeria; Mazza, Renato; Gamberini, Luciano

    2017-01-01

    The core characteristics of tactile stimuli, i.e., recognition reliability and tolerance to ambient interference, make them an ideal candidate to be integrated into a symbiotic system. The selection of the appropriate stimulation is indeed important in order not to hinder the interaction from...... the user’s perspective. Here we present the process of selecting the most adequate tactile stimulation delivered by a tactile vest while users were engaged in an absorbing activity, namely playing a video-game. A total of 20 participants (mean age 24.78; SD= 1.57) were involved. Among the eight tactile...

  5. Dinitrogen fixation associated with shoots of aquatic carnivorous plants: is it ecologically important?

    Science.gov (United States)

    Sirová, Dagmara; Santrůček, Jiří; Adamec, Lubomír; Bárta, Jiří; Borovec, Jakub; Pech, Jiří; Owens, Sarah M; Santrůčková, Hana; Schäufele, Rudi; Storchová, Helena; Vrba, Jaroslav

    2014-07-01

    Rootless carnivorous plants of the genus Utricularia are important components of many standing waters worldwide, as well as suitable model organisms for studying plant-microbe interactions. In this study, an investigation was made of the importance of microbial dinitrogen (N2) fixation in the N acquisition of four aquatic Utricularia species and another aquatic carnivorous plant, Aldrovanda vesiculosa. 16S rRNA amplicon sequencing was used to assess the presence of micro-organisms with known ability to fix N2. Next-generation sequencing provided information on the expression of N2 fixation-associated genes. N2 fixation rates were measured following (15)N2-labelling and were used to calculate the plant assimilation rate of microbially fixed N2. Utricularia traps were confirmed as primary sites of N2 fixation, with up to 16 % of the plant-associated microbial community consisting of bacteria capable of fixing N2. Of these, rhizobia were the most abundant group. Nitrogen fixation rates increased with increasing shoot age, but never exceeded 1·3 μmol N g(-1) d. mass d(-1). Plant assimilation rates of fixed N2 were detectable and significant, but this fraction formed less than 1 % of daily plant N gain. Although trap fluid provides conditions favourable for microbial N2 fixation, levels of nif gene transcription comprised carnivorous plants under their typical growth conditions; however, on an annual basis the plant-microbe system can supply nitrogen in the order of hundreds of mg m(-2) into the nutrient-limited littoral zone, where it may thus represent an important N source. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  6. Legume-rhizobium symbiotic promiscuity and effectiveness do not affect plant invasiveness.

    Science.gov (United States)

    Keet, Jan-Hendrik; Ellis, Allan G; Hui, Cang; Le Roux, Johannes J

    2017-06-01

    The ability to fix atmospheric nitrogen is thought to play an important role in the invasion success of legumes. Interactions between legumes and nitrogen-fixing bacteria (rhizobia) span a continuum of specialization, and promiscuous legumes are thought to have higher chances of forming effective symbioses in novel ranges. Using Australian Acacia species in South Africa, it was hypothesized that widespread and highly invasive species will be more generalist in their rhizobial symbiotic requirements and more effective in fixing atmospheric nitrogen compared with localized and less invasive species. To test these hypotheses, eight localized and 11 widespread acacias were examined using next-generation sequencing data for the nodulation gene, nodC , to compare the identity, species richness, diversity and compositional similarity of rhizobia associated with these acacias. Stable isotope analysis was also used to determine levels of nitrogen obtained from the atmosphere via symbiotic nitrogen fixation. No differences were found in richness, diversity and community composition between localized and widespread acacias. Similarly, widespread and localized acacias did not differ in their ability to fix atmospheric nitrogen. However, for some species by site comparisons, significant differences in δ15N isotopic signatures were found, indicating differential symbiotic effectiveness between these species at specific localities. Overall, the results support recent findings that root nodule rhizobial diversity and community composition do not differ between acacias that vary in their invasiveness. Differential invasiveness of acacias in South Africa is probably linked to attributes such as differences in propagule pressure, reasons for (e.g. forestry vs. ornamental) and extent of, plantings in the country.

  7. Diversity and symbiotic effectiveness of indigenous rhizobia-nodulating Adesmia bicolor in soils of Central Argentina.

    Science.gov (United States)

    Bianco, Luciana; Angelini, Jorge; Fabra, Adriana; Malpassi, Rosana

    2013-02-01

    Native perennial legume Adesmia bicolor reveals characteristics that are key to securing persistence under grazing. Literature on the diversity and symbiotic effectiveness of indigenous rhizobia-nodulating A. bicolor in central Argentina is limited. The purpose of this study was therefore to determine phenotypic and genotypic variability as well as biological N-fixation effectiveness in rhizobia isolated from A. bicolor nodules. To this end, repetitive genomic regions were analyzed using ERIC primers. In the greenhouse, plants were grown under a (i) N-fertilized treatment, (ii) N-free control treatment, and (iii) rhizobia inoculation treatment. Dry weight and N-content were analyzed. All isolates belonged to Rhizobium genus and showed high symbiotic effectiveness. The N-content/subterranean N-content ratio in aerial and subterranean parts of inoculated plants was higher than that observed in N-fertilized plants during the vegetative stage. Results from this study demonstrate that symbiosis between native rhizobial strains and A. bicolor is very effective.

  8. Toxic effects of arsenic on Sinorhizobium-Medicago sativa symbiotic interaction

    Energy Technology Data Exchange (ETDEWEB)

    Pajuelo, Eloisa [Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville (Spain); Rodriguez-Llorente, Ignacio D. [Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville (Spain)], E-mail: irodri@us.es; Dary, Mohammed; Palomares, Antonio J. [Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville (Spain)

    2008-07-15

    Recently, the Rhizobium-legume symbiotic interaction has been proposed as an interesting tool in bioremediation. However, little is known about the effect of most common contaminants on this process. The phytotoxic effects of arsenic on nodulation of Medicago sativa have been examined in vitro using the highly arsenic resistant and symbiotically effective Sinorhizobium sp. strain MA11. The bacteria were able to grow on plates containing As concentrations as high as 10 mM. Nevertheless, as little as 25-35 {mu}M arsenite produced a 75% decrease in the total number of nodules, due to a 90% reduction in the number of rhizobial infections, as could be determined using the strain MA11 carrying a lacZ reporter gene. This effect was associated to root hair damage and a shorter infective root zone. However, once nodulation was established nodule development seemed to continue normally, although earlier senescence could be observed in nodules of arsenic-grown plants. - First steps of nodulation of alfalfa, in particular infection thread formation, are more sensitive to As than nitrogen fixation due to plant effects.

  9. Pesticides reduce symbiotic efficiency of nitrogen-fixing rhizobia and host plants.

    Science.gov (United States)

    Fox, Jennifer E; Gulledge, Jay; Engelhaupt, Erika; Burow, Matthew E; McLachlan, John A

    2007-06-12

    Unprecedented agricultural intensification and increased crop yield will be necessary to feed the burgeoning world population, whose global food demand is projected to double in the next 50 years. Although grain production has doubled in the past four decades, largely because of the widespread use of synthetic nitrogenous fertilizers, pesticides, and irrigation promoted by the "Green Revolution," this rate of increased agricultural output is unsustainable because of declining crop yields and environmental impacts of modern agricultural practices. The last 20 years have seen diminishing returns in crop yield in response to increased application of fertilizers, which cannot be completely explained by current ecological models. A common strategy to reduce dependence on nitrogenous fertilizers is the production of leguminous crops, which fix atmospheric nitrogen via symbiosis with nitrogen-fixing rhizobia bacteria, in rotation with nonleguminous crops. Here we show previously undescribed in vivo evidence that a subset of organochlorine pesticides, agrichemicals, and environmental contaminants induces a symbiotic phenotype of inhibited or delayed recruitment of rhizobia bacteria to host plant roots, fewer root nodules produced, lower rates of nitrogenase activity, and a reduction in overall plant yield at time of harvest. The environmental consequences of synthetic chemicals compromising symbiotic nitrogen fixation are increased dependence on synthetic nitrogenous fertilizer, reduced soil fertility, and unsustainable long-term crop yields.

  10. The Mekong River plume fuels nitrogen fixation and determines phytoplankton species distribution in the South China Sea during low- and high-discharge season

    DEFF Research Database (Denmark)

    Grosse, Julia; Bombar, Deniz; Doan, Hai Nhu

    2010-01-01

    , which potentially hosted diazotrophs, were most abundant in waters where N2 fixation rates were highest, nitrate concentrations were at the detection limit, and phosphate and silicate were still available. Filamentous cyanobacteria like Trichodesmium were present only in marine waters with salinities...... above 33.5. Overall, N2 fixation accounts for 1-47% of the nitrogen demand of primary production....

  11. Symbiotic regulation of plant growth, development and reproduction

    Science.gov (United States)

    Russell J. Rodriguez; D. Carl Freeman; E. Durant McArthur; Yong Ok Kim; Regina S. Redman

    2009-01-01

    The growth and development of rice (Oryzae sativa) seedlings was shown to be regulated epigenetically by a fungal endophyte. In contrast to un-inoculated (nonsymbiotic) plants, endophyte colonized (symbiotic) plants preferentially allocated resources into root growth until root hairs were well established. During that time symbiotic roots expanded at...

  12. Symbiotic effectiveness of acid-tolerant Bradyrhizobium strains with ...

    African Journals Online (AJOL)

    Further, symbiotic effectiveness of these strains was determined under the polyhouse conditions in sterilized soil (pH 4.5). Highest and lowest symbiotic characters, dry matter production and nitrogen improvement per plant were observed in PSR001 and NSR008 inoculated plants, respectively. All the examined isolates ...

  13. Softly broken N=2 QCD

    CERN Document Server

    Alvarez-Gaumé, Luís; Kounnas, Costas; Marino, M; Alvarez-Gaume, Luis; Distler, Jacques; Kounnas, Costas; Marino, Marcos

    1996-01-01

    We analyze the possible soft breaking of N=2 supersymmetric Yang-Mills theory with and without matter flavour preserving the analyticity properties of the Seiberg-Witten solution. For small supersymmetry breaking parameter with respect to the dynamical scale of the theory we obtain an exact expression for the effective potential. We describe in detail the onset of the confinement transition and some of the patterns of chiral symmetry breaking. If we extrapolate the results to the limit where supersymmetry decouples, we obtain hints indicating that perhaps a description of the QCD vacuum will require the use of Lagrangians containing simultaneously mutually non-local degrees of freedom (monopoles and dyons).

  14. Microelectronic systems N2 checkbook

    CERN Document Server

    Vears, R E

    2013-01-01

    Microelectronic Systems N2 Checkbook provides coverage of the Business and Technician Education Council level NII unit in Microelectronic Systems. However, it can be regarded as a textbook in microelectronic systems for a much wider range of studies. The aim of this book is to provide a foundation in microelectronic systems hardware and software techniques. Each topic considered in the text is presented in a way that assumes in the reader only the knowledge attained in BTEC Information Technology Studies F, Engineering Fundamentals F, or equivalent. This book concentrates on the highly popular

  15. Symbiotic Nitrogen Fixation and the Challenges to Its Extension to Nonlegumes

    OpenAIRE

    Mus, Florence; Crook, Matthew B.; Garcia, Kevin; Garcia Costas, Amaya; Geddes, Barney A.; Kouri, Evangelia D.; Paramasivan, Ponraj; Oldroyd, Giles E. D.; Poole, Philip S.; Udvardi, Michael K.; Ané, Jean-Michel; Peters, John W.; Voigt, Christopher A.; Ryu, Min-Hyung

    2016-01-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixati...

  16. Symbiotic nitrogen fixation and the challenges to its extension to nonlegumes

    OpenAIRE

    Mus, F; Crook, MB; Garcia, K; Garcia Costas, A; Geddes, BA; Kouri, ED; Paramasivan, P; Ryu, M-H; Oldroyd, GED; Poole, PS; Udvardi, MK; Voigt, CA; Ané, J-M; Peters, JW

    2016-01-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixati...

  17. Relationships between Nitrate and Oxygen Supply in Symbiotic Nitrogen Fixation by White Clover

    DEFF Research Database (Denmark)

    Minchin, F. R.; Ines Minguez, M.; Sheedy, J. E.

    1986-01-01

    Exposure of mature, nodulated plants of white clover (Trifolium repens) cv. Blanca to 330 mg dm−3 NO3-N for 8 d caused nitrogenase activity per plant to decrease by 80%. Total nodulated root respiration was not significantly affected but analysis of its components showed an 81% decrease in nitrog...

  18. Biomass production, symbiotic nitrogen fixation and inorganic N use in dual tri-component annual intercrops

    DEFF Research Database (Denmark)

    Andersen, M.K.; Hauggaard-Nielsen, H.; Ambus, P.

    2005-01-01

    The interspecific complementary and competitive interactions between pea (Pisum sativum L.), barley (Hordeum vulgare L.) and oilseed rape (Brassica napus L.), grown as dual and tri-component intercrops were assessed in a field study in Denmark. Total biomass production and N use at two levels of ...

  19. CIRCUMSTELLAR SHELL FORMATION IN SYMBIOTIC RECURRENT NOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Kevin; Bildsten, Lars [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106 (United States)

    2012-12-20

    We present models of spherically symmetric recurrent nova shells interacting with circumstellar material (CSM) in a symbiotic system composed of a red giant (RG) expelling a wind and a white dwarf accreting from this material. Recurrent nova eruptions periodically eject material at high velocities ({approx}> 10{sup 3} km s{sup -1}) into the RG wind profile, creating a decelerating shock wave as CSM is swept up. High CSM densities cause the shocked wind and ejecta to have very short cooling times of days to weeks. Thus, the late-time evolution of the shell is determined by momentum conservation instead of energy conservation. We compute and show evolutionary tracks of shell deceleration, as well as post-shock structure. After sweeping up all the RG wind, the shell coasts at a velocity {approx}100 km s{sup -1}, depending on system parameters. These velocities are similar to those measured in blueshifted CSM from the symbiotic nova RS Oph, as well as a few Type Ia supernovae that show evidence of CSM, such as 2006X, 2007le, and PTF 11kx. Supernovae occurring in such systems may not show CSM interaction until the inner nova shell gets hit by the supernova ejecta, days to months after the explosion.

  20. Developing symbiotic consortia for lignocellulosic biofuel production

    Energy Technology Data Exchange (ETDEWEB)

    Zuroff, Trevor R.; Curtis, Wayne R. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Chemical Engineering

    2012-02-15

    The search for petroleum alternatives has motivated intense research into biological breakdown of lignocellulose to produce liquid fuels such as ethanol. Degradation of lignocellulose for biofuel production is a difficult process which is limited by, among other factors, the recalcitrance of lignocellulose and biological toxicity of the products. Consolidated bioprocessing has been suggested as an efficient and economical method of producing low value products from lignocellulose; however, it is not clear whether this would be accomplished more efficiently with a single organism or community of organisms. This review highlights examples of mixtures of microbes in the context of conceptual models for developing symbiotic consortia for biofuel production from lignocellulose. Engineering a symbiosis within consortia is a putative means of improving both process efficiency and stability relative to monoculture. Because microbes often interact and exist attached to surfaces, quorum sensing and biofilm formation are also discussed in terms of consortia development and stability. An engineered, symbiotic culture of multiple organisms may be a means of assembling a novel combination of metabolic capabilities that can efficiently produce biofuel from lignocellulose. (orig.)

  1. Monogamy in a Hyper-Symbiotic Shrimp.

    Directory of Open Access Journals (Sweden)

    J Antonio Baeza

    Full Text Available Theory predicts that monogamy is adaptive in resource-specialist symbiotic crustaceans inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in Pontonia manningi, a hyper-symbiotic shrimp that dwells in the mantle cavity of the Atlantic winged oyster Pteria colymbus that, in turn, infects gorgonians from the genus Pseudopterogorgia in the Caribbean Sea. In agreement with theory, P. manningi were found dwelling as heterosexual pairs in oysters more frequently than expected by chance alone. Males and females also inhabited the same host individual independent of the female gravid condition or of the developmental stage of brooded embryos. While the observations above argue in favor of monogamy in P. manningi, there is evidence to suggest that males of the studied species are moderately promiscuous. That females found living solitary in oysters most often brooded embryos, and that males allocated more to weaponry (major claw size than females at any given size suggest that males might be roaming among host individuals in search of and, fighting for, receptive females. All available information depicts a rather complex mating system in P. manningi: primarily monogamous but with moderately promiscuous males.

  2. Symbiotic diversity in the cosmopolitan genus Acacia

    Science.gov (United States)

    James K. Leary; Paul W. Singleton; Paul G. Scowcroft; Dulal Borthakur

    2006-01-01

    Acacia is the second largest genus within the Leguminosae, with 1352 species identified. This genus is now known to be polyphyletic and the international scientific community will presumably split Acacia into five new genera. This review examines the diversity of biological nitrogen fixation symbiosis within Acacia as a single genus. Due to its global importance, an...

  3. Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching

    KAUST Repository

    Pogoreutz, Claudia

    2017-04-21

    The disruption of the coral-algae symbiosis (coral bleaching) due to rising sea surface temperatures has become an unprecedented global threat to coral reefs. Despite decades of research, our ability to manage mass bleaching events remains hampered by an incomplete mechanistic understanding of the processes involved. In this study, we induced a coral bleaching phenotype in the absence of heat and light stress by adding sugars. The sugar addition resulted in coral symbiotic breakdown accompanied by a fourfold increase of coral-associated microbial nitrogen fixation. Concomitantly, increased N:P ratios by the coral host and algal symbionts suggest excess availability of nitrogen and a disruption of the nitrogen limitation within the coral holobiont. As nitrogen fixation is similarly stimulated in ocean warming scenarios, here we propose a refined coral bleaching model integrating the cascading effects of stimulated microbial nitrogen fixation. This model highlights the putative role of nitrogen-fixing microbes in coral holobiont functioning and breakdown.

  4. Posterior transodontoid fixation: A new fixation (Kotil technique

    Directory of Open Access Journals (Sweden)

    Kadir Kotil

    2011-01-01

    Full Text Available Anterior odontoid screw fixation or posterior C1-2 fusion techniques are routinely used in the treatment of Type II odontoid fractures, but these techniques may be inadequate in some types of odontoid fractures. In this new technique (Kotil technique, through a posterior bilateral approach, transarticular screw fixation was performed at the non-dominant vertebral artery (VA side and posterior transodontoid fixation technique was performed at the dominant VA side. C1-2 complex fusion was aimed with unilateral transarticular fixation and odontoid fixation with posterior transodontoid screw fixation. Cervical spinal computed tomography (CT of a 40-year-old male patient involved in a motor vehicle accident revealed an anteriorly dislocated Type II oblique dens fracture, not reducible by closed traction. Before the operation, the patient was found to have a dominant right VA with Doppler ultrasound. He was operated through a posterior approach. At first, transarticular screw fixation was performed at the non-dominant (left side, and then fixation of the odontoid fracture was achieved by directing the contralateral screw (supplemental screw medially and toward the apex. Cancellous autograft was scattered for fusion without the need for structural bone graft or wiring. Postoperative cervical spinal CT of the patient revealed that stabilization was maintained with transarticular screw fixation and reduction and fixation of the odontoid process was achieved completely by posterior transodontoid screw fixation. The patient is at the sixth month of follow-up and complete fusion has developed. With this new surgical technique, C1-2 fusion is maintained with transarticular screw fixation and odontoid process is fixed by concomitant contralateral posterior transodontoid screw (supplemental screw fixation; thus, this technique both stabilizes the C1-2 complex and fixes the odontoid process and the corpus in atypical odontoid fractures, appearing as an

  5. The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium.

    Science.gov (United States)

    Hong, Haizheng; Shen, Rong; Zhang, Futing; Wen, Zuozhu; Chang, Siwei; Lin, Wenfang; Kranz, Sven A; Luo, Ya-Wei; Kao, Shuh-Ji; Morel, François M M; Shi, Dalin

    2017-05-05

    Acidification of seawater caused by anthropogenic carbon dioxide (CO 2 ) is anticipated to influence the growth of dinitrogen (N 2 )-fixing phytoplankton, which contribute a large fraction of primary production in the tropical and subtropical ocean. We found that growth and N 2 -fixation of the ubiquitous cyanobacterium Trichodesmium decreased under acidified conditions, notwithstanding a beneficial effect of high CO 2 Acidification resulted in low cytosolic pH and reduced N 2 -fixation rates despite elevated nitrogenase concentrations. Low cytosolic pH required increased proton pumping across the thylakoid membrane and elevated adenosine triphosphate production. These requirements were not satisfied under field or experimental iron-limiting conditions, which greatly amplified the negative effect of acidification. Copyright © 2017, American Association for the Advancement of Science.

  6. A Mathematic Approach to Nitrogen Fixation Through Earth History

    Science.gov (United States)

    Delgado-Bonal, Alfonso; Martín-Torres, F. Javier

    Nitrogen is essential for life as we know it. According to phylogenetic studies, all organisms capable of fixing nitrogen are prokaryotes, both bacteria and archaea, suggesting that nitrogen fixation and ammonium assimilation were metabolic features of the Last Universal Common Ancestor of all organisms. At present time the amount of biologically fixed nitrogen is around 2 × 1{0}^{13} g/year (Falkowski 1997), an amount much larger than the corresponding to the nitrogen fixed abiotically (between 2. 6 ×109 and 3 × 1{0}^{11} g/year) (Navarro-González et al. 2001). The current amount of nitrogen fixed is much higher than it was on Earth before the Cambrian explosion, where the symbiotic associations with leguminous plants, the major nitrogen fixer currently, did not exist and nitrogen was fixed only by free-living organisms as cyanobacteria. It has been suggested (Navarro-González et al. 2001) that abiotic sources of nitrogen fixation during Early Earth times could have an important role triggering a selection pressure favoring the evolution of nitrogenase and an increase in the nitrogen fixation rate. In this study we present briefly a method to analyze the amount of fixed nitrogen, both biotic and abiotic, through Earth's history.

  7. Improving carbon fixation pathways.

    Science.gov (United States)

    Ducat, Daniel C; Silver, Pamela A

    2012-08-01

    A recent resurgence in basic and applied research on photosynthesis has been driven in part by recognition that fulfilling future food and energy requirements will necessitate improvements in crop carbon-fixation efficiencies. Photosynthesis in traditional terrestrial crops is being reexamined in light of molecular strategies employed by photosynthetic microbes to enhance the activity of the Calvin cycle. Synthetic biology is well-situated to provide original approaches for compartmentalizing and enhancing photosynthetic reactions in a species independent manner. Furthermore, the elucidation of alternative carbon-fixation routes distinct from the Calvin cycle raises possibilities that novel pathways and organisms can be utilized to fix atmospheric carbon dioxide into useful materials. Copyright © 2012 Elsevier Ltd. All rights reserved.

  8. Dinitrogen fixation by blue-green algae from paddy fields

    International Nuclear Information System (INIS)

    Thomas, Joseph

    1977-01-01

    Recent work using radioactive nitrogen on the blue-green algae of paddy fields has been reviewed. These algae fix dinitrogen and photoassimilate carbon evolving oxygen, thereby augmenting nitrogen and carbon status of the soil and also providing oxygen to the water-logged rice paddies. Further studies using radioactive isotopes 13 N, 24 Na and 22 Na on their nitrogen fixation, nitrogen assimilation pathways; regulation of nitrogenase, heterocysts production and sporulation and sodium transport and metabolism have been carried out and reported. The field application of blue green algae for N 2 fixation was found to increase the status of soil nitrogen and yield of paddy. (M.G.B.)

  9. Brow lift fixation.

    Science.gov (United States)

    Gold, Alan H; Bernard, Robert W; Hamas, Robert S; McKinney, Peter; Paul, Malcolm D

    2003-05-01

    One of the more difficult and controversial aspects of forehead and brow lift is fixation with control and stabilization of the result. Aesthetic Surgery Journal has invited Robert W. Bernard, MD; Robert S. Hamas, MD; Peter McKinney, MD; and Malcolm D. Paul, MD to share their preferred brow lift techniques. Here are their responses to questions posed by "Comparing Notes" editor, Alan H. Gold, MD. (Aesthetic Surg J 2003;23:217-219.).

  10. Improving Carbon Fixation Pathways

    OpenAIRE

    Ducat, Daniel C.; Silver, Pamela A.

    2012-01-01

    A recent resurgence in basic and applied research on photosynthesis has been driven in part by recognition that fulfilling future food and energy requirements will necessitate improvements in crop carbon-fixation efficiencies. Photosynthesis in traditional terrestrial crops is being reexamined in light of molecular strategies employed by photosynthetic microbes to enhance the activity of the Calvin cycle. Synthetic biology is well-situated to provide original approaches for compartmentalizing...

  11. CARBON DIOXIDE FIXATION.

    Energy Technology Data Exchange (ETDEWEB)

    FUJITA,E.

    2000-01-12

    Solar carbon dioxide fixation offers the possibility of a renewable source of chemicals and fuels in the future. Its realization rests on future advances in the efficiency of solar energy collection and development of suitable catalysts for CO{sub 2} conversion. Recent achievements in the efficiency of solar energy conversion and in catalysis suggest that this approach holds a great deal of promise for contributing to future needs for fuels and chemicals.

  12. Kinematics of the symbiotic system R Aqr

    Science.gov (United States)

    Navarro, S.; Corral, L. J.; Steffen, W.

    2014-04-01

    We present the results of the kinematical analysis of the symbiotic system R Aqr. We obtained high dispersion spectra with the MES spectrograph at the 2.1 m telescope of San Pedro Mártir (MEZCAL). The used filter were Ha + [NII], (λc = 6575Å, Δλ = 90Å). We analyse the [NII] λλ6583 line. When the observations are compared with previous ones by Solf (1992) we detected an important change in the projected velocities of the observed knots, supporting the idea of a precessing jet. We are working also in a 3-D kinematic model for the object using the measured velocities and the state of the model is presented.

  13. Distinguishing between symbiotic stars and planetary nebulae

    Science.gov (United States)

    Iłkiewicz, K.; Mikołajewska, J.

    2017-10-01

    Context. The number of known symbiotic stars (SySt) is still significantly lower than their predicted population. One of the main problems in finding the total population of SySt is the fact that their spectrum can be confused with other objects, such as planetary nebulae (PNe) or dense H II regions. This problem is reinforced by the fact that in a significant fraction of established SySt the emission lines used to distinguish them from other objects are not present. Aims: We aim at finding new diagnostic diagrams that could help separate SySt from PNe. Additionally, we examine a known sample of extragalactic PNe for candidate SySt. Methods: We employed emission line fluxes of known SySt and PNe from the literature. Results: We found that among the forbidden lines in the optical region of spectrum, only the [O III] and [N II] lines can be used as a tool for distinguishing between SySt and PNe, which is consistent with the fact that they have the highest critical densities. The most useful diagnostic that we propose is based on He I lines, which are more common and stronger in SySt than forbidden lines. All these useful diagnostic diagrams are electron density indicators that better distinguish PNe and ionized symbiotic nebulae. Moreover, we found six new candidate SySt in the Large Magellanic Cloud and one in M 81. If confirmed, the candidate in M 81 would be the farthest known SySt thus far.

  14. Symbiote transmission and maintenance of extra-genomic associations

    Directory of Open Access Journals (Sweden)

    Benjamin Minault Fitzpatrick

    2014-02-01

    Full Text Available Symbiotes can be transmitted from parents to offspring or horizontally from unrelated hosts or the environment. A key question is whether symbiote transmission is similar enough to Mendelian gene transmission to generate and maintain coevolutionary associations between host and symbiote genes. Recent papers come to opposite conclusions, with some suggesting that any horizontal transmission eliminates genetic association. These studies are hard to compare owing to arbitrary differences in modeling approach, parameter values, and assumptions about selection. I show that associations between host and symbiote genes (extra-genomic associations can be described by the same dynamic model as conventional linkage disequilibria between genes in the same genome. Thus, covariance between host and symbiote genomes depends on population history, geographic structure, selection, and co-transmission rate, just as covariance between genes within a genome. The conclusion that horizontal transmission rapidly erodes extra-genomic associations is equivalent to the conclusion that recombination rapidly erodes associations between genes within a genome. The conclusion is correct in the absence of population structure or selection. However, population structure can maintain spatial associations between host and symbiote traits, and non-additive selection (interspecific epistasis can generate covariances between host and symbiote genotypes. These results can also be applied to cultural or other nongenetic traits. This work contributes to a growing consensus that genomic, symbiotic, and gene-culture evolution can be analyzed under a common theoretical framework. In terms of coevolutionary potential, symbiotes can be viewed as lying on a continuum between the intimacy of genes and the indifference of casually co-occuring species.

  15. Deepwater Nitrogen Fixation: Who's Doing it, Where, and Why?

    Science.gov (United States)

    Montoya, J. P.; Weber, S.; Vogts, A.; Voss, M.; Saxton, M.; Joye, S. B.

    2016-02-01

    Nitrogen availability frequently limits marine primary production and N2-fixation plays an important role in supporting biological production in surface waters of many oligotrophic regions. Although subsurface waters typically contain high concentrations of nitrate and other nutrients, measurements from a variety of oceanic settings show measurable, and at times high rates of N2-fixation in deep, dark waters below the mixed layer. We have explored the distribution of N2-fixation throughout the water column of the Gulf of Mexico (GoM) during a series of cruises beginning shortly after the Deepwater Horizon (DWH) spill in 2010 and continuing at roughly annual intervals. These cruises allowed us to sample oligotrophic waters across a range of depths, and to explore the connections between the C and N cycles mediated by release of oil and gas (petrocarbon) from natural seeps as well as anthropogenic sources (e.g., the DWH). We used stable isotope abundances (15N and 13C) in particles and zooplankton in combination with experimental measurements of N2-fixation and CH4 assimilation to assess the contribution of oil- and gas-derived C to the pelagic food web, and the impact of CH4 releases on the pelagic C and N cycles. Our isotopic measurements document the movement of petrocarbon into the pelagic food web, and our experiments revealed that high rates of N2-fixation were widespread in deep water immediately after the DWH incident, and restricted to the vicinity of natural seeps in subsequent years. Unfortunately, these approaches provided no insight into the organisms actually responsible for N2-fixation and CH4-assimilation. We used nano-scale Secondary Ion Mass Spectrometry (nanoSIMS) to image the organisms responsible for these processes, and molecular approaches to explore the diversity of methanotrophs and diazotrophs present in the system. The ability to resolve isotopic distributions on the scale of individual cells is a critical part of bridging the gap between

  16. Nitrogen symbiotically fixed by cowpea and gliricidia in traditional and agroforestry systems under semiarid conditions

    Directory of Open Access Journals (Sweden)

    Júlio César Rodrigues Martins

    2015-02-01

    Full Text Available The objective of this work was to estimate the amounts of N fixed by cowpea in a traditional system and by cowpea and gliricidia in an agroforestry system in the Brazilian Northeast semiarid. The experiment was carried out in a randomized complete block design, in a split-plot arrangement, with four replicates, in the semiarid region of the state of Paraíba, Brazil. Plots consisted of agroforestry and traditional systems (no trees, and split-plots of the three crops planted between the tree rows in the agroforestry system. To estimate N fixation, plant samples were collected in the fourth growth cycle of the perennial species and in the fourth planting cycle of the annual species. In the agroforestry system with buffel grass and prickly-pear cactus, gliricidia plants symbiotically fix high proportions of N (>50% and contribute with higher N amounts (40 kg ha-1 in leaves than in the traditional system (11 kg ha-1 in grain and 18 kg ha-1 in straw. In the agroforestry system with maize and cowpea, gliricidia plants do not fix nitrogen, and N input is limited to the fixation by cowpea (2.7 kg ha-1, which is lower than in the traditional system due to its lower biomass production.

  17. Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation.

    Science.gov (United States)

    Pepe-Ranney, Charles; Koechli, Chantal; Potrafka, Ruth; Andam, Cheryl; Eggleston, Erin; Garcia-Pichel, Ferran; Buckley, Daniel H

    2016-02-01

    Biological soil crusts (BSCs) are key components of ecosystem productivity in arid lands and they cover a substantial fraction of the terrestrial surface. In particular, BSC N2-fixation contributes significantly to the nitrogen (N) budget of arid land ecosystems. In mature crusts, N2-fixation is largely attributed to heterocystous cyanobacteria; however, early successional crusts possess few N2-fixing cyanobacteria and this suggests that microorganisms other than cyanobacteria mediate N2-fixation during the critical early stages of BSC development. DNA stable isotope probing with (15)N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate (15)N2 in early successional crusts. The Clostridiaceae identified are divergent from previously characterized isolates, though N2-fixation has previously been observed in this family. The Proteobacteria identified share >98.5% small subunit rRNA gene sequence identity with isolates from genera known to possess diazotrophs (for example, Pseudomonas, Klebsiella, Shigella and Ideonella). The low abundance of these heterotrophic diazotrophs in BSCs may explain why they have not been characterized previously. Diazotrophs have a critical role in BSC formation and characterization of these organisms represents a crucial step towards understanding how anthropogenic change will affect the formation and ecological function of BSCs in arid ecosystems.

  18. The cyanobacterial nitrogen fixation paradox in natural waters.

    Science.gov (United States)

    Paerl, Hans

    2017-01-01

    Nitrogen fixation, the enzymatic conversion of atmospheric N (N 2 ) to ammonia (NH 3 ), is a microbially mediated process by which "new" N is supplied to N-deficient water bodies. Certain bloom-forming cyanobacterial species are capable of conducting N 2 fixation; hence, they are able to circumvent N limitation in these waters. However, this anaerobic process is highly sensitive to oxygen, and since cyanobacteria produce oxygen in photosynthesis, they are faced with a paradoxical situation, where one critically important (for supporting growth) biochemical process is inhibited by another. N 2 -fixing cyanobacterial taxa have developed an array of biochemical, morphological, and ecological adaptations to minimize the "oxygen problem"; however, none of these allows N 2 fixation to function at a high enough efficiency so that it can supply N needs at the ecosystem scale, where N losses via denitrification, burial, and advection often exceed the inputs of "new" N by N 2 fixation. As a result, most marine and freshwater ecosystems exhibit chronic N limitation of primary production. Under conditions of perpetual N limitation, external inputs of N from human sources (agricultural, urban, and industrial) play a central role in determining ecosystem fertility and, in the case of N overenrichment, excessive primary production or eutrophication. This points to the importance of controlling external N inputs (in addition to traditional phosphorus controls) as a means of ensuring acceptable water quality and safe water supplies. Nitrogen fixation, the enzymatic conversion of atmospheric N 2 to ammonia (NH 3 ) is a  microbially-mediated process by which "new" nitrogen is supplied to N-deficient water bodies.  Certain bloom-forming cyanobacterial species are capable of conducting N 2 fixation; hence they are able to circumvent nitrogen limitation in these waters. However, this anaerobic process is highly sensitive to oxygen, and since cyanobacteria produce oxygen in

  19. Modeling the impact of Trichodesmium and nitrogen fixation in the Atlantic Ocean

    Science.gov (United States)

    Coles, Victoria J.; Hood, Raleigh R.; Pascual, Mercedes; Capone, Douglas G.

    2004-06-01

    In this paper we use a biological-physical model with an explicit representation of Trichodesmium to examine the influence of N2 fixation in the Atlantic. Three solutions are examined, one where the N2 fixation rate has been set to observed levels, one where the rate has been increased to levels comparable to geochemical estimates, and one with no N2 fixation. All solutions are tuned to reproduce satellite surface chlorophyll concentrations, so that differences in the runs are manifested in productivity and export. Model runs with N2 fixation have different phytoplankton production and export distributions than runs without. Over the Atlantic basin the ecosystem "fixes" nitrogen at the rate of 1.47 × 1012 mol N yr-1, when tuned to observed phytoplankton and Trichodesmium biomass. This rate is comparable to the lower range of direct estimates of 1.3-2.2 × 1012mol N yr-1 [, 1997; J. N. Galloway et al., manuscript in preparation, 2003; D. Capone et al., New nitrogen input in the tropical North Atlantic Ocean by nitrogen fixation, submitted to Nature, 2004, hereinafter referred to as Capone et al., submitted manuscript, 2004] but less than geochemical indirect estimates over a reduced domain (2.0 × 1012 mol N yr-1 [, 1997] versus 0.55 × 1012 mol N yr-1 for the model). The nitrogen from N2 fixation increases new production by 30% and total production by 5%. However, it does not supplement upwelled nitrate sufficiently to bring production and export into line with remote sensing and geochemically derived estimates. Simulations with N2 fixation rates comparable to geochemical estimates show that reasonable phytoplankton concentrations can be maintained if export is increased. Moreover, phytoplankton productivity increases to values approaching remote-sensing-based estimates in the oligotrophic ocean. However, Trichodesmium biomass may be higher than observed.

  20. Buckminsterfullerenes: a non-metal system for nitrogen fixation.

    Science.gov (United States)

    Nishibayashi, Yoshiaki; Saito, Makoto; Uemura, Sakae; Takekuma, Shin-Ichi; Takekuma, Hideko; Yoshida, Zen-Ichi

    2004-03-18

    In all nitrogen-fixation processes known so far--including the industrial Haber-Bosch process, biological fixation by nitrogenase enzymes and previously described homogeneous synthetic systems--the direct transformation of the stable, inert dinitrogen molecule (N2) into ammonia (NH3) relies on the powerful redox properties of metals. Here we show that nitrogen fixation can also be achieved by using a non-metallic buckminsterfullerene (C60) molecule, in the form of a water-soluble C60:gamma-cyclodextrin (1:2) complex, and light under nitrogen at atmospheric pressure. This metal-free system efficiently fixes nitrogen under mild conditions by making use of the redox properties of the fullerene derivative.

  1. Photosynthetic and nitrogen fixation capability in several soybean mutant lines

    International Nuclear Information System (INIS)

    Gandanegara, S.; Hendratno, K.

    1987-01-01

    Photosynthetic and nitrogen fixation capability in several soybean mutant lines. A greenhouse experiment has been carried out to study photosynthetic and nitrogen fixation capability of five mutant lines and two soybean varieties. An amount of 330 uCi of 14 CO 2 was fed to the plants including of the non-fixing reference crop (Chippewa non-nodulating isoline). Nitrogen fixation measurements was carried out using 15 N isotope dilution technique according to A-value concept. Results showed that beside variety/mutant lines, plant growth also has important role in photosynthetic and N fixing capability. Better growth and a higher photosynthetic capability in Orba, mutant lines nos. 63 and 65 resulted in a greater amount of N 2 fixed (mg N/plant) than other mutant lines. (author). 12 refs.; 5 figs

  2. Nitrogen fixation apparatus

    Science.gov (United States)

    Chen, Hao-Lin

    1984-01-01

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O.sub.2 /cm promotes the formation of vibrationally excited N.sub.2. Atomic oxygen interacts with vibrationally excited N.sub.2 at a much quicker rate than unexcited N.sub.2, greatly improving the rate at which NO is formed.

  3. Stress as a Normal Cue in the Symbiotic Environment.

    Science.gov (United States)

    Schwartzman, Julia A; Ruby, Edward G

    2016-05-01

    All multicellular hosts form associations with groups of microorganisms. These microbial communities can be taxonomically diverse and dynamic, and their persistence is due to robust, and sometimes coevolved, host-microbe and microbe-microbe interactions. Chemical and physical sources of stress are prominently situated in this molecular exchange, as cues for cellular responses in symbiotic microbes. Stress in the symbiotic environment may arise from three sources: host tissues, microbe-induced immune responses, or other microbes in the host environment. The responses of microbes to these stresses can be general or highly specialized, and collectively may contribute to the stability of the symbiotic system. In this review, we highlight recent work that emphasizes the role of stress as a cue in the symbiotic environment of plants and animals. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Symbiotic and phenotypic characterization of Rhizobium isolates of ...

    African Journals Online (AJOL)

    Pisum sativum L.) Fabaceae, from central and southern Ethiopia. ... and NSRlFP18 were the elite rhizobia that can be selected and further tested for their genetic and symbiotic performance in field trials for future bio-inoculant formulation.

  5. Nitrogen fixed by wheat plants as affected by nitrogen fertilizer levels and Non-symbiotic bacteria

    International Nuclear Information System (INIS)

    Soliman, S.; Aly, S.S.M.; Gadalla, A.M.; Abou Seeda, M.

    1995-01-01

    Inorganic nitrogen is required for all egyptian soils for wheat. Free living and N 2-fixing microorganisms are able associate closely related with the roots of geraminacae. Pot experiment studies were carried out to examine the response of wheat plants to inoculation with Azospirillum Brasilense and Azotobacter Chroococcum, single or in combination, under various levels of ammonium sulfate interaction between both the inoculants increased straw or grain yield as well as N-uptake by wheat plants with increasing N levels. Results showed that grains of wheat plants derived over 19,24 and 15% of its N content from the atmospheric - N 2 (Ndfa) with application of 25,50 and 75 mg N kg-1 soil in the presence of + Azospirillum + azotobacter. The final amount of N 2-fixers. The highest values of N 2-fixed were observed with mixed inoculants followed by inoculation with Azospirillum and then azotobacter. The recovery of applied ammonium sulfate-N was markedly increased by inoculation with combined inoculants, but less in uninoculated treatments. Seeds inoculated with non-symbiotic fixing bacteria could be saved about 25 kg N without much affecting the grain yield. i fig., 4 tabs

  6. Regional constraints to biological nitrogen fixation in post-fire forest communities

    Science.gov (United States)

    Yelenik, Stephanie; Perakis, Steven S.; Hibbs, David

    2013-01-01

    Biological nitrogen fixation (BNF) is a key ecological process that can restore nitrogen (N) lost in wildfire and shape the pace and pattern of post-fire forest recovery. To date, there is limited information on how climate and soil fertility interact to influence different pathways of BNF in early forest succession. We studied asymbiotic (forest floor and soil) and symbiotic (the shrub Ceanothus integerrimus) BNF rates across six sites in the Klamath National Forest, California, USA. We used combined gradient and experimental phosphorus (P) fertilization studies to explore cross-site variation in BNF rates and then related these rates to abiotic and biotic variables. We estimate that our measured BNF rates 22 years after wildfire (6.1–12.1 kg N·ha-1·yr-1) are unlikely to fully replace wildfire N losses. We found that asymbiotic BNF is P limited, although this is not the case for symbiotic BNF in Ceanothus. In contrast, Ceanothus BNF is largely driven by competition from other vegetation: in high-productivity sites with high potential evapotranspiration (Et), shrub biomass is suppressed as tree biomass increases. Because shrub biomass governed cross-site variation in Ceanothus BNF, this competitive interaction led to lower BNF in sites with high productivity and Et. Overall, these results suggest that the effects of nutrients play a larger role in driving asymbiotic than symbiotic fixation across our post-fire sites. However, because symbiotic BNF is 8–90x greater than asymbiotic BNF, it is interspecific plant competition that governs overall BNF inputs in these forests.

  7. Regional constraints to biological nitrogen fixation in post-fire forest communities.

    Science.gov (United States)

    Yelenik, Stephanie; Perakis, Steven; Hibbs, David

    2013-03-01

    Biological nitrogen fixation (BNF) is a key ecological process that can restore nitrogen (N) lost in wildfire and shape the pace and pattern of post-fire forest recovery. To date, there is limited information on how climate and soil fertility interact to influence different pathways of BNF in early forest succession. We studied asymbiotic (forest floor and soil) and symbiotic (the shrub Ceanothus integerrimus) BNF rates across six sites in the Klamath National Forest, California, USA. We used combined gradient and experimental phosphorus (P) fertilization studies to explore cross-site variation in BNF rates and then related these rates to abiotic and biotic variables. We estimate that our measured BNF rates 22 years after wildfire (6.1-12.1 kg N x ha(-1) x yr(-1)) are unlikely to fully replace wildfire N losses. We found that asymbiotic BNF is P limited, although this is not the case for symbiotic BNF in Ceanothus. In contrast, Ceanothus BNF is largely driven by competition from other vegetation: in high-productivity sites with high potential evapotranspiration (Et), shrub biomass is suppressed as tree biomass increases. Because shrub biomass governed cross-site variation in Ceanothus BNF, this competitive interaction led to lower BNF in sites with high productivity and Et. Overall, these results suggest that the effects of nutrients play a larger role in driving asymbiotic than symbiotic fixation across our post-fire sites. However, because symbiotic BNF is 8-90x greater than asymbiotic BNF, it is interspecific plant competition that governs overall BNF inputs in these forests.

  8. Local supertwistors and N=2 conformal supergravity

    International Nuclear Information System (INIS)

    Merkulov, S.A.

    1989-01-01

    N = 2 sypersymmetric extension of the local twistor theory is formulated. A supertwistor superconnection determined by the superconformal structure of the base superspace is introduced on the bundle of N = 2 local supertwistors. It is proved that the Yang - Mills equations for this superconnection coincide exactly with the Bach equations describing the dynamics of N 2 conformal supergravity

  9. Quantization of N=2 relaxed hypermultiplet

    International Nuclear Information System (INIS)

    Dahmen, H.D.; Marculescu, S.

    1986-01-01

    The gauge-fixing conditions for N=2 relaxed hypermultiplet coupled to an N=2 Yang Mills superfield are presented. They allow for the quantization in N=2 superspace. One-loop propagators and Faddeev-Popov terms are explicitly computed. (orig.)

  10. Microbiome change by symbiotic invasion in lichens

    Science.gov (United States)

    Maier, Stefanie; Wedin, Mats; Fernandez-Brime, Samantha; Cronholm, Bodil; Westberg, Martin; Weber, Bettina; Grube, Martin

    2016-04-01

    Biological soil crusts (BSC) seal the soil surface from erosive forces in many habitats where plants cannot compete. Lichens symbioses of fungi and algae often form significant fraction of these microbial assemblages. In addition to the fungal symbiont, many species of other fungi can inhabit the lichenic structures and interact with their hosts in different ways, ranging from commensalism to parasitism. More than 1800 species of lichenicolous (lichen-inhabiting) fungi are known to science. One example is Diploschistes muscorum, a common species in lichen-dominated BSC that infects lichens of the genus Cladonia. D. muscorum starts as a lichenicolous fungus, invading the lichen Cladonia symphycarpa and gradually develops an independent Diploschistes lichen thallus. Furthermore, bacterial groups, such as Alphaproteobacteria and Acidobacteria, have been consistently recovered from lichen thalli and evidence is rapidly accumulating that these microbes may generally play integral roles in the lichen symbiosis. Here we describe lichen microbiome dynamics as the parasitic lichen D. muscorum takes over C. symphycarpa. We used high-throughput 16S rRNA gene and photobiont-specific ITS rDNA sequencing to track bacterial and algal transitions during the infection process, and employed fluorescence in situ hybridization to localize bacteria in the Cladonia and Diploschistes lichen thalli. We sampled four transitional stages, at sites in Sweden and Germany: A) Cladonia with no visible infection, B) early infection stage defined by the first visible Diploschistes thallus, C) late-stage infection with parts of the Cladonia thallus still identifiable, and D) final stage with a fully developed Diploschistes thallus, A gradual microbiome shift occurred during the transition, but fractions of Cladonia-associated bacteria were retained during the process of symbiotic reorganization. Consistent changes observed across sites included a notable decrease in the relative abundance of

  11. Rhizobial exopolysaccharides: genetic control and symbiotic functions

    Directory of Open Access Journals (Sweden)

    Mazur Andrzej

    2006-02-01

    Full Text Available Abstract Specific complex interactions between soil bacteria belonging to Rhizobium, Sinorhizobium, Mesorhizobium, Phylorhizobium, Bradyrhizobium and Azorhizobium commonly known as rhizobia, and their host leguminous plants result in development of root nodules. Nodules are new organs that consist mainly of plant cells infected with bacteroids that provide the host plant with fixed nitrogen. Proper nodule development requires the synthesis and perception of signal molecules such as lipochitooligosaccharides, called Nod factors that are important for induction of nodule development. Bacterial surface polysaccharides are also crucial for establishment of successful symbiosis with legumes. Sugar polymers of rhizobia are composed of a number of different polysaccharides, such as lipopolysaccharides (LPS, capsular polysaccharides (CPS or K-antigens, neutral β-1, 2-glucans and acidic extracellular polysaccharides (EPS. Despite extensive research, the molecular function of the surface polysaccharides in symbiosis remains unclear. This review focuses on exopolysaccharides that are especially important for the invasion that leads to formation of indetermined (with persistent meristem type of nodules on legumes such as clover, vetch, peas or alfalfa. The significance of EPS synthesis in symbiotic interactions of Rhizobium leguminosarum with clover is especially noticed. Accumulating data suggest that exopolysaccharides may be involved in invasion and nodule development, bacterial release from infection threads, bacteroid development, suppression of plant defense response and protection against plant antimicrobial compounds. Rhizobial exopolysaccharides are species-specific heteropolysaccharide polymers composed of common sugars that are substituted with non-carbohydrate residues. Synthesis of repeating units of exopolysaccharide, their modification, polymerization and export to the cell surface is controlled by clusters of genes, named exo/exs, exp or

  12. Interactions between non-symbiotic N2-fixing bacteria and plant roots in plant-microbial associations

    OpenAIRE

    Calvo Alegre, Olga-Cristina

    2009-01-01

    The development of biofertilizers on the basis of plant growth promoting rhizobacteria (PGPR) may be a promising approach to partially substitute costly and energy-consuming mineral fertilizers in agricultural plant production and to support agriculture in developing countries. A successful and competitive rhizosphere colonization of PGPR strains has been identified as a prerequisite for the expression of plant growth promoting effects. Apart from a wide range of external factors with an impa...

  13. Growth and N2 fixation in an Alnus hirsuta (Turcz.) var. sibirica stand ...

    Indian Academy of Sciences (India)

    2013-10-01

    Oct 1, 2013 ... The nodules of actinorhizal plants, such as Alnus species, are perennial (Baker and Schwintzer 1990; Huss-Danell 1997). In a naturally regenerated Alnus hirsuta var. sibirica stand on the roadside in the central part of Japan, we found as well as the nodule biomass per tree, the nodule size distribution, as.

  14. N2 fixation and dehydrogenation of methanol and formic acid with late transition metal complexes

    NARCIS (Netherlands)

    van de Watering, F.F.

    2017-01-01

    The transformation to a society that runs on sustainable energy can be facilitated by new technologies that allow solar energy to fuel conversions. Catalytic processes play a crucial role in such technology. In the introduction Chapter an overview of homogeneous catalysts is given, which are able to

  15. Elevated CO2 Increases Nitrogen Fixation at the Reproductive Phase Contributing to Various Yield Responses of Soybean Cultivars

    Directory of Open Access Journals (Sweden)

    Yansheng Li

    2017-09-01

    Full Text Available Nitrogen deficiency limits crop performance under elevated CO2 (eCO2, depending on the ability of plant N uptake. However, the dynamics and redistribution of N2 fixation, and fertilizer and soil N use in legumes under eCO2 have been little studied. Such an investigation is essential to improve the adaptability of legumes to climate change. We took advantage of genotype-specific responses of soybean to increased CO2 to test which N-uptake phenotypes are most strongly related to enhanced yield. Eight soybean cultivars were grown in open-top chambers with either 390 ppm (aCO2 or 550 ppm CO2 (eCO2. The plants were supplied with 100 mg N kg−1 soil as 15N-labeled calcium nitrate, and harvested at the initial seed-filling (R5 and full-mature (R8 stages. Increased yield in response to eCO2 correlated highly (r = 0.95 with an increase in symbiotically fixed N during the R5 to R8 stage. In contrast, eCO2 only led to small increases in the uptake of fertilizer-derived and soil-derived N during R5 to R8, and these increases did not correlate with enhanced yield. Elevated CO2 also decreased the proportion of seed N redistributed from shoot to seeds, and this decrease strongly correlated with increased yield. Moreover, the total N uptake was associated with increases in fixed-N per nodule in response to eCO2, but not with changes in nodule biomass, nodule density, or root length.

  16. Nitrogen Fixation in Cyanobacteria

    NARCIS (Netherlands)

    Stal, L.J.

    2008-01-01

    Cyanobacteria are oxygenic photosynthetic bacteria that are widespread in marine, freshwater and terrestrial environments and many of them are capable of fixing atmospheric nitrogen. But ironically, nitrogenase, the enzyme that is responsible for the reduction of N2, is extremely sensitive to O2.

  17. Fixation Time for Evolutionary Graphs

    Science.gov (United States)

    Nie, Pu-Yan; Zhang, Pei-Ai

    Evolutionary graph theory (EGT) is recently proposed by Lieberman et al. in 2005. EGT is successful for explaining biological evolution and some social phenomena. It is extremely important to consider the time of fixation for EGT in many practical problems, including evolutionary theory and the evolution of cooperation. This study characterizes the time to asymptotically reach fixation.

  18. Complement fixation test to C burnetii

    Science.gov (United States)

    ... complement fixation test; Coxiella burnetii - complement fixation test; C burnetii - complement fixation test ... a specific foreign substance ( antigen ), in this case, C burnetii . Antibodies defend the body against bacteria, viruses, ...

  19. Nitrogen fixation in four dryland tree species in central Chile

    International Nuclear Information System (INIS)

    Ovalle, C.; Arredondo, S.; Aronson, J.; Longeri, L.; Avendano, J.

    1998-01-01

    Results are presented from a 5-year experiment using 15 N-enriched fertilizer to determine N 2 fixation in four tree species on degraded soils in a Mediterranean-climate region of central Chile in which there are 5 months of drought. Species tested included three slow-growing but long-lived savannah trees native to southers South America, (acacia caven, Prosopic alba and P. chilensis; Mimosoideae), and Tagasaste (Chamaecytisus proliferus ssp. palmensis; Papilonoideae), a fast-growing but medium-lived tree from the Canary Islands. Tagasaste produced four- to twenty-fold more biomass than the other species, but showed declining N 2 fixation and biomass accumulation during the 5th year, corresponding to the juvenile-to-adult developmental transition. Nitrogen content was significantly higher in Tagasaste and Acacia caven than in the other species. The data revealed inter-specific differences in resource allocation and phenology of N 2 fixation rarely detailed for woody plants in dryland regions. (author)

  20. Eighth international congress on nitrogen fixation

    Energy Technology Data Exchange (ETDEWEB)

    1990-01-01

    This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

  1. Infrared spectra and anharmonic coupling of proton-bound nitrogen dimers N2-H+-N2, N2-D+-N2, and15N2-H+-15N2in solid para-hydrogen.

    Science.gov (United States)

    Liao, Hsin-Yi; Tsuge, Masashi; Tan, Jake A; Kuo, Jer-Lai; Lee, Yuan-Pern

    2017-08-09

    The proton-bound nitrogen dimer, N 2 -H + -N 2 , and its isotopologues were investigated by means of vibrational spectroscopy. These species were produced upon electron bombardment of mixtures of N 2 (or 15 N 2 ) and para-hydrogen (p-H 2 ) or normal-D 2 (n-D 2 ) during deposition at 3.2 K. Reduced-dimension anharmonic vibrational Schrödinger equations were constructed to account for the strong anharmonic effects in these protonated species. The fundamental lines of proton motions in N 2 -H + -N 2 were observed at 715.0 (NH + N antisymmetric stretch, ν 4 ), 1129.6 (NH + N bend, ν 6 ), and 2352.7 (antisymmetric NN/NN stretch, ν 3 ) cm -1 , in agreement with values of 763, 1144, and 2423 cm -1 predicted with anharmonic calculations using the discrete-variable representation (DVR) method at the CCSD/aug-cc-pVDZ level. The lines at 1030.2 and 1395.5 cm -1 were assigned to combination bands involving nν 2 + ν 4 (n = 1 and 2) according to theoretical calculations; ν 2 is the N 2 N 2 stretching mode. For 15 N 2 -H + - 15 N 2 in solid p-H 2 , the corresponding major lines were observed at 710.0 (ν 4 ), 1016.7 (ν 2 + ν 4 ), 1124.3 (ν 6 ), 1384.8 (2ν 2 + ν 4 ), and 2274.9 (ν 3 ) cm -1 . For N 2 -D + -N 2 in solid n-D 2 , the corresponding major lines were observed at 494.0 (ν 4 ), 840.7 (ν 2 + ν 4 ), 825.5 (ν 6 ), and 2356.2 (ν 3 ) cm -1 . In addition, two lines at 762.0 (weak) and 808.3 cm -1 were tentatively assigned to be some modes of N 2 -H + -N 2 perturbed or activated by a third N 2 near the proton.

  2. Manifestly N = 2 supersymmetric regularization for N = 2 supersymmetric field theories

    Science.gov (United States)

    Buchbinder, I. L.; Pletnev, N. G.; Stepanyantz, K. V.

    2015-12-01

    We formulate the higher covariant derivative regularization for N = 2 supersymmetric gauge theories in N = 2 harmonic superspace. This regularization is constructed by adding the N = 2 supersymmetric higher derivative term to the classical action and inserting the N = 2 supersymmetric Pauli-Villars determinants into the generating functional for removing one-loop divergencies. Unlike all other regularization schemes in N = 2 supersymmetric quantum field theory, this regularization preserves by construction the manifest N = 2 supersymmetry at all steps of calculating loop corrections to the effective action. Together with N = 2 supersymmetric background field method this regularization allows to calculate quantum corrections without breaking the manifest gauge symmetry and N = 2 supersymmetry. Thus, we justify the assumption about existence of a regularization preserving N = 2 supersymmetry, which is a key element of the N = 2 non-renormalization theorem. As a result, we give the proof of the N = 2 non-renormalization theorem which does not require any additional assumptions.

  3. The role of phosphorus in nitrogen fixation by young pea plants (Pisum sativum)

    DEFF Research Database (Denmark)

    Jakobsen, Iver

    1985-01-01

    The influence of P on N2 fixation and dry matter production of young pea (P. sativum L. cv. Bodil) plants grown in a soil-sand mixture was investigated in growth cabinet experiments. Nodule dry weight, specific C2H2 reduction and P concentration in shoots responded to P addition before any growth...... response could be observed. The P concentration in nodules responded only slightly to P addition. A supply of P to P-deficient plants increased both the nodule dry weight, specific C2H2 reduction and P concentration in shoots relatively faster than it increased shoot dry weight and P concentration...... in nodules. Combined N applied to plants when N2 fixation had commenced, increased shoot dry weight only at the highest P levels. The smaller plant growth at the low P levels did not result from N deficiency. The reduced nodulation and N2 fixation in P-deficient plants were apparently caused by impaired...

  4. Symbiotic Properties of Sinorhizobium Fredii, J-TGS50 an Indonesian Soybean Nodule Forming Bacteria

    International Nuclear Information System (INIS)

    Setiyo Hadi Waluyo

    2004-01-01

    Green House experiments were conducted to study symbiotic properties of Sinorhizobium Fredii, J-TGS50. Sinorhizobium Fredii USDA 192, USDA 201, USDA 205, USDA 206, USDA 217 and Bradyrhizobium japonicum USDA 110 were used as references. Yeast extract mannitol broth culture of the bacteria were made and used as inoculation for several local and imported soybean varieties used in this study. Plants were harvested at 20 days after inoculation. Number of nodules were counted, fresh weight of nodules and shoot were determined. S. Fredii J-TGS50 and S. Fredii USDA 192, USDA 201, USDA 205, USDA 206, USDA 217 were found different in their symbiotic properties. S. Fredii J-TGS50 formed nodules on same imported soybean. While there were no nodules obtained from the plant inoculated with S. Fredii USDA 192, USDA 201, USDA 205, USDA 206, USDA 217. S. Fredii J-TGS50 and recommended B. Japonicum USDA 110 formed nodule on several local soybean varieties. There was no differences between those two bacteria either in nodulation efficiency or in the effectiveness of the formed nodules. Results of this study can be concluded that S. Fredii, J-TGS50 is a native to Indonesian soil and it is a promising soybean nodule forming bacteria in Indonesia. Using indigenous bacteria is valuable. Since they are mostly more tolerant and adaptable than the introduced ones. An important aspect for the success of Biological Nitrogen Fixation (BNF) is insight in the structure of indigenous soybean rhizobia populations. Study on the biodiversity of soybean rhizobia was important conducted. (author)

  5. Dinitrogen fixation in white clover grown in pure stand and mixture with ryegrass estimated by the immobilized 15N isotope dilution method

    DEFF Research Database (Denmark)

    Jørgensen, F.V.; Jensen, E.S.; Schjørring, J.K.

    1999-01-01

    labelling methods gave, nonetheless, a similar estimate of the percentage of clover N derived from N-2 fixation. In pure stand clover, 75-94% of the N was derived from N-2 fixation and in the mixture 85-97%. The dry matter yield of the clover in mixture as percentage of total dry matter yield was relatively...

  6. Biological Nitrogen Fixation: Perspective and Limitation

    Directory of Open Access Journals (Sweden)

    N D Purwantari

    2008-03-01

    Full Text Available The demand of chemical fertilizer, N in particular will be increasing until 2020. In Indonesia, the demand of fertilizer from 1999 – 2002 increased 37.5 and 12.4% for urea and ammonium sulphate, respectively. At the same time, the price of this fertilizer is also increasing and it can not be afforded by the farmer. Other problem in using chemical fertilizer is damaging to the soil and environment. One of the problem solvings for this condition is to maximize biological nitrogen fixation (BNF. BNF is the fixation of N atmosphere by association between soil bacteria rhizobia and leguminous plant. BNF is sustainable and environmentally friendly in providing nitrogen fertilizer. Therefore, it would reduce the requirement of chemical nitrogen fertilizer for the plant. Gliricidia sepium fixes 170 kg N/ha/12 months, equivalent with 377 kg urea, Sesbania sesban 179 kg N/ha/10 months, equivalent 397 kg with urea, soybean 26 – 57 kg/2 months equivalent with 57 – 126 kg urea. The amount of N2- fixed varies, affected by species, environmental and biological factors. There are some limitations in applying this technology. The effect of N contribution is very slow at the beginning but in the long term, it would be beneficial for plant production and at the same time, maintain condition of physical and chemical of soil, soil microbes and therefore soil fertility.

  7. Outbursts In Symbiotic Binaries (FUSE 2000)

    Science.gov (United States)

    Kenyon, Scott J.; Sonneborn, George (Technical Monitor)

    2002-01-01

    During the past year, we made good progress on analysis of FUSE observations of the symbiotic binary Z And. For background, Z And is a binary system composed of a red giant and a hot component of unknown status. The orbital period is roughly 750 days. The hot component undergoes large-scale eruptions every 10-20 yr. An outburst began several years ago, triggering this FUSE opportunity. First, we obtained an excellent set of ground-based optical data in support, of the FUSE observations. We used FAST, a high throughput low resolution spectrograph on the 1.5-m telescope at Mt. Hopkins, Arizona. A 300 g/ mm grating blazed at 4750 A, a 3 in. slit, and a thinned Loral 512 x 2688 CCD gave us spectra covering 3800-7500 A at a resolution of 6 A. The wavelength solution for each spectrum has a probable error of +/- 0.5 A or better. Most of the resulting spectra have moderate signal-to-noise, S/.N approx. greater than 30 per pixel. The time coverage for these spectra is excellent. Typically, we acquired spectra every 1-2 nights during dark runs at Mt. Hopkins. These data cover most of the rise and all of the decline of the recent outburst. The spectra show a wealth of emission lines, including H I, He I, He II, [Fe V11], and the Raman scattering bands at 6830 A and 7088 A. The Raman bands and other high ionization features vary considerably throughout the outburst. These features will enable us to correlate variations in the FUSE spectra with variations in the optical spectra. Second, we began an analysis of FUSE spectra of Z And. We have carefully examined the spectra, identifying real features and defects. We have identified and measured fluxes for all strong emission lines, including the O VI doublet at 1032 A and 1038 A. These and several other strong emission lines display pronounced P Cygni absorption components indicative of outgrowing gas. We will attempt to correlate these velocities with similar profiles observed on optical spectra. The line velocities - together

  8. Mitigation of soil N2O emission by inoculation with a mixed culture of indigenous Bradyrhizobium diazoefficiens

    Science.gov (United States)

    Akiyama, Hiroko; Hoshino, Yuko Takada; Itakura, Manabu; Shimomura, Yumi; Wang, Yong; Yamamoto, Akinori; Tago, Kanako; Nakajima, Yasuhiro; Minamisawa, Kiwamu; Hayatsu, Masahito

    2016-09-01

    Agricultural soil is the largest source of nitrous oxide (N2O), a greenhouse gas. Soybean is an important leguminous crop worldwide. Soybean hosts symbiotic nitrogen-fixing soil bacteria (rhizobia) in root nodules. In soybean ecosystems, N2O emissions often increase during decomposition of the root nodules. Our previous study showed that N2O reductase can be used to mitigate N2O emission from soybean fields during nodule decomposition by inoculation with nosZ++ strains [mutants with increased N2O reductase (N2OR) activity] of Bradyrhizobium diazoefficiens. Here, we show that N2O emission can be reduced at the field scale by inoculation with a mixed culture of indigenous nosZ+ strains of B. diazoefficiens USDA110 group isolated from Japanese agricultural fields. Our results also suggested that nodule nitrogen is the main source of N2O production during nodule decomposition. Isolating nosZ+ strains from local soybean fields would be more applicable and feasible for many soybean-producing countries than generating mutants.

  9. Comprehensive EST analysis of the symbiotic sea anemone, Anemonia viridis

    Directory of Open Access Journals (Sweden)

    Deleury Emeline

    2009-07-01

    Full Text Available Abstract Background Coral reef ecosystems are renowned for their diversity and beauty. Their immense ecological success is due to a symbiotic association between cnidarian hosts and unicellular dinoflagellate algae, known as zooxanthellae. These algae are photosynthetic and the cnidarian-zooxanthellae association is based on nutritional exchanges. Maintenance of such an intimate cellular partnership involves many crosstalks between the partners. To better characterize symbiotic relationships between a cnidarian host and its dinoflagellate symbionts, we conducted a large-scale EST study on a symbiotic sea anemone, Anemonia viridis, in which the two tissue layers (epiderm and gastroderm can be easily separated. Results A single cDNA library was constructed from symbiotic tissue of sea anemones A. viridis in various environmental conditions (both normal and stressed. We generated 39,939 high quality ESTs, which were assembled into 14,504 unique sequences (UniSeqs. Sequences were analysed and sorted according to their putative origin (animal, algal or bacterial. We identified many new repeated elements in the 3'UTR of most animal genes, suggesting that these elements potentially have a biological role, especially with respect to gene expression regulation. We identified genes of animal origin that have no homolog in the non-symbiotic starlet sea anemone Nematostella vectensis genome, but in other symbiotic cnidarians, and may therefore be involved in the symbiosis relationship in A. viridis. Comparison of protein domain occurrence in A. viridis with that in N. vectensis demonstrated an increase in abundance of some molecular functions, such as protein binding or antioxidant activity, suggesting that these functions are essential for the symbiotic state and may be specific adaptations. Conclusion This large dataset of sequences provides a valuable resource for future studies on symbiotic interactions in Cnidaria. The comparison with the closest

  10. Controlling cyanobacterial blooms in hypertrophic Lake Taihu, China: will nitrogen reductions cause replacement of non-N2 fixing by N2 fixing taxa?

    Directory of Open Access Journals (Sweden)

    Hans W Paerl

    Full Text Available Excessive anthropogenic nitrogen (N and phosphorus (P inputs have caused an alarming increase in harmful cyanobacterial blooms, threatening sustainability of lakes and reservoirs worldwide. Hypertrophic Lake Taihu, China's third largest freshwater lake, typifies this predicament, with toxic blooms of the non-N2 fixing cyanobacteria Microcystis spp. dominating from spring through fall. Previous studies indicate N and P reductions are needed to reduce bloom magnitude and duration. However, N reductions may encourage replacement of non-N2 fixing with N2 fixing cyanobacteria. This potentially counterproductive scenario was evaluated using replicate, large (1000 L, in-lake mesocosms during summer bloom periods. N+P additions led to maximum phytoplankton production. Phosphorus enrichment, which promoted N limitation, resulted in increases in N2 fixing taxa (Anabaena spp., but it did not lead to significant replacement of non-N2 fixing with N2 fixing cyanobacteria, and N2 fixation rates remained ecologically insignificant. Furthermore, P enrichment failed to increase phytoplankton production relative to controls, indicating that N was the most limiting nutrient throughout this period. We propose that Microcystis spp. and other non-N2 fixing genera can maintain dominance in this shallow, highly turbid, nutrient-enriched lake by outcompeting N2 fixing taxa for existing sources of N and P stored and cycled in the lake. To bring Taihu and other hypertrophic systems below the bloom threshold, both N and P reductions will be needed until the legacy of high N and P loading and sediment nutrient storage in these systems is depleted. At that point, a more exclusive focus on P reductions may be feasible.

  11. Fighting malaria with engineered symbiotic bacteria from vector mosquitoes

    Science.gov (United States)

    Wang, Sibao; Ghosh, Anil K.; Bongio, Nicholas; Stebbings, Kevin A.; Lampe, David J.; Jacobs-Lorena, Marcelo

    2012-01-01

    The most vulnerable stages of Plasmodium development occur in the lumen of the mosquito midgut, a compartment shared with symbiotic bacteria. Here, we describe a strategy that uses symbiotic bacteria to deliver antimalaria effector molecules to the midgut lumen, thus rendering host mosquitoes refractory to malaria infection. The Escherichia coli hemolysin A secretion system was used to promote the secretion of a variety of anti-Plasmodium effector proteins by Pantoea agglomerans, a common mosquito symbiotic bacterium. These engineered P. agglomerans strains inhibited development of the human malaria parasite Plasmodium falciparum and rodent malaria parasite Plasmodium berghei by up to 98%. Significantly, the proportion of mosquitoes carrying parasites (prevalence) decreased by up to 84% for two of the effector molecules, scorpine, a potent antiplasmodial peptide and (EPIP)4, four copies of Plasmodium enolase–plasminogen interaction peptide that prevents plasminogen binding to the ookinete surface. We demonstrate the use of an engineered symbiotic bacterium to interfere with the development of P. falciparum in the mosquito. These findings provide the foundation for the use of genetically modified symbiotic bacteria as a powerful tool to combat malaria. PMID:22802646

  12. N=2 current algebra and coset models

    International Nuclear Information System (INIS)

    Hull, C.M.; Spence, B.

    1990-01-01

    The N=2 supersymmetric extension of the Kac-Moody algebra and the corresponding Sugawara construction of the N=2 superconformal algebra are discussed both in components and in N=1 superspace. A formulation of the Kac-Moody algebra and Sugawara construction is given in N=2 superspace in terms of supercurrents satisfying a non-linear chiral constraint. The operator product of two supercurrents includes terms that are non-linear in the supercurrents. The N=2 generalization of the GKO coset construction is then given and the conditions found by Kazama and Suzuki are seen to arise from the non-linearity of the algebra. (orig.)

  13. Nitrogen fixation of the blue lupins and soybean by 15N-dilution method

    International Nuclear Information System (INIS)

    Hayas, B.

    2005-01-01

    Legume species differ in duration and response to nitrogen fertilization during growth stages, this was studied on new lines of soybean 172 and blue lupins boriginie and reaction to inoculation and nitrogen fertilization in pot experiments. Results show inoculation increased total dry matter and total N 2 -fixation in both species comparative to control without inoculation. Blue lupins has fixed 60% from atmosphere after flowering. Soybean fixed only 12% nitrogen at seeding and has reduced N 2 - fixation and nodules-Number. Application at flowering has not effected by blue lupins and has increased total seed dry matter and total seed nitrogen in soybean. (author)

  14. The Sinorhizobium meliloti RNA chaperone Hfq influences central carbon metabolism and the symbiotic interaction with alfalfa

    Directory of Open Access Journals (Sweden)

    Jiménez-Zurdo José I

    2010-03-01

    Full Text Available Abstract Background The bacterial Hfq protein is able to interact with diverse RNA molecules, including regulatory small non-coding RNAs (sRNAs, and thus it is recognized as a global post-transcriptional regulator of gene expression. Loss of Hfq has an extensive impact in bacterial physiology which in several animal pathogens influences virulence. Sinorhizobium meliloti is a model soil bacterium known for its ability to establish a beneficial nitrogen-fixing intracellular symbiosis with alfalfa. Despite the predicted general involvement of Hfq in the establishment of successful bacteria-eukaryote interactions, its function in S. meliloti has remained unexplored. Results Two independent S. meliloti mutants, 2011-3.4 and 1021Δhfq, were obtained by disruption and deletion of the hfq gene in the wild-type strains 2011 and 1021, respectively, both exhibiting similar growth defects as free-living bacteria. Transcriptomic profiling of 1021Δhfq revealed a general down-regulation of genes of sugar transporters and some enzymes of the central carbon metabolism, whereas transcripts specifying the uptake and metabolism of nitrogen sources (mainly amino acids were more abundant than in the wild-type strain. Proteomic analysis of the 2011-3.4 mutant independently confirmed these observations. Symbiotic tests showed that lack of Hfq led to a delayed nodulation, severely compromised bacterial competitiveness on alfalfa roots and impaired normal plant growth. Furthermore, a large proportion of nodules (55%-64% elicited by the 1021Δhfq mutant were non-fixing, with scarce content in bacteroids and signs of premature senescence of endosymbiotic bacteria. RT-PCR experiments on RNA from bacteria grown under aerobic and microoxic conditions revealed that Hfq contributes to regulation of nifA and fixK1/K2, the genes controlling nitrogen fixation, although the Hfq-mediated regulation of fixK is only aerobiosis dependent. Finally, we found that some of the recently

  15. New combination bands of N2O-CO2, N2O-OCS, and N2O-N2 complexes in the N2O ν1 region

    International Nuclear Information System (INIS)

    Rezaei, M.; Moazzen-Ahmadi, N.; Michaelian, K. H.

    2014-01-01

    Spectra of the weakly bound complexes N 2 O-CO 2 , N 2 O-OCS, and N 2 O-N 2 were studied in the region of the ν 1 fundamental of N 2 O (∼2224 cm −1 ) using a tunable quantum cascade laser to probe a pulsed supersonic jet expansion with an effective rotational temperature of about 2.5 K. One new combination band was observed for each complex: a band involving an intermolecular in-plane bending mode for N 2 O-N 2 , a band involving the disrotation (in-plane geared bend) for of N 2 O-CO 2 , and a band involving the out-of-plane torsional vibration for isomer b of N 2 O-OCS. Small perturbations were noted for the N 2 O-OCS band. Because of the absence of theoretical prediction, the nature of the intermolecular bending mode for N 2 O-N 2 has not been identified. The resulting intermolecular frequencies are 34.175(1), 17.107(1), and 22.334(1) cm −1 for N 2 O-CO 2 , N 2 O-OCS, and N 2 O-N 2 , respectively. In addition, the previously known fundamental band of N 2 O-N 2 at 2225.99 cm −1 was analyzed in improved detail. This band exhibits very weak a-type transitions which were not detected in the first infrared observation of this complex, indicating that N 2 O-N 2 is not exactly T-shaped. That is, the N 2 O molecular axis is not exactly perpendicular to the a-inertial axis, in agreement with a previous structural determination of this complex by rotational spectroscopy

  16. New combination bands of N2O-CO2, N2O-OCS, and N2O-N2 complexes in the N2O ν1 region

    Science.gov (United States)

    Rezaei, M.; Michaelian, K. H.; Moazzen-Ahmadi, N.

    2014-01-01

    Spectra of the weakly bound complexes N2O-CO2, N2O-OCS, and N2O-N2 were studied in the region of the ν1 fundamental of N2O (˜2224 cm-1) using a tunable quantum cascade laser to probe a pulsed supersonic jet expansion with an effective rotational temperature of about 2.5 K. One new combination band was observed for each complex: a band involving an intermolecular in-plane bending mode for N2O-N2, a band involving the disrotation (in-plane geared bend) for of N2O-CO2, and a band involving the out-of-plane torsional vibration for isomer b of N2O-OCS. Small perturbations were noted for the N2O-OCS band. Because of the absence of theoretical prediction, the nature of the intermolecular bending mode for N2O-N2 has not been identified. The resulting intermolecular frequencies are 34.175(1), 17.107(1), and 22.334(1) cm-1 for N2O-CO2, N2O-OCS, and N2O-N2, respectively. In addition, the previously known fundamental band of N2O-N2 at 2225.99 cm-1 was analyzed in improved detail. This band exhibits very weak a-type transitions which were not detected in the first infrared observation of this complex, indicating that N2O-N2 is not exactly T-shaped. That is, the N2O molecular axis is not exactly perpendicular to the a-inertial axis, in agreement with a previous structural determination of this complex by rotational spectroscopy.

  17. Symbiotic relationship of Thiothrix spp. with an echinoderm

    Energy Technology Data Exchange (ETDEWEB)

    Brigmon, R.L. [Westinghouse Savannah River Co., Aiken, SC (United States); De Ridder, C. [Univ. Libre de Bruxelles, Brussels (Belgium). Lab. de Biologie Marine

    1998-09-01

    Thiothrix-like bacteria have been reported as symbionts in invertebrates from sulfide-rich habitats. Isolation of these symbiotic Thiothrix-like bacteria has failed, and the organisms have not been previously identified with certainty. The genus Thiothrix was created for ensheathed filamentous bacteria that oxidize sulfide and deposit sulfur granules internally, attach to substrates, produce gliding gonidia, and form rosettes. Immunoassay procedures were used to investigate the symbiotic relationship of Thiothrix spp. in the intestinal cecum of the spatangoid species Echinocardium cordatum. Thiothrix spp. were identified in nodule samples from E. cordatum digestive tubes based on microscopic examination, enzyme-linked immunosorbent assay, and indirect immunofluorescence. Thiothrix spp. protein made up as much as 84% of the total protein content of the nodules. This is the first identification of Thiothrix spp. internally symbiotic with marine invertebrates.

  18. Non-symbiotic hemoglobin and its relation with hypoxic stress

    Directory of Open Access Journals (Sweden)

    Alejandro Riquelme

    2015-08-01

    Full Text Available Today we know that several types of hemoglobins exist in plants. The symbiotic hemoglobins were discovered in 1939 and are only found in nodules of plants capable of symbiotically fixing atmospheric N. Another class, called non-symbiotic hemoglobin, was discovered 32 yr ago and is now thought to exist throughout the plant kingdom, being expressed in different organs and tissues. Recently the existence of another type of hemoglobin, called truncated hemoglobin, was demonstrated in plants. Although the presence of hemoglobins is widespread in the plant kingdom, their role has not yet been fully elucidated. This review discusses recent findings regarding the role of plant hemoglobins, with special emphasis on their relationship to plants adaptation to hypoxia. It also discusses the role of nitric oxide in plant cells under hypoxic conditions, since one of the functions of hemoglobin appears to be modulating nitric oxide levels in the cells.

  19. Nodulation outer proteins: double-edged swords of symbiotic rhizobia.

    Science.gov (United States)

    Staehelin, Christian; Krishnan, Hari B

    2015-09-15

    Rhizobia are nitrogen-fixing bacteria that establish a nodule symbiosis with legumes. Nodule formation depends on signals and surface determinants produced by both symbiotic partners. Among them, rhizobial Nops (nodulation outer proteins) play a crucial symbiotic role in many strain-host combinations. Nops are defined as proteins secreted via a rhizobial T3SS (type III secretion system). Functional T3SSs have been characterized in many rhizobial strains. Nops have been identified using various genetic, biochemical, proteomic, genomic and experimental approaches. Certain Nops represent extracellular components of the T3SS, which are visible in electron micrographs as bacterial surface appendages called T3 (type III) pili. Other Nops are T3 effector proteins that can be translocated into plant cells. Rhizobial T3 effectors manipulate cellular processes in host cells to suppress plant defence responses against rhizobia and to promote symbiosis-related processes. Accordingly, mutant strains deficient in synthesis or secretion of T3 effectors show reduced symbiotic properties on certain host plants. On the other hand, direct or indirect recognition of T3 effectors by plant cells expressing specific R (resistance) proteins can result in effector triggered defence responses that negatively affect rhizobial infection. Hence Nops are double-edged swords that may promote establishment of symbiosis with one legume (symbiotic factors) and impair symbiotic processes when bacteria are inoculated on another legume species (asymbiotic factors). In the present review, we provide an overview of our current understanding of Nops. We summarize their symbiotic effects, their biochemical properties and their possible modes of action. Finally, we discuss future perspectives in the field of T3 effector research. © 2015 Authors; published by Portland Press Limited.

  20. Symbiotic fungal associations in 'lower' land plants.

    Science.gov (United States)

    Read, D J; Ducket, J G; Francis, R; Ligron, R; Russell, A

    2000-06-29

    An analysis of the current state of knowledge of symbiotic fungal associations in 'lower' plants is provided. Three fungal phyla, the Zygomycota, Ascomycota and Basidiomycota, are involved in forming these associations, each producing a distinctive suite of structural features in well-defined groups of 'lower' plants. Among the 'lower' plants only mosses and Equisetum appear to lack one or other of these types of association. The salient features of the symbioses produced by each fungal group are described and the relationships between these associations and those formed by the same or related fungi in 'higher' plants are discussed. Particular consideration is given to the question of the extent to which root fungus associations in 'lower' plants are analogous to 'mycorrhizas' of 'higher' plants and the need for analysis of the functional attributes of these symbioses is stressed. Zygomycetous fungi colonize a wide range of extant lower land plants (hornworts, many hepatics, lycopods, Ophioglossales, Psilotales and Gleicheniaceae), where they often produce structures analogous to those seen in the vesicular-arbuscular (VA) mycorrhizas of higher plants, which are formed by members of the order Glomales. A preponderance of associations of this kind is in accordance with palaeohbotanical and molecular evidence indicating that glomalean fungi produced the archetypal symbioses with the first plants to emerge on to land. It is shown, probably for the first time, that glomalean fungi forming typical VA mycorrhiza with a higher plant (Plantago lanceolata) can colonize a thalloid liverwort (Pellia epiphylla), producing arbuscules and vesicles in the hepatic. The extent to which these associations, which are structurally analogous to mycorrhizas, have similar functions remains to be evaluated. Ascomycetous associations are found in a relatively small number of families of leafy liverworts. The structural features of the fungal colonization of rhizoids and underground axes of

  1. N2-fixing legumes are linked to enhanced mineral dissolution and microbiome modulations in Neotropical rainforests

    Science.gov (United States)

    Epihov, Dimitar; Batterman, Sarah; Hedin, Lars; Saltonstall, Kristin; Hall, Jefferson; Leake, Jonathan; Beerling, David

    2017-04-01

    Legumes represent the dominant family of many tropical forests with estimates of 120 billion legume trees in the Amazon basin alone. Many rainforest legume trees form symbioses with N2-fixing bacteria. In the process of atmospheric N2-fixation large amounts of nitrogen-rich litter are generated, supplying half of all nitrogen required to support secondary rainforest succession. However, it is unclear how N2-fixers affect the biogeochemical cycling of other essential nutrients by affecting the rates of mineral dissolution and rock weathering. Here we show that N2-fixing legumes in young Panamanian rainforests promote acidification and enhance silicate rock weathering by a factor of 2 compared to non-fixing trees. We report that N2-fixers also associate with enhanced dissolution of Al- and Fe-bearing secondary minerals native to tropical oxisols. In legume-rich neighbourhoods, non-fixers benefited from raised weathering rates relative to those of legume-free zones thus suggesting a positive community effect driven by N2-fixers. These changes in weathering potential were tracked by parallel functional and structural changes in the soil and rock microbiomes. Our findings support the view that N2-fixing legumes are central components of biogeochemical cycling, associated with enhanced release of Fe- and Al-bound P and primary mineral products (Mg, Mo). Rainforest legume services therefore bear important implications to short-term C cycling related to forest growth and the long-term C cycle related to marine carbonate deposition fuelled by silicate weathering.

  2. Molecular Catalysts for N2Reduction: State of the Art, Mechanism, and Challenges.

    Science.gov (United States)

    Roux, Yoann; Duboc, Carole; Gennari, Marcello

    2017-10-06

    Fixation of atmospheric nitrogen is central for the production of ammonia, which is the source of nitrogen fertilizers and is also emerging as a promising renewable fuel. While the development of efficient molecular-based artificial nitrogen fixation systems working under mild conditions is probably a Holy Grail, the catalytic reduction of N 2 by transition-metal complexes is-above all-the main instrument to progress in the mechanistic understanding of N 2 splitting. In this Minireview we first give an overview of molecular-based catalytic systems, including recent breakthroughs, and then we illustrate the alternative pathways for N 2 reduction. We mainly focus on multistep hydrogenation of N 2 by separated proton and electron sources, with a particular attention for the possibility of proton-coupled electron transfer events. Finally, we try to identify the key factors to achieve catalytic reduction of dinitrogen by metal complexes and to enhance their efficiency. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Symbiotic competence in Lotus japonicus is affected by plant nitrogen status: transcriptomic identification of genes affected by a new signalling pathway.

    Science.gov (United States)

    Omrane, Selim; Ferrarini, Alberto; D'Apuzzo, Enrica; Rogato, Alessandra; Delledonne, Massimo; Chiurazzi, Maurizio

    2009-01-01

    In leguminous plants, symbiotic nitrogen (N) fixation performances and N environmental conditions are linked because nodule initiation, development and functioning are greatly influenced by the amount of available N sources. We demonstrate here that N supply also controls, beforehand, the competence of leguminous plants to perform the nodulation program. Lotus japonicus plants preincubated for 10 d in high-N conditions, and then transferred to low N before the Mesorhizobium loti inoculation, had reduced nodulation. This phenotype was maintained for at least 6 d and a complete reacquisition of the symbiotic competence was observed only after 9 d. The time-course analysis of the change of the symbiotic phenotype was analysed by transcriptomics. The differentially expressed genes identified are mostly involved in metabolic pathways. However, the transcriptional response also includes genes belonging to other functional categories such as signalling, stress response and transcriptional regulation. Some of these genes show a molecular identity and a regulation profile, that suggest a role as possible molecular links between the N-dependent plant response and the nodule organogenesis program.

  4. Effect of Subliminal Stimulation of Symbiotic Fantasies on Behavior Modification Treatment of Obesity.

    Science.gov (United States)

    And Others; Silverman, Lloyd H.

    1978-01-01

    Obese women were treated in behavior modification programs for overeating. Behavior programs were accompanied by subliminal stimulation and by symbiotic and control messages. The symbiotic condition gave evidence of enhancing weight loss. This finding supports the proposition that subliminal stimulation of symbiotic fantasies can enhance the…

  5. Improvement in nitrogen fixation capacity could be part of the domestication process in soybean

    Science.gov (United States)

    Muñoz, N; Qi, X; Li, M-W; Xie, M; Gao, Y; Cheung, M-Y; Wong, F-L; Lam, H-M

    2016-01-01

    Biological nitrogen fixation (BNF) in soybeans is a complex process involving the interplay between the plant host and the symbiotic rhizobia. As nitrogen supply has a crucial role in growth and development, higher nitrogen fixation capacity would be important to achieve bigger plants and larger seeds, which were important selection criteria during plant domestication by humans. To test this hypothesis, we monitored the nitrogen fixation-related performance in 31 cultivated and 17 wild soybeans after inoculation with the slow-growing Bradyrhizobium diazoefficiens sp. nov. USDA110 and the fast-growing Sinorhizobium (Ensifer) fredii CCBAU45436. Our results showed that, in general, cultivated soybeans gave better performance in BNF. Electron microscopic studies indicated that there was an exceptionally high accumulation of poly-β-hydroxybutyrate bodies in bacteroids in the nodules of all wild soybeans tested, suggesting that the C/N balance in wild soybeans may not be optimized for nitrogen fixation. Furthermore, we identified new quantitative trait loci (QTLs) for total ureides and total nodule fresh weight by employing a recombinant inbred population composed of descendants from a cross between a cultivated and a wild parent. Using nucleotide diversity (θπ), divergence index (Fst) and distribution of fixed single-nucleotide polymorphisms as parameters, we found that some regions in the total ureides QTL on chromosome 17 and the total nodule fresh weight QTL on chromosome 12 exhibited very low diversity among cultivated soybeans, suggesting that these were traits specially selected during the domestication and breeding process. PMID:27118154

  6. SYMBIOTIC STAR BLOWS BUBBLES INTO SPACE

    Science.gov (United States)

    2002-01-01

    A tempestuous relationship between an unlikely pair of stars may have created an oddly shaped, gaseous nebula that resembles an hourglass nestled within an hourglass. Images taken with Earth-based telescopes have shown the larger, hourglass-shaped nebula. But this picture, taken with NASA's Hubble Space Telescope, reveals a small, bright nebula embedded in the center of the larger one (close-up of nebula in inset). Astronomers have dubbed the entire nebula the 'Southern Crab Nebula' (He2-104), because, from ground-based telescopes, it looks like the body and legs of a crab. The nebula is several light-years long. The possible creators of these shapes cannot be seen at all in this Wide Field and Planetary Camera 2 image. It's a pair of aging stars buried in the glow of the tiny, central nebula. One of them is a red giant, a bloated star that is exhausting its nuclear fuel and is shedding its outer layers in a powerful stellar wind. Its companion is a hot, white dwarf, a stellar zombie of a burned-out star. This odd duo of a red giant and a white dwarf is called a symbiotic system. The red giant is also a Mira Variable, a pulsating red giant, that is far away from its partner. It could take as much as 100 years for the two to orbit around each other. Astronomers speculate that the interaction between these two stars may have sparked episodic outbursts of material, creating the gaseous bubbles that form the nebula. They interact by playing a celestial game of 'catch': as the red giant throws off its bulk in a powerful stellar wind, the white dwarf catches some of it. As a result, an accretion disk of material forms around the white dwarf and spirals onto its hot surface. Gas continues to build up on the surface until it sparks an eruption, blowing material into space. This explosive event may have happened twice in the 'Southern Crab.' Astronomers speculate that the hourglass-shaped nebulae represent two separate outbursts that occurred several thousand years apart

  7. Estimate of symbiotically fixed nitrogen in field grown soybeans using variations in 15N natural abundance

    International Nuclear Information System (INIS)

    Amarger, N.; Durr, J.C.; Bourguignon, C.; Lagacherie, B.; Mariotti, A.; Mariotti, F.

    1979-01-01

    The use of variations in natural abundance of 15 N between nitrogen fixing and non nitrogen fixing soybeans was investigated for quantitative estimate of symbiotic nitrogen fixation. Isotopic analysis of 4 varieties of inoculated and non-inoculated soybeans growing under field conditions, with and without N-fertilizer was determined. It was found that inoculated soybeans had a significantly lower 15 N content than non-inoculated ones. Estimates of the participation of fixed N to the total nitrogen content of inoculated soybeans were calculated from these differences. They were compared to estimates calculated from differences in N yield between inoculated and non-inoculated plants and to the nitrogenase activity, measured by the C 2 H 2 reduction assay over the growing season. Estimates given by the 15 N measurements were correlated with the C 2 H 2 reducing activity but not with the differences in the N yield. This shows that the isotopic composition was dependent on the amount of fixed nitrogen and consequently that the estimates of fixed nitrogen based on natural 15 N abundance should be reliable. The absence of correlation between estimates based on 15 N content and estimates based on N yield was explained by differences in the uptake of soil nitrogen between inoculated and non inoculated soybeans. (Auth.)

  8. Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat

    DEFF Research Database (Denmark)

    Steunou, Anne-Soisig; Jensen, Sheila I; Brecht, Eric

    2008-01-01

    Nitrogen fixation, a prokaryotic, O(2)-inhibited process that reduces N(2) gas to biomass, is of paramount importance in biogeochemical cycling of nitrogen. We analyzed the levels of nif transcripts of Synechococcus ecotypes, NifH subunit and nitrogenase activity over the diel cycle in the microb...... of N(2) fixation over the diel cycle.The ISME Journal (2008) 2, 364-378; doi:10.1038/ismej.2007.117; published online 6 March 2008. Udgivelsesdato: 2008-Apr...

  9. Nitrogen fixation in sediments along a depth transect through the Eastern Boundary Upwelling Systems off Peru and Mauritania

    Science.gov (United States)

    Gier, J.; Sommer, S.; Löscher, C. R.; Dale, A.; Schmitz, R. A.; Treude, T.

    2015-12-01

    The distribution of benthic nitrogen (N2) fixation and its relevance for N cycling in the Eastern Boundary Upwelling Systems (EBUS) are still unknown. Recent studies confirm that benthic N2 fixation can be coupled to sulfate reduction (SR) and that several species of sulfate reducing bacteria have the genetic ability to fix N due to the presence of the gene encoding for the nitrogenase enzyme. We investigated benthic N2 fixation and SR in the Peruvian oxygen minimum zone at 12°S and in the Mauritanian upwelling system at 18°N along a depth transect. Sediments were retrieved by a multicorer and a benthic lander at six stations in both regions. Benthic N2 fixation occurred throughout the sediment in both EBUS. Off Peru the highest integrated (0-20 cm) N2 fixation rate of 0.4 mmol N/m2/d was measured inside the core of the OMZ at 253 m water depth. Off Mauritania the highest integrated (0-20 cm) N2 fixation rate of 0.15 mmol N/m2/d was measured at 90 m, coinciding with a low bottom water oxygen concentration (30 μM). N2 fixation depth profiles often overlapped with SR activity. Moreover, sequencing data yielded insights into the composition and diversity of the nifH gene pool in EBUS sediments. Interestingly, detected sequences in both EBUS clustered with SR bacteria, such as Desulfovibrio vulgaris and several of the novel detected clades belonged to uncultured diazotrophs. Our results suggest that N2 fixation and SR were coupled to a large extent in both regions. However, potential environmental factors controlling benthic diazotrophs in the EBUS appear to be the availability of sulfide and organic matter. Additionally, no inhibition of N2 fixation at high ammonium concentrations was found, which highlights gaps in our knowledge regards the interaction between ammonium availability and diazotrophy. Our results contribute to a better understanding of N cycling in EBUS sediments and sources of fixed N.

  10. Interacting Winds in Eclipsing Symbiotic Systems – The Case Study ...

    Indian Academy of Sciences (India)

    The most adopted physical modeling for many symbiotic stars is that of interacting binaries: a cool giant, a hot .... envelopes the area behind the hot component; and if mw > 1, the hot wind predom- inates the cool wind. ...... Tomov, N., Tomova, M. 2001, Astrophysics and Space Science, 278, 311. Torbett, M. V., Campbell, B.

  11. Diversity of the Symbiotic Alga Symbiodinium in Tanzanian ...

    African Journals Online (AJOL)

    Abstract—With the current increase in frequency of coral bleaching events, knowledge on the genetic diversity of symbiotic algae in the genus Symbiodinium harboured by reef-building corals is important to understand how coral reefs will respond to global climate change. This study was undertaken as very little is known.

  12. Survivability of probiotics in symbiotic low fat buffalo milk yogurt ...

    African Journals Online (AJOL)

    In present study, symbiotic low fat buffalo milk yogurt prototypes (plain and blueberry) were developed using a commercial starter containing probiotics. Samples were analyzed for physicochemical and microbiological properties, and the survivability of probiotics during 10 weeks of storage. Gross composition results were: ...

  13. Interacting Winds in Eclipsing Symbiotic Systems–The Case Study ...

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... We report the mathematical representation of the so called eccentric eclipse model, whose numerical solutions can be used to obtain the physical parameters of a quiescent eclipsing symbiotic system. Indeed the nebular region produced by the collision of the stellar winds should be shifted to the orbital ...

  14. Symbiotic Blue Green Algae (Azolla): A Potential Bio fertilizer for ...

    African Journals Online (AJOL)

    Symbiotic Blue Green Algae (Azolla): A Potential Bio fertilizer for Paddy Rice Production in Fogera Plain, Northwestern Ethiopia. ... They were maintained and multiplied in plastic containers at Adet in a greenhouse and then inoculated into concrete tanks for testing their adaptability. Both strains were well adapted to Adet ...

  15. Competitive interactions among symbiotic fungi of the southern pine beetle

    Science.gov (United States)

    Kier D. Klepzig; Richard T. Wilkens

    1997-01-01

    The southern pine beetle, a damaging pest of conifers, is intimately linked to three symbiotic fungi.Two fungi, Ceratocystiopsis ranaculosus and Entomocorticium sp. A, are transported within specialized structures (mycangia) in the beetle exoskeleton and are mutualists of the beetle.A third fungus, Ophiostoma minus, is transported externally on the beetle exoskeleton (...

  16. Symbiotic effectiveness of pea-rhizobia associations and the ...

    African Journals Online (AJOL)

    微软用户

    2011-05-02

    May 2, 2011 ... Interactions between pea (Pisum sativa L.) cultivars and Rhizobium strain affect the symbiotic relationship and ultimately both the nitrogen fixing capacity and the yield. Since Pisum sativum L. is poorly nodulated in the Loess Plateau of China where this crop is grown, the response of pea cultivars. Yannong ...

  17. Binding Cultures: A Symbiotic Vision of Francis Bebey in Agatha ...

    African Journals Online (AJOL)

    Binding Cultures: A Symbiotic Vision of Francis Bebey in Agatha Moudio's Son. Kelvin Ngong Toh. Abstract. No Abstract. LWATI: A Journal of Contemporary Research, 9(3), 126-135, 2012. Full Text: EMAIL FULL TEXT EMAIL FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · AJOL African Journals Online.

  18. Optical flickering of the symbiotic star CH Cyg

    Science.gov (United States)

    Stoyanov, K. A.; Martí, J.; Zamanov, R.; Dimitrov, V. V.; Kurtenkov, A.; Sánchez-Ayaso, E.; Bujalance-Fernández, I.; Latev, G. Y.; Nikolov, G.

    2018-02-01

    Here we present quasi-simultaneous observations of the flickering of the symbiotic binary star CH Cyg in U, B and V bands. We calculate the flickering source parameters and discuss the possible reason for the flickering cessation in the period 2010-2013.

  19. The symbiotic intestinal ciliates and the evolution of their hosts

    NARCIS (Netherlands)

    Moon-van der Staay, S.Y.; Staay, G.W. van der; Michalowski, T.; Jouany, J.P.; Pristas, P.; Javorsky, P.; Kisidayova, S.; Varadyova, Z.; McEwan, N.R.; Newbold, C.J.; Alen, T. van; Graaf, R. de; Schmid, M.; Huynen, M.A.; Hackstein, J.H.

    2014-01-01

    The evolution of sophisticated differentiations of the gastro-intestinal tract enabled herbivorous mammals to digest dietary cellulose and hemicellulose with the aid of a complex anaerobic microbiota. Distinctive symbiotic ciliates, which are unique to this habitat, are the largest representatives

  20. Biodiversity and studies of marine symbiotic siphonostomatoids off ...

    African Journals Online (AJOL)

    Current knowledge of the biodiversity of the symbiotic marine siphonostomatoids from South African waters (136 species) is sparse compared to that globally (1 388 species). The difference is especially apparent when taking into account the diversity of fish (more than 2 000 species) and invertebrates (approximately 12 ...

  1. A symbiotic shell-encrusting bryozoan provides subtidal whelks with ...

    African Journals Online (AJOL)

    The subtidal whelk Burnupena papyracea co-occurs with a voracious predator, the rock lobster Jasus lalandii, in situations where other potential prey are largely eliminated. The survival of B. papyracea has been ascribed to a symbiotic bryozoan, Alcyonidium nodosum, which characteristically encrusts the shells of this ...

  2. Putative N2-fixing heterotrophic bacteria associated with dinoflagellate-Cyanobacteria consortia in the low-nitrogen Indian Ocean

    DEFF Research Database (Denmark)

    Farnelid, H.; Tarangkoon, Woraporn; Hansen, Gert

    2010-01-01

    , cloning, and sequencing. Cyanobacteria, heterotrophic bacteria and eukaryotic algae were recognized as symbionts of the heterotrophic dinoflagellates. nifH gene sequences were obtained from 23 of 37 (62%) specimens of dinoflagellates (Ornithocercus spp. and Amphisolenia spp.). Interestingly, only 2...... assemblages were often found in single host cells. This study provides the first insights into the nifH diversity of dinoflagellate symbionts and suggests a symbiotic co-existence of non-diazotrophic cyanobacteria and N2-fixing heterotrophic bacteria in heterotrophic dinoflagellates...

  3. Molecular and biochemical analysis of symbiotic plant receptor kinase complexes

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Douglas R; Riely, Brendan K

    2010-09-01

    DE-FG02-01ER15200 was a 36-month project, initiated on Sept 1, 2005 and extended with a one-year no cost extension to August 31, 2009. During the project period we published seven manuscripts (2 in review). Including the prior project period (2002-2005) we published 12 manuscripts in journals that include Science, PNAS, The Plant Cell, Plant Journal, Plant Physiology, and MPMI. The primary focus of this work was to further elucidate the function of the Nod factor signaling pathway that is involved in initiation of the legume-rhizobium symbiosis and in particular to explore the relationship between receptor kinase-like proteins and downstream effectors of symbiotic development. During the project period we have map-base cloned two additional players in symbiotic development, including an ERF transcription factor and an ethylene pathway gene (EIN2) that negatively regulates symbiotic signaling; we have also further characterized the subcellular distribution and function of a nuclear-localized symbiosis-specific ion channel, DMI1. The major outcome of the work has been the development of systems for exploring and validating protein-protein interactions that connect symbiotic receptor-like proteins to downstream responses. In this regard, we have developed both homologous (i.e., in planta) and heterologous (i.e., in yeast) systems to test protein interactions. Using yeast 2-hybrid screens we isolated the only known interactor of the nuclear-localized calcium-responsive kinase DMI3. We have also used yeast 2-hybrid methodology to identify interactions between symbiotic signaling proteins and certain RopGTPase/RopGEF proteins that regulate root hair polar growth. More important to the long-term goals of our work, we have established a TAP tagging system that identifies in planta interactions based on co-immuno precipitation and mass spectrometry. The validity of this approach has been shown using known interactors that either co-iummnoprecipate (i.e., remorin) or co

  4. MALDI mass spectrometry-assisted molecular imaging of metabolites during nitrogen fixation in the Medicago truncatula-Sinorhizobium meliloti symbiosis.

    Science.gov (United States)

    Ye, Hui; Gemperline, Erin; Venkateshwaran, Muthusubramanian; Chen, Ruibing; Delaux, Pierre-Marc; Howes-Podoll, Maegen; Ané, Jean-Michel; Li, Lingjun

    2013-07-01

    Symbiotic associations between leguminous plants and nitrogen-fixing rhizobia culminate in the formation of specialized organs called root nodules, in which the rhizobia fix atmospheric nitrogen and transfer it to the plant. Efficient biological nitrogen fixation depends on metabolites produced by and exchanged between both partners. The Medicago truncatula-Sinorhizobium meliloti association is an excellent model for dissecting this nitrogen-fixing symbiosis because of the availability of genetic information for both symbiotic partners. Here, we employed a powerful imaging technique - matrix-assisted laser desorption/ionization (MALDI)/mass spectrometric imaging (MSI) - to study metabolite distribution in roots and root nodules of M. truncatula during nitrogen fixation. The combination of an efficient, novel MALDI matrix [1,8-bis(dimethyl-amino) naphthalene, DMAN] with a conventional matrix 2,5-dihydroxybenzoic acid (DHB) allowed detection of a large array of organic acids, amino acids, sugars, lipids, flavonoids and their conjugates with improved coverage. Ion density maps of representative metabolites are presented and correlated with the nitrogen fixation process. We demonstrate differences in metabolite distribution between roots and nodules, and also between fixing and non-fixing nodules produced by plant and bacterial mutants. Our study highlights the benefits of using MSI for detecting differences in metabolite distributions in plant biology. © 2013 The Authors The Plant Journal © 2013 John Wiley & Sons Ltd.

  5. Femoral Reconstruction Using External Fixation

    Directory of Open Access Journals (Sweden)

    Yevgeniy Palatnik

    2011-01-01

    Full Text Available Background. The use of an external fixator for the purpose of distraction osteogenesis has been applied to a wide range of orthopedic problems caused by such diverse etiologies as congenital disease, metabolic conditions, infections, traumatic injuries, and congenital short stature. The purpose of this study was to analyze our experience of utilizing this method in patients undergoing a variety of orthopedic procedures of the femur. Methods. We retrospectively reviewed our experience of using external fixation for femoral reconstruction. Three subgroups were defined based on the primary reconstruction goal lengthening, deformity correction, and repair of nonunion/bone defect. Factors such as leg length discrepancy (LLD, limb alignment, and external fixation time and complications were evaluated for the entire group and the 3 subgroups. Results. There was substantial improvement in the overall LLD, femoral length discrepancy, and limb alignment as measured by mechanical axis deviation (MAD and lateral distal femoral angle (LDFA for the entire group as well as the subgroups. Conclusions. The Ilizarov external fixator allows for decreased surgical exposure and preservation of blood supply to bone, avoidance of bone grafting and internal fixation, and simultaneous lengthening and deformity correction, making it a very useful technique for femoral reconstruction.

  6. Environmental forcing of nitrogen fixation in the eastern tropical and sub-tropical North Atlantic Ocean.

    Science.gov (United States)

    Rijkenberg, Micha J A; Langlois, Rebecca J; Mills, Matthew M; Patey, Matthew D; Hill, Polly G; Nielsdóttir, Maria C; Compton, Tanya J; Laroche, Julie; Achterberg, Eric P

    2011-01-01

    During the winter of 2006 we measured nifH gene abundances, dinitrogen (N(2)) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 10(6) L(-1)nifH gene copies, unicellular group A cyanobacteria with up to 10(5) L(-1)nifH gene copies and gamma A proteobacteria with up to 10(4) L(-1)nifH gene copies. N(2) fixation rates were low and ranged between 0.032-1.28 nmol N L(-1) d(-1) with a mean of 0.30 ± 0.29 nmol N L(-1) d(-1) (1σ, n = 65). CO(2)-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2 ± 3.2 in surface waters. Nevertheless, N(2) fixation rates contributed only 0.55 ± 0.87% (range 0.03-5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N(2) fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N(2) fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the

  7. Nitrogen fixation in different chickpea cultivars as affected by iron application N-15 Technique

    International Nuclear Information System (INIS)

    Gadalla, A.M.; Soliman, S.M.; Abdelmonem, M.

    1995-01-01

    With development of new cultivars of winter chickpea, it became important to evaluate the potential of these cultivars to fix nitrogen from air, and the effect of different agronomic factors on this important process. Greenhouse experiment was conducted to screen five cultivars of chickpea for N 2- fixation ability as affected by iron application. These cultivars were Giza 1,2,531 and 88 as compared with L 3 which was developed from the genotype NEC 1055 by irradiation. N 2- fixation was estimated using N-15 technique. Plant materials were collected after 55 days from planing. Plants samples were analysed for total N-15 atom excess. Results show that Giza 88 gave the highest dry matter as well as nitrogen fixation. Nitrogen derived from air (NDFA) ranged from 27 to 50% due to variety difference and iron treatment. 1 fig., 3 tabs

  8. Appraisal of the nitrogen-15 natural-abundance method for quantifying dinitrogen fixation

    International Nuclear Information System (INIS)

    Bremer, E.; van Kessel, C.

    1990-01-01

    Several investigators have questioned the use of the 15 N natural-abundance method of estimating N 2 fixation because of variability in soil δ 15 N and small differences between the δ 15 N of soil N and atmospheric N. Investigations were conducted to compare the 15 N natural-abundance and 15 N-isotope-dilution methods for estimating N 2 fixation of field-grown pea (Pisum sativum L.) and lentil (Lens culinaris Medik.). Spatial variability was assessed at three sites by determining the δ 15 N of non-N 2 -fixing plants. Seasonal variation in δ 15 N for spring and winter wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), barley (Hordeum vulgare L.), rape (Brassica napus L.) and lentil was determined at one site. Comparisons between δ 15 N and 15 N-enriched isotope-dilution methods for estimating N 2 fixation by lentil were conducted at several sites over a 3-yr period. Variability in δ 15 N of the reference plant was site dependent: the δ 15 N ranged from 2.8 to 9.3 at the first site, 3.4 to 8.8 at the second site, and 3.5 to 6.2 at the third site. The average δ 15 N of four of the five non-N 2 -fixing plants increased from 5.4 at 42 d after planting to 6.9 at the final harvest. The fifth non-N 2 -fixing plant, rape, accumulated most of its N during the first 42 d after planting, and its δ 15 N value declined from 8.1 at 42 d after planting to 7.3 at the final harvest. Estimates of N 2 fixation were not significantly different in 18 out of 21 comparisons; in two comparisons in the δ 15 N method and in one comparison the 15 N-enriched method provided higher estimates of N 2 fixation. Overall, both methods appeared to provide equally reliable estimates of N 2 fixation for lentil

  9. Manifestly N=2 supersymmetric regularization for N=2 supersymmetric field theories

    Directory of Open Access Journals (Sweden)

    I.L. Buchbinder

    2015-12-01

    Full Text Available We formulate the higher covariant derivative regularization for N=2 supersymmetric gauge theories in N=2 harmonic superspace. This regularization is constructed by adding the N=2 supersymmetric higher derivative term to the classical action and inserting the N=2 supersymmetric Pauli–Villars determinants into the generating functional for removing one-loop divergencies. Unlike all other regularization schemes in N=2 supersymmetric quantum field theory, this regularization preserves by construction the manifest N=2 supersymmetry at all steps of calculating loop corrections to the effective action. Together with N=2 supersymmetric background field method this regularization allows to calculate quantum corrections without breaking the manifest gauge symmetry and N=2 supersymmetry. Thus, we justify the assumption about existence of a regularization preserving N=2 supersymmetry, which is a key element of the N=2 non-renormalization theorem. As a result, we give the proof of the N=2 non-renormalization theorem which does not require any additional assumptions.

  10. Nitrogen Fixation By Sulfate-Reducing Bacteria in Coastal and Deep-Sea Sediments

    Science.gov (United States)

    Bertics, V. J.; Löscher, C.; Salonen, I.; Schmitz-Streit, R.; Lavik, G.; Kuypers, M. M.; Treude, T.

    2011-12-01

    Sulfate-reducing bacteria (SRB) can greatly impact benthic nitrogen (N) cycling, by for instance inhibiting coupled denitrification-nitrification through the production of sulfide or by increasing the availability of fixed N in the sediment via dinitrogen (N2)-fixation. Here, we explored several coastal and deep-sea benthic habitats within the Atlantic Ocean and Baltic Sea, for the occurrence of N2-fixation mediated by SRB. A combination of different methods including microbial rate measurements of N2-fixation and sulfate reduction, geochemical analyses (porewater nutrient profiles, mass spectrometry), and molecular analyses (CARD-FISH, HISH-SIMS, "nested" PCR, and QPCR) were applied to quantify and identify the responsible processes and organisms, respectively. Furthermore, we looked deeper into the question of whether the observed nitrogenase activity was associated with the final incorporation of N into microbial biomass or whether the enzyme activity served another purpose. At the AGU Fall Meeting, we will present and compare data from numerous stations with different water depths, temperatures, and latitudes, as well as differences in key geochemical parameters, such as organic carbon content and oxygen availability. Current metabolic and molecular data indicate that N2-fixation is occurring in many of these benthic environments and that a large part of this activity may linked to SRB.

  11. The interactive effects of temperature and moisture on nitrogen fixation in two temperate-arctic mosses

    DEFF Research Database (Denmark)

    Rousk, Kathrin; Pedersen, Pia Agerlund; Dyrnum, Kristine

    2017-01-01

    Nitrogen (N) fixation in moss-cyanobacteria associations is one of the main sources of ‘new’ N in pristine ecosystems like subarctic and arctic tundra. This fundamental ecosystem process is driven by temperature as well as by moisture. Yet, the effects of temperature and moisture stress on N2 fix...

  12. Will Elevated Carbon Dioxide Concentration Amplify the Benefits of Nitrogen Fixation in Legumes?

    Science.gov (United States)

    Current evidence suggests there are three key features of the response of legumes to elevated [CO2]: (1) unlike other non-leguminous C3 plants, only legumes have the potential to maximize the benefit of elevated [CO2] by matching stimulated photosynthesis with increased N2 fixation; (2) this potenti...

  13. Cowpea symbiotic efficiency, pH and aluminum tolerance in nitrogen-fixing bacteria

    Directory of Open Access Journals (Sweden)

    Bruno Lima Soares

    2014-06-01

    Full Text Available Cowpea (Vigna unguiculata cultivation in northern and northeastern Brazil provides an excellent source of nutrients and carbohydrates for the poor and underprivileged. Production surplus leads to its consumption in other regions of Brazil and also as an export commodity. Its capacity to establish relationships with atmospheric nitrogen-fixing bacteria is crucial to the reduction of production costs and the environmental impact of nitrogen fertilizers. This study assessed the symbiotic efficiency of new strains of symbiotic nitrogen-fixing bacteria with cowpea and their tolerance to pH and aluminum. Twenty-seven strains of bacteria from different soils were evaluated under axenic conditions. These strains were compared to the following inoculant strains: INPA03-11B, UFLA03-84 and BR3267 and two controls that were not inoculated (with and without mineral nitrogen. Six strains and the three strains approved as inoculants were selected to increase the dry weight production of the aerial part (DWAP and were tested in pots with soil that had a high-density of nitrogen-fixing native rhizobia. In this experiment, three strains (UFLA03-164, UFLA03-153, and UFLA03-154 yielded higher DWAP values. These strains grow at pH levels of 5.0, 6.0, 6.8 and at high aluminum concentration levels, reaching 10(9 CFU mL-1. In particular UFLA03-84, UFLA03-153, and UFLA03-164 tolerate up to 20 mmol c dm-3 of Al+3. Inoculation with rhizobial strains, that had been carefully selected according to their ability to nodulate and fix N2, combined with their ability to compete in soils that are acidic and contain high levels of Al, is a cheaper and more sustainable alternative that can be made available to farmers than mineral fertilizers.

  14. Comparison of Outcomes of Operatively Treated Bicondylar Tibial Plateau Fractures by External Fixation and Internal Fixation

    Directory of Open Access Journals (Sweden)

    CC Chan

    2012-03-01

    Full Text Available The outcome of bicondylar tibial plateau fractures treated with either external fixation (35 patients or internal fixation (24 patients was reviewed. Outcome measures included the Rasmussen score, clinical complications, development of osteoarthritis and the requirement for total knee replacement (TKR. Twenty-two (92% anatomical reductions were achieved in the internal fixation group compared to 27 (77% in the external fixation group. Infective complications were more common in the external fixation group (9 patients, 26% due to pin tract infection. There were no deep infections in the internal fixation group. The mean Rasmussen score was not significantly different (mean score 32 in external fixation and 29 in internal fixation between the two groups and the incidence of osteoarthritis was the same in both groups. Four patients in the external fixation group underwent a TKR compared to 5 patients in the internal fixation group. Bicondylar tibial plateau fractures have similar outcomes following external or internal fixation.

  15. The significance of nitrogen fixation to new production during early summer in the Baltic Sea

    Directory of Open Access Journals (Sweden)

    U. Ohlendieck

    2007-01-01

    Full Text Available Rates of dinitrogen (N2 fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June–July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m−2 (1998 and 33 mmol N m−2 (1999 to new production (sensu Dugdale and Goering, 1967. This constitutes 12–26% more new N than other annual estimates (mid July–mid October from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasizes the need for multiple stations and seasonal sampling strategies in biogeochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73% and 1999 (81%. The between-station variability was high however, and ranged from 28–150% of N needed to meet the rate of C incorporation by primary production. The molar C:N rate incorporation ratio (C:NRATE in filamentous cyanobacterial cells was variable (range 7–28 and the average almost twice as high as the Redfield ratio (6.6 in both years. Since the molar C:N mass ratio (C:NMASS in filamentous cyanobacterial cells was generally lower than C:NRATE at a number of stations, we suggest that the diazotrophs incorporated excess C on a short term basis (carbohydrate ballasting and buoyancy regulation, released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4–24 in 1998 and 18% (range 2–45 in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be

  16. δ15N values of forage grasses and preliminary evaluation of their dinitrogen fixation potential for them

    International Nuclear Information System (INIS)

    Yao Yunyin; Chen Ming; Ma Changlin; Wang Zhidong; Hou Jingqin; Zhang Lihong; Luo Yongyun

    1992-01-01

    There exist different δ 15 N values in shoots of different species and varieties of leguminosae grasses, showing that the potentialities of their dinitrogen fixation were apparently different. The δ 15 N values in shoots of some grasses tested were too low, and very close to δ 15 N value of atmospheric N 2 (0%). It is possible that they get N to meet the needs of their growth through some associative dinitrogen fixation processes. Further study should be done

  17. The ${\\mathcal N}=2$ superconformal bootstrap

    CERN Document Server

    Beem, Christopher; Liendo, Pedro; Rastelli, Leonardo; van Rees, Balt C

    2016-01-01

    In this work we initiate the conformal bootstrap program for ${\\mathcal N}=2$ superconformal field theories in four dimensions. We promote an abstract operator-algebraic viewpoint in order to unify the description of Lagrangian and non-Lagrangian theories, and formulate various conjectures concerning the landscape of theories. We analyze in detail the four-point functions of flavor symmetry current multiplets and of ${\\mathcal N}=2$ chiral operators. For both correlation functions we review the solution of the superconformal Ward identities and describe their superconformal block decompositions. This provides the foundation for an extensive numerical analysis discussed in the second half of the paper. We find a large number of constraints for operator dimensions, OPE coefficients, and central charges that must hold for any ${\\mathcal N}=2$ superconformal field theory.

  18. Integrability in N=2 superconformal gauge theories

    International Nuclear Information System (INIS)

    Pomoni, Elli; National Technical Univ. of Athens

    2013-10-01

    Any N=2 superconformal gauge theory (including N=4 SYM) contains a set of local operators made only out of fields in the N=2 vector multiplet that is closed under renormalization to all loops, namely the SU(2,1 vertical stroke 2) sector. For planar N=4 SYM the spectrum of local operators can be obtained by mapping the problem to an integrable model (a spin chain in perturbation theory), in principle for any value of the coupling constant. We present a diagrammatic argument that for any planar N=2 superconformal gauge theory the SU(2,1 vertical stroke 2) Hamiltonian acting on infinite spin chains is identical to all loops to that of N=4 SYM, up to a redefinition of the coupling constant. Thus, this sector is integrable and anomalous dimensions can be, in principle, read off from the N=4 ones up to this redefinition.

  19. Integrability in N=2 superconformal gauge theorie

    Energy Technology Data Exchange (ETDEWEB)

    Pomoni, Elli [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany). Theory Group; National Technical Univ. of Athens (Greece). Physics Div.

    2013-10-15

    Any N=2 superconformal gauge theory (including N=4 SYM) contains a set of local operators made only out of fields in the N=2 vector multiplet that is closed under renormalization to all loops, namely the SU(2,1 vertical stroke 2) sector. For planar N=4 SYM the spectrum of local operators can be obtained by mapping the problem to an integrable model (a spin chain in perturbation theory), in principle for any value of the coupling constant. We present a diagrammatic argument that for any planar N=2 superconformal gauge theory the SU(2,1 vertical stroke 2) Hamiltonian acting on infinite spin chains is identical to all loops to that of N=4 SYM, up to a redefinition of the coupling constant. Thus, this sector is integrable and anomalous dimensions can be, in principle, read off from the N=4 ones up to this redefinition.

  20. Contribution of dinitrogen fixation to bacterial and primary productivity in the Gulf of Aqaba (Red Sea)

    Science.gov (United States)

    Rahav, E.; Herut, B.; Mulholland, M. R.; Voß, B.; Stazic, D.; Steglich, C.; Hess, W. R.; Berman-Frank, I.

    2013-06-01

    We evaluated the seasonal contribution of heterotrophic and autotrophic diazotrophy to the total dinitrogen (N2) fixation in a representative pelagic station in the northern Gulf of Aqaba in early spring when the water column was mixed and during summer under full thermal stratification. N2 fixation rates were low during the mixed period (˜ 0.1 nmol N L-1 d-1) and were significantly coupled with both primary and bacterial productivity. During the stratified period N2 fixation rates were four-fold higher (˜ 0.4 nmol N L-1 d-1) and were significantly correlated solely with bacterial productivity. Furthermore, while experimental enrichment of seawater by phosphorus (P) enhanced bacterial productivity and N2 fixation rates during both seasons primary productivity was stimulated by P only in the early spring. Metatranscriptomic analyses from the stratified period identified the major diazotrophic contributors as related to heterotrophic prokaryotes from the Euryarchaeota and Desulfobacterales (Deltaproteobacteria) or Chlorobiales (Chlorobia). Moreover, during this season, experimental amendments to seawater applying a combination of the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and a mixture of amino acids increased both bacterial productivity and N2 fixation rates. Our findings from the northern Gulf of Aqaba indicate a~shift in the diazotrophic community from phototrophic and heterotrophic populations, including small blooms of the cyanobacterium Trichodesmium, in winter/early spring, to predominantly heterotrophic diazotrophs in summer that may be both P and carbon limited as the additions of P and amino acids illustrated.

  1. Co-inoculation of a Pea Core-Collection with Diverse Rhizobial Strains Shows Competitiveness for Nodulation and Efficiency of Nitrogen Fixation Are Distinct traits in the Interaction.

    Science.gov (United States)

    Bourion, Virginie; Heulin-Gotty, Karine; Aubert, Véronique; Tisseyre, Pierre; Chabert-Martinello, Marianne; Pervent, Marjorie; Delaitre, Catherine; Vile, Denis; Siol, Mathieu; Duc, Gérard; Brunel, Brigitte; Burstin, Judith; Lepetit, Marc

    2017-01-01

    Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum . The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation.

  2. Covariant n2-plet mass formulas

    International Nuclear Information System (INIS)

    Davidson, A.

    1979-01-01

    Using a generalized internal symmetry group analogous to the Lorentz group, we have constructed a covariant n 2 -plet mass operator. This operator is built as a scalar matrix in the (n;n*) representation, and its SU(n) breaking parameters are identified as intrinsic boost ones. Its basic properties are: covariance, Hermiticity, positivity, charge conjugation, quark contents, and a self-consistent n 2 -1, 1 mixing. The GMO and the Okubo formulas are obtained by considering two different limits of the same generalized mass formula

  3. Rotational Energy Transfer in N2

    Science.gov (United States)

    Huo, Winifred M.

    1994-01-01

    Using the N2-N2 intermolecular potential of van der Avoird et al. rotational energy transfer cross sections have been calculated using both the coupled state (CS) and infinite order sudden (IOS) approximations. The rotational energy transfer rate constants at 300 K, calculated in the CS approximation, are in reasonable agreement with the measurements of Sitz and Farrow. The IOS approximation qualitatively reproduces the dependence of the rate constants on the rotational quantum numbers, but consistently overestimates their magnitudes. The treatment of exchange symmetry will be discussed.

  4. N=2 Born-Infeld Attractors

    CERN Document Server

    Ferrara, S.; Sagnotti, A.

    2014-01-01

    We derive new types of $U(1)^n$ Born-Infeld actions based on N=2 special geometry in four dimensions. As in the single vector multiplet (n=1) case, the non--linear actions originate, in a particular limit, from quadratic expressions in the Maxwell fields. The dynamics is encoded in a set of coefficients $d_{ABC}$ related to the third derivative of the holomorphic prepotential and in an SU(2) triplet of N=2 Fayet-Iliopoulos charges, which must be suitably chosen to preserve a residual N=1 supersymmetry.

  5. Synthesis of Gemcitabine-13C, 15N2 and Gemcitabine-13C, 15N2 Metabolites

    Directory of Open Access Journals (Sweden)

    ZHU Cheng-gu;YANG Shao-zu;YAN Sheng-wang;FANG Ning-jing;CAI Ding-long;LI Gang

    2014-02-01

    Full Text Available Homemade urea-13C, 15N2 was used to react with 3-methyl acrylonitrile closure to form cytosine-13C, 15N2 (2,which was protected by trimethylsilylation with BSA and condensed with 2-deoxy-2,2-difluoro-D-erythro-pentofuranose-3,5-dibenzoate-1-methanesulfonate at 120 ℃ to afford blocked gemcitabine-13C, 15N2. Hydrolytic removal of the blocking groups of gemcitabine-13C, 15N2 with NaOH gave gemcitabine-13C, 15N2, and its metabolite was obtained by further hydrolytic deamination of gemcitabine-13C, 15N2. The final products were characterized and detected by HPLC, LC-MS and NMR, and confirmed that the chemical purities were higher than 98%, isotopic abundances were 99% 13C, 98% 15N, and they were suitable for drug metabolism studies.

  6. Understanding Nitrogen Fixation

    Energy Technology Data Exchange (ETDEWEB)

    Paul J. Chirik

    2012-05-25

    synthesis of ammonia, NH{sub 3}, from its elements, H{sub 2} and N{sub 2}, via the venerable Haber-Bosch process is one of the most significant technological achievements of the past century. Our research program seeks to discover new transition metal reagents and catalysts to disrupt the strong N {triple_bond} N bond in N{sub 2} and create new, fundamental chemical linkages for the construction of molecules with application as fuels, fertilizers and fine chemicals. With DOE support, our group has discovered a mild method for ammonia synthesis in solution as well as new methods for the construction of nitrogen-carbon bonds directly from N{sub 2}. Ideally these achievements will evolve into more efficient nitrogen fixation schemes that circumvent the high energy demands of industrial ammonia synthesis. Industrially, atmospheric nitrogen enters the synthetic cycle by the well-established Haber-Bosch process whereby N{sub 2} is hydrogenated to ammonia at high temperature and pressure. The commercialization of this reaction represents one of the greatest technological achievements of the 20th century as Haber-Bosch ammonia is responsible for supporting approximately 50% of the world's population and serves as the source of half of the nitrogen in the human body. The extreme reaction conditions required for an economical process have significant energy consequences, consuming 1% of the world's energy supply mostly in the form of pollution-intensive coal. Moreover, industrial H{sub 2} synthesis via the water gas shift reaction and the steam reforming of methane is fossil fuel intensive and produces CO{sub 2} as a byproduct. New synthetic methods that promote this thermodynamically favored transformation ({Delta}G{sup o} = -4.1 kcal/mol) under milder conditions or completely obviate it are therefore desirable. Most nitrogen-containing organic molecules are derived from ammonia (and hence rely on the Haber-Bosch and H{sub 2} synthesis processes) and direct synthesis from

  7. Flexible fixation and fracture healing

    DEFF Research Database (Denmark)

    Schmal, Hagen; Strohm, Peter C; Jaeger, Martin

    2011-01-01

    External and internal fixators use bone screws that are locked to a plate or bar to prevent periosteal compression and associated impairment of blood supply. Both osteosynthesis techniques rely on secondary bone healing with callus formation with the exception of compression plating of simple...

  8. Global trends and uncertainties in terrestrial denitrification and N2O emissions

    Science.gov (United States)

    Bouwman, A. F.; Beusen, A. H. W.; Griffioen, J.; Van Groenigen, J. W.; Hefting, M. M.; Oenema, O.; Van Puijenbroek, P. J. T. M.; Seitzinger, S.; Slomp, C. P.; Stehfest, E.

    2013-01-01

    Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr−1 (Tg = teragram; 1 Tg = 1012 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr−1 by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr−1, and this may remain stable or further increase to 275 Tg yr−1 by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr−1 between 1900 and 2000, and N2O–N emissions from 10 to 12 Tg N yr−1. The scenarios foresee a further increase to 142 Tg N2–N and 16 Tg N2O–N yr−1 by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O–N yr−1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans. PMID:23713114

  9. Tillage effects on N2O emission from soils under corn and soybeans in eastern Canada

    International Nuclear Information System (INIS)

    Gregorich, E.G.; St-Georges, P.; McKim, U.F.; Chan, C.; Rochette, P.

    2008-01-01

    New research has suggested that no-till agricultural practices will result in higher levels of nitrous oxide (N 2 O) emissions due to increased levels of denitrification. This study was evaluated and compared N 2 O emissions from tilled and no-till soils. Data used in the study were comprised of more than 1500 flux measurements of N 2 O taken between April and October over a period of 3 years at a site in Ottawa, Ontario. Soybean and corn crop rotations were used. Treatment effects of tillage, crop, and time of season on N 2 O fluxes were assessed using analysis of variance (ANOVA) methods. The study evaluated the responses of tillage during periods when soil temperatures were above 0 degrees C. Results of the studies demonstrated that fertilization management practices contributed to the higher N 2 O emissions observed in soils planted with corn when compared with soils planted with soybeans. Biological nitrogen (N) fixation in soybeans did not contribute to annual N 2 O emissions, and the effects of tillage on N 2 O emissions varied from year to year. The tilled soils typically had better aeration, higher temperatures, and lower water content than no-till soils. N 2 O emissions from no-till soils were lower than rates observed in tilled soils in 2 of the 3 years studied. Higher emissions observed in no-till soils were attributed to timing and the method of fertilizer placement. It was concluded that further studies are needed to develop methods of improving N use efficiency within tillage systems. 30 refs., 5 tabs., 2 figs

  10. Relative symbiont input and the lichen symbiotic outcome.

    Science.gov (United States)

    Spribille, Toby

    2018-03-09

    The term symbiosis was first used in biology to describe the 'living together' of fungi and algae in lichens. For much of the 20th century, the fungal partner was assumed to be invested with the ability to produce the lichen body plan in presence of a photosynthesizing partner. However, studies of fungal evolution have uncovered discordance between lichen symbiotic outcomes and genome evolution of the fungus. At the same time, evidence has emerged that the structurally important lichen cortex contains lichen-specific, single-celled microbes, suggesting it may function like a biofilm. Together, these observations suggest we may not have a complete overview of symbiotic interactions in lichens. Understanding phenotype development and evolution in lichens will require greater insight into fungal-fungal and fungal-bacterial interplay and the physical properties of the cortex. Copyright © 2018 Elsevier Ltd. All rights reserved.

  11. Symbiotic properties of Bradyrhizobium sp. (Lupinus assayed on serradella plants

    Directory of Open Access Journals (Sweden)

    Mieczysława Deryło

    2014-01-01

    Full Text Available Physiological and symbiotic properties of Bradyrhizobium sp. (Lupinus nodule isolates were compared to the standard slow-growing Bradyrhizobium sp. (Lupinus strain USDA 3045. Lupine nodules isolates showed typical characteristics for bradyrhizobial strains and nodulated small seed legume, serradella (Ornithopus sativus, in tube test. We observed a permanent physiological segregation of the effective (Fix' and ineffective (Fix- symbiotic phenotype for all tested bradyrhizobial strains during the growth of serradella in plant tube test. The ultrastructural differences between Fix* and Fix serradella nodules were observed. Rapid and visible nodulation as well as easy assay of the reduction of acetylene make serradella a convenient system for studies of Bradyrhizobium sp. (Lupinus strains in laboratory conditions.

  12. Leguminous plants: inventors of root nodules to accommodate symbiotic bacteria.

    Science.gov (United States)

    Suzaki, Takuya; Yoro, Emiko; Kawaguchi, Masayoshi

    2015-01-01

    Legumes and a few other plant species can establish a symbiotic relationship with nitrogen-fixing rhizobia, which enables them to survive in a nitrogen-deficient environment. During the course of nodulation, infection with rhizobia induces the dedifferentiation of host cells to form primordia of a symbiotic organ, the nodule, which prepares plants to accommodate rhizobia in host cells. While these nodulation processes are known to be genetically controlled by both plants and rhizobia, recent advances in studies on two model legumes, Lotus japonicus and Medicago truncatula, have provided great insight into the underlying plant-side molecular mechanism. In this chapter, we review such knowledge, with particular emphasis on two key processes of nodulation, nodule development and rhizobial invasion. Copyright © 2015 Elsevier Inc. All rights reserved.

  13. Flickering of the symbiotic variable CH Cygni during outburst

    International Nuclear Information System (INIS)

    Slovak, M.H.; Africano, J.

    1978-01-01

    High-speed and conventional BVRI photometry are reported for the bright symbiotic variable CH Cygni (M6 IIIe), obtained during the course of a recent outburst. Unlike the quiescent symbiotic stars, the presence of flickering similar in nature to that seen in the cataclysmic variables has been confirmed during this active phase. The BVRI photometry for a sample of stars in the field is used to derive the reddening and the distance to CH Cyg. A composite energy distribution is derived from 0.35 to 11.0 μm which clearly establishes the existence of a variable, blue continuum. The lack of variability in the near infrared suggests that the blue continuum arises from a hot companion. A binary model including a subluminous hot companion accreting material from the stellar wind of an SRa variable is discussed to account for the observed photometric properties. (author)

  14. Discovery of optical flickering from the symbiotic star EF Aquilae

    Science.gov (United States)

    Zamanov, R. K.; Boeva, S.; Nikolov, Y. M.; Petrov, B.; Bachev, R.; Latev, G. Y.; Popov, V. A.; Stoyanov, K. A.; Bode, M. F.; Martí, J.; Tomov, T.; Antonova, A.

    2017-07-01

    We report optical CCD photometry of the recently identified symbiotic star EF Aql. Our observations in Johnson V and B bands clearly show the presence of stochastic light variations with an amplitude of about 0.2 mag on a time scale of minutes. The observations point toward a white dwarf (WD) as the hot component in the system. It is the 11-th object among more than 200 symbiotic stars known with detected optical flickering. Estimates of the mass accretion rate onto the WD and the mass loss rate in the wind of the Mira secondary star lead to the conclusion that less than 1 per cent of the wind is captured by the WD. Eight further candidates for the detection of flickering in similar systems are suggested.

  15. Training Feedforward Neural Networks Using Symbiotic Organisms Search Algorithm.

    Science.gov (United States)

    Wu, Haizhou; Zhou, Yongquan; Luo, Qifang; Basset, Mohamed Abdel

    2016-01-01

    Symbiotic organisms search (SOS) is a new robust and powerful metaheuristic algorithm, which stimulates the symbiotic interaction strategies adopted by organisms to survive and propagate in the ecosystem. In the supervised learning area, it is a challenging task to present a satisfactory and efficient training algorithm for feedforward neural networks (FNNs). In this paper, SOS is employed as a new method for training FNNs. To investigate the performance of the aforementioned method, eight different datasets selected from the UCI machine learning repository are employed for experiment and the results are compared among seven metaheuristic algorithms. The results show that SOS performs better than other algorithms for training FNNs in terms of converging speed. It is also proven that an FNN trained by the method of SOS has better accuracy than most algorithms compared.

  16. Extremal black holes in N=2 supergravity

    NARCIS (Netherlands)

    Katmadas, S.

    2011-01-01

    An explanation for the entropy of black holes has been an outstanding problem in recent decades. A special case where this is possible is that of extremal black holes in N=2 supergravity in four and five dimensions. The best developed case is for black holes preserving some supersymmetry (BPS),

  17. N=2 supergravity in five dimensions revisited

    NARCIS (Netherlands)

    Bergshoeff, E; Cucu, S; de Wit, T; Gheerardyn, J; Vandoren, S; Van Proeyen, A

    2004-01-01

    We construct matter-coupled N = 2 supergravity in five dimensions, using the superconformal approach. For the matter sector we take an arbitrary number of vector, tensor and hypermultiplets. By allowing off-diagonal vector-tensor couplings we find more general results than currently known in the

  18. Plant, Microbiome, and Biogeochemistry: Quantifying moss-associated N fixation in Alaska

    Science.gov (United States)

    Stuart, J.; Mack, M. C.; Holland Moritz, H.; Fierer, N.; McDaniels, S.; Lewis, L.

    2017-12-01

    The future carbon (C) sequestration potential of the Arctic and boreal zones, currently the largest terrestrial C sink globally, is linked to nitrogen (N) cycling and N availability vis-a-vis C accumulation and plant species composition. Pristine environments in Alaska have low anthropogenic N deposition (<1 kg N ha-1 yr-1), and the main source of new N to these ecosystems is through previously overlooked N-fixation from microbial communities on mosses. Despite the importance of moss associated N-fixation, the relationship between moss species, microbial communities, and fixation rates remains ambiguous. In the summer of 2016, the fixation rates of 20 moss species from sites around both Fairbanks and Toolik Lake were quantified using 15N2 incubations. Subsequently, the microbial community and moss genome of the samples were also analyzed by collaborators. The most striking result is that all sampled moss genera fixed N, including well-studied feather mosses such as Hylocomium splendens and Pleurozium schreberi as well as less common but ecologically relevant mosses such as Aulacomnium spp., Dicranum spp., Ptilium crista-castrensis, and Tomentypnum nitens. Across all samples, preliminary fixation rates ranged from 0.004-19.994 µg N g-1 moss d-1. Depending upon percent cover, moss-associated N fixation is the largest input of new N to the ecosystem. Given this, linking variation in N-fixation rates to microbial and moss community structures can be helpful in predicting future trends of C and N cycling in northern latitudes. Vegetation changes, alterations in downstream biogeochemical N processes, and anthropogenic N deposition could all interact with or alter moss associated N-fixation, thereby changing ecosystem N inputs. Further elucidation of the species level signal in N-fixation rates and microbial community will augment our knowledge of N cycling in northern latitudes, both current and future.

  19. Nutrient acquisition by symbiotic fungi governs Palaeozoic climate transition.

    Science.gov (United States)

    Mills, Benjamin J W; Batterman, Sarah A; Field, Katie J

    2018-02-05

    Fossil evidence from the Rhynie chert indicates that early land plants, which evolved in a high-CO 2 atmosphere during the Palaeozoic Era, hosted diverse fungal symbionts. It is hypothesized that the rise of early non-vascular land plants, and the later evolution of roots and vasculature, drove the long-term shift towards a high-oxygen, low CO 2 climate that eventually permitted the evolution of mammals and, ultimately, humans. However, very little is known about the productivity of the early terrestrial biosphere, which depended on the acquisition of the limiting nutrient phosphorus via fungal symbiosis. Recent laboratory experiments have shown that plant-fungal symbiotic function is specific to fungal identity, with carbon-for-phosphorus exchange being either enhanced or suppressed under superambient CO 2 By incorporating these experimental findings into a biogeochemical model, we show that the differences in these symbiotic nutrient acquisition strategies could greatly alter the plant-driven changes to climate, allowing drawdown of CO 2 to glacial levels, and altering the nature of the rise of oxygen. We conclude that an accurate depiction of plant-fungal symbiotic systems, informed by high-CO 2 experiments, is key to resolving the question of how the first terrestrial ecosystems altered our planet.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'. © 2017 The Authors.

  20. Formulation of a peach ice cream as potential symbiotic food

    Directory of Open Access Journals (Sweden)

    Fernando Josué VILLALVA

    Full Text Available Abstract Today’s population increasingly demands and consumes healthy products. For this reason, the food industry has been developing and marketing food with added bioactive components. The aim of this work was to formulate a peach ice cream reduced in calories with an added probiotic (Bifidobacterium lactis Bb-12 and prebiotics (inulin, and to evaluate its sensory quality and acceptability as potential symbiotic food. The moisture content was 76.47%; 7.14% protein; 0.15% fat; 6.37%; carbohydrates; 9.87% inulin; 1.22% ash; 0.201% calcium, 0.155% phosphorus and 0.168% sodium. On the first and 21th day of storage counts of B. lactis Bb – 12 was 4 x 108 CFU/mL and 1.5 x 107 CFU/mL, respectively. It was possible to formulate a peach ice cream reduced in calories, fat, and sugar and with potential symbiotic effect, by addition of B. lactis Bb – 12. A product with suitable organoleptic characteristics, creamy texture, peachy colour, taste and flavour, and no ice crystals was obtained. This ice cream would be a suitable food matrix to incorporate prebiotic and probiotic ingredients as a potential symbiotic food.

  1. Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures.

    Science.gov (United States)

    Karakasli, Ahmet; Hapa, Onur; Erduran, Mehmet; Dincer, Cemal; Cecen, Berivan; Havitcioglu, Hasan

    2015-01-01

    For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues. Copyright © 2015 American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.

  2. Filtration via Conventional Glass Fiber Filters in 15N2 Tracer Assays Fails to Capture All Nitrogen-Fixing Prokaryotes

    OpenAIRE

    Deniz Bombar; Ryan W. Paerl; Ruth Anderson; Lasse Riemann

    2018-01-01

    Biological dinitrogen fixation (BNF) represents a major input of reduced nitrogen (N) to the oceans. Accurate direct measurements of BNF rates are crucial for reliably determining the biogeochemical significance of diazotrophy at local and global scales. Traditionally, borosilicate glass fiber filters (GF/F, Whatman) with a nominal pore size of 0.7 μm are used to collect suspended particles by filtration after incubations with added 15N2 tracer. We carried out BNF experiments in the Baltic Se...

  3. Anterior cervical decompression and fusion with caspar plate fixation

    International Nuclear Information System (INIS)

    Rehman, L.; Akbar, H.; Das, G.; Hashim, A.S.M.

    2013-01-01

    Objective: To evaluate the role of anterior cervical decompression and fixation with Caspar plating in cervical spine injury on neurological outcome. Study Design: A case series. Place and Duration of Study: Department of Neurosurgery, Jinnah Postgraduate Medical Centre, Karachi, from July 2008 to March 2011. Methodology: Thirty patients admitted with cervical spine injuries were inducted in the study. All cases were evaluated for their clinical features, level of injury and degree of neurological injury was assessed using Frankel grading. Pre and postoperative record with X-rays and MRI were maintained. Cervical traction was applied to patients with sub-luxation. All patients underwent anterior cervical decompression, fusion and Caspar plate fixation. The follow-up period was 6 months with clinical and radiological assessment. Results: Among 30 patients, 24 (80%) were males and 6 (20%) were females. Age ranged from 15 to 55 years. Causes of injury were road traffic accident (n = 20), fall (n = 8) and assault (n = 2). Commonest mode of injury was road traffic accident (66.6%). Postoperative follow-up showed that pain and neurological deficit were improved in 21 patients. There was no improvement in 7 patients, one patient deteriorated and one expired. All patients developed pain at donor site. Conclusion: Anterior decompression, fusion and fixation with Caspar plate is an effective method with good neurological and radiological outcome. However, it is associated with pain at donor site. (author)

  4. Isometries, gaugings and N=2 supergravity decoupling

    Energy Technology Data Exchange (ETDEWEB)

    Antoniadis, Ignatios [Laboratoire de Physique Théorique et Hautes Energies, Sorbonne Universités,CNRS UMR 7589, UPMC Paris 6, 4 place Jussieu, 75005 Paris (France); Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics,University of Bern,Sidlerstrasse 5, 3012 Bern (Switzerland); Derendinger, Jean-Pierre [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics,University of Bern,Sidlerstrasse 5, 3012 Bern (Switzerland); Petropoulos, P. Marios [Centre de Physique Théorique, Ecole Polytechnique, CNRS UMR 7644, Université Paris-Saclay,91128 Palaiseau Cedex (France); Laboratoire de Physique Théorique et Hautes Energies, Sorbonne Universités,CNRS UMR 7589, UPMC Paris 6, 4 place Jussieu, 75005 Paris (France); Siampos, Konstantinos [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics,University of Bern,Sidlerstrasse 5, 3012 Bern (Switzerland)

    2016-11-28

    We study off-shell rigid limits for the kinetic and scalar-potential terms of a single N=2 hypermultiplet. In the kinetic term, these rigid limits establish relations between four-dimensional quaternion-Kähler and hyper-Kähler target spaces with symmetry. The scalar potential is obtained by gauging the graviphoton along an isometry of the quaternion-Kähler space. The rigid limits unveil two distinct cases. A rigid N=2 theory on Minkowski or on AdS{sub 4} spacetime, depending on whether the isometry is translational or rotational respectively. We apply these results to the quaternion-Kähler space with Heisenberg⋉U(1) isometry, which describes the universal hypermultiplet at type-II string one-loop.

  5. On classification of N=2 supersymmetric theories

    International Nuclear Information System (INIS)

    Cecotti, S.; Vafa, C.

    1993-01-01

    We find a relation between the spectrum of solitons of massive N=2 quantum field theories in d=2 and the scaling dimensions of chiral fields at the conformal point. The condition that the scaling dimensions be real imposes restrictions on the soliton numbers and leads to a classification program for symmetric N=2 conformal theories and their massive deformations in terms of a suitable generalization of Dynkin diagrams (which coincides with the A-D-E Dynkin diagrams for minimal models). The Landau-Ginzburg theories are a proper subset of this classification. In the particular case of LG theories we relate the soliton numbers with intersection of vanishing cycles of the corresponding singularity; the relation between soliton numbers and the scaling dimensions in this particular case is a well known application of Picard-Lefschetz theory. (orig.)

  6. N=2 supersymmetric dynamics for pedestrians

    CERN Document Server

    Tachikawa, Yuji

    2015-01-01

    Understanding the dynamics of gauge theories is crucial, given the fact that all known interactions are based on the principle of local gauge symmetry. Beyond the perturbative regime, however, this is a notoriously difficult problem. Requiring invariance under supersymmetry turns out to be a suitable tool for analyzing supersymmetric gauge theories over a larger region of the space of parameters. Supersymmetric quantum field theories in four dimensions with extended N=2 supersymmetry are further constrained and have therefore been a fertile field of research in theoretical physics for quite some time. Moreover, there are far-reaching mathematical ramifications that have led to a successful dialogue with differential and algebraic geometry. These lecture notes aim to introduce students of modern theoretical physics to the fascinating developments in the understanding of N=2 supersymmetric gauge theories in a coherent fashion. Starting with a gentle introduction to electric-magnetic duality, the author guides r...

  7. Tetrachlorido[N2,N2′-(dimethylsilanediylbis(N-tert-butyl-3-methylbenzimidamidato-κ2N2,N2′]hafnium(IV

    Directory of Open Access Journals (Sweden)

    Sheng-Di Bai

    2013-12-01

    Full Text Available The symmetric title molecule, [Hf(C26H40N4SiCl4], lies about a twofold rotation axis. The HfIV and Si atoms lie on the rotation axis with all other atoms being in general positions. The HfIV atom is six-coordinated by two N atoms from the N2,N2′-(dimethylsilanediylbis(N-tert-butyl-3-methylbenzimidamidate ligand and four Cl− ions in a slightly distorted octahedral geometry. The two amidinate moieties are connected through the central Si atom with Si—N bond length of 1.762 (3 Å, generating the characteristic N—C—N—Si—N—C—N skeleton of a silyl-linked ansa-bis(amidine species.

  8. Phases of N = 2 necklace quivers

    Science.gov (United States)

    Amariti, Antonio; Orlando, Domenico; Reffert, Susanne

    2018-01-01

    We classify the phases of N = 2 elliptic models in terms of their global properties i.e. the spectrum of line operators. We show the agreement between the field theory and the M-theory analysis and how the phases form orbits under the action of the S-duality group which corresponds to the mapping class group of the Riemann surface in M-theory.

  9. N2O formation in combustion systems

    International Nuclear Information System (INIS)

    1989-11-01

    The objective of this project is to characterize N 2 O emissions from combustion sources emphasizing N 2 O emissions from post-combustion selective gas phase NO x reduction processes and reburning. The processes to be evaluated include ammonia, urea and cyanuric acid injection and reburning. The project includes pilot-scale testing at two facilities supported by chemical kinetic modeling. Testing will be performed on both a gas-fired plug flow combustor and a pulverized-coal fired combustor. Work performed to date has included the performance of the initial detailed chemical kinetics calculations. These calculations showed that both urea and cyanuric acid produce significant quantities of N 2 O, while NH 3 injection produced negligible amounts. These kinetics data support limited test results reported for cyanuric acid and ammonia injection. Laboratory work to evaluate the selective gas phase NO x reduction processes listed above will begin in the gas-fired facility early in CY 1990. Testing to evaluate reburning at the coal-fired facility is currently planned to be performed in parallel with the testing at the gas-fired facility. Following completion of that work, additional kinetics calculations will be performed

  10. [Ilizarov fixation of supramalleolar fractures].

    Science.gov (United States)

    Mseddi, M B E; Mseddi, M; Siala, A; Dahmene, J; Ben Hamida, R; Ben Ayeche, M

    2005-02-01

    Supramalleolar fractures are generally considered to be a difficult surgical challenge because they occur in a area where the tibia lies superficially with a precarious blood supply to the skin, exposing to the risk of infection and necrosis after internal fixation. These fractures are also situated close to the tibiotalar joint making centromedullary nailing difficult, even with distal locking. The Ilizarov external fixator could be an attractive alternative in this indication. We report a series of 17 supramalleolar fractures in 17 patients, 14 men and 3 women, treated with the Ilizarov external fixator between 1991 and 2001. Most were traffic accident victims and most had complex fractures resulting from high-energy trauma. There were many associated lesions. Fractures were open in ten patients. The Ilizarov fixator was used as the first intention treatment in seven patients and as a second line treatment in ten. The system allowed early weight bearing in all patients. Tolerance was generally good with a relatively low rate of superficial pin track infections (two cases). There was one case of osteitis which developed in a patient with an open fracture. There were no thromboembolic complications and no nerve involvement. Bone healing was achieved within three months in thirteen patients. There were three cases of late healing which were treated by the ascension technique using a cancellous graft and fibular osteotomy. The overall healing rate with this method was 94%. The one case of nonunion was successfully treated with an inter tibiofibular graft. The overall functional outcome was satisfactory in 76% of the patients, based on the Alho-Klemm criteria. Axial deformation predominated in the frontal plane: three patients had > 10 degrees varus in one case. These results could be improved by better operative technique. We advocate installing the patient in the supine position with transcalcaneal traction allowing good restitution of the leg axis. The assembly

  11. N2 fixing alder (Alnus viridis spp.fruticosa) effects on soil properties across a secondary successional chronosequence in interior Alaska

    Science.gov (United States)

    Jennifer S. Mitchell; Roger W. Ruess

    2009-01-01

    Green alder (Alnus viridis ssp. fruticosa) is a dominant understory shrub during secondary successional development of upland forests throughout interior Alaska, where it contributes substantially to the nitrogen (N) economy through atmospheric N2 fixation. Across a replicated 200+ year old vegetation...

  12. Diversity and Symbiotic Characteristics of Cowpea Bradyrhizobium Strains in Ghanaian Soils

    International Nuclear Information System (INIS)

    Fening, Joseph Opoku

    1999-08-01

    This study reports investigation of the biodiversity of bradyrhizobia isolates that nodulate cowpea in Ghanaian soils. As a prelude, some components of nitrogen fixation of cowpea in the various soils were examined through: (1) assessment of the natural nodulation of 45 cowpea cultivars in 20 soils sampled from 5 ecozones (coastal savanna, tain forest, semi deciduous forest, forest savanna transition and guinea savanna), (2) determination of the numbers of bradyrhizobial isolates in the soils and (3) determination of the response of cowpea to nitrogen fertilization. The results of the ability of 45 cowpea cultivars to nodulate naturally in different soil types showed large variability among the cultivars. Counts of the indigenous bradyrhizobia population in the soils showed that most of the soils in Ghana harbour large populations of bradyrhizobia (in the range of 0.6 x 10 to 31 x 10 3 ) capable of nodulating cowpea. Response of cowpea to nitrogen fertilizer differed in the different soils. In general all the cultivars showed significant responses to increasing levels of nitrogen, an indication that nitrogen fixation was not supplying the plants with all the external nitrogen required for maximum yield. A combination of morpho-physiological and molecular analysis was used to assess the diversity of the bradyrhizobia isolates. A total of 100 isolates were assessed. The results of the morpho physiological analysis indicated that cowpea is nodulated by both fast and slow growing rhizobia. The results also showed that the isolates were versatile and could survive under different soil conditions particularly acidity and salt stress. A cross inoculation study of the isolates with nine legume species produced seven major groupings with 28 subgroups based on distinct nodulation patterns. Results of the serology (ELISA) assay indicated that only a small fraction of the isolates reacted strongly with antisera of each other. The greater proportion showed no cross reactivity

  13. Smaller Fixation Target Size Is Associated with More Stable Fixation and Less Variance in Threshold Sensitivity.

    Directory of Open Access Journals (Sweden)

    Kazunori Hirasawa

    Full Text Available The aims of this randomized observational case control study were to quantify fixation behavior during standard automated perimetry (SAP with different fixation targets and to evaluate the relationship between fixation behavior and threshold variability at each test point in healthy young participants experienced with perimetry. SAP was performed on the right eyes of 29 participants using the Octopus 900 perimeter, program 32, dynamic strategy. The fixation targets of Point, Cross, and Ring were used for SAP. Fixation behavior was recorded using a wearable eye-tracking glass. All participants underwent SAP twice with each fixation target in a random fashion. Fixation behavior was quantified by calculating the bivariate contour ellipse area (BCEA and the frequency of deviation from the fixation target. The BCEAs (deg2 of Point, Cross, and Ring targets were 1.11, 1.46, and 2.02, respectively. In all cases, BCEA increased significantly with increasing fixation target size (p < 0.05. The logarithmic value of BCEA demonstrated the same tendency (p < 0.05. A positive correlation was identified between fixation behavior and threshold variability for the Point and Cross targets (ρ = 0.413-0.534, p < 0.05. Fixation behavior increased with increasing fixation target size. Moreover, a larger fixation behavior tended to be associated with a higher threshold variability. A small fixation target is recommended during the visual field test.

  14. The role of symbiotic nitrogen fixation in nitrogen availability, competition and plant invasion into the sagebrush steppe

    Science.gov (United States)

    Erin M. Goergen

    2009-01-01

    In the semi-arid sagebrush steppe of the Northeastern Sierra Nevada, resources are both spatially and temporally variable, arguably making resource availability a primary factor determining invasion success. N fixing plant species, primarily native legumes, are often relatively abundant in sagebrush steppe and can contribute to ecosystem nitrogen budgets. ...

  15. Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle.

    Science.gov (United States)

    Sullivan, Benjamin W; Smith, W Kolby; Townsend, Alan R; Nasto, Megan K; Reed, Sasha C; Chazdon, Robin L; Cleveland, Cory C

    2014-06-03

    Biological nitrogen fixation (BNF) is the largest natural source of exogenous nitrogen (N) to unmanaged ecosystems and also the primary baseline against which anthropogenic changes to the N cycle are measured. Rates of BNF in tropical rainforest are thought to be among the highest on Earth, but they are notoriously difficult to quantify and are based on little empirical data. We adapted a sampling strategy from community ecology to generate spatial estimates of symbiotic and free-living BNF in secondary and primary forest sites that span a typical range of tropical forest legume abundance. Although total BNF was higher in secondary than primary forest, overall rates were roughly five times lower than previous estimates for the tropical forest biome. We found strong correlations between symbiotic BNF and legume abundance, but we also show that spatially free-living BNF often exceeds symbiotic inputs. Our results suggest that BNF in tropical forest has been overestimated, and our data are consistent with a recent top-down estimate of global BNF that implied but did not measure low tropical BNF rates. Finally, comparing tropical BNF within the historical area of tropical rainforest with current anthropogenic N inputs indicates that humans have already at least doubled reactive N inputs to the tropical forest biome, a far greater change than previously thought. Because N inputs are increasing faster in the tropics than anywhere on Earth, both the proportion and the effects of human N enrichment are likely to grow in the future.

  16. Spatially robust estimates of biological nitrogen (N) fixation imply substantial human alteration of the tropical N cycle

    Science.gov (United States)

    Sullivan, Benjamin W.; Smith, William K.; Townsend, Alan R.; Nasto, Megan K.; Reed, Sasha C.; Chazdon, Robin L.; Cleveland, Cory C.

    2014-01-01

    Biological nitrogen fixation (BNF) is the largest natural source of exogenous nitrogen (N) to unmanaged ecosystems and also the primary baseline against which anthropogenic changes to the N cycle are measured. Rates of BNF in tropical rainforest are thought to be among the highest on Earth, but they are notoriously difficult to quantify and are based on little empirical data. We adapted a sampling strategy from community ecology to generate spatial estimates of symbiotic and free-living BNF in secondary and primary forest sites that span a typical range of tropical forest legume abundance. Although total BNF was higher in secondary than primary forest, overall rates were roughly five times lower than previous estimates for the tropical forest biome. We found strong correlations between symbiotic BNF and legume abundance, but we also show that spatially free-living BNF often exceeds symbiotic inputs. Our results suggest that BNF in tropical forest has been overestimated, and our data are consistent with a recent top-down estimate of global BNF that implied but did not measure low tropical BNF rates. Finally, comparing tropical BNF within the historical area of tropical rainforest with current anthropogenic N inputs indicates that humans have already at least doubled reactive N inputs to the tropical forest biome, a far greater change than previously thought. Because N inputs are increasing faster in the tropics than anywhere on Earth, both the proportion and the effects of human N enrichment are likely to grow in the future.

  17. Exopolysaccharides produced by the symbiotic nitrogen-fixing bacteria of leguminosae

    Directory of Open Access Journals (Sweden)

    Cleide Aparecida Bomfeti

    2011-06-01

    Full Text Available The process of biological nitrogen fixation (BNF, performed by symbiotic nitrogen fixing bacteria with legume species, commonly known as α and β rhizobia, provides high sustainability for the ecosystems. Its management as a biotechnology is well succeeded for improving crop yields. A remarkable example of this success is the inoculation of Brazilian soybeans with Bradyrhizobium strains. Rhizobia produce a wide diversity of chemical structures of exopolysaccharides (EPS. Although the role of EPS is relatively well studied in the process of BNF, their economic and environmental potential is not yet explored. These EPS are mostly species-specific heteropolysaccharides, which can vary according to the composition of sugars, their linkages in a single subunit, the repeating unit size and the degree of polymerization. Studies have showed that the EPS produced by rhizobia play an important role in the invasion process, infection threads formation, bacteroid and nodule development and plant defense response. These EPS also confer protection to these bacteria when exposed to environmental stresses. In general, strains of rhizobia that produce greater amounts of EPS are more tolerant to adverse conditions when compared with strains that produce less. Moreover, it is known that the EPS produced by microorganisms are widely used in various industrial activities. These compounds, also called biopolymers, provide a valid alternative for the commonly used in food industry through the development of products with identical properties or with better rheological characteristics, which can be used for new applications. The microbial EPS are also able to increase the adhesion of soil particles favoring the mechanical stability of aggregates, increasing levels of water retention and air flows in this environment. Due to the importance of EPS, in this review we discuss the role of these compounds in the process of BNF, in the adaptation of rhizobia to environmental

  18. Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation

    Science.gov (United States)

    Mohr, Wiebke; Vagner, Tomas; Kuypers, Marcel M. M.; Ackermann, Martin; LaRoche, Julie

    2013-01-01

    Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N2 fixation and photosynthesis commonly observed. However, N2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell. PMID:23805199

  19. Abnormal Fixational Eye Movements in Amblyopia.

    Science.gov (United States)

    Shaikh, Aasef G; Otero-Millan, Jorge; Kumar, Priyanka; Ghasia, Fatema F

    2016-01-01

    Fixational saccades shift the foveal image to counteract visual fading related to neural adaptation. Drifts are slow eye movements between two adjacent fixational saccades. We quantified fixational saccades and asked whether their changes could be attributed to pathologic drifts seen in amblyopia, one of the most common causes of blindness in childhood. Thirty-six pediatric subjects with varying severity of amblyopia and eleven healthy age-matched controls held their gaze on a visual target. Eye movements were measured with high-resolution video-oculography during fellow eye-viewing and amblyopic eye-viewing conditions. Fixational saccades and drifts were analyzed in the amblyopic and fellow eye and compared with controls. We found an increase in the amplitude with decreased frequency of fixational saccades in children with amblyopia. These alterations in fixational eye movements correlated with the severity of their amblyopia. There was also an increase in eye position variance during drifts in amblyopes. There was no correlation between the eye position variance or the eye velocity during ocular drifts and the amplitude of subsequent fixational saccade. Our findings suggest that abnormalities in fixational saccades in amblyopia are independent of the ocular drift. This investigation of amblyopia in pediatric age group quantitatively characterizes the fixation instability. Impaired properties of fixational saccades could be the consequence of abnormal processing and reorganization of the visual system in amblyopia. Paucity in the visual feedback during amblyopic eye-viewing condition can attribute to the increased eye position variance and drift velocity.

  20. Functional significance of dinitrogen fixation in sustaining coral productivity under oligotrophic conditions.

    Science.gov (United States)

    Cardini, Ulisse; Bednarz, Vanessa N; Naumann, Malik S; van Hoytema, Nanne; Rix, Laura; Foster, Rachel A; Al-Rshaidat, Mamoon M D; Wild, Christian

    2015-11-07

    Functional traits define species by their ecological role in the ecosystem. Animals themselves are host-microbe ecosystems (holobionts), and the application of ecophysiological approaches can help to understand their functioning. In hard coral holobionts, communities of dinitrogen (N2)-fixing prokaryotes (diazotrophs) may contribute a functional trait by providing bioavailable nitrogen (N) that could sustain coral productivity under oligotrophic conditions. This study quantified N2 fixation by diazotrophs associated with four genera of hermatypic corals on a northern Red Sea fringing reef exposed to high seasonality. We found N2 fixation activity to be 5- to 10-fold higher in summer, when inorganic nutrient concentrations were lowest and water temperature and light availability highest. Concurrently, coral gross primary productivity remained stable despite lower Symbiodinium densities and tissue chlorophyll a contents. In contrast, chlorophyll a content per Symbiodinium cell increased from spring to summer, suggesting that algal cells overcame limitation of N, an essential element for chlorophyll synthesis. In fact, N2 fixation was positively correlated with coral productivity in summer, when its contribution was estimated to meet 11% of the Symbiodinium N requirements. These results provide evidence of an important functional role of diazotrophs in sustaining coral productivity when alternative external N sources are scarce. © 2015 The Author(s).

  1. Diazotroph diversity and nitrogen fixation in the coral Stylophora pistillata from the Great Barrier Reef.

    Science.gov (United States)

    Lesser, Michael P; Morrow, Kathleen M; Pankey, Sabrina M; Noonan, Sam H C

    2018-03-01

    Diazotrophs, both Bacteria and Archaea, capable of fixing nitrogen (N 2 ), are present in the tissues and mucous, of corals and can supplement the coral holobiont nitrogen budget with fixed nitrogen (N) in the form of ammonia (NH 3 ). Stylophora pistillata from Heron Island on the Great Barrier Reef collected at 5 and 15 m, and experimentally manipulated in the laboratory, showed that the rates of net photosynthesis, steady state quantum yields of photosystem II (PSII) fluorescence (∆F v /F m ') and calcification varied based on irradiance as expected. Rates of N 2 fixation were, however, invariant across treatments while the amount of fixed N contributing to Symbiodinium spp. N demand is irradiance dependent. Additionally, both the Symbiodinium and diazotrophic communities are significantly different based on depth, and novel Cluster V nifH gene phylotypes, which are not known to fix nitrogen, were recovered. A functional analysis using PICRUSt also showed that shallow corals were enriched in genes involved in nitrogen metabolism, and N 2 fixation specifically. Corals have evolved a number of strategies to derive nitrogen from organic (e.g., heterotrophic feeding) and inorganic sources (e.g., N 2 fixation) to maintain critical pathways such as protein synthesis to succeed ecologically in nitrogen-limited habitats.

  2. Abnormal fixational eye movements in strabismus.

    Science.gov (United States)

    Ghasia, Fatema F; Otero-Millan, Jorge; Shaikh, Aasef G

    2018-02-01

    Fixational saccades are miniature eye movements that constantly change the gaze during attempted visual fixation. Visually guided saccades and fixational saccades represent an oculomotor continuum and are produced by common neural machinery. Patients with strabismus have disconjugate binocular horizontal saccades. We examined the stability and variability of eye position during fixation in patients with strabismus and correlated the severity of fixational instability with strabismus angle and binocular vision. Eye movements were measured in 13 patients with strabismus and 16 controls during fixation and visually guided saccades under monocular viewing conditions. Fixational saccades and intersaccadic drifts were analysed in the viewing and non-viewing eye of patients with strabismus and controls. We found an increase in fixational instability in patients with strabismus compared with controls. We also found an increase in the disconjugacy of fixational saccades and intrasaccadic ocular drift in patients with strabismus compared with controls. The disconjugacy was worse in patients with large-angle strabismus and absent stereopsis. There was an increase in eye position variance during drifts in patients with strabismus. Our findings suggest that both fixational saccades and intersaccadic drifts are abnormal and likely contribute to the fixational instability in patients with strabismus. Fixational instability could be a useful tool for mass screenings of children to diagnose strabismus in the absence of amblyopia and latent nystagmus. The increased disconjugacy of fixational eye movements and visually guided saccades in patients with strabismus reflects the disruption of the fine-tuning of the motor and visual systems responsible for achieving binocular fusion in these patients. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

  3. Genomes of three facultatively symbiotic Frankia sp. strainsreflect host plant biogeography

    Energy Technology Data Exchange (ETDEWEB)

    Normand, Philippe; Lapierre, Pascal; Tisa, Louis S.; Gogarten, J.Peter; Alloisio, Nicole; Bagnarol, Emilie; Bassi, Carla A.; Berry,Alison; Bickhart, Derek M.; Choisne, Nathalie; Couloux, Arnaud; Cournoyer, Benoit; Cruveiller, Stephane; Daubin, Vincent; Demange, Nadia; Francino, M. Pilar; Ggoltsman, Eugene; Huang, Ying; Kopp, Olga; Labarre,Laurent; Lapidus, Alla; Lavire, Celine; Marechal, Joelle; Martinez,Michele; Mastronunzio, Juliana E.; Mullin, Beth; Niemann, James; Pujic,Pierre; Rawnsley, Tania; Rouy, Zoe; Schenowitz, Chantal; Sellstedt,Anita; Tavares, Fernando; Tomkins, Jeffrey P.; Vallenet, David; Valverde,Claudio; Wall, Luis; Wang, Ying; Medigue, Claudine; Benson, David R.

    2006-02-01

    Filamentous actinobacteria from the genus Frankia anddiverse woody trees and shrubs together form N2-fixing actinorhizal rootnodule symbioses that are a major source of new soil nitrogen in widelydiverse biomes 1. Three major clades of Frankia sp. strains are defined;each clade is associated with a defined subset of plants from among theeight actinorhizal plant families 2,3. The evolution arytrajectoriesfollowed by the ancestors of both symbionts leading to current patternsof symbiont compatibility are unknown. Here we show that the competingprocesses of genome expansion and contraction have operated in differentgroups of Frankia strains in a manner that can be related to thespeciation of the plant hosts and their geographic distribution. Wesequenced and compared the genomes from three Frankia sp. strains havingdifferent host plant specificities. The sizes of their genomes variedfrom 5.38 Mbp for a narrow host range strain (HFPCcI3) to 7.50Mbp for amedium host range strain (ACN14a) to 9.08 Mbp for a broad host rangestrain (EAN1pec.) This size divergence is the largest yet reported forsuch closely related bacteria. Since the order of divergence of thestrains is known, the extent of gene deletion, duplication andacquisition could be estimated and was found to be inconcert with thebiogeographic history of the symbioses. Host plant isolation favoredgenome contraction, whereas host plant diversification favored genomeexpansion. The results support the idea that major genome reductions aswell as expansions can occur in facultatively symbiotic soil bacteria asthey respond to new environments in the context of theirsymbioses.

  4. Assessing the biological potential of N2-fixing Leguminosae in ...

    African Journals Online (AJOL)

    Administrator

    2007-02-19

    Feb 19, 2007 ... their symbiotic adaptation to this harsh environment. Yet few studies, if any, have ... this drought-prone, low-nutrient environment. Whether in .... Pisum sativum. Maun, Western, Gaborone, Central, Southern. Papilionaceae food. Cajanus cajan. Maun, Western, Gaborone, Central, Southern. Papilionaceae ...

  5. Ad-hoc Symbiotic Interactive Displays through DLNA

    DEFF Research Database (Denmark)

    Bitsch, Jannick Elimar; Bouvin, Niels Olof

    2012-01-01

    - tructure means that the concept has seen little use. We design and implement a solution for using DLNA playback devices as symbiotic screens. DLNA devices are not designed to support interactive content, but to share and play media content in the home. Our work includes constructing a mechanism for real...... time generation of a video stream containing screen content, as well as a buffer starving mechanism that reduces buffer induced playback latency. The resulting system allows Android applications to use DLNA devices as a secondary screens. Latencies and update rates are such, that only applications...

  6. Microsatellite Primers in the Lichen Symbiotic Alga Trebouxia decolorans (Trebouxiophyceae

    Directory of Open Access Journals (Sweden)

    Francesco Dal Grande

    2013-03-01

    Full Text Available Premise of the study: Polymorphic microsatellite markers were developed for the symbiotic green alga Trebouxia decolorans to study fine-scale population structure and clonal diversity. Methods and Results: Using Illumina pyrosequencing, 20 microsatellite primer sets were developed for T. decolorans. The primer sets were tested on 43 individuals sampled from four subpopulations in Germany. The primers amplified di-, tri-, and tetranucleotide repeats with three to 15 alleles per locus, and the unbiased haploid diversity per locus ranged from 0.636 to 0.821. Conclusions: The identified microsatellite markers will be useful to study the genetic diversity, dispersal, and reproductive mode of this common lichen photobiont.

  7. A multi-frequency study of symbiotic stars: Pt. 1

    International Nuclear Information System (INIS)

    Ivison, R.J.; Bode, M.F.; Roberts, J.A.

    1991-01-01

    The relationship between optical line flux and 5 GHz radio flux is investigated for a sample of 17 northern sky symbiotic stars. Data were obtained near-simultaneously with the Manchester Echelle Spectrograph mounted on the Isaac Newton Telescope, La Palma and the Broad Band Interferometer at Jodrell Bank. Colour excesses, calculated from Balmer hydrogen line fluxes assuming Case B recombination ratios, are compared with other reddening estimates and also combined with extinction maps to provide improved distance estimates. Optical line fluxes are used in combination with radio fluxes to estimate physical parameters of these objects, including mass-loss rates. (author)

  8. The 1982 ultraviolet eclipse of the symbiotic binary AR Pav

    Science.gov (United States)

    Hutchings, J. B.; Cowley, A. P.; Ake, T. B.; Imhoff, C. L.

    1983-01-01

    Observations with the International Ultraviolet Explorer (IUE) of the symbiotic binary AR Pav through its 1982 eclipse show that the hot star is not eclipsed. The hot star is associated with an extended region of continuum emission which is partially eclipsed. The eclipsed radiation is hotter near to its center, with a maximum temperature of about 9000 K. The uneclipsed flux is hotter than this. UV emission lines are not measurably eclipsed and presumably arise in a much larger region than the continuum. These data provide new constraints on models of the system but also are apparently in contradiction to those based on ground-based data.

  9. On the nature of the symbiotic binary CI Cygni

    International Nuclear Information System (INIS)

    Kenyon, S.J.; Oliversen, N.A.; Mikolajewska, J.; Mikolajewski, M.; Stencel, R.E.

    1991-01-01

    An analysis of ultraviolet and optical spectroscopy is presented for the symbiotic binary CI Cyg. This system contains an M5 II asymptotic branch giant Mg of about 1.5 solar mass, transfering material at a few times 0.00001 solar mass/yr into a large accretion disk surrounding a main-sequence star with Mh of about 0.5 solar mass. A boundary layer at the inner edge of the disk photoionizes a small nebula approximately confined to the Roche volume of the accreting star. An extended, more highly ionized region forms when material ejected from the disk interacts with the red giant wind. 115 refs

  10. Symbiotic and nonsymbiotic hemoglobin genes of Casuarina glauca

    DEFF Research Database (Denmark)

    Jacobsen-Lyon, K; Jensen, Erik Østergaard; Jørgensen, Jan-Elo

    1995-01-01

    Casuarina glauca has a gene encoding hemoglobin (cashb-nonsym). This gene is expressed in a number of plant tissues. Casuarina also has a second family of hemoglobin genes (cashb-sym) expressed at a high level in the nodules that Casuarina forms in a nitrogen-fixing symbiosis with the actinomycete...... of the Casuarina gene. The finding that the nonsymbiotic Casuarina gene is also correctly expressed in L. corniculatus suggests to us that a comparable non-symbiotic hemoglobin gene will be found in legume species. Udgivelsesdato: 1995-Feb...

  11. The cyanobacterial nitrogen fixation paradox in natural waters [version 1; referees: 2 approved

    Directory of Open Access Journals (Sweden)

    Hans Paerl

    2017-03-01

    Full Text Available Nitrogen fixation, the enzymatic conversion of atmospheric N (N2 to ammonia (NH3, is a microbially mediated process by which “new” N is supplied to N-deficient water bodies. Certain bloom-forming cyanobacterial species are capable of conducting N2 fixation; hence, they are able to circumvent N limitation in these waters. However, this anaerobic process is highly sensitive to oxygen, and since cyanobacteria produce oxygen in photosynthesis, they are faced with a paradoxical situation, where one critically important (for supporting growth biochemical process is inhibited by another. N2-fixing cyanobacterial taxa have developed an array of biochemical, morphological, and ecological adaptations to minimize the “oxygen problem”; however, none of these allows N2 fixation to function at a high enough efficiency so that it can supply N needs at the ecosystem scale, where N losses via denitrification, burial, and advection often exceed the inputs of “new” N by N2 fixation. As a result, most marine and freshwater ecosystems exhibit chronic N limitation of primary production. Under conditions of perpetual N limitation, external inputs of N from human sources (agricultural, urban, and industrial play a central role in determining ecosystem fertility and, in the case of N overenrichment, excessive primary production or eutrophication. This points to the importance of controlling external N inputs (in addition to traditional phosphorus controls as a means of ensuring acceptable water quality and safe water supplies. Nitrogen fixation, the enzymatic conversion of atmospheric N2 to ammonia (NH3 is a  microbially-mediated process by which “new” nitrogen is supplied to N-deficient water bodies.  Certain bloom-forming cyanobacterial species are capable of conducting N2 fixation; hence they are able to circumvent nitrogen limitation in these waters. However, this anaerobic process is highly sensitive to oxygen, and since cyanobacteria produce

  12. Overcoming fixation with repeated memory suppression.

    Science.gov (United States)

    Angello, Genna; Storm, Benjamin C; Smith, Steven M

    2015-01-01

    Fixation (blocks to memories or ideas) can be alleviated not only by encouraging productive work towards a solution, but, as the present experiments show, by reducing counterproductive work. Two experiments examined relief from fixation in a word-fragment completion task. Blockers, orthographically similar negative primes (e.g., ANALOGY), blocked solutions to word fragments (e.g., A_L_ _GY) in both experiments. After priming, but before the fragment completion test, participants repeatedly suppressed half of the blockers using the Think/No-Think paradigm, which results in memory inhibition. Inhibiting blockers did not alleviate fixation in Experiment 1 when conscious recollection of negative primes was not encouraged on the fragment completion test. In Experiment 2, however, when participants were encouraged to remember negative primes at fragment completion, relief from fixation was observed. Repeated suppression may nullify fixation effects, and promote creative thinking, particularly when fixation is caused by conscious recollection of counterproductive information.

  13. Evaluating the impact of atmospheric depositions on springtime dinitrogen fixation in the Cretan Sea (Eastern Mediterranean - A mesocosm approach

    Directory of Open Access Journals (Sweden)

    Eyal Rahav

    2016-09-01

    Full Text Available Large amounts of dust and atmospheric aerosols, originating from surrounding desert areas (e.g., Sahara and Middle East are deposited annually on the surface of the Eastern Mediterranean Sea. These depositions can provide high amounts of micro (such as Fe, Zn, Co and macro nutrients (such as P and N to supplement nutrient-poor surface waters- that typically limit primary productivity and also dinitrogen (N2 fixation in many marine environments. Here, we studied the impact of the atmospheric deposition of dust and aerosols on N2 fixation in the Cretan Sea (Eastern Mediterranean Sea. Mixed polluted aerosols (hereafter A and Saharan dust (hereafter SD were added to nine mesocosms (3-m3 each containing surface mixed layer seawater (~10 m, and N2 fixation was evaluated for 6 days during May 2012 (springtime. The addition of SD triggered a rapid (30 h and robust (2-4 fold increase in N2 fixation rates that remained high for 6 days and contributed 3-8% of the primary productivity. The A addition also resulted in higher N2 fixation rates compared to the unamended control mesocosms, although the responses were less profound (1.5-2 fold and accounted for only 2-4% of the primary productivity. The microbial community responded differently to the two additions. Heterotrophic bacterial N2 fixers dominated the diazotroph community in A and the control mesocosms, while the non-filamentous cyanobacterial group Trichodesmium prevailed in the SD treatment (68% of all the operational taxonomic units, verified by qPCR analyses. Our results indicate that the aerosol source, its route prior to deposition, and its specific chemical composition, can alter the diazotrophic diversity and activity in the Eastern Mediterranean Sea and may thus impact both the N and C dynamics in this impoverished environment.

  14. Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene

    Science.gov (United States)

    Landolfi, A.; Somes, C. J.; Koeve, W.; Zamora, L. M.; Oschlies, A.

    2017-08-01

    There is currently no consensus on how humans are affecting the marine nitrogen (N) cycle, which limits marine biological production and CO2 uptake. Anthropogenic changes in ocean warming, deoxygenation, and atmospheric N deposition can all individually affect the marine N cycle and the oceanic production of the greenhouse gas nitrous oxide (N2O). However, the combined effect of these perturbations on marine N cycling, ocean productivity, and marine N2O production is poorly understood. Here we use an Earth system model of intermediate complexity to investigate the combined effects of estimated 21st century CO2 atmospheric forcing and atmospheric N deposition. Our simulations suggest that anthropogenic perturbations cause only a small imbalance to the N cycle relative to preindustrial conditions (˜+5 Tg N y-1 in 2100). More N loss from water column denitrification in expanded oxygen minimum zones (OMZs) is counteracted by less benthic denitrification, due to the stratification-induced reduction in organic matter export. The larger atmospheric N load is offset by reduced N inputs by marine N2 fixation. Our model predicts a decline in oceanic N2O emissions by 2100. This is induced by the decrease in organic matter export and associated N2O production and by the anthropogenically driven changes in ocean circulation and atmospheric N2O concentrations. After comprehensively accounting for a series of complex physical-biogeochemical interactions, this study suggests that N flux imbalances are limited by biogeochemical feedbacks that help stabilize the marine N inventory against anthropogenic changes. These findings support the hypothesis that strong negative feedbacks regulate the marine N inventory on centennial time scales.

  15. Phylogenetic diversity of nitrogen fixation genes in the intestinal tract of Reticulitermes chinensis Snyder.

    Science.gov (United States)

    Du, Xin; Li, Xiaojuan; Wang, Yin; Peng, Jianxin; Hong, Huazhu; Yang, Hong

    2012-11-01

    Wood-feeding termites live on cellulolytic materials that typically lack of nitrogen sources. It was reported that symbiotic microbes play important roles in the maintenance of a normal nitrogen contents in termite by different metabolisms including nitrogen fixation. In this study, the diversity of nitrogen-fixing organisms in the symbiotic intestinal microflora of Reticulitermes chinensis Snyder was investigated with culture independent method. Fragments of the nifH genes, which encode dinitrogenase reductase, were directly amplified from the DNA of the mixed microbial population in the termite gut with four sets of primers corresponding to the conserved regions of the genes. Clones were randomly selected and analyzed by RFLP. Sequence analysis revealed that a large number of nifH sequences retrieved from the termite gut were most closely related to strict anaerobic bacteria such as clostridia and spirochetes, some of the others were affiliated with proteobacteria, bacteroides, or methanogenic archaea. The results showed that there was a remarkable diversity of nitrogenase genes in the gut of Reticulitermes chinensis Snyder.

  16. Nitrogen fixation in Acacia auriculiformis and Albizia lebbeck and their contributions to crop-productivity improvement

    International Nuclear Information System (INIS)

    Mbaya, N.; Mwange, K.Nk.; Luyindula, N.

    1998-01-01

    Pot and field experiments assessed N 2 fixation by Albizia lebbeck and Acacia auriculiformis and contributions from prunings to yields of corn and hibiscus. Nitrogen fixation in these tree legumes was poor, with less than 50% N derived from fixation (%Ndfa) when grown in pots, but higher (>70%) in field conditions, after inoculation with compatible Bradyrhizobium strains. Prunings from A. lebbeck, as green manure improved growth of maize and hibiscus, inducing greater corn-kernel yields than did urea. Acacia auriculiformis prunings were similarly beneficial when mixed with leaves of A. lebbeck or L. leucocephala. Application of slow- and fast-nutrient-releasing leaves is required to maximize their contributions to crop productivity. (author)

  17. Nitrogen fixation method and apparatus

    Science.gov (United States)

    Chen, H.L.

    1983-08-16

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O[sub 2]/cm promotes the formation of vibrationally excited N[sub 2]. Atomic oxygen interacts with vibrationally excited N[sub 2] at a much quicker rate than unexcited N[sub 2], greatly improving the rate at which NO is formed. 1 fig.

  18. Polymeric media for tritium fixation. Supplement I

    International Nuclear Information System (INIS)

    Franz, J.A.; Burger, L.L.

    1976-01-01

    Procedures for the fixation of tritium as TH or THO in two different polymeric media are described. The complete procedure for THO fixation in a polyureylene-polyurethane polumer, including polymer molding procedures and leach tests is presented. The catalytic tritiation of polystyrene under very mild conditions using a rhodium catalyst is also described. Thermal stabilities and cost estimates for the polymers examined under this program are discussed. Organic polymers were found to have attractive features for the fixation and storage of concentrated tritium wastes due to the convenience of fixation procedures and favorable properties of the resulting media

  19. Percutaneous Fixation of Displaced Calcaneal Fracture

    Directory of Open Access Journals (Sweden)

    Yeung Yip-Kan

    2011-06-01

    Conclusion: Percutaneous fixation of displaced tongue-type calcaneal fractures is an effective treatment with acceptable clinical outcome, short hospital stay, minimal skin complications, and quick recovery.

  20. A symbiosome membrane is not required for the actions of two host signalling compounds regulating photosynthesis in symbiotic algae isolated from cnidarians.

    Science.gov (United States)

    Grant, A J; Trautman, D A; Frankland, S; Hinde, R

    2003-06-01

    In many cnidarians, symbiotic algae live within host-derived symbiosomes. We determined whether a symbiosome membrane alters the response of isolated symbiotic algae to two signalling compounds that regulate algal carbon metabolism. Host release factor (HRF), which stimulates photosynthate release, and photosynthesis inhibiting factor (PIF), which inhibits photosynthetic carbon fixation, are found in homogenised tissue of the scleractinian coral Plesiastrea versipora. Compared with seawater controls, photosynthate release from isolated algae incubated in P. versipora homogenate for 2 h in the light was: 6 to 19-fold higher from its own algae (free of symbiosomes); 19 to 32-fold higher from Zoanthid robustus algae (within symbiosomes) and 3 to 24-fold higher from Z. robustus algae (free of symbiosomes); and from cultured algae (free of symbiosomes) was seven-fold higher from Montipora verrucosa and four-fold higher from Cassiopeia xamachana. Incubation of algae in P. versipora homogenate inhibited photosynthesis by: 33-49% in P. versipora algae; 29-47% in Z. robustus algae (regardless of whether or not the symbiosome was present); and 25% in M. verrucosa algae. In C. xamachana algae, photosynthesis increased. We conclude that the symbiosome is not essential for, yet does not block, the effects of HRF and PIF.

  1. Nonlegume Parasponia andersonii deploys a broad rhizobium host range strategy resulting in largely variable symbiotic effectiveness

    NARCIS (Netherlands)

    Camp, op den R.H.M.; Polone, E.; Fedorova, E.; Roelofsen, W.; Squartini, A.; Camp, op den H.J.M.; Bisseling, T.; Geurts, R.

    2012-01-01

    The non-legume genus Parasponia has evolved the rhizobium symbiosis independent from legumes and has done so only recently. We aim to study the promiscuity of such newly evolved symbiotic engagement and determine the symbiotic effectiveness of infecting rhizobium species. It was found that

  2. Effect of Subliminal Stimulation of Symbiotic Fantasies on College Student Self-Disclosure in Group Counseling.

    Science.gov (United States)

    Linehan, Edward; O'Toole, James

    1982-01-01

    Studied subliminal symbiotic stimulation as a treatment aid in conjunction with counselor self-disclosures in group counseling. Results showed that subliminal exposure to MOMMY AND I ARE ONE stimulus would lead to more client self-disclosures in group counseling. Suggests impact of symbiotic stimulus can be affected by counselor behavior. (RC)

  3. Gene expression in gut symbiotic organ of stinkbug affected by extracellular bacterial symbiont.

    Directory of Open Access Journals (Sweden)

    Ryo Futahashi

    Full Text Available The bean bug Riptortus pedestris possesses a specialized symbiotic organ in a posterior region of the midgut, where numerous crypts harbor extracellular betaproteobacterial symbionts of the genus Burkholderia. Second instar nymphs orally acquire the symbiont from the environment, and the symbiont infection benefits the host by facilitating growth and by occasionally conferring insecticide resistance. Here we performed comparative transcriptomic analyses of insect genes expressed in symbiotic and non-symbiotic regions of the midgut dissected from Burkholderia-infected and uninfected R. pedestris. Expression sequence tag analysis of cDNA libraries and quantitative reverse transcription PCR identified a number of insect genes expressed in symbiosis- or aposymbiosis-associated patterns. For example, genes up-regulated in symbiotic relative to aposymbiotic individuals, including many cysteine-rich secreted protein genes and many cathepsin protease genes, are likely to play a role in regulating the symbiosis. Conversely, genes up-regulated in aposymbiotic relative to symbiotic individuals, including a chicken-type lysozyme gene and a defensin-like protein gene, are possibly involved in regulation of non-symbiotic bacterial infections. Our study presents the first transcriptomic data on gut symbiotic organ of a stinkbug, which provides initial clues to understanding of molecular mechanisms underlying the insect-bacterium gut symbiosis and sheds light on several intriguing commonalities between endocellular and extracellular symbiotic associations.

  4. The response of Anabaena -free Azolla and the symbiotic Azolla to ...

    African Journals Online (AJOL)

    The performance of Anabaena-free (algae free) and symbiotic types of three speeies of Azolla (A. filiculoides, A. pinnata and A. microphylla) were studied in a phytotron at two average temperatures (22 and 33 oC). The growth of both the Anabaena-free and symbiotic types were depressed at a high temperature (33 DC) to ...

  5. Effects of plant breeding and selection on yields and nitrogen fixation in soybeans under two soil nitrogen regimes

    International Nuclear Information System (INIS)

    Coale, F.J.; Meisinger, J.J.; Wiebold, W.J.

    1985-01-01

    Soybeans (Glycine max (L.) Merr.) have a high N requirement which is fulfilled by soil N uptake and N 2 -fixation. This study was concerned with the effects of past yield selection on N 2 -fixation in soybeans. The soybean cultivars, ‘Lincoln’, ‘Shelby’, and ‘Williams’, which represent successive improvements in the ‘Lincoln’ germplasm, and a non-nodulating control were planted in a soil containing 15 N labelled organic matter. Two replications occurred on soil previously cropped to alfalfa and two on soil previously cropped to soybeans. Plants were harvested at five growth stages and leaf area, plant weight, total N, and atom percent 15 N were determined. Mature grain was harvested and yield components were also determined, as well as the total N and 15 N content. Cultivar differences in total dry matter were only evident at physiological maturity, when Williams contained the greatest dry matter. Williams exhibited the longest period of seed formation and seed fill and also had the highest grain yield which resulted from a larger weight per seed. The N content of the cultivars did not vary until physiological maturity when Williams contained the highest percent N. The quantity of N fixed at physiological maturity was highest for Williams and lowest for Lincoln. Fixed N contained in the harvested grain was greater for Williams than for the other two cultivars. The fraction of the total plant N derived from fixation was not greatly affected by cultivar and all cultivars acquired an average of 50% of their total N through N 2 -fixation. Previous cropping history greatly affected the quantity of N fixed and the fraction of the total plant N derived from fixation. Soybeans following soybeans were more dependent upon N 2 -fixation than soybeans following alfalfa with the former deriving 65% of the total plant N from fixation and the latter only 32%. These soybean cultivars apparently utilized soil N first and then used N 2 -fixation to satisfy their N

  6. Symbiotic propagation of seedlings of Cyrtopodium glutiniferum Raddi (Orchidaceae

    Directory of Open Access Journals (Sweden)

    Fernanda Aparecida Rodrigues Guimarães

    2013-09-01

    Full Text Available In nature, orchid seeds obtain the nutrients necessary for germination by degrading intracellular fungal structures formed after colonization of the embryo by mycorrhizal fungi. Protocols for asymbiotic germination of orchid seeds typically use media with high concentrations of soluble carbohydrate and minerals. However, when reintroduced into the field, seedlings obtained via asymbiotic germination have lower survival rates than do seedlings obtained via symbiotic germination. Tree fern fiber, the ideal substrate for orchid seedling acclimatization, is increasingly scarce. Here, we evaluated seed germination and protocorm development of Cyrtopodium glutiniferum Raddi cultivated in asymbiotic media (Knudson C and Murashige & Skoog and in oatmeal agar (OA medium inoculated with the mycorrhizal fungus Epulorhiza sp., using non-inoculated OA medium as a control. We also evaluated the performance of tree fern fiber, pine bark, eucalyptus bark, corncob and sawdust as substrates for the acclimatization of symbiotically propagated plants. We determined germination percentages, protocorm development and growth indices at 35 and 70 days of cultivation. Relative growth rates and the effects of substrates on mycorrhizal formation were calculated after 165 days of cultivation. Germination efficiency and growth indices were best when inoculated OA medium was used. Corncob and pine bark showed the highest percentages of colonized system roots. The OA medium inoculated with Epulorhiza sp. shows potential for C. glutiniferum seedling production. Corncob and pine bark are promising substitutes for tree fern fiber as substrates for the acclimatization of orchid seedlings.

  7. Concept evaluation of nuclear fusion driven symbiotic energy systems

    International Nuclear Information System (INIS)

    Renier, J.P.; Hoffman, T.J.

    1979-01-01

    This paper analyzes systems based on D-T and semi-catalyzed D-D fusion-powered U233 breeders. Two different blanket types were used: metallic thorium pebble-bed blankets with a batch reprocessing mode and a molten salt blanket with on-line continuous or batch reprocessing. All fusion-driven blankets are assumed to have spherical geometries, with a 85% closure. Neutronics depletion calculations were performed with a revised version of the discrete ordinates code XSDRN-PM, using multigroup (100 neutron, 21 gamma-ray groups) coupled cross-section libraries. These neutronics calculations are coupled with a scenario optimization and cost analysis code. Also, the fusion burn was shaped so as to keep the blanket maximum power density below a preset value, and to improve the performance of the fusion-driven systems. The fusion-driven symbiotes are compared with LMFBR-driven energy systems. The nuclear fission breeders that were used as drivers have parameters characteristic of heterogeneous, oxide LMFBRs. They are net plutonium users - the plutonium is obtained from the discharges of LWRs - and U233 is bred in the fission breeder thorium blankets. The analyses of the symbiotic energy systems were performed at equilibrium, at maximum rate of grid expansion, and for a given nuclear power demand

  8. Symbiotic symbolization by hand and mouth in sign language.

    Science.gov (United States)

    Sandler, Wendy

    2009-04-01

    Current conceptions of human language include a gestural component in the communicative event. However, determining how the linguistic and gestural signals are distinguished, how each is structured, and how they interact still poses a challenge for the construction of a comprehensive model of language. This study attempts to advance our understanding of these issues with evidence from sign language. The study adopts McNeill's criteria for distinguishing gestures from the linguistically organized signal, and provides a brief description of the linguistic organization of sign languages. Focusing on the subcategory of iconic gestures, the paper shows that signers create iconic gestures with the mouth, an articulator that acts symbiotically with the hands to complement the linguistic description of objects and events. A new distinction between the mimetic replica and the iconic symbol accounts for the nature and distribution of iconic mouth gestures and distinguishes them from mimetic uses of the mouth. Symbiotic symbolization by hand and mouth is a salient feature of human language, regardless of whether the primary linguistic modality is oral or manual. Speakers gesture with their hands, and signers gesture with their mouths.

  9. Symbiotic symbolization by hand and mouth in sign language*

    Science.gov (United States)

    Sandler, Wendy

    2010-01-01

    Current conceptions of human language include a gestural component in the communicative event. However, determining how the linguistic and gestural signals are distinguished, how each is structured, and how they interact still poses a challenge for the construction of a comprehensive model of language. This study attempts to advance our understanding of these issues with evidence from sign language. The study adopts McNeill’s criteria for distinguishing gestures from the linguistically organized signal, and provides a brief description of the linguistic organization of sign languages. Focusing on the subcategory of iconic gestures, the paper shows that signers create iconic gestures with the mouth, an articulator that acts symbiotically with the hands to complement the linguistic description of objects and events. A new distinction between the mimetic replica and the iconic symbol accounts for the nature and distribution of iconic mouth gestures and distinguishes them from mimetic uses of the mouth. Symbiotic symbolization by hand and mouth is a salient feature of human language, regardless of whether the primary linguistic modality is oral or manual. Speakers gesture with their hands, and signers gesture with their mouths. PMID:20445832

  10. Ecology of planktonic foraminifera and their symbiotic algae

    International Nuclear Information System (INIS)

    Gastrich, M.D.

    1986-01-01

    Two types of symbiotic algae occurred abundantly and persistently in the cytoplasm of several species of planktonic Foraminifera over a ten year period in different tropical and subtropical areas of the North Atlantic Ocean. These planktonic Foraminifera host species consistently harbored either dinoflagellates or a newly described minute coccoid algal type. There appeared to be a specific host-symbiont relationship in these species regardless of year, season or geographic locality. The larger ovoid dinoflagellates (Pyrrhophycophyta) occur in the spinose species Globigerinoides ruber, Globigerinoides sacculifer, G. conglobatus and Orbulina universa. The smaller alga, from 1.5 to 3.5 um in diameter, occurs in one spinose species Globigerinella aequilateralis and also in the non-spinose species Globigerinita glutinata, Globoquadrina dutertrei, Globorotalia menardii, Globorotalia cristata, Globorotalia inflata, Candeina nitida, in various juvenile specimens and at all seasons except the winter months in Pulleniatina obliquiloculata and Globorotalial hirsuta. Controlled laboratory studies indicated a significant C incorporation into the host cytoplasm and inorganic calcium carbonate test of Globigerinoides ruber. During incubation for up to two hours, the 14 C uptake into the cytoplasm and test in the light was significantly greater than uptake in the dark by living specimens or by dead foraminifers. There appears to be light-enhanced uptake of 14 C into the test with dinoflagellate photosynthesis contributing to host calcification. In culture, symbiotic algae were observed to survive for the duration of the lifespan of their hosts

  11. Adaptive symbiotic organisms search (SOS algorithm for structural design optimization

    Directory of Open Access Journals (Sweden)

    Ghanshyam G. Tejani

    2016-07-01

    Full Text Available The symbiotic organisms search (SOS algorithm is an effective metaheuristic developed in 2014, which mimics the symbiotic relationship among the living beings, such as mutualism, commensalism, and parasitism, to survive in the ecosystem. In this study, three modified versions of the SOS algorithm are proposed by introducing adaptive benefit factors in the basic SOS algorithm to improve its efficiency. The basic SOS algorithm only considers benefit factors, whereas the proposed variants of the SOS algorithm, consider effective combinations of adaptive benefit factors and benefit factors to study their competence to lay down a good balance between exploration and exploitation of the search space. The proposed algorithms are tested to suit its applications to the engineering structures subjected to dynamic excitation, which may lead to undesirable vibrations. Structure optimization problems become more challenging if the shape and size variables are taken into account along with the frequency. To check the feasibility and effectiveness of the proposed algorithms, six different planar and space trusses are subjected to experimental analysis. The results obtained using the proposed methods are compared with those obtained using other optimization methods well established in the literature. The results reveal that the adaptive SOS algorithm is more reliable and efficient than the basic SOS algorithm and other state-of-the-art algorithms.

  12. Fatty acid variations in symbiotic dinoflagellates from Okinawan corals.

    Science.gov (United States)

    Zhukova, Natalia V; Titlyanov, Eduard A

    2003-01-01

    The fatty acid composition of polar lipids and triacylglycerols was determined in different morphophysiological types of symbiotic dinoflagellates (SD) isolated from the hydrocoral Millepora intricata and the scleractinian corals Pocillopora damicornis, Seriatopora caliendrum, Seriatopora hystrix and Stylophora pistillata from a fringing reef of Sesoko Island, Okinawa, Japan. The distribution of the fatty acids among the morphophysiologically distinct types of SD reported in these corals makes it possible to readily distinguish one type of SD from the other. Moreover, differences were found both in polar lipids and triacylglycerols. The polar lipids of SD from M. intricata showed a very distinctive fatty acid profile. A combination of large proportions of 18:4 (n-3), 18:5 (n-3), 22:5 (n-6), and 22:6 (n-3) and negligible amounts of 20:4 (n-6), and 20:5 (n-3) in SD from M. intricata was particularly noteworthy. The fatty acid profiles of SD from P. damicornis and SD isolated from S. caliendrum and S. hystrix differed in the proportion of 18:4 (n-3) and 22:6 (n-3). It is suggested that fatty acids might provide useful information on possible taxonomic differences among symbiotic dinoflagellates. It is assumed that biochemical differences can reflect the genetic diversity of the morphophysiological types of SD associated with several species of hermatypic corals from this region.

  13. N2-fixation and residual N effect of four legume species and four companion grass species

    DEFF Research Database (Denmark)

    Rasmussen, Jim; Søegaard, Karen; Pirhofer-Walzl, Karin

    2012-01-01

    and climatic conditions. We conducted a field experiment on a sandy soil at two nitrogen levels with seven two-species forage mixtures: alfalfa, bird's-foot trefoil, red clover, or white clover in mixture with perennial ryegrass, and white clover in mixture with meadow fescue, timothy, or hybrid ryegrass. We...... found high N2-fixation of more than 300 kg N ha-1 from both red clover and alfalfa even when the two mixtures received 300 kg total-N ha-1 in cattle slurry. The addition of cattle slurry N fertilizer lowered N2-fixation for white clover and red clover as expected, but for bird's-foot trefoil and alfalfa...... no changes in the proportion of N derived from N2-fixation was observed. We conclude that the competition for available soil N from perennial ryegrass in mixture was an important factor for the proportion of N in alfalfa, white clover, and bird's-foot trefoil obtained from N2-fixation. White clover had...

  14. Background harmonic superfields in N=2 supergravity

    International Nuclear Information System (INIS)

    Zupnik, B.M.

    1998-01-01

    A modification of the harmonic superfield formalism in D=4, N=2 supergravity using a subsidiary condition of covariance under the background supersymmetry with a central charge (B-covariance) is considered. Conservation of analyticity together with the B-covariance leads to the appearance of linear gravitational superfields. Analytic prepotentials arise in a decomposition of the background linear superfields in terms of spinor coordinates and transform in a nonstandard way under the background supersymmetry. The linear gravitational superfields can be written via spinor derivatives of nonanalytic spinor prepotentials. The perturbative expansion of supergravity action in terms of the B-covariant superfields and the corresponding version of the differential-geometric formalism are considered. We discuss the dual harmonic representation of the linearized extended supergravity, which corresponds to the dynamical condition of Grassmann analyticity

  15. N-(2-Amino-5-chlorophenyl-2-bromobenzenesulfonamide

    Directory of Open Access Journals (Sweden)

    Maria Altamura

    2012-12-01

    Full Text Available In the title compound, C12H10BrClN2O2S, the sulfonamide group adopts a staggered conformation about the N—S bond [the C—S—N—H torsion angle is 97 (3°] with the N-atom lone pair bisecting the O=S=O angle. For the C(Ar—S bond, the ortho-substituted C atom bisects one of O=S–N angles [the C—C—S—N torsion angle is −57.7 (3°]. The mean planes of the aromatic rings form a dihedral angle of 75.1 (1°. In the crystal, molecules form inversion dimers through pairs of N—H...NH2 hydrogen bonds. The molecules are further consolidated into layers along the bc plane by weaker N—H...O interactions.

  16. Multi Groups Cooperation based Symbiotic Evolution for TSK-type Neuro-Fuzzy Systems Design.

    Science.gov (United States)

    Cheng, Yi-Chang; Hsu, Yung-Chi; Lin, Sheng-Fuu

    2010-07-01

    In this paper, a TSK-type neuro-fuzzy system with multi groups cooperation based symbiotic evolution method (TNFS-MGCSE) is proposed. The TNFS-MGCSE is developed from symbiotic evolution. The symbiotic evolution is different from traditional GAs (genetic algorithms) that each chromosome in symbiotic evolution represents a rule of fuzzy model. The MGCSE is different from the traditional symbiotic evolution; with a population in MGCSE is divided to several groups. Each group formed by a set of chromosomes represents a fuzzy rule and cooperate with other groups to generate the better chromosomes by using the proposed cooperation based crossover strategy (CCS). In this paper, the proposed TNFS-MGCSE is used to evaluate by numerical examples (Mackey-Glass chaotic time series and sunspot number forecasting). The performance of the TNFS-MGCSE achieves excellently with other existing models in the simulations.

  17. Effects of removing symbiotic green algae on the response of Hydra viridissima (Pallas 1776) to metals.

    Science.gov (United States)

    Karntanut, W; Pascoe, D

    2005-03-01

    Hydra viridissima is distinctively green due to symbiotic algae within the endodermal cells. The current investigation was designed to see if these algae influenced the response of Hydra to pollutants, by comparing the toxicity of copper, cadmium, and zinc to both symbiotic and aposymbiotic (free of their endosymbiotic algae) H. viridissima. The results demonstrated that the toxicity of the metals was generally similar for both groups of Hydra. However, at the lowest copper concentrations there was a difference between the two group of polyps, with aposymbiotic animals dying at concentrations where symbiotic Hydra survived. The lowest observed effect concentrations were 0.0068 and 0.016 mg/L for aposymbiotic and symbiotic Hydra, respectively. It is suggested that the symbiotic Hydra derive benefits from the association that enable them to better tolerate the toxicant. This work demonstrated that experimental manipulation of symbionts can help to explain their complex interactions and the ways in which they respond to pollutants.

  18. Occurrence and Localization of Phycoerythrin in Symbiotic Nostoc of Cycas revoluta and in the Free-Living Isolated Nostoc 7422.

    Science.gov (United States)

    Lindblad, P; Bergman, B

    1989-03-01

    The phycobiliprotein phycoerythrin was localized in symbiotic and free-living Nostoc of the cycad Cycas using immunocytochemistry. In symbiotic Nostoc, phycoerythrin was associated with the thylakoid membranes of vegetative cells and absent from heterocysts. Similar cellular/subcellular localization was observed between symbiotic Nostoc and the free-living Cycas isolate Nostoc 7422.

  19. Endophytic nitrogen fixation in sugarcane: Present knowledge and future applications

    International Nuclear Information System (INIS)

    Boddey, Robert M.; Urquiaga, Segundo; Alves, Bruno J.R.; Reis, Veronica

    2001-01-01

    In Brazil the long-term continuous cultivation of sugarcane with low N fertiliser inputs, without apparent depletion of soil-N reserves, led to the suggestion that N 2 -fixing bacteria associated with the plants may be the source of agronomically significant N inputs to this crop. From the 1950s to 1970s, considerable numbers of N 2 -fixing bacteria were found to be associated with the crop, but it was not until the late 1980s that evidence from N balance and 15 N dilution experiments showed that some Brazilian varieties of sugarcane were able to obtain significant contributions from this source. The results of these studies renewed the efforts to search for N 2 -fixing bacteria, but this time the emphasis was on those diazotrophs that infected the interior of the plants. Within a few years several species of such 'endophytic diazotrophs' were discovered including Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, H. rubrisubalbicans and Burkholderia sp. Work has continued on these endophytes within sugarcane plants, but to date little success has been attained in elucidating which endophyte is responsible for the observed BNF and in what site, or sites, within the cane plants the N 2 fixation mainly occurs. Until such important questions are answered further developments or extension of this novel N 2 -fixing system to other economically important non-legumes (e.g. cereals) will be seriously hindered. As far as application of present knowledge to maximise BNF with sugarcane is concerned, molybdenum is an essential micronutrient. An abundant water supply favours high BNF inputs, and the best medium term strategy to increase BNF would appear to be based on cultivar selection on irrigated N deficient soils fertilised with Mo. (author)

  20. Layered-Double-Hydroxide Nanosheets as Efficient Visible-Light-Driven Photocatalysts for Dinitrogen Fixation.

    Science.gov (United States)

    Zhao, Yufei; Zhao, Yunxuan; Waterhouse, Geoffrey I N; Zheng, Lirong; Cao, Xingzong; Teng, Fei; Wu, Li-Zhu; Tung, Chen-Ho; O'Hare, Dermot; Zhang, Tierui

    2017-11-01

    Semiconductor photocatalysis attracts widespread interest in water splitting, CO 2 reduction, and N 2 fixation. N 2 reduction to NH 3 is essential to the chemical industry and to the Earth's nitrogen cycle. Industrially, NH 3 is synthesized by the Haber-Bosch process under extreme conditions (400-500 °C, 200-250 bar), stimulating research into the development of sustainable technologies for NH 3 production. Herein, this study demonstrates that ultrathin layered-double-hydroxide (LDH) photocatalysts, in particular CuCr-LDH nanosheets, possess remarkable photocatalytic activity for the photoreduction of N 2 to NH 3 in water at 25 °C under visible-light irradiation. The excellent activity can be attributed to the severely distorted structure and compressive strain in the LDH nanosheets, which significantly enhances N 2 chemisorption and thereby promotes NH 3 formation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Intraocular pressure variations during zygomatic fracture reduction and fixation: a clinical study.

    LENUS (Irish Health Repository)

    Murray, Dylan J

    2012-02-03

    BACKGROUND: The reduction of midface fractures has been associated with the rare but devastating complication of blindness. An increase in intraocular pressure is important in the mechanism of blindness in this setting. In this study, the authors assessed the intraocular pressure in patients who underwent zygomatic fracture reduction (with or without fixation). METHODS: Using applanation tonometry, 29 patients underwent intraocular pressure measurements before, during, and after fracture fixation. The contralateral pressures were measured and used as the control. RESULTS: There were 29 patients with a mean age of 35 years, and the mean time to surgery was 5 days. Preoperatively, all patients had normal intraocular pressures and normal visual acuity. All patients underwent a Gillies lift and 18 patients required open reduction and fixation of the frontozygomatic suture (n = 4) or the infraorbital margin (n = 2), and the remainder (n = 12) required fixation of both points. There was no statistically significant increase in the intraocular pressures following the reduction of uncomplicated zygomatic fractures. Statistically significant pressure reductions were noted immediately after reduction and fixation. CONCLUSIONS: The surgical reduction of uncomplicated zygomatic fractures has no adverse effect on the intraocular pressure. It is the authors\\' opinion that adjunctive measures to reduce the pressures are unnecessary.

  2. "N"-2 Repetition Costs Depend on Preparation in Trials "n"-1 and "n"-2

    Science.gov (United States)

    Scheil, Juliane; Kleinsorge, Thomas

    2014-01-01

    In task switching, a common result supporting the notion of inhibitory processes as a determinant of switch costs is the occurrence of "n"-2 repetition costs. Evidence suggests that this effect is not affected by preparation. However, the role of preparation on preceding trials has been neglected so far. In this study, evidence for an…

  3. Comparison of inoculant and indigenous rhizobial dinitrogen fixation in cowpeas by direct nitrogen-15 analyses

    International Nuclear Information System (INIS)

    ElHassan, G.A.; Focht, D.D.

    1986-01-01

    Soil that contained 15 N enriched organic matter (0.461 % 15 N) was used to determine competitiveness of six strains at different logarithmic inoculum densities against indigenous rhizobia and against a previous surviving inoculant (strain P132). Analyses of N content of plant tissues by direct 15 N technique showed that cowpeas (Vigna unguiculata L. Walp.) were capable of deriving 60 to 98% of shoot N from N 2 fixation. The two fast-growing strains (176A26 and 176A28) were poorer competitors and fixed less N 2 compared to the other slow-growing strains. Inoculum density had no effect upon yield response of cowpeas, but inoculation with strains P132, 401, and 22A1 effected greater seed yield, shoot dry matter, total N, and percentage of N derived from fixation (86-98%) than other strains and the uninoculated control (60-73%). By contrast, N 2 fixation and yield parameters in inoculated cowpeas were not significantly different from inoculated controls that contained residual P132 from a previous inoculum study. The higher hydrogen uptake (Hup) efficiency of nodules containing residual P132 (98 ± 2%) facilitated presumptive identification of P132 (100% ± 0 Hup efficiency axenically) as the surviving and infecting inoculant strain since nodules infected by indigenous rhizobia had lower Hup efficiencies (88 ± 2%)

  4. Eighth international congress on nitrogen fixation. Final program

    Energy Technology Data Exchange (ETDEWEB)

    1990-12-31

    This volume contains the proceedings of the Eighth International Congress on Nitrogen Fixation held May 20--26, 1990 in Knoxville, Tennessee. The volume contains abstracts of individual presentations. Sessions were entitled Recent Advances in the Chemistry of Nitrogen Fixation, Plant-microbe Interactions, Limiting Factors of Nitrogen Fixation, Nitrogen Fixation and the Environment, Bacterial Systems, Nitrogen Fixation in Agriculture and Industry, Plant Function, and Nitrogen Fixation and Evolution.

  5. Recurrent evolution of gut symbiotic bacteria in pentatomid stinkbugs.

    Science.gov (United States)

    Hosokawa, Takahiro; Matsuura, Yu; Kikuchi, Yoshitomo; Fukatsu, Takema

    2016-01-01

    Diverse animals are intimately associated with microbial symbionts. How such host-symbiont associations have evolved is a fundamental biological issue. Recent studies have revealed a variety of evolutionary relationships, such as obligatory, facultative, and free-living, of gut bacterial symbiosis within the stinkbug family Pentatomidae, although the whole evolutionary picture remains elusive. Here we investigated a comprehensive assembly of Japanese pentatomid stinkbugs representing 28 genera, 35 species, and 143 populations. Polymerase chain reaction (PCR), cloning, and sequencing of bacterial 16S rRNA gene from their midgut symbiotic organ consistently detected a single bacterial species from each of the insect samples, indicating a general tendency toward monosymbiotic gut association. Bacterial sequences detected from different populations of the same species were completely or nearly identical, indicating that the majority of the gut symbiotic associations are stably maintained at the species level. Furthermore, bacterial sequences detected from different species in the same genus tended to form well-supported clades, suggesting that host-symbiont associations are often stable even at the genus level. Meanwhile, when we compared such sequences with published sequences available in DNA databases, we found a number of counter-examples to such stable host-symbiont relationships; i.e., symbionts from different host species in the same genus may be phylogenetically distant, and symbionts from the same host species may be phylogenetically diverse. Likewise, symbionts of diverse pentatomid species may be closely related to symbionts of other stinkbug families, and symbionts of diverse pentatomid species may even be allied to free-living bacteria. Molecular evolutionary analyses revealed that higher molecular evolutionary rates, higher AT nucleotide compositions, and smaller genome sizes tended to be associated with the pentatomid symbionts constituting the stable

  6. Linking N2O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community

    Science.gov (United States)

    Harter, Johannes; Krause, Hans-Martin; Schuettler, Stefanie; Ruser, Reiner; Fromme, Markus; Scholten, Thomas; Kappler, Andreas; Behrens, Sebastian

    2014-01-01

    Nitrous oxide (N2O) contributes 8% to global greenhouse gas emissions. Agricultural sources represent about 60% of anthropogenic N2O emissions. Most agricultural N2O emissions are due to increased fertilizer application. A considerable fraction of nitrogen fertilizers are converted to N2O by microbiological processes (that is, nitrification and denitrification). Soil amended with biochar (charcoal created by pyrolysis of biomass) has been demonstrated to increase crop yield, improve soil quality and affect greenhouse gas emissions, for example, reduce N2O emissions. Despite several studies on variations in the general microbial community structure due to soil biochar amendment, hitherto the specific role of the nitrogen cycling microbial community in mitigating soil N2O emissions has not been subject of systematic investigation. We performed a microcosm study with a water-saturated soil amended with different amounts (0%, 2% and 10% (w/w)) of high-temperature biochar. By quantifying the abundance and activity of functional marker genes of microbial nitrogen fixation (nifH), nitrification (amoA) and denitrification (nirK, nirS and nosZ) using quantitative PCR we found that biochar addition enhanced microbial nitrous oxide reduction and increased the abundance of microorganisms capable of N2-fixation. Soil biochar amendment increased the relative gene and transcript copy numbers of the nosZ-encoded bacterial N2O reductase, suggesting a mechanistic link to the observed reduction in N2O emissions. Our findings contribute to a better understanding of the impact of biochar on the nitrogen cycling microbial community and the consequences of soil biochar amendment for microbial nitrogen transformation processes and N2O emissions from soil. PMID:24067258

  7. N=2 super - W3(2) algebra in superfields

    International Nuclear Information System (INIS)

    Krivonos, S.; Sorin, A.

    1995-05-01

    It is presented a manifestly N=2 supersymmetric formulation of N=2 super-W 3 (2) algebra (its classical version) in terms of the spin 1 unconstrained generating a N=2 superconformal subalgebra and the spins 1/2, 2 fermionic constrained supercurrents. It is considered a superfield reduction of N=2 super-W 3 (2) to N=2 super-W 3 and construct a family of evolution equations for which N=2 super-W 3 (2) provides the second Hamiltonian structure

  8. SEARCHING FOR NEW YELLOW SYMBIOTIC STARS: POSITIVE IDENTIFICATION OF StHα63

    Energy Technology Data Exchange (ETDEWEB)

    Baella, N. O. [Unidad de Astronomía, Instituto Geofísico del Perú, Lima, Per (Peru); Pereira, C. B.; Alvarez-Candal, A. [Observatório Nacional/MCTI, Rua Gen. José Cristino, 77, 20921-400, Rio de Janeiro (Brazil); Miranda, L. F., E-mail: nobar.baella@gmail.com, E-mail: claudio@on.br, E-mail: alvarez@on.br, E-mail: lfm@iaa.es [Instituto de Astrofísica de Andalucía- CSIC, C/Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

    2016-04-15

    Yellow symbiotic stars are useful targets for probing whether mass transfer has happened in their binary systems. However, the number of known yellow symbiotic stars is very scarce. We report spectroscopic observations of five candidate yellow symbiotic stars that were selected by their positions in the 2MASS (J − H) versus (H − K{sub s}) diagram and which were included in some emission-line catalogs. Among the five candidates, only StHα63 is identified as a new yellow symbiotic star because of its spectrum and its position in the [TiO]{sub 1}–[TiO]{sub 2} diagram, which indicates a K4–K6 spectral type. In addition, the derived electron density (∼10{sup 8.4} cm{sup −3}) and several emission-line intensity ratios provide further support for that classification. The other four candidates are rejected as symbiotic stars because three of them actually do not show emission lines and the fourth one only Balmer emission lines. We also found that the WISE W3–W4 index clearly separates normal K-giants from yellow symbiotic stars and therefore can be used as an additional tool for selecting candidate yellow symbiotic stars.

  9. [Response of arbuscular mycorrhizal fungal lipid metabolism to symbiotic signals in mycorrhiza].

    Science.gov (United States)

    Tian, Lei; Li, Yuanjing; Tian, Chunjie

    2016-01-04

    Arbuscular mycorrhizal (AM) fungi play an important role in energy flow and nutrient cycling, besides their wide distribution in the cosystem. With a long co-evolution, AM fungi and host plant have formed a symbiotic relationship, and fungal lipid metabolism may be the key point to find the symbiotic mechanism in arbusculart mycorrhiza. Here, we reviewed the most recent progress on the interaction between AM fungal lipid metabolism and symbiotic signaling networks, especially the response of AM fungal lipid metabolism to symbiotic signals. Furthermore, we discussed the response of AM fungal lipid storage and release to symbiotic or non-symbiotic status, and the correlation between fungal lipid metabolism and nutrient transfer in mycorrhiza. In addition, we explored the feedback of the lipolysis process to molecular signals during the establishment of symbiosis, and the corresponding material conversion and energy metabolism besides the crosstalk of fungal lipid metabolism and signaling networks. This review will help understand symbiotic mechanism of arbuscular mycorrhiza fungi and further application in ecosystem.

  10. Transformation of leguminous plants to study symbiotic interactions.

    Science.gov (United States)

    Iantcheva, Anelia; Mysore, Kirankumar S; Ratet, Pascal

    2013-01-01

    Legume plants are important in agriculture because they represent an important source of protein for human and animal consumption. This high protein content results from their capacity to use atmospheric nitrogen for their nutrition as a consequence of their symbiotic interaction with rhizobia. Understanding this interaction at the molecular level is a prerequisite for its better use in agriculture and for the long term objective of its transfer to other crops. Agrobacterium-mediated transformation is a tool of choice for studying this interaction and for unraveling the function of the different genes discovered through classical genetic approaches. However, legume plants are often recalcitrant to regeneration and transformation. This paper describes the technology developments (regeneration, transformation, insertion mutagenesis) related to Agrobacterium transformations that were established in the legume plants, as well as different examples of the technology developments or gene discoveries resulting from these studies.

  11. Effects of subliminal symbiotic stimuli on anxiety reduction.

    Science.gov (United States)

    Malik, R; Krasney, M S; Aldworth, B; Ladd, H W

    1996-06-01

    The present study assessed the effectiveness of subliminal psychodynamic stimuli in reducing anxiety. 50 male and 50 female college students were tachistoscopically exposed to one of five stimuli: MOMMY AND I ARE ONE, DADDY AND I ARE ONE, I AM HAPPY WITH MYSELF, ONE, or a control stimulus MYMMO NAD I REA ENO. It was hypothesized that men would show a significant decrease in anxiety to the MOMMY stimulus, while women were expected to respond favorably to either the MOMMY or DADDY stimulus, or to both. Results showed that the subliminal stimuli did not produce differential effects on anxiety. This finding did not support previous claims for subliminal psychodynamic activation that the stimulation of symbiotic fantasy with the maternal figure produces positive behavioral effects. Despite this negative finding women's response to the MOMMY message was predicted by measures of self-perception.

  12. An update on probiotics, prebiotics and symbiotics in clinical nutrition.

    Science.gov (United States)

    Olveira, Gabriel; González-Molero, Inmaculada

    2016-11-01

    The concept of prebiotics, probiotics, and symbiotics and their use in different situations of daily clinical practice related to clinical nutrition is reviewed, as well as their role in the treatment/prevention of diarrhea (acute, induced by antibiotics, secondary to radiotherapy), inflammatory bowel disease (ulcerative colitis and pouchitis), in colonic health (constipation, irritable bowel), in liver disease (steatosis and minimum encephalopathy), and in intensive care, surgical, and liver transplantation. While their effectiveness for preventing antibiotic-induced diarrhea and pouchitis in ulcerative colitis appears to be shown, additional studies are needed to establish recommendations in most clinical settings. The risk of infection associated to use of probiotics is relatively low; however, there are selected groups of patients in whom they should be used with caution (as jejunum infusion). Copyright © 2016 SEEN. Publicado por Elsevier España, S.L.U. All rights reserved.

  13. The 1984 eclipse of the symbiotic binary SY Muscae

    Science.gov (United States)

    Kenyon, S. J.; Michalitisianos, A. G.; Lutz, J. H.; Kafatos, M.

    1985-01-01

    Data from IUE spectra obtained with the 10 x 20-arcsec aperture on May 13, 1984, and optical spectrophotometry obtained with an SIT vidicon on the 1.5-m telescope at CTIO on April 29-May 1, 1984, are reported for the symbiotic binary SY Mus. The data are found to be consistent with a model of a red-giant secondary of 60 solar radii which completely eclipses the hot primary every 627 d but only partially eclipses the 75-solar-radius He(+) region surrounding the primary. The distance to SY Mus is estimated as 1.3 kpc. It is suggested that the large Balmer decrement in eclipse, with (H-alpha)/(H-beta) = 8.3 and (H-beta)/(H-gamma) = 1.5, is associated with an electron density of about 10 to the 10th/cu cm.

  14. On the nature of the symbiotic star BF Cygni

    International Nuclear Information System (INIS)

    Mikolajewska, J.; Mikolajewski, M.; Kenyon, S.J.

    1989-01-01

    Optical and ultraviolet spectroscopy of the symbiotic binary BF Cyg obtained during 1979-1988 is discussed. This system consists of a low-mass M5 giant filling about 50 percent of its tidal volume and a hot, luminous compact object similar to the central star of a planetary nebula. The binary is embedded in an asymmetric nebula which includes a small, high-density region and an extended region of lower density. The larger nebula is formed by a slow wind ejected by the cool component and ionized by the hot star, while the more compact nebula is material expelled by the hot component in the form of a bipolar wind. The analysis indicates that disk accretion is essential to maintain the nuclear burning shell of the hot star. 84 refs

  15. Transcriptomic profiling of Burkholderia phymatum STM815, Cupriavidus taiwanensis LMG19424 and Rhizobium mesoamericanum STM3625 in response to Mimosa pudica root exudates illuminates the molecular basis of their nodulation competitiveness and symbiotic evolutionary history.

    Science.gov (United States)

    Klonowska, Agnieszka; Melkonian, Rémy; Miché, Lucie; Tisseyre, Pierre; Moulin, Lionel

    2018-01-30

    Rhizobial symbionts belong to the classes Alphaproteobacteria and Betaproteobacteria (called "alpha" and "beta"-rhizobia). Most knowledge on the genetic basis of symbiosis is based on model strains belonging to alpha-rhizobia. Mimosa pudica is a legume that offers an excellent opportunity to study the adaptation toward symbiotic nitrogen fixation in beta-rhizobia compared to alpha-rhizobia. In a previous study (Melkonian et al., Environ Microbiol 16:2099-111, 2014) we described the symbiotic competitiveness of M. pudica symbionts belonging to Burkholderia, Cupriavidus and Rhizobium species. In this article we present a comparative analysis of the transcriptomes (by RNAseq) of B. phymatum STM815 (BP), C. taiwanensis LMG19424 (CT) and R. mesoamericanum STM3625 (RM) in conditions mimicking the early steps of symbiosis (i.e. perception of root exudates). BP exhibited the strongest transcriptome shift both quantitatively and qualitatively, which mirrors its high competitiveness in the early steps of symbiosis and its ancient evolutionary history as a symbiont, while CT had a minimal response which correlates with its status as a younger symbiont (probably via acquisition of symbiotic genes from a Burkholderia ancestor) and RM had a typical response of Alphaproteobacterial rhizospheric bacteria. Interestingly, the upregulation of nodulation genes was the only common response among the three strains; the exception was an up-regulated gene encoding a putative fatty acid hydroxylase, which appears to be a novel symbiotic gene specific to Mimosa symbionts. The transcriptional response to root exudates was correlated to each strain nodulation competitiveness, with Burkholderia phymatum appearing as the best specialised symbiont of Mimosa pudica.

  16. Biological Nitrogen Fixation on Legume

    Directory of Open Access Journals (Sweden)

    Armiadi

    2009-03-01

    Full Text Available Nitrogen (N is one of the major limiting factors for crop growth and is required in adequate amount, due to its function as protein and enzyme components. In general, plants need sufficient nitrogen supply at all levels of growth, especially at the beginning of growth phase. Therefore, the availability of less expensive N resources would reduce the production cost. The increasing use of chemical fertilizer would probably disturb soil microorganisms, reduce the physical and chemical characteristics of soil because not all of N based fertilizer applied can be absorbed by the plants. Approximately only 50% can be used by crops, while the rest will be altered by microorganism into unavailable N for crops or else dissappear in the form of gas. Leguminous crops have the capacity to immobilize N2 and convert into the available N if innoculated with Rhizobium. The amount of N2 fixed varies depending on legume species and their environment.

  17. Nitrogen fixation by the Azolla-Anabaena azollae symbiosis

    International Nuclear Information System (INIS)

    Becking, J.H.

    1985-01-01

    A concise outline is presented on the main characteristics of the Azolla association in relation to tropical wetland rice cultivation and the nitrogen economy of paddy soils. Due to the presence of a nitrogen fixing cyanobiont occurring in a special leaf cavity of the Azolla leaf, the water fern Azolla can grow in a nitrogen-deficient environment and is able to contribute considerably to the nitrogen status of the soil. An experimental set-up is presented for how the nitrogen-fixing capacity of Azolla plants can be measured in the field by means of the acetylene reduction assay using a rather simple glass vessel. A comparison was made between 15 N 2 fixation by Azolla and acetylene reduction of Azolla plants under identical conditions

  18. Salt stress sensitivity of nitrogen fixation in Enterobacter agglomerans strains.

    Science.gov (United States)

    Rai, Raman; Rieder, Gabriele

    1998-12-01

    Two strains 333 to 339 of Enterobacter agglomerans were selected in the present study to evaluate the response of increasing concentrations of NaCl on growth, N(2)-fixation, and nitrogenase activity/synthesis. E. agglomerans strains 333 and 339 showed optimum growth and acetylene-reducing activity with 0.5 to 1.0% NaCl in a nitrogen-free minimal medium (NFDM) with glucose, respectively, in 28 h incubation, although both strains displayed better growth and acetylene-reducing activity with 3.0% and 2.0% NaCl after 52 h and 100 h incubation periods than the 28 h culture did. Our experiments with shiftings of salt concentrations in NFDM medium indicated that a synthesis of nitrogenase enzyme was generally more sensitive to higher concentrations of NaCl than nitrogenase activity was.

  19. Solar Water Splitting and Nitrogen Fixation with Layered Bismuth Oxyhalides.

    Science.gov (United States)

    Li, Jie; Li, Hao; Zhan, Guangming; Zhang, Lizhi

    2017-01-17

    Hydrogen and ammonia are the chemical molecules that are vital to Earth's energy, environmental, and biological processes. Hydrogen with renewable, carbon-free, and high combustion-enthalpy hallmarks lays the foundation of next-generation energy source, while ammonia furnishes the building blocks of fertilizers and proteins to sustain the lives of plants and organisms. Such merits fascinate worldwide scientists in developing viable strategies to produce hydrogen and ammonia. Currently, at the forefronts of hydrogen and ammonia syntheses are solar water splitting and nitrogen fixation, because they go beyond the high temperature and pressure requirements of methane stream reforming and Haber-Bosch reaction, respectively, as the commercialized hydrogen and ammonia production routes, and inherit the natural photosynthesis virtues that are green and sustainable and operate at room temperature and atmospheric pressure. The key to propelling such photochemical reactions lies in searching photocatalysts that enable water splitting into hydrogen and nitrogen fixation to make ammonia efficiently. Although the past 40 years have witnessed significant breakthroughs using the most widely studied TiO 2 , SrTiO 3 , (Ga 1-x Zn x )(N 1-x O x ), CdS, and g-C 3 N 4 for solar chemical synthesis, two crucial yet still unsolved issues challenge their further progress toward robust solar water splitting and nitrogen fixation, including the inefficient steering of electron transportation from the bulk to the surface and the difficulty of activating the N≡N triple bond of N 2 . This Account details our endeavors that leverage layered bismuth oxyhalides as photocatalysts for efficient solar water splitting and nitrogen fixation, with a focus on addressing the above two problems. We first demonstrate that the layered structures of bismuth oxyhalides can stimulate an internal electric field (IEF) that is capable of efficiently separating electrons and holes after their formation and of

  20. Kennedy Space Center Fixation Tube (KFT)

    Science.gov (United States)

    Richards, Stephanie E.; Levine, Howard G.; Romero, Vergel

    2016-01-01

    Experiments performed on the International Space Station (ISS) frequently require the experimental organisms to be preserved until they can be returned to earth for analysis in the appropriate laboratory facility. The Kennedy Fixation Tube (KFT) was developed to allow astronauts to apply fixative, chemical compounds that are often toxic, to biological samples without the use of a glovebox while maintaining three levels of containment (Fig. 1). KFTs have been used over 200 times on-orbit with no leaks of chemical fixative. The KFT is composed of the following elements: a polycarbonate main tube where the fixative is loaded preflight, the sample tube where the plant or other biological specimens is placed during operations, the expansion plug, actuator, and base plug that provides fixative containment (Fig. 2). The main tube is pre-filled with 25 mL of fixative solution prior to flight. When actuated, the specimen contained within the sample tube is immersed with approximately 22 mL (+/- 2 mL) of the fixative solution. The KFT has been demonstrated to maintain its containment at ambient temperatures, 4degC refrigeration and -100 C freezing conditions.

  1. Sutureless Intrascleral Fixated Intraocular Lens Implantation.

    Science.gov (United States)

    Karadag, Remzi; Celik, Haci Ugur; Bayramlar, Huseyin; Rapuano, Christopher J

    2016-08-01

    To review sutureless intrascleral intraocular lens (IOL) fixation methods. Review of published literature. Sutureless intrascleral IOL fixation methods are newer and have been developed to eliminate the suture-related complications of sutured scleral fixation methods such as suture-induced inflammation or infection and IOL dislocation or subluxation due to suture degradation or suture breakage. Sutureless intrascleral fixation methods aim for intrascleral haptic fixation to achieve stability of the IOL. Various methods of sutureless scleral fixation have been described. Using a needle, a blade, or a trochar, sclerostomies are created in all techniques for intraocular access. Some surgeons prefer to create scleral tunnels, whereas others use scleral flaps for scleral fixation of haptics. The stability of IOLs is attained by the scar tissue formed around the haptics. Short-term results of these new methods are acceptable; studies including more cases with longer follow-up are needed to determine their long-term success. [J Cataract Refract Surg. 2016;32(9):586-597.]. Copyright 2016, SLACK Incorporated.

  2. Biomechanical Analysis of Latarjet Screw Fixation: Comparison of Screw Types and Fixation Methods.

    Science.gov (United States)

    Shin, Jason J; Hamamoto, Jason T; Leroux, Timothy S; Saccomanno, Maristella F; Jain, Akshay; Khair, Mahmoud M; Mellano, Christen R; Shewman, Elizabeth F; Nicholson, Gregory P; Romeo, Anthony A; Cole, Brian J; Verma, Nikhil N

    2017-09-01

    To compare the initial fixation stability, failure strength, and mode of failure of 5 different screw types and fixation methods commonly used for the classic Latarjet procedure. Thirty-five fresh-frozen cadaveric shoulder specimens were allocated into 5 groups. A 25% anteroinferior glenoid defect was created, and a classic Latarjet coracoid transfer procedure was performed. All grafts were fixed with 2 screws, differing by screw type and/or fixation method. The groups included partially threaded solid 4.0-mm cancellous screws with bicortical fixation, partially threaded solid 4.0-mm cancellous screws with unicortical fixation, fully threaded solid 3.5-mm cortical screws with bicortical fixation, partially threaded cannulated 4.0-mm cancellous screws with bicortical fixation, and partially threaded cannulated 4.0-mm captured screws with bicortical fixation. All screws were stainless steel. Outcomes included cyclic creep and secant stiffness during cyclic loading, as well as load and work to failure during the failure test. Intergroup comparisons were made by a 1-way analysis of variance. There were no significant differences among different screw types or fixation methods in cyclic creep or secant stiffness after cyclic loading or in load to failure or work to failure during the failure test. Post-failure radiographs showed evidence of screw bending in only 1 specimen that underwent the Latarjet procedure with partially threaded solid cancellous screws with bicortical fixation. The mode of failure for all specimens analyzed was screw cutout. In this biomechanical study, screw type and fixation method did not significantly influence biomechanical performance in a classic Latarjet procedure. When performing this procedure, surgeons may continue to select the screw type and method of fixation (unicortical or bicortical) based on preference; however, further studies are required to determine the optimal method of treatment. Surgeons may choose the screw type and

  3. Natural isotopes abundance of 15N and 13C in leaves of some N2-fixing and non N2-fixing trees and shrubs in Syria

    International Nuclear Information System (INIS)

    Kurdali, F.; Al-Shamma'a, M.

    2007-12-01

    Variability in the natural abundance isotopes of 15 N and 13 C in leaves of several legume and non-legume plant species grown at different sites of two areas in semi-arid regions of Syria was determined. In the first area (non-saline soil), the 15 N values of a number of fixing and non-fixing reference plants ranged from -2.09 to +9.46, depending on plant species and studied site. 15 N in a number of legume species including Acacia cyanopylla (-1.73), Acacia farnesiana (-0.55), Prosopis juliflora (-1.64) and Medicago arborea (+1.6) were close to the atmospheric value pointing to a major contribution of N 2 fixing in these species; whereas, those of reference plants were highly positive (between +3.6 and +9.46%). In the actinorhizal tree, Elaeagnus angustifolia, the 15 N abundance was far lower (-0.46 to -2.1%) strongly suggesting that the plant obtained large proportional contribution from BNF. In contrast, δ 15 N values in some other legumes and actinorhizal plants were relatively similar to those of reference plants, suggesting that the contribution of fixed N 2 is negligible. On the other hand, δ 13 C% values in leaves of C3 plants were affected by plant species, ranging from a minimum of -28.67% to a maximum of -23%. However, they were the same within each plant species although they were grown at different sites. Moreover, dual stable isotope analysis in leaves of Prosopis juliflora and other non- legumes grown on a salt affected soil (second area) was also conducted. Results showed that salinity did not affect C assimilation in this woody legume since a higher carbon discrimination was obtained indicating that this plant is a salt tolerant species; whereas, N2-fixation was drastically affected (δ 15 N= +7.03). (Author)

  4. QCL N2O data final MayAugust2016

    Data.gov (United States)

    U.S. Environmental Protection Agency — The dataset consists of daily measurements of N2O, N2O isotopic abundance and site preference, and CO2 flux. Data are presented as a daily averages of 10 second...

  5. Miniaturized Airborne Instrument for N2O, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Nitrous Oxide (N2O) is an important greenhouse gas, as well as a tracer for stratospheric air mass. We propose to design a miniaturized N2O detector based on direct...

  6. Systems biology of bacterial nitrogen fixation: High-throughput technology and its integrative description with constraint-based modeling

    Directory of Open Access Journals (Sweden)

    Resendis-Antonio Osbaldo

    2011-07-01

    Full Text Available Abstract Background Bacterial nitrogen fixation is the biological process by which atmospheric nitrogen is uptaken by bacteroids located in plant root nodules and converted into ammonium through the enzymatic activity of nitrogenase. In practice, this biological process serves as a natural form of fertilization and its optimization has significant implications in sustainable agricultural programs. Currently, the advent of high-throughput technology supplies with valuable data that contribute to understanding the metabolic activity during bacterial nitrogen fixation. This undertaking is not trivial, and the development of computational methods useful in accomplishing an integrative, descriptive and predictive framework is a crucial issue to decoding the principles that regulated the metabolic activity of this biological process. Results In this work we present a systems biology description of the metabolic activity in bacterial nitrogen fixation. This was accomplished by an integrative analysis involving high-throughput data and constraint-based modeling to characterize the metabolic activity in Rhizobium etli bacteroids located at the root nodules of Phaseolus vulgaris (bean plant. Proteome and transcriptome technologies led us to identify 415 proteins and 689 up-regulated genes that orchestrate this biological process. Taking into account these data, we: 1 extended the metabolic reconstruction reported for R. etli; 2 simulated the metabolic activity during symbiotic nitrogen fixation; and 3 evaluated the in silico results in terms of bacteria phenotype. Notably, constraint-based modeling simulated nitrogen fixation activity in such a way that 76.83% of the enzymes and 69.48% of the genes were experimentally justified. Finally, to further assess the predictive scope of the computational model, gene deletion analysis was carried out on nine metabolic enzymes. Our model concluded that an altered metabolic activity on these enzymes induced

  7. Rotational Energy Transfer Cross Sections in N2-N2 Collisions

    Science.gov (United States)

    Huo, Winifred M.; Green, Sheldon; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Rotational inelastic transitions of N2 have been studied in the coupled state (CS, also called centrifugal sudden) and infinite-order-sudden (IOS) approximations, using the N2-N2 rigid-rotor potential of van der Avoird et al. For benchmarking purposes, close coupling (CC) calculations have also been carried out over a limited energy range and for even j - even j collisions only. Both the CC and CS cross sections have been obtained with and without exchange symmetry, whereas exchange is neglected in the IOS calculations. The CS results track the CC cross sections rather well. At total energies between 113 to 219 cm(exp -1) the average deviation is 14%. The deviation decrease with increasing energy, indicating that the CS approximation can be used as a substitute at higher energies when the CC calculations become impractical. Comparison between the CS and IOS cross sections at the high energy end of the CS calculation, 500 - 680 cm(exp-1), shows significant differences between the two. In addition, the IOS results exhibits sensitivity to the amount of inelasticity and the results for large DELTA J transitions are subjected to bigger errors. At total energy 113 cm(exp -1) and above, the average deviation between state-to-state cross sections calculated with even and odd exchange symmetries is 1.5%.

  8. Effect of Rhizobium sp. BARIRGm901 inoculation on nodulation, nitrogen fixation and yield of soybean (Glycine max) genotypes in gray terrace soil.

    Science.gov (United States)

    Alam, Faridul; Bhuiyan, M A H; Alam, Sadia Sabrina; Waghmode, Tatoba R; Kim, Pil Joo; Lee, Yong Bok

    2015-01-01

    Soybean plants require high amounts of nitrogen, which are mainly obtained from biological nitrogen fixation. A field experiment was conducted by soybean (Glycine max) genotypes, growing two varieties (Shohag and BARI Soybean6) and two advanced lines (MTD10 and BGM02026) of soybean with or without Rhizobium sp. BARIRGm901 inoculation. Soybean plants of all genotypes inoculated with Rhizobium sp. BARIRGm901 produced greater nodule numbers, nodule weight, shoot and root biomass, and plant height than non-inoculated plants. Similarly, inoculated plants showed enhanced activity of nitrogenase (NA) enzyme, contributing to higher nitrogen fixation and assimilation, compared to non-inoculated soybean plants in both years. Plants inoculated with Rhizobium sp. BARIRGm901 also showed higher pod, stover, and seed yield than non-inoculated plants. Therefore, Rhizobium sp. BARIRGm901 established an effective symbiotic relationship with a range of soybean genotypes and thus increased the nodulation, growth, and yield of soybean grown in gray terrace soils in Bangladesh.

  9. Effect of combined N applied at low level on the nitrogen fixation by grasses and contribution to nitrogen fertility in soil

    International Nuclear Information System (INIS)

    Yao Yunyin; Chen Ming; Ma Changlin

    1990-01-01

    This paper reports the study on the effect of combined N applied at low level on teh nitrogen fixation by alfalfa in monoculture and mixed culture with meadow fescue, and the effect on the absorption and utilization of indigenous soil nitrogen and nitrogen fertilizer. Amount of nitrogen fixed by alfalfa could be raised and duration of high peak of symbiotic nitrogen fixation activity could be extended when nitrogen fertilizer was applied reasonably. It was especially important for the early pastures or pastures with low supporting nitrogen capacity. Transfer of nitrogen fixed by alfalfa to meadow fescue occured in mixed culture. Nitrogen fixed from alfalfa was uptaken more easily than indigenous nitrogen in soil. Planting alfalfa could raise soil fertility significantly. Meadow fescue may be able to fix nitrogen from the air in some way. When combined N was appropriately applied to soil, on which alfalfa and meadow fescue had been planted, it could promote increasing nitrogen fertility in soil

  10. Metabolic changes of iron uptake in N(2)-fixing common bean nodules during iron deficiency.

    Science.gov (United States)

    Slatni, Tarek; Vigani, Gianpiero; Salah, Imen Ben; Kouas, Saber; Dell'Orto, Marta; Gouia, Houda; Zocchi, Graziano; Abdelly, Chedly

    2011-08-01

    Iron is an important nutrient in N(2)-fixing legume nodules. The demand for this micronutrient increases during the symbiosis establishment, where the metal is utilized for the synthesis of various iron-containing proteins in both the plant and the bacteroid. Unfortunately, in spite of its importance, iron is poorly available to plant uptake since its solubility is very low when in its oxidized form Fe(III). In the present study, the effect of iron deficiency on the activity of some proteins involved in Strategy I response, such as Fe-chelate reductase (FC-R), H(+)-ATPase, and phosphoenolpyruvate carboxylase (PEPC) and the protein level of iron regulated transporter (IRT1) and H(+)-ATPase proteins has been investigated in both roots and nodules of a tolerant (Flamingo) and a susceptible (Coco blanc) cultivar of common bean plants. The main results of this study show that the symbiotic tolerance of Flamingo can be ascribed to a greater increase in the FC-R and H(+)-ATPase activities in both roots and nodules, leading to a more efficient Fe supply to nodulating tissues. The strong increase in PEPC activity and organic acid content, in the Flamingo root nodules, suggests that under iron deficiency nodules can modify their metabolism in order to sustain those activities necessary to acquire Fe directly from the soil solution. Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.

  11. Carbon dioxide fixation in isolated Kalanchoe chloroplasts

    Energy Technology Data Exchange (ETDEWEB)

    Levi, C.; Gibbs, M.

    1975-07-01

    Chloroplasts isolated from Kalanchoe diagremontiana leaves were capable of photosynthesizing at a rate of 5.4 ..mu..moles of CO/sub 2/ per milligram of chlorophyll per hour. The dark rate of fixation was about 1 percent of the light rate. A high photosynthetic rate was associated with low starch content of the leaves. Ribose 5-phosphate, fructose 1, 6-diphosphate, and dithiothreitol stimulated fixation, whereas phosphoenolpyruvate and azide were inhibitors. The products of CO/sub 2/ fixation were primarily those of the photosynthetic carbon reduction cycle. (auth)

  12. Vacuum suction fixation versus staple fixation in TAPP laparoscopic hernia repair: introduction of a new technique for mesh fixation.

    Science.gov (United States)

    Zhang, Guangyong; Zhang, Xiang; Zhan, Hanxiang; Hu, Sanyuan

    2016-01-01

    Proper mesh fixation is critical for successful TAPP laparoscopic hernia repair. Conventional mesh fixation may cause chronic neuralgia, groin paresthesia or other complications. This study aimed at introducing a new vacuum suction technique for mesh fixation and evaluating its efficacy and safety compared with traditional staple fixation way. Clinical data of 242 patients undergoing TAPP from July 2011 to March 2014 were retrospectively analyzed. Patients were divided into vacuum suction fixation group and staple fixation group. The operation time, hospital stay, complications, recurrence, visual analogue scale pain score and cost were evaluated. All surgeries were successful. The operation time of staple group was (42.34 ± 10.15) min for unilateral hernia and (64.08 ± 16.01) min for bilateral hernias. The postoperative hospital stay was (2.76 ± 0.84) days. One recurrence was observed (0.90%). For vacuum group, the operation time was (42.66 ± 7.76) min and (63.92 ± 10.49) min, and hospital stay was (2.60 ± 0.74) days. No recurrence was observed. There was no significant difference in recurrence, operation time, postoperative pain and hospital stay between two groups (P > 0.05). Average cost were (11,714 ± 726) RMB for vacuum group which was lower than staple group (14,837 ± 1568) RMB (P vacuum group, they were scrotal seroma (3.82%), temporary nerve paresthesia (3.05%), scrotal emphysema (1.53%) and uroschesis (1.53%). The incidence of scrotal emphysema was lower in vacuum group (P 0.05). Both techniques for mesh fixation are safe and effective. There is no significant difference in recurrence, operation time, postoperative pain or hospital stay. The vacuum suction fixation technique is more economical with lower incidence of scrotal emphysema.

  13. OxyR-regulated catalase activity is critical for oxidative stress resistance, nodulation and nitrogen fixation in Azorhizobium caulinodans.

    Science.gov (United States)

    Zhao, Yue; Nickels, Logan M; Wang, Hui; Ling, Jun; Zhong, Zengtao; Zhu, Jun

    2016-07-01

    The legume-rhizobial interaction results in the formation of symbiotic nodules in which rhizobia fix nitrogen. During the process of symbiosis, reactive oxygen species (ROS) are generated. Thus, the response of rhizobia to ROS is important for successful nodulation and nitrogen fixation. In this study, we investigated how Azorhizobium caulinodans, a rhizobium that forms both root and stem nodules on its host plant, regulates ROS resistance. We found that in-frame deletions of a gene encoding the putative catalase-peroxidase katG or a gene encoding a LysR-family regulatory protein, oxyR, exhibited increased sensitivity to H2O2 We then showed that OxyR positively regulated katG expression in an H2O2-independent fashion. Furthermore, we found that deletion of katG or oxyR led to significant reduction in the number of stem nodules and decrease of nitrogen fixation capacities in symbiosis. Our results revealed that KatG and OxyR are not only critical for antioxidant defense in vitro, but also important for nodule formation and nitrogen fixation during interaction with plant hosts. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  14. Metatranscriptomics of N2-fixing cyanobacteria in the Amazon River plume.

    Science.gov (United States)

    Hilton, Jason A; Satinsky, Brandon M; Doherty, Mary; Zielinski, Brian; Zehr, Jonathan P

    2015-07-01

    Biological N2 fixation is an important nitrogen source for surface ocean microbial communities. However, nearly all information on the diversity and gene expression of organisms responsible for oceanic N2 fixation in the environment has come from targeted approaches that assay only a small number of genes and organisms. Using genomes of diazotrophic cyanobacteria to extract reads from extensive meta-genomic and -transcriptomic libraries, we examined diazotroph diversity and gene expression from the Amazon River plume, an area characterized by salinity and nutrient gradients. Diazotroph genome and transcript sequences were most abundant in the transitional waters compared with lower salinity or oceanic water masses. We were able to distinguish two genetically divergent phylotypes within the Hemiaulus-associated Richelia sequences, which were the most abundant diazotroph sequences in the data set. Photosystem (PS)-II transcripts in Richelia populations were much less abundant than those in Trichodesmium, and transcripts from several Richelia PS-II genes were absent, indicating a prominent role for cyclic electron transport in Richelia. In addition, there were several abundant regulatory transcripts, including one that targets a gene involved in PS-I cyclic electron transport in Richelia. High sequence coverage of the Richelia transcripts, as well as those from Trichodesmium populations, allowed us to identify expressed regions of the genomes that had been overlooked by genome annotations. High-coverage genomic and transcription analysis enabled the characterization of distinct phylotypes within diazotrophic populations, revealed a distinction in a core process between dominant populations and provided evidence for a prominent role for noncoding RNAs in microbial communities.

  15. Fixation of distal fibular fractures: A biomechanical study of plate fixation techniques.

    Science.gov (United States)

    Marvan, Jiri; Horak, Zdenek; Vilimek, Miloslav; Horny, Lukas; Kachlik, David; Baca, Vaclav

    2017-01-01

    Ankle fractures are complex injuries with variable prognoses that depend upon many factors. The aim of the treatment is to restore the ankle joint biomechanical stability with maximum range of motion. Most ankle fractures are fibular fractures, which have a typical oblique fracture line in the distal fibula located in the area of the tibiofibular syndesmosis. The aim of this study was to simulate numerically several fixation techniques of the distal fibular fractures, evaluate their stability, determine their impact on surrounding tissue load, and correlate the results to clinical treatment experience. The following three models of fibular fracture fixation were used: (a) plate fixation with three screws attached above/below and lag screws, (b) plate fixation with two screws attached above/below and lag screws, and (c) three lag screws only. All three fracture fixation models were analyzed according to their use in both healthy physiological bone and osteoporotic bone tissue. Based on the results of Finite Element Analysis for these simulations, we found that the most appropriate fixation method for Weber-B1 fibular fractures was an unlocked plate fixation using six screws and lag screws, both in patients with physiological and osteoporotic bone tissue. Conversely, the least appropriate fixation method was an unlocked plate fixation with four screws and lag screws. Although this fixation method reduces the stress on patients during surgery, it greatly increased loading on the bone and, thus, the risk of fixation failure. The final fixation model with three lag screws only was found to be appropriate only for very limited indications.

  16. Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions

    Directory of Open Access Journals (Sweden)

    Qi Wang

    2018-03-01

    Full Text Available Legumes are able to form a symbiotic relationship with nitrogen-fixing soil bacteria called rhizobia. The result of this symbiosis is to form nodules on the plant root, within which the bacteria can convert atmospheric nitrogen into ammonia that can be used by the plant. Establishment of a successful symbiosis requires the two symbiotic partners to be compatible with each other throughout the process of symbiotic development. However, incompatibility frequently occurs, such that a bacterial strain is unable to nodulate a particular host plant or forms nodules that are incapable of fixing nitrogen. Genetic and molecular mechanisms that regulate symbiotic specificity are diverse, involving a wide range of host and bacterial genes/signals with various modes of action. In this review, we will provide an update on our current knowledge of how the recognition specificity has evolved in the context of symbiosis signaling and plant immunity.

  17. Superfield realizations of N=2 super-W3

    International Nuclear Information System (INIS)

    Ivanov, E.; Krivonos, S.

    1992-04-01

    We present a manifestly N=2 supersymmetric formulation of N=2 super-W 3 algebra (its classical version) in terms of the spin 1 and spin 2 supercurrents. Two closely related types of the Feigin-Fuchs representation for these supercurrents are found: via two chiral spin 1/2 superfields generating N=2 extended U(1) Kac-Moody algebras and via two free chiral spin 0 superfields. We also construct a one-parameter family of N=2 super Boussinesq equations for which N=2 super-W 3 provides the second Hamiltonian structure. (author). 17 refs

  18. Biomechanics of intramedullary fracture fixation.

    Science.gov (United States)

    Kyle, R F

    1985-11-01

    Intramedullary rodding allows excellent control of bending forces on long bone fractures when adequate sized rods are used. This is made possible by reaming when necessary. Torsional stability is poor if adequate bone nail contact is not obtained and there is little bone fragment interdigitation. This can be optimized with the interlocking system, especially with proximal and distal fractures. Intramedullary rods allow transmission of compressive load so there must be adequate bone to bone contact without comminution to prevent shortening. If a great deal of comminution is present, an interlocking system must be used to resist compressive loads. The interlocked devices have not been proven to be a detriment to union and indeed are a semi-rigid fixation system when used in comminuted shaft fractures. The strength of an osteosynthesis with an intramedullary rod depends on the geometry of the rod and the geometry of the fracture complex. Both locked and nonlocked intramedullary rods perform extremely well when one understands the mechanical principles involved in intramedullary rodding and pays close attention to detail.

  19. Fixation probability on clique-based graphs

    Science.gov (United States)

    Choi, Jeong-Ok; Yu, Unjong

    2018-02-01

    The fixation probability of a mutant in the evolutionary dynamics of Moran process is calculated by the Monte-Carlo method on a few families of clique-based graphs. It is shown that the complete suppression of fixation can be realized with the generalized clique-wheel graph in the limit of small wheel-clique ratio and infinite size. The family of clique-star is an amplifier, and clique-arms graph changes from amplifier to suppressor as the fitness of the mutant increases. We demonstrate that the overall structure of a graph can be more important to determine the fixation probability than the degree or the heat heterogeneity. The dependence of the fixation probability on the position of the first mutant is discussed.

  20. Fixation of Selenium by Clay Minerals and Iron Oxides

    DEFF Research Database (Denmark)

    Hamdy, A. A.; Nielsen, Gunnar Gissel

    1977-01-01

    In studying Se fixation, soil components capable of retaining Se were investigated. The importance of Fe hydrous oxides in the fixation of Se was established. The clay minerals common to soils, such as kaolinite, montmorillonite and vermiculite, all exhibited Se fixation, but greater fixation...

  1. Renormalizable N=2 supersymmetric and gauge invariant interactions from the N=2 harmonic superspace with central charges

    International Nuclear Information System (INIS)

    Saidi, E.H.

    1986-04-01

    The N=2 harmonic-superspace in the presence of central charges is developed. Renormalizable interactions unusual in N=2 supersymmetric theories, are derived in a consistent way. Symmetries generated by the central charges are discussed. A certain equivalence between N=2 harmonic superspace with and without central charges is established. A non-abelian generalization of the model is given. (author)

  2. ESTs analysis reveals putative genes involved in symbiotic seed germination in Dendrobium officinale.

    Directory of Open Access Journals (Sweden)

    Ming-Ming Zhao

    Full Text Available Dendrobiumofficinale (Orchidaceae is one of the world's most endangered plants with great medicinal value. In nature, D. officinale seeds must establish symbiotic relationships with fungi to germinate. However, the molecular events involved in the interaction between fungus and plant during this process are poorly understood. To isolate the genes involved in symbiotic germination, a suppression subtractive hybridization (SSH cDNA library of symbiotically germinated D. officinale seeds was constructed. From this library, 1437 expressed sequence tags (ESTs were clustered to 1074 Unigenes (including 902 singletons and 172 contigs, which were searched against the NCBI non-redundant (NR protein database (E-value cutoff, e(-5. Based on sequence similarity with known proteins, 579 differentially expressed genes in D. officinale were identified and classified into different functional categories by Gene Ontology (GO, Clusters of orthologous Groups of proteins (COGs and Kyoto Encyclopedia of Genes and Genomes (KEGG pathways. The expression levels of 15 selected genes emblematic of symbiotic germination were confirmed via real-time quantitative PCR. These genes were classified into various categories, including defense and stress response, metabolism, transcriptional regulation, transport process and signal transduction pathways. All transcripts were upregulated in the symbiotically germinated seeds (SGS. The functions of these genes in symbiotic germination were predicted. Furthermore, two fungus-induced calcium-dependent protein kinases (CDPKs, which were upregulated 6.76- and 26.69-fold in SGS compared with un-germinated seeds (UGS, were cloned from D. officinale and characterized for the first time. This study provides the first global overview of genes putatively involved in D. officinale symbiotic seed germination and provides a foundation for further functional research regarding symbiotic relationships in orchids.

  3. Three Replicons of Rhizobium sp. Strain NGR234 Harbor Symbiotic Gene Sequences

    Science.gov (United States)

    Flores, Margarita; Mavingui, Patrick; Girard, Lourdes; Perret, Xavier; Broughton, William J.; Martínez-Romero, Esperanza; Dávila, Guillermo; Palacios, Rafael

    1998-01-01

    Rhizobium sp. strain NGR234 contains three replicons: the symbiotic plasmid or pNGR234a, a megaplasmid (pNGR234b), and the chromosome. Symbiotic gene sequences not present in pNGR234a were analyzed by hybridization. DNA sequences homologous to the genes fixLJKNOPQGHIS were found on the chromosome, while sequences homologous to nodPQ and exoBDFLK were found on pNGR234b. PMID:9811668

  4. Optical Manipulation of Symbiotic Chlorella in Paramecium Bursaria Using a Fiber Axicon Microlens

    International Nuclear Information System (INIS)

    Taguchi, K; Hirota, S; Nakayama, H; Kunugihara, D; Mihara, Y

    2012-01-01

    In this paper, chemically etched axicon fiber was proposed for laser trapping of symbiotic chlorella from paramecium bursaria. We fabricated axicon micro lenses on a single-mode bare optical fiber by selective chemical etching technique. The laser beam from fiber axicon microlens was strongly focused and optical forces were sufficient to move a symbiotic chlorella. From experimental results, it was found that our proposed fiber axicon microlens was a promising tool for cell trapping without physical contact.

  5. Optical Manipulation of Symbiotic Chlorella in Paramecium Bursaria Using a Fiber Axicon Microlens

    Science.gov (United States)

    Taguchi, K.; Hirota, S.; Nakayama, H.; Kunugihara, D.; Mihara, Y.

    2012-03-01

    In this paper, chemically etched axicon fiber was proposed for laser trapping of symbiotic chlorella from paramecium bursaria. We fabricated axicon micro lenses on a single-mode bare optical fiber by selective chemical etching technique. The laser beam from fiber axicon microlens was strongly focused and optical forces were sufficient to move a symbiotic chlorella. From experimental results, it was found that our proposed fiber axicon microlens was a promising tool for cell trapping without physical contact.

  6. Host Preference between Symbiotic and Aposymbiotic Aphis fabae, by the Aphid Parasitoid, Lysiphlebus ambiguus

    Science.gov (United States)

    Cheng, Rui-Xia; Meng, Ling; Mills, Nickolas J; Li, Baoping

    2011-01-01

    Few empirical studies have directly explored the association between Buchnera aphidicola (Enterobacteriales: Enterobacteriaceae), the primary endosymbiont of aphids, and the life history strategies of aphid parasitoids. A series of paired-choice experiments were conducted to explore the preference of the parasitoid Lysiphlebus ambiguus Halliday (Hymenoptera: Aphididae) for symbiotic and aposymbiotic Aphis fabae Scopoli (Hemiptera: Aphididae) and the suitability of these hosts for parasitoid development. When given a choice between symbiotic and aposymbiotic aphids of the same instar, the parasitoid significantly preferred symbiotic over aposymbiotic aphids only during the later instars (L4 and adult). The suitability of aposymbiotic aphids for parasitoid development was equal to that of symbiotic aphids in terms of survivorship and sex ratio, but was significantly lower than that of symbiotic aphids for L4 and adult instars in development rate and/or female adult size. When given a choice between similar-sized symbiotic L2 and aposymbiotic L4 aphids, the parasitoid preferred the former. No significant differences in preference or host suitability were demonstrated when the parasitoid was given a choice between different instars of aposymbiotic aphids. While parasitoid lifetime fecundity increased with aphid instar at the time of oviposition, there was no significant influence of previous development from symbiotic versus aposymbiotic aphids. These results suggest that while L. ambiguus can discriminate between symbiotic and aposymbiotic A. fabae during later instars and when the aphids are of a similar size, the primary endosymbiont is not needed for successful parasitoid development; and its absence only compromises parasitoid growth reared from later instar aposymbiotic host. PMID:21870967

  7. New Results in {mathcal {N}}=2 N = 2 Theories from Non-perturbative String

    Science.gov (United States)

    Bonelli, Giulio; Grassi, Alba; Tanzini, Alessandro

    2018-03-01

    We describe the magnetic phase of SU(N) $\\mathcal{N}=2$ Super Yang-Mills theories in the self-dual Omega background in terms of a new class of multi-cut matrix models. These arise from a non-perturbative completion of topological strings in the dual four dimensional limit which engineers the gauge theory in the strongly coupled magnetic frame. The corresponding spectral determinants provide natural candidates for the tau functions of isomonodromy problems for flat spectral connections associated to the Seiberg-Witten geometry.

  8. Maxwellian Eye Fixation during Natural Scene Perception

    Science.gov (United States)

    Duchesne, Jean; Bouvier, Vincent; Guillemé, Julien; Coubard, Olivier A.

    2012-01-01

    When we explore a visual scene, our eyes make saccades to jump rapidly from one area to another and fixate regions of interest to extract useful information. While the role of fixation eye movements in vision has been widely studied, their random nature has been a hitherto neglected issue. Here we conducted two experiments to examine the Maxwellian nature of eye movements during fixation. In Experiment 1, eight participants were asked to perform free viewing of natural scenes displayed on a computer screen while their eye movements were recorded. For each participant, the probability density function (PDF) of eye movement amplitude during fixation obeyed the law established by Maxwell for describing molecule velocity in gas. Only the mean amplitude of eye movements varied with expertise, which was lower in experts than novice participants. In Experiment 2, two participants underwent fixed time, free viewing of natural scenes and of their scrambled version while their eye movements were recorded. Again, the PDF of eye movement amplitude during fixation obeyed Maxwell's law for each participant and for each scene condition (normal or scrambled). The results suggest that eye fixation during natural scene perception describes a random motion regardless of top-down or of bottom-up processes. PMID:23226987

  9. Maxwellian Eye Fixation during Natural Scene Perception

    Directory of Open Access Journals (Sweden)

    Jean Duchesne

    2012-01-01

    Full Text Available When we explore a visual scene, our eyes make saccades to jump rapidly from one area to another and fixate regions of interest to extract useful information. While the role of fixation eye movements in vision has been widely studied, their random nature has been a hitherto neglected issue. Here we conducted two experiments to examine the Maxwellian nature of eye movements during fixation. In Experiment 1, eight participants were asked to perform free viewing of natural scenes displayed on a computer screen while their eye movements were recorded. For each participant, the probability density function (PDF of eye movement amplitude during fixation obeyed the law established by Maxwell for describing molecule velocity in gas. Only the mean amplitude of eye movements varied with expertise, which was lower in experts than novice participants. In Experiment 2, two participants underwent fixed time, free viewing of natural scenes and of their scrambled version while their eye movements were recorded. Again, the PDF of eye movement amplitude during fixation obeyed Maxwell’s law for each participant and for each scene condition (normal or scrambled. The results suggest that eye fixation during natural scene perception describes a random motion regardless of top-down or of bottom-up processes.

  10. Estimating N2O processes during grassland renewal and grassland conversion to maize cropping using N2O isotopocules

    Science.gov (United States)

    Buchen, Caroline; Well, Reinhard; Flessa, Heinz; Fuß, Roland; Helfrich, Mirjam; Lewicka-Szczebak, Dominika

    2017-04-01

    Grassland break-up due to grassland renewal and grassland conversion to cropland can lead to a flush of mineral nitrogen from decomposition of the old grass sward and the decomposition of soil organic matter. Moreover, increased carbon and nitrogen mineralisation can result in enhanced nitrous oxide (N2O) emissions. As N2O is known to be an important greenhouse gas and a major precursor for ozone depletion, its emissions need to be mitigated by adjusting agricultural management practices. Therefore, it is necessary to understand the N2O processes involved, as well as the contribution of N2O reduction to N2. Apart from the widely used 15N gas flux method, natural abundance isotopic analysis of the four most abundant isotopocules of N2O species is a promising alternative to assess N2O production pathways. We used stable isotope analyses of soil-emitted N2O (δ18ON2O, δ15NN2Obulk and δ15NN2OSP= intramolecular distribution of 15N within the linear N2O molecule) with an isotopocule mapping approach to simultaneously estimate the magnitude of N2O reduction to N2 and the fraction of N2O originating from the bacterial denitrification pathway or fungal denitrification and/or nitrification. This approach is based on endmember areas of isotopic values for the N2O produced from different sources reported in the literature. For this purpose, we calculated two main scenarios with different assumptions for N2O produced: N2O is reduced to N2 before residual N2O is mixed with N2O of various sources (Scenario a) and vice versa (Scenario b). Based on this, we applied seven different scenario variations, where we evaluated the range of possible values for the potential N2O production pathways (heterotrophic bacterial denitrification and/or nitrifier denitrification and fungal denitrification and/or nitrification). This was done by using a range of isotopic endmember values and assuming different fractionation factors of N2O reduction in order to find the most reliable scenario

  11. Feasibility of N2 Binding and Reduction to Ammonia on Fe-Deposited MoS2 2D Sheets: A DFT Study

    KAUST Repository

    Azofra Mesa, Luis

    2017-05-19

    Based on the structure of the nitrogenase FeMo cofactor (FeMoco), it is reported that Fe deposited on MoS2 2D sheets exhibits high selectivity towards the spontaneous fixation of N2 against chemisorption of CO2 and H2 O. DFT predictions also indicate the ability of this material to convert N2 into NH3 with a maximum energy input of 1.02 eV as an activation barrier for the first proton-electron pair transfer.

  12. Linked linear mixed models: A joint analysis of fixation locations and fixation durations in natural reading.

    Science.gov (United States)

    Hohenstein, Sven; Matuschek, Hannes; Kliegl, Reinhold

    2017-06-01

    The complexity of eye-movement control during reading allows measurement of many dependent variables, the most prominent ones being fixation durations and their locations in words. In current practice, either variable may serve as dependent variable or covariate for the other in linear mixed models (LMMs) featuring also psycholinguistic covariates of word recognition and sentence comprehension. Rather than analyzing fixation location and duration with separate LMMs, we propose linking the two according to their sequential dependency. Specifically, we include predicted fixation location (estimated in the first LMM from psycholinguistic covariates) and its associated residual fixation location as covariates in the second, fixation-duration LMM. This linked LMM affords a distinction between direct and indirect effects (mediated through fixation location) of psycholinguistic covariates on fixation durations. Results confirm the robustness of distributed processing in the perceptual span. They also offer a resolution of the paradox of the inverted optimal viewing position (IOVP) effect (i.e., longer fixation durations in the center t