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)

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

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.

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

The effect of phosphorus application and liming in corn and soybean intercrop on the plant yield and symbiotic N fixation

International Nuclear Information System (INIS)

Sisworo, W.H.; Abdullah, N.; Rasyid, Havid; Soeminto, Bagyo

1986-01-01

A field experiment consisting of seven treatments and six replications was arranged in a randomized block design. The objectives of experiment were to study the effect of phosphorus placement and liming in corn and soybean intercrop on the plant yield and the amount of N fixed symbiotically by soybean. Results obtained shows the grain yield of soybean was influenced significantly by phosphorus placement, but corn was not. Fertilizer which was banded in the plant rows bellow seeds shows the higher grain yield of soybean that those broad-casted and incorporated with the soil or banded near the plant rows. Liming increased grain yield of soybean or corn as much as 31 percent higher than without lime. Lime also increased the amount of soybean N obtained from symbiotic N fixation. The partitioning of plant N requirement from soil, fixation, and fertilizer were subsequently 58, 36 and 6 percent. (author). 14 refs

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...... tree species across the entire forest age sequence. These findings show that symbiotic N 2 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 CO 2....

Genotypic Variation in Phosphorus Use Efficiency for Symbiotic Nitrogen Fixation in Voandzou (Vigna Subterranea)

Energy Technology Data Exchange (ETDEWEB)

Andriamananjara, A.; Rabeharisoa, L. [Laboratoire des Radio-isotopes, Universite d' Antananarivo, Antananarivo (Madagascar); Abdou, M. Malam [Laboratoire Banques de genes CERRA / KOLLO, Institut National de Recherche Agronomique du Niger (INRAN), Niamey (Niger); Masse, D. [Institut de Recherche pour le Developpement, UMR Eco and Sols, Montpellier, (France); Amenc, L.; Pernot, C.; Drevon, J. J. [Institut National de la Recherche Agronomique, UMR Eco and Sols, Montpellier (France)

2013-11-15

Vigna subterranea, known as voandzou or Bambara groundnut as an African indigenous crop which is often neglected or under-used in African subsistence agriculture. Preliminary research and country perceptions have shown its agronomic and nutritional properties, in particular under atypical climates of arid and tropical areas, and in saline soils. There is a high potential to increase the production by optimizing symbiotic nitrogen fixation (SNF) through effective inoculation even in nitrate-rich environments. In this study, Vigna subterranea inoculated with the reference strain of Bradyrhizobium sp. Vigna CB756 was studied in order to assess the symbiotic fixation potential of different cultivars and landraces of Madagascar, Niger and Mali under low-P and sufficient-P conditions. Six voandzou cultivars inoculated with Bradyrhizobium sp. Vigna CB756, were grown under hydroaeroponic culture for 6 weeks supplied with four phosphorus levels of 15, 30, 75 and 250 {mu}mol plant{sup -1} week{sup -1} in order to establish the response curve of voandzou to P supply, and to induce P deficient and sufficient levels. In another experiment five tolerant cultivars with high SNF and five sensitive cultivars with low SNF were chosen after a preliminary screening of 54 voandzou genotypes, including 50 landraces from Madagascar, Niger and Mali supplied with 2 P levels as P deficient and P sufficient (30 and 75 {mu}mol plant{sup -1} week{sup -1} ) under hydroaeroponic conditions. Genotypic variation in SFN for the high phosphorus use efficiency (PUE) was observed among the 54 cultivars and landraces. Variability was especially related to the nodule and shoot biomass, nodule permeability, nodule respiration and gene phytase expression. Contrasting cultivars and landraces in terms of PUE for SNF were selected for further evaluation under field conditions. (author)

Transcriptome analysis of two recombinant inbred lines of common bean contrasting for symbiotic nitrogen fixation

Science.gov (United States)

Common bean (Phaseolus vulgaris L.) is able to fix atmospheric nitrogen (N2) through symbiotic nitrogen fixation (SNF). Effective utilization of existing variability for SNF in common bean for genetic improvement requires an understanding of underlying genes and molecular mechanisms. The utility of ...

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.

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

2013-10-10

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 (50,000 kg carbon per hectare) in the first 12 years. 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.

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,

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......) in Danish and German experiments was 20% higher in the intercrop (P50B50) than in the respective sole crops, possibly influencing general crop yields and thereby competitive ability for other resources. Comparing all sites and seasons, the benefits of organic pea-barley intercropping for N acquisition were...

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.

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

Symbiotic N2 fixation by legumes growing in pots. 2. Uptake of VN-labelled NO3 , C2H2 reduction and H2 evolution by Trifolium subterraneum L. , Medicago truncatula Gaertn. and Acacia dealbata Link

Energy Technology Data Exchange (ETDEWEB)

Hopmans, P.; Chalk, P.M.; Douglas, L.A.

1983-01-01

The objectives of this study were to estimate symbiotic nitrogen fixation by two common pasture legumes, Trifolium subterraneum L. and Medicago truncatula Gaertn., and an Australian native legume, Acacia dealbata Link, growing in pots using an indirect isotopic method. This method was also used to calibrate the C2H2 reduction assay of the intact plants. In addition, hydrogen evolution was measured in an attempt to explain the variations in C2H2:N2 ratios between the species. 25 refs.; 1 figure; 4 tabs.

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

Estimating legume N-2 fixation in grass-clover mixtures of a grazed organic cropping system using two N-15 methods

DEFF Research Database (Denmark)

Vinther, F.P.; Jensen, E.S.

2000-01-01

The input of Nitrogen (N) through symbiotic N-2 fixation (SNF) in grass-clover mixtures was determined in an organic cropping. system for grazing during 3 years. The mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) was established by undersowing in spring...... barley (Hordeum vulgare L.) and maintained subsequently for two production years. Dinitrogen fixation was determined using the N-15 isotope dilution techniques and two labelling procedures. Using either pre-labelling of the soil with immobilisation of the N-15 by addition of a carbon source before...

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.

Biological Nitrogen Fixation Efficiency in Brazilian Common Bean Genotypes as Measured by {sup 15}N Methodology

Energy Technology Data Exchange (ETDEWEB)

Franzini, V. I.; Mendes, F. L. [Brazilian Agricultural Research Corporation, EMBRAPA-Amazonia Oriental, Belem, PA (Brazil); Muraoka, T.; Trevisam, A. R. [Center for Nuclear Energy in Agriculture, University of Sao Paulo, Piracicaba, SP (Brazil); Adu-Gyamfi, J. J. [Soil and Water Management and Crop Nutrition Laboratory, International Atomic Energy Agency, Seibersdorf (Austria)

2013-11-15

Common bean (Phaseolus vulgaris L.) represents the main source of protein for the Brazilian and other Latin-American populations. Unlike soybean, which is very efficient in fixing atmospheric N{sub 2} symbiotically, common bean does not dispense with the need for N fertilizer application, as the biologically fixed N (BNF) seems incapable to supplement the total N required by the crop. A experiment under controlled conditions was conducted in Piracicaba, Brazil, to assess N{sub 2} fixation of 25 genotypes of common bean (Phaseolus vulgaris L.). BNF was measured by {sup 15}N isotope dilution using a non-N{sub 2} fixing bean genotype as a reference crop. The common bean genotypes were grown in low (2.2 mg N kg{sup -1} soil) or high N content soil (200 mg N kg{sup -1} soil), through N fertilizer application, as urea-{sup 15}N (31.20 and 1.4 atom % {sup 15}N, respectively). The bean seeds were inoculated with Rhizobium tropici CIAT 899 strain and the plants were harvested at grain maturity stage. The contribution of BNF was on average 75% of total plant N content, and there were differences in N fixing capacity among the bean genotypes. The most efficient genotypes were Horizonte, Roxo 90, Grafite, Apore and Vereda, when grown in high N soil. None of the genotypes grown in low N soil was efficient in producing grains compared to those grown in high N soil, and therefore the BNF was not able to supply the total N demand of the bean crop. (author)

Phosphorus Use Efficiency for Symbiotic Fixation Nitrogen in Voandzou (Vigna Subterranea) Using Isotopic Exchange Method in Rhizotron

Energy Technology Data Exchange (ETDEWEB)

Andriamananjara, A.; Rabeharisoa, L. [Laboratoire des Radio-isotopes, Universite d' Antananarivo, Antananarivo (Madagascar); Masse, D. [Institut de Recherche pour le Developpement, UMR Eco and Sols, Montpellier, (France); Amenc, L.; Pernot, C.; Drevon, J. J. [Institut National de la Recherche Agronomique, UMR Eco and Sols, Montpellier, (France); Morel, C. [INRA-ENITA, Villenave d' Ornon (France)

2013-11-15

Low bioavailability of nitrogen and phosphorus is one of the main constraints in the acid soils with high P-fixing capacity. Plants adapt to low nutrient availability through various biological and physico-chemical mechanisms. Since genetic variation of N{sub 2} fixation exists in numerous legume species, optimization of symbiotic nitrogen fixation (SNF) under P deficiency could be a way to the replenishment of soil fertility in tropical soils. As the genetic potential of crops like Vigna subterranea (Bambara groundnut or voandzou) is little studied, although its agronomic potential is interesting for the farmers of Africa, a physiological study through legume screening for N{sub 2} fixation was performed with 54 cultivars from Madagascar, Niger and Mali, inoculated with the reference strain of Bradyrhizobium sp. Vigna CB756 in hydroponic culture under P deficiency and sufficiency (30 and 75 {mu}mol KH{sub 2}PO{sub 4} plant{sup -1} week {sup -1}, respectively), corresponding respectively to 28 and 70 mg P kg{sup -1} of soil. Large variability of nodulation and plant biomass was found among cultivars. These two parameters were generally correlated and the slope of the plant biomass regression as a function of nodulation was considered as an indicator of the efficiency in use of the rhizobial symbiosis. For the two cultivars most tolerant to P deficiency, V1 and V4 from Madagascar, the increase in use efficiency of the rhizobial symbiosis under P deficiency was linked with an increase in nodulated root O{sub 2} consumption linked to N{sub 2} fixation, and in phytase gene expression observed on the nodule sections by in situ RT- PCR. As the complexity of P compartments makes it difficult to assess the P bioavailability in the plant rhizosphere, an isotopic {sup 32}P exchange method was carried out in a rhizotron in order to assess the direct effect of the roots on P mobilization in rhizosphere soil, comparing V1 and V4 with 28 or 70 mg P kg{sup -1} of soil. Throughout

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

Nodulation, dry matter production and N2 fixation by fababean and chickpea as affected by soil moisture and potassium fertilizer

International Nuclear Information System (INIS)

Kurdali, F.; Al-Ain, F.; Al-Ahamma, M.

2003-01-01

The impact of three rates of K-fertilizer (0, 75, and 150 kg K 2 O/ha)on nodulation, dry matter production and N 2 fixation by fababean (Vicia faba L.) and chickpea (Cirer arietinum L.) was evaluated in a pot experiment. The plants were subjected to three soil moisture regimes (low, 45-50%; moderate, 55-60% and high 75-80% of field capacity). 15 N-isotope dilution method was employed to evaluate N 2 fixation using a non-fixing chickpea genotype as a reference crop. Water restriction drastically affected dry matter production, nodulation and N 2 fixation by both plant species. The negative effect of water stress on %N 2 fixed was more prominent in chickpea (11-58%) than in fababean (68-81%) under low and high % of field capacity, respectively. Plant species differed in their response to K-fertilizer as a mean to enhance growth and overcome the stress conditions. The higher level of K fertilizer increased both dry matter production and total N 2 fixed in fababean, but did not have any impact on chickpea. %N 2 fixed, however, appeared to be unaffected by K fertilizer as a mean of alleviating drought stress in both plant species. Therefore, it appears that, under the experimental conditions, the beneficial effect of potassium on water-stressed fababean resulted from stimulation the growth rather than improving the N 2 -fixation efficiency. However, under well-watered plants, a high requirement of the symbiotic system to potassium is needed to ensure and optimal growth and N 2 -fixation. (author)

A Medicago truncatula Tobacco Retrotransposon Insertion Mutant Collection with Defects in Nodule Development and Symbiotic Nitrogen Fixation1[W][OA

Science.gov (United States)

Pislariu, Catalina I.; D. Murray, Jeremy; Wen, JiangQi; Cosson, Viviane; Muni, RajaSekhara Reddy Duvvuru; Wang, Mingyi; A. Benedito, Vagner; 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.

2012-01-01

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. PMID:22679222

Elevated CO2 concentration around alfalfa nodules increases N2 fixation

OpenAIRE

Fischinger, Stephanie A.; Hristozkova, Marieta; Mainassara, Zaman-Allah; Schulze, Joachim

2009-01-01

Nodule CO2 fixation via PEPC provides malate for bacteroids and oxaloacetate for N assimilation. The process is therefore of central importance for efficient nitrogen fixation. Nodule CO2 fixation is known to depend on external CO2 concentration. The hypothesis of the present paper was that nitrogen fixation in alfalfa plants is enhanced when the nodules are exposed to elevated CO2 concentrations. Therefore nodulated plants of alfalfa were grown in a hydroponic system that allowed separate ae...

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

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

N2-fixation by freshly isolated Nostoc from coralloid roots of the cycad Macrozamia riedlei (Fisch. ex Gaud.) Gardn

International Nuclear Information System (INIS)

Lindblad, P.; Atkins, C.A.; Pate, J.S.

1991-01-01

Nitrogenase (EC 1.7.99.2) activity (acetylene reduction) and nitrogen fixation ( 15 N 2 fixation) were measured in cyanobacteria freshly isolated from the coralloid roots of Macrozamia riedlei (Fisch. ex Gaud.) Gardn. The data indicate that cyanobacteria within cycad coralloid roots are differentiated specifically for symbiotic functioning in a microaerobic environment. Specializations include a high heterocyst frequency, enhanced permeability to O 2 , and a direct dependence on the cycad for substrates to support nitrogenase activity

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)

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

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

Science.gov (United States)

Pohajda, Ines; Babić, Katarina Huić; Rajnović, Ivana; Kajić, Sanja; Sikora, Sanja

2016-12-01

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 populations of 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 amplification 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 S 17/2 and S 21/6 . 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 S 21/6 . These results indicate different symbiotic

Symbiotic N2 fixation activity in relation to C economy of Pisum sativum L. as a function of plant phenology.

Science.gov (United States)

Voisin, A S; Salon, C; Jeudy, C; Warembourg, F R

2003-12-01

The relationships between symbiotic nitrogen fixation (SNF) activity and C fluxes were investigated in pea plants (Pisum sativum L. cv. Baccara) using simultaneous 13C and 15N labelling. Analysis of the dynamics of labelled CO2 efflux from the nodulated roots allowed the different components associated with SNF activity to be calculated, together with root and nodule synthetic and maintenance processes. The carbon costs for the synthesis of roots and nodules were similar and decreased with time. Carbon lost by turnover, associated with maintenance processes, decreased with time for nodules while it increased in the roots. Nodule turnover remained higher than root turnover until flowering. The effect of the N source on SNF was investigated using plants supplied with nitrate or plants only fixing N2. SNF per unit nodule biomass (nodule specific activity) was linearly related to the amount of carbon allocated to the nodulated roots regardless of the N source, with regression slopes decreasing across the growth cycle. These regression slopes permitted potential values of SNF specific activity to be defined. SNF activity decreased as the plants aged, presumably because of the combined effects of both increasing C costs of SNF (from 4.0 to 6.7 g C g-1 N) and the limitation of C supply to the nodules. SNF activity competed for C against synthesis and maintenance processes within the nodulated roots. Synthesis was the main limiting factor of SNF, but its importance decreased as the plant aged. At seed-filling, SNF was probably more limited by nodule age than by C supply to the nodulated roots.

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)

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)

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

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.

Medicago truncatula copper transporter 1 (MtCOPT1) delivers copper for symbiotic nitrogen fixation.

Science.gov (United States)

Senovilla, Marta; Castro-Rodríguez, Rosario; Abreu, Isidro; Escudero, Viviana; Kryvoruchko, Igor; Udvardi, Michael K; Imperial, Juan; González-Guerrero, Manuel

2018-04-01

Copper is an essential nutrient for symbiotic nitrogen fixation. This element is delivered by the host plant to the nodule, where membrane copper (Cu) transporter would introduce it into the cell to synthesize cupro-proteins. COPT family members in the model legume Medicago truncatula were identified and their expression determined. Yeast complementation assays, confocal microscopy and phenotypical characterization of a Tnt1 insertional mutant line were carried out in the nodule-specific M. truncatula COPT family member. Medicago truncatula genome encodes eight COPT transporters. MtCOPT1 (Medtr4g019870) is the only nodule-specific COPT gene. It is located in the plasma membrane of the differentiation, interzone and early fixation zones. Loss of MtCOPT1 function results in a Cu-mitigated reduction of biomass production when the plant obtains its nitrogen exclusively from symbiotic nitrogen fixation. Mutation of MtCOPT1 results in diminished nitrogenase activity in nodules, likely an indirect effect from the loss of a Cu-dependent function, such as cytochrome oxidase activity in copt1-1 bacteroids. These data are consistent with a model in which MtCOPT1 transports Cu from the apoplast into nodule cells to provide Cu for essential metabolic processes associated with symbiotic nitrogen fixation. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Genome-wide association analysis of symbiotic nitrogen fixation in common bean

Science.gov (United States)

A genome-wide association study (GWAS) was conducted to explore the genetic basis of variation for symbiotic nitrogen fixation (SNF) and related traits in the Andean diversity panel (ADP) comprised of 259 common bean (Phaseolus vulgaris) genotypes. The ADP was evaluated for SNF and related traits in...

Irradiation Effect on the symbiotic fixation of nitrogen in Bean (Phaseolus vulgaris L)

International Nuclear Information System (INIS)

Roveda Hoyos, Gabriel; Rozo Avila, Liliana; Sierra Daza, Soraya

1997-01-01

The efficiency of legume - Rhizobium association is determined by biological (plant and bacteria) and environmental factors (soil and climate); for that reason, the best cultivars -Rhizobium strains combinations for each specie of legume must be selected according to the specifics environmental conditions. One of the most important sun light qualities are the irradiance levels to which the plants are exposed, because these levels have a close relation with the photosynthetic process, and also affect the biological nitrogen fixation, which has a high energetic requirements for symbiosis. The propose of this work was to determine the effect of irradiance on the Biological Nitrogen Fixation in common bean seedlings, under two environments conditions 100 and 500 moles m - 2 seg - 1 (IA and IB respectively), an nutrition control. The experimental results suggest that in the case of common bean, the irradiance requirements change depending on the Rhizobium strain that has be used in the symbiotic association. Both inoculated and non-inoculated plants with Rhizobium showed different behavior according to the levels of irradiance under which the plants were exposed. Under the irradiance of 500 moles m 2 seg - 1 (IA) the highest values of weight, area of plants, number and weight of nodules, nitrogen and phosphors content in leaves were founded, however under the lowest irradiance 100 μ moles m 2 seg - 1 (IB), the plants showed the largest root and steam, as a result of increase of bud distance, this behavior is known etiolation. The irradiance levels under which the plants are exposed determine the efficiency of symbiosis. The experimental results showed that the irradiance levels, no only affect the plant growth, but also the strains behavior. These results were easily observed in the treatments where ICA P-12 and ICA P-19 strains were used, for the dry weight of leaves, root and leaves area, number and weight of nodules, and nitrogen content of leaves in the plant. The

Nitrogen fixation by legumes in retorted shale

Energy Technology Data Exchange (ETDEWEB)

Hersman, L E; Molitoris, E; Klein, D A

1981-01-01

A study was made to determine whether retorted shale additions would significantly affect symbiotic N/sub 2/ fixation. Results indicate that small additions of the shale may stimulate plant growth but with higher concentrations plants are stressed, resulting in a decreased biomass and a compensatory effect of an increased number of nodules and N/sub 2/ fixation potential. (JMT)

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...... fixation (SNF). In legumes, SNF occurs in specialized organs, called nodules, which contain millions of nitrogen-fixing rhizobia, called bacteroids. The induction of nodule-specific plant genes, including those encoding symbiotic leghemoglobins (Lb), accompanies nodule development. Leghemoglobins...... 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...

How can increased use of biological N2 fixation in agriculture benefit the environment?

International Nuclear Information System (INIS)

Jensen, Erik Steen; Hauggaard-Nielsen, Henrik

2001-01-01

Asymbiotic, associative or symbiotic biological N 2 fixation (BNF), is a free and renewable resource, which should constitute an integral part of sustainable agro-ecosystems. Yet there has been a rapid increase in use of fertiliser N and a parallel decline in the cultivation of leguminous plants and BNF, especially in the developed world. Fertilisers have boosted crop yields, but intensive agricultural systems have increasingly negative effects on the atmospheric and aquatic environments. BNF, either alone or in combination with fertilisers and animal manures, may prove to be a better solution to supply nitrogen to the cropping systems of the future. This review focuses on the potential benefit of BNF on the environment especially on soil acidification, rhizosphere processes and plant CO 2 fixation. As fertiliser N has supplanted BNF in agriculture the re-substitution of BNF is considered. What is the consequence of fertiliser N production on energy use? The effect of fertiliser use on the release of the greenhouse gas CO 2 is estimated at approximately 1 % of the global anthropogenic emission of CO 2 . The role of BNF on nitrogen cycling, ammonia volatilisation, N 2 O emission and NO 3 leaching suggests that BNF is less likely than fertilisers to cause losses during pre-cropping and cropping. Sometimes however the post-harvest losses may be greater, due to the special qualities of legume residues. Nevertheless, legumes provide other 'ecological services' including improved soil structure, erosion protection and greater biological diversity. (author)

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

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...

Effect of lentil cultivar on N2 fixation and N partitioning

International Nuclear Information System (INIS)

Kurdali, F.; Kalifa, K.; Al-Shamma, M.

1996-12-01

The study conducted on five lentil cultivars. the results showed that dry matter production, nodulation and N sup 2 fixation were influenced by the cultivar. Beyond flowering, N sup 2 fixation, soil N uptake, and N and P remobilization differed by the cultivar. (author). 32 Refs., 7 Figs., 9 Tabs

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

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

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.

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.

Dinitrogen fixation measurements in some legume crops grown under irrigated condition without bacteria inoculation using 15N

International Nuclear Information System (INIS)

Kurdali, F.; Sharabi, N.D.

1991-01-01

N 2 -fixation in some legume crops: Faba bean Vicia faba, common bean pisum sativum, lentil lens esculenta, chick pea cicer artinum and vetch vicia arvillia grown under irrigated conditions without Rhizobium inoculation was estimated using 15 N-labelled fertilizer method. Barley was used as a reference crop. Significant differences occured in N 2 -fixation capacity among legume crops at flowering and podding stages. The highest percentage of Nitrogen fixed occured in faba bean (88% of total N), while lower values were observed in the other crops: Lentil 84%, vetch 68%, common pea 67% and chick pea 57%. Moreover, amounts of N 2 -fixed were 171, 138, 100, 90 and 13 Kg. N. ha -1 respectively for faba bean, lentil, vetch, common pea and chick pea. This clearly indicates the importance of biological dinitrogen fixation in local legume crops nodulated with indigenous Rhizobium strains regarding to N-soil enrichment. Further investigations must be focused on the selection of both plant species and Rhizobium strains in order to obtain a good symbiotic system. (author). 2 figs

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

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.

Studies in Sri Lanka on cowpea: N2 fixation, growth, yield, and effects on cereals

International Nuclear Information System (INIS)

Senaratne, R.; Dayatilake, G.A.; Subasinghe, S.

1998-01-01

The impact of seed inoculation and N-fertilization on nodulation, plant dry-matter production, and seed yield was studied through a series of field experiments with cultivars of cowpea. In some instances there were positive growth responses to applied N, indicating the potential to improve N 2 fixation and yields by combining compatible genotypes and bradyrhizobial strains. Beneficial residual effects on growth of subsequent maize could not be related to N 2 fixation by the preceding cowpea. Although there was no evidence of direct transfer of N from cowpea to intercropped maize, there was greater efficiency of use of N for total crop production during intercropping

Genomic resources for identification of the minimal N2 -fixing symbiotic genome.

Science.gov (United States)

diCenzo, George C; Zamani, Maryam; Milunovic, Branislava; Finan, Turlough M

2016-09-01

The lack of an appropriate genomic platform has precluded the use of gain-of-function approaches to study the rhizobium-legume symbiosis, preventing the establishment of the genes necessary and sufficient for symbiotic nitrogen fixation (SNF) and potentially hindering synthetic biology approaches aimed at engineering this process. Here, we describe the development of an appropriate system by reverse engineering Sinorhizobium meliloti. Using a novel in vivo cloning procedure, the engA-tRNA-rmlC (ETR) region, essential for cell viability and symbiosis, was transferred from Sinorhizobium fredii to the ancestral location on the S. meliloti chromosome, rendering the ETR region on pSymB redundant. A derivative of this strain lacking both the large symbiotic replicons (pSymA and pSymB) was constructed. Transfer of pSymA and pSymB back into this strain restored symbiotic capabilities with alfalfa. To delineate the location of the single-copy genes essential for SNF on these replicons, we screened a S. meliloti deletion library, representing > 95% of the 2900 genes of the symbiotic replicons, for their phenotypes with alfalfa. Only four loci, accounting for < 12% of pSymA and pSymB, were essential for SNF. These regions will serve as our preliminary target of the minimal set of horizontally acquired genes necessary and sufficient for SNF. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

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.

Symbiotic dinitrogen fixation measurement in vetch-barley mixed swards using 15 N methodology

International Nuclear Information System (INIS)

Kurdali, F.; Sharabi, N.E.

1995-01-01

Field experiment on vetch and barley grown in monoculture and in mixed culture (3:1) under rain-fed conditions was conducted in 1991-1992 and 1992-1993 growing season. Three harvests were effectuated on one treatment throughout the growing season. While, other plots were harvested once at physiological maturity stage. Our results showed the importance of mixed cropping system of vetch and barley grown under rain fed conditions in terms of dry matter production, total nitrogen content and land use efficiency expressed as land equivalent ration (L.E.R). This advantage is clear in the plants harvested once at the end of the season. Therefore, it is important to grow legumes and cereals under rain fed conditions and to be left until late stage of growth and fed by animals directly. On the other hand, only two harvests could be done in the season with no additional harvests because this may weaken the plant growth, and as a result of the last approach we will obtained poor production due to unpredicated an appropriate rain fall after the second harvest (April). Nitrogen fixation efficiency in vetch measured by sup 1 sup 5 N isotop dilution method varied with the number of harvests and the procedure adopted in culture. Comparing the results of %Ndfa of vetch between monoculture and mixed culture showed that the values in most cases were higher in mixed culture. The competition between vetch and barley in the mixed stand for soil N-uptake made the barley supplements its N requirements from soil. The poor competitiveness of vetch capability for soil N-uptake enhanced it to fix more nitrogen. On the other hand, N residual after harvest was higher in the mixed treatment than the others. Positive and high final nitrogen balance were observed with the inclusion of vetch in the mixture. We excluded, under the current experimental conditions, the possibility of N-transfer from vetch to barley due to the insignificant differences in the value of sup 1 sup 5 N atom excess for

Effect of neem cake/fertilizers on symbiotic and non-symbiotic N2 fixing bacteria

International Nuclear Information System (INIS)

Akhtar, S.; Solangi, A.H.; Gilani, G.; Pirzada, M.H.

2002-01-01

Neem cake amendment in soil at 1.3% no adverse effect on the population of four symbiotic Rhizobium species viz., japonicum, R. leguminosarum, R. Phaseoli and R. Fredii and three non-symbiotic free living nitrogen fixers bacteria viz., Pseudomonas diazotrophicus, Klebsiella planticola and Enterobacter cloacae. Neem cake extracted with n-hexane stimulated the growth of Rhizobium species in vitro, whereas Neem cake expeller extracted neither inhibited nor stimulated the growth of Rhizobium species except for R. Fredii, whose was slightly retarded. The fertilizers (urea, NPK and DAP) had no adverse effect on these bacteria even at the dosage ten times higher the recommended dose. (author)

Symbiotic dinitrogen fixation measurement in vetch-barley mixed swards using {sup 15} N methodology

Energy Technology Data Exchange (ETDEWEB)

Kurdali, F; Sharabi, N E [Atomic Energy Commission, Damascus (Syrian Arab Republic). Dept. of Radiation Agriculture

1995-01-01

Field experiment on vetch and barley grown in monoculture and in mixed culture (3:1) under rain-fed conditions was conducted in 1991-1992 and 1992-1993 growing season. Three harvests were effectuated on one treatment throughout the growing season. Our results showed the importance of mixed cropping system of vetch and barley grown under rain fed conditions in terms of dry matter production, total nitrogen content and land use efficiency expressed as land equivalent ration (L.E.R). This advantage is clear in the plants harvested once at the end of the season. Therefore, it is important to grow legumes and cereals under rain fed conditions and to be left until late stage of growth and fed by animals directly. On the other hand, only two harvests could be done in the season with no additional harvests because this may weaken the plant growth, and as a result of the last approach we obtained poor production due to unpredicated an appropriate rain fall after the second harvest (April). Nitrogen fixation efficiency in vetch measured by {sup 1 5} N isotope dilution method varied with the number of harvests and the procedure adopted in culture. Comparing the results of %Ndfa of vetch between monoculture and mixed culture showed that the values in most cases were higher in mixed culture. The competition between vetch and barley in the mixed stand for soil N-uptake made the barley supplements its N requirements from soil. The poor competitiveness of vetch capability for soil N-uptake enhanced it to fix more nitrogen. On the other hand, N residual after harvest was higher in the mixed treatment than the others. Positive and high final nitrogen balance were observed with the inclusion of vetch in the mixture. We excluded, under the current experimental conditions, the possibility of N-transfer from vetch to barley due to the insignificant differences in the value of {sup 1 5} N atom excess for barley between the two types of farming. 35 refs., 2 figs., 15 tabs.

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

Symbiotic N fixation and fertilizer nitrogen use efficiency in legume-cereal intercropping systems

International Nuclear Information System (INIS)

Jena, D.; Misra, C.

1990-01-01

On a lateritic soil at Bhubaneswar short duration rice, finger millet, maize, groundnut, pigeon pea, black gram were grown alone or as intercrop in microplots (1mx1m). Thirty days after germination, 15 N tagged urea (3% a.e.) solutions was applied to all the treatments so as to provide 40 kg N ha -1 for the cereals, 10 kg n ha -1 for the legumes and 20 kg N ha -1 for cereal plus legumes. The results show the fertilizer efficiency values to be nearly 62 to 69 per cent for rice, 53 per cent for maize and 22 percent for finger millet. These values were 12 to 17 per cent for pigeon pea, 18 percent for black gram and 23 percent for groundnut. Averaged over the cropping system and fertilizer doses, the nitrogen fixed by legumes, viz,pigeon-pea, black gram and groundnut were 16.3, 15.5 and 17.5 kg ha -1 , respectively, within 60 days of crop growth. Horse gram grown as a sequence crop during the dry season (after the harvest of wet season crops) using the residual soil water and nutrients appears to utilize the residual 15 N better when it follows the non-legumes compared with that when it follows the legumes. (author). 5 refs., 5 tabs

Taxonomic identity determines N2 fixation by canopy trees across lowland tropical forests.

Science.gov (United States)

Wurzburger, Nina; Hedin, Lars O

2016-01-01

Legumes capable of fixing atmospheric N2 are abundant and diverse in many tropical forests, but the factors determining ecological patterns in fixation are unresolved. A long-standing idea is that fixation depends on soil nutrients (N, P or Mo), but recent evidence shows that fixation may also differ among N2-fixing species. We sampled canopy-height trees across five species and one species group of N2-fixers along a landscape P gradient, and manipulated P and Mo to seedlings in a shadehouse. Our results identify taxonomy as the major determinant of fixation, with P (and possibly Mo) only influencing fixation following tree-fall disturbances. While 44% of trees did not fix N2, other trees fixed at high rates, with two species functioning as superfixers across the landscape. Our results raise the possibility that fixation is determined by biodiversity, evolutionary history and species-specific traits (tree growth rate, canopy stature and response to disturbance) in the tropical biome. © 2015 John Wiley & Sons Ltd/CNRS.

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...

Optimising biological N2 fixation by legumes in farming systems

International Nuclear Information System (INIS)

Hardarson, Gudni; Atkins, Craig

2001-01-01

Whether grown as pulses for grain, as green manure, as pastures or as the tree components of agro-forestry systems, the value of leguminous crops lies in their ability to fix atmospheric N 2 , so reducing the use of expensive fertiliser N and enhancing soil fertility. N 2 fixing legumes provide the basis for developing sustainable farming systems that incorporate integrated nutrient management. By exploiting the stable nitrogen isotope 15 N, it has been possible to reliably measure rates of N 2 fixation in a wide range of agro-ecological field situations involving many leguminous species. The accumulated data demonstrate that there is a wealth of genetic diversity among legumes and their Rhizobium symbionts which can be used to enhance N 2 fixation. Practical agronomic and microbiological means to maximise N inputs by legumes have also been identified. (author)

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.

N2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise

Directory of Open Access Journals (Sweden)

M. Caffin

2018-05-01

Full Text Available We performed nitrogen (N budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP Ocean during austral summer conditions (February–March 2015. Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N2 fixation, nitrate turbulent diffusion, atmospheric deposition and leaving the photic layer (particulate N export. The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C. N2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m−2 d−1 and LD B (706 ± 302 µmol N m−2 d−1, and the diazotroph community was dominated by Trichodesmium. N2 fixation rates were lower (59 ± 16 µmol N m−2 d−1 at LD C, and the diazotroph community was dominated by unicellular N2-fixing cyanobacteria (UCYN. At all stations, N2 fixation was the major source of new N (> 90 % before atmospheric deposition and upward nitrate fluxes induced by turbulence. N2 fixation contributed circa 13–18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio  =  particulate carbon export ∕ primary production was maximum at LD A (9.7 % and was higher than the e ratio in most studied oligotrophic regions (< 5 %, indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to

Assessment of N2 fixing efficiency of Beijerinckia indica and Azospirillum brasilense in Sorghum (Sorghum bicolor (L.) moench) using 15N tracer

International Nuclear Information System (INIS)

Kanimoli, S.; Marimuthu, P.; Arulmozhiselvan, K.

2010-01-01

For studying the benefits of inoculation of N 2 fixing diazotrophs in the root zone of sorghum crop, a pot culture was conducted on neutral red sandy loam soil with sorghum cv. CO26, using 15 N tracer. At the end of 45 days duration after sowing, Beijerinckia indica inoculation contributed 56.9 per cent N derived from N 2 fixation, out of total N concentration in whole drymatter of sorghum plant. It proved to be the efficient N 2 fixer by contributing N from N 2 fixation to the tune of 17.6 Kg -1 . Accumulation of N derived from N 2 fixation from B. indica was primarily in leaf blade (50.0%) followed by stem (31.8%), leaf sheath (14.0%) and root (4.2%). Inoculation of Azospirillum brasllense accelerated uptake of N from soil and fertilizer N sources compared to B. indica and hence registered low N fixation. (author)

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.

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.

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.

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...

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

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

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.

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

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

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.

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

Science.gov (United States)

Nina Wurzburger; Chelcy Ford Miniat

2013-01-01

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...

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.

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

Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean

Science.gov (United States)

Benavides, Mar; Shoemaker, Katyanne M.; Moisander, Pia H.; Niggemann, Jutta; Dittmar, Thorsten; Duhamel, Solange; Grosso, Olivier; Pujo-Pay, Mireille; Hélias-Nunige, Sandra; Fumenia, Alain; Bonnet, Sophie

2018-05-01

The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L-1 d-1) but consistently detected across all depths and stations, representing ˜ 6-88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed

Measurement of N2 fixation in Sesbania aculeata and Sorghum bicolor L. grown in intercropping system using 15N isotopic dilution technique

International Nuclear Information System (INIS)

Kurdali, F.; Khalifa, K.; Janat, M.

2001-09-01

A field experiment on Sesbania aculeata and Sorghum bicolor grown in mono cropping and in inter cropping systems was conducted under non-saline conditions (soil EC e 0.16, water EC w 1dS/m) to evaluate dry matter production, total N yield, soil N uptake and N 2 -fixation using 15 N isotope dilution method. Three different row ratios of sesbania (ses) and sorghum (sor) were subjected in the inter cropping system (2ses: 1sot; 1ses: 1sor and 1ses: 2sor row ratio). Dry matter yield of sole sorghum was higher than that of sole sesbania, and it was similar to that produced by the inter cropping treatments. However, total N yield of sole sorghum was significantly the lowest, with no differences being obtained between sole sesbania and inter cropping treatments. The LERs of total N yield were, in all cases, higher than 1, reflecting a greater advantage of inter cropping system in terms of land use efficiency. Percentages of N 2 fixation in the inter cropped sesbania were considerably enhanced compared with the pure stand of sesbania. This was mainly attributed to the depletion of soil N resulting from the greater apparent competitiveness of sorghum for soil N, and consequently, a greater dependence of sesbania on N 2 fixation. However, the degree of the intraspecific competition for soil N uptake was affected by the proportion of crops in the mixture, and it was considerably reduced in the 2ses: 1sor row ratio. This was demonstrated when an equal depletion of soil and fertilizer N uptake occurred for both crops. We excluded in all-inter cropping treatments the possibility of N transfer from sesbania to sorghum. Row inter cropping, with crops grown in alternation of two rows of sesbania with one row of sorghum, seemed to be the most adequate row ratio in terms of total N yield, LER, N 2 -fixation and soil N uptake balance of the component crops. (author)

N2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)

Science.gov (United States)

Caffin, Mathieu; Moutin, Thierry; Foster, Rachel Ann; Bouruet-Aubertot, Pascale; Michelangelo Doglioli, Andrea; Berthelot, Hugo; Guieu, Cécile; Grosso, Olivier; Helias-Nunige, Sandra; Leblond, Nathalie; Gimenez, Audrey; Petrenko, Anne Alexandra; de Verneil, Alain; Bonnet, Sophie

2018-05-01

We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (February-March 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N2 fixation rates were extremely high at both LD A (593 ± 51 µmol N m-2 d-1) and LD B (706 ± 302 µmol N m-2 d-1), and the diazotroph community was dominated by Trichodesmium. N2 fixation rates were lower (59 ± 16 µmol N m-2 d-1) at LD C, and the diazotroph community was dominated by unicellular N2-fixing cyanobacteria (UCYN). At all stations, N2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N2 fixation contributed circa 13-18 % of primary production in the MA region and 3 % in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio = particulate carbon export / primary production) was maximum at LD A (9.7 %) and was higher than the e ratio in most studied oligotrophic regions (leading to N accumulation in the upper layer appears as a characteristic of the WTSP during the summer season.

Biological nitrogen (N) fixation - The source of N nutrient to increase yield

International Nuclear Information System (INIS)

Heiling, M.; Hardarson, G.

2006-01-01

Nitrogen is an essential plant nutrient. It is the nutrient that is most commonly deficient, contributing to reduced agricultural yields throughout the world. Developing countries used more than 85 million metric tones of nitrogenous fertilizer in 2003, worth billions of US dollars. Such fertilizer expenditure can be significantly reduced by incorporating biological nitrogen fixed leguminous crops into a growing rotation. In leguminous crops, a symbiotic relationship between a bacterium called Rhizobium and legumes can provide large amounts of nitrogen to the plant and subsequently to soils where they are grown. In this process the bacteria form nodules on the root system and convert the nitrogen coming from air into molecules that can be absorbed by the plants. Beside their fertilizing properties, legumes are rich in protein and constitute a very important role in the human and animal nutrition. In the Soil Science Unit (SSU) of the FAO/IAEA Agriculture and Biotechnology Laboratory fellows from all over the world receive training in the use of 15 N stable isotope techniques to optimise the nitrogen fixation. Several parameters such as the placement of the nodules on the legume root system, the amount of soil mineral nitrogen and phosphorus fertilizer applied and the temperature have an impact on the amount of nitrogen fixed by the plant. It is therefore important to identify relative importance of these parameters on biological N fixation. The 15 N isotope dilution method is an appropriate technique to test the biological nitrogen fixation in the laboratory first. This useful knowledge can then be communicated to the farmers and can be tested under field conditions

Breeding for traits supportive of nitrogen fixation in legumes

International Nuclear Information System (INIS)

Herridge, David F.

2001-01-01

As the potential economic benefits of enhancing dinitrogen (N 2 ) fixation of crop, pasture and forage legumes are substantial, the idea that legume breeding could play a role in enhancing N 2 fixation was advanced more than 50 years ago. Various programmes have sought to genetically improve a wide range of species, from pasture legumes such as red clover (Trifolium pratense) to the crop legumes like soybean (Glycine max) and common bean (Phaseolus vulgaris). In some the selection trait was yield, whilst in others it was high plant reliance on N 2 fixation (%Ndfa). A third strategy was to optimise legume nodulation through specific nodulation traits, e.g. mass, duration, promiscuous and selective nodulation. Plant genetic variation was sought from natural populations or created through mutagenesis. Although methods for assessing single plants and populations of plants for yield and %Ndfa varied over the years, it is now clear that measurements based on either 15 N or xylem solute analysis are the most reliable. Methodological issues as well as poor focus plagued many of the earlier programmes, since enhancing N 2 fixation essentially involves adapting legumes to fix more N when growing in N-poor soils. Programmes in which plant genotypes are inoculated with effective rhizobia and screened under conditions of low soil N maximise the symbiotic potential of the legume. (author)

Co-occurrence of methanogenesis and N{sub 2} fixation in oil sands tailings

Energy Technology Data Exchange (ETDEWEB)

Collins, C.E. Victoria [Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2G7 (Canada); Foght, Julia M. [Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9 (Canada); Siddique, Tariq, E-mail: tariq.siddique@ualberta.ca [Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2G7 (Canada)

2016-09-15

Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N{sub 2} fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N{sub 2} headspace. Some cultures were further amended with citrate, which is used in oil sands processing, as a relevant carbon source, and/or with PAM. After an initial delay, N-deficient cultures with or without PAM produced methane (CH{sub 4}) at the same rate as N-containing cultures, indicating a mechanism of overcoming apparent N-deficiency. Acetylene reduction and {sup 15}N{sub 2} incorporation in all N-deficient cultures (with or without PAM) suggested active N{sub 2} fixation concurrently with methanogenesis but inability to use PAM as a N source. 16S rRNA gene pyrosequencing revealed little difference between archaeal populations regardless of N content. However, bacterial sequences in N-deficient cultures showed enrichment of Hyphomicrobiaceae and Clostridium members that might contain N{sub 2}-fixing species. The results are important in understanding long-term production of biogenic greenhouse gases in oil sands tailings. - Highlights: • Methanogenesis in oil sands tailings can occur under nitrogen depleted conditions. • {sup 15}N{sub 2} isotopic analysis reveals that indigenous microbes can fix N{sub 2} for microbial metabolism and methanogenesis. • 16S rRNA gene analysis suggests that members of Hyphomicrobiaceae and Clostridium may be involved in N{sub 2} fixation. • This is the first report that describes co-occurrence of methanogenesis and nitrogen fixation in oil sands tailings.

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)

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.

Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean

Directory of Open Access Journals (Sweden)

M. Benavides

2018-05-01

Full Text Available The western tropical South Pacific (WTSP Ocean has been recognized as a global hot spot of dinitrogen (N2 fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L−1 d−1 but consistently detected across all depths and stations, representing ∼ 6–88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW. This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2

New Perspectives on Nitrogen Fixation Measurements Using 15N2 Gas

Directory of Open Access Journals (Sweden)

Nicola Wannicke

2018-04-01

Full Text Available Recently, the method widely used to determine 15N2 fixation rates in marine and freshwater environments was found to underestimate rates because the dissolution of the added 15N2 gas bubble in seawater takes longer than theoretically calculated. As a solution to the potential underestimate of rate measurements, the usage of the enriched water method was proposed to provide constant 15N2 enrichment. Still, the superiority of enriched water method over the previously used bubble injection remains inconclusive. To clarify this issue, we performed laboratory based experiments and implemented the results into an error analysis of 15N2 fixation rates. Moreover, we conducted a literature search on the comparison of the two methods to calculate a mean effect size using a meta-analysis approach. Our results indicate that the error potentially introduced by an equilibrium phase of the 15N2 gas is −72% at maximum for experiments with very short incubation times of 1 h. In contrast, the underestimation was negligible for incubations lasting 12–24 h (error is −0.2%. Our meta-analysis indicates that 84% of the measurements in the two groups will overlap and there is a 61% chance that a sample picked at random from the enriched water group will have a higher value than one picked at random from the bubble group. Overall, the underestimation of N2 fixation rates when using the bubble method relative to the enriched water method is highly dependent on incubation time and other experimental conditions and cannot be generalized.

Effects of N management on growth, N-2 fixation and yield of soybean

NARCIS (Netherlands)

Gan, YB; Stulen, [No Value; Posthumus, F; van Keulen, H; Kuiper, P

Soybean (Glycine max) is one of the most important food and cash crops in China. Although soybean has the capacity to obtain a large proportion of its N from N-2 fixation, it is common farmer's practice to apply an N top dressing to maximize grain yield. A field experiment was conducted to study the

Evaluation of hedgerow trees in alley cropping for phosphorus use efficiency and N{sub 2} fixation in low P soils in moist savanna in Nigeria

Energy Technology Data Exchange (ETDEWEB)

Sanginga, N [International Inst. of Tropical Agriculture, Ibadan (Nigeria); Danso, S K.A. [Joint FAO/IAEA Div. of Nuclear Techniques in Food and Agriculture, Vienna (Austria). Soil Fertility and Crop Production Section; Zapata, F [FAO/IAEA Agriculture and Biotechnology Lab., Seibersdorf (Austria). Soils Science Unit; Bowen, G D [Commonwealth Scientific and Industrial Research Organization, Glen Osmond (Australia). Div. of Soils

1996-07-01

Soils low in P and N are common in the moist savanna climatic zones and consequently growth of hedgerow trees in alley cropping systems might require addition of N and P fertilizers. This is difficult for small scale farmers who have limited access to fertilizers and therefore depend only on limited input cropping systems. Exploiting genetic differences in P use efficiency and using hedgerow trees selected for high N{sub 2} fixation ability can improve tree establishment and growth on N and P-poor soils, restore soil fertility and preserve soil from degradation. Field experiments carried out at Fashola (moist savanna) have shown that large differences in growth and P use efficiency occurred between N{sub 2} fixing trees such as Gliricidia sepium, and non N{sub 2}-fixing trees such as Senna siamea and Senna spectabilis. Provenances or isoline differences in P use efficiency also occurred within species and was also influenced by level of P and period of growth. Differences between species and provenances in P uptake and growth were largely related to differences in physiological P-use efficiency (PPUE), root length and VAM infection rate, especially at low P. In general, nodulation was improved by P application, but varied among provenances. Gliricidia Sepium fixed about 61% of its N from atmospheric N{sub 2} in the pot experiment and 40% in the field. The percentage of N fixed was not affected by rate of P application. Differences in P and N accumulation and use efficiency were also influenced by management practices such as pruning. The distribution of total P followed the same trend as that of dry matter yield, while no significant correlations were found between partitioning of dry matter and total N. Uncut and cut G. Sepium derived 35 and 54% respectively of their N from atmospheric N{sub 2}. About 54% of the fixed N{sub 2} was partitioned to shoots and roots and this was not proportional to the size of these organs relative the whole plant. 17refs,2figs,2tabs.

Evaluation of isotopic dilution method for measuring N2 fixation in azolla: comparison with other methods

International Nuclear Information System (INIS)

Sah, R.N.; Goyal, S.S.; Rains, D.W.; Paige, D.F.

1989-01-01

An isotopic dilution method that overcomes the drawbacks of commonly used methods for measuring N 2 fixation by aquatic N‐fixers such as Azolla pinnata‐Anabaena azollae association (Azolla) is presented. The method was compared with 15 N2 gas (while maintaining CO 2 ) and the difference methods of measuring N 2 fixation. The isotopic dilution method was used for two conditions: a. For 15 N‐free growth medium, Azolla was pre‐enriched with 15 N, and N 2 fixation was determined by measuring the dilution of 15 N in the tissue. b. For the growth medium containing N, N2 fixation was determined by providing 15 N enriched ammonium sulfate in the growth medium and measuring 15 N to 14 N ratio in the tissue. An airtight chamber, necessary for 15 N 2 gas and acetylene reduction methods, was not representative of the growing environment of Azolla. Temperature in the airtight chamber was far from uniform and CO 2 was rapidly depleted. The isotopic dilution method is simpler, relatively inexpensive, subject to fewer errors and applicable to more diverse conditions, and yet was as accurate as 15 N2‐gas method. (author)

Relationship between C2H2 reduction, H2 evolution and 15N2 fixation in root nodules of pea (Pisum sativum)

DEFF Research Database (Denmark)

Skøt, Leif

1983-01-01

for N2 reduction, is often stated as the relative efficiency (1-H2/C2H2). This factor varied significantly (P 2 and N2, expressed as the H2/N2 ratio, was independent of plant age, however. This discrepancy and the observation......The quantitative relationship between C2H2 reduction, H2 evolution and 15N2 fixation was investigated in excised root nodules from pea plants (Pisum sativum L. cv. Bodil) grown under controlled conditions. The C2H2/N2 conversion factor varied from 3.31 to 5.12 between the 32nd and the 67th day...... after planting. After correction for H2 evolution in air, the factor (C2H2-H2)/N2 decreased to values near the theoretical value 3, or in one case to a value significantly (P 2 production but used...

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.

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

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

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.)

Measurement of N{sub 2} fixation in Sesbania aculeata and Sorghum bicolor L. grown in intercropping system using {sup 15}N isotopic dilution technique

Energy Technology Data Exchange (ETDEWEB)

Kurdali, F; Khalifa, K; Janat, M [Atomic Energy Commission, Damascus (Syrian Arab Republic). Dept. of Agriculture

2001-09-01

A field experiment on Sesbania aculeata and Sorghum bicolor grown in mono cropping and in inter cropping systems was conducted under non-saline conditions (soil EC{sub e} 0.16, water EC{sub w}1dS/m) to evaluate dry matter production, total N yield, soil N uptake and N{sub 2}-fixation using {sup 15}N isotope dilution method. Three different row ratios of sesbania (ses) and sorghum (sor) were subjected in the inter cropping system (2ses: 1sot; 1ses: 1sor and 1ses: 2sor row ratio). Dry matter yield of sole sorghum was higher than that of sole sesbania, and it was similar to that produced by the inter cropping treatments. However, total N yield of sole sorghum was significantly the lowest, with no differences being obtained between sole sesbania and inter cropping treatments. The LERs of total N yield were, in all cases, higher than 1, reflecting a greater advantage of inter cropping system in terms of land use efficiency. Percentages of N{sub 2} fixation in the inter cropped sesbania were considerably enhanced compared with the pure stand of sesbania. This was mainly attributed to the depletion of soil N resulting from the greater apparent competitiveness of sorghum for soil N, and consequently, a greater dependence of sesbania on N{sub 2} fixation. However, the degree of the intraspecific competition for soil N uptake was affected by the proportion of crops in the mixture, and it was considerably reduced in the 2ses: 1sor row ratio. This was demonstrated when an equal depletion of soil and fertilizer N uptake occurred for both crops. We excluded in all-inter cropping treatments the possibility of N transfer from sesbania to sorghum. Row inter cropping, with crops grown in alternation of two rows of sesbania with one row of sorghum, seemed to be the most adequate row ratio in terms of total N yield, LER, N{sub 2}-fixation and soil N uptake balance of the component crops. (author)

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.

The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements.

Science.gov (United States)

Dabundo, Richard; Lehmann, Moritz F; Treibergs, Lija; Tobias, Craig R; Altabet, Mark A; Moisander, Pia H; Granger, Julie

2014-01-01

We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2 gas must be ensured prior to use in future N2 fixation rate determinations.

Dissolved Organic Matter Influences N2 Fixation in the New Caledonian Lagoon (Western Tropical South Pacific

Directory of Open Access Journals (Sweden)

Mar Benavides

2018-03-01

Full Text Available Specialized prokaryotes performing biological dinitrogen (N2 fixation (“diazotrophs” provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. In these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non-cyanobacterial diazotrophs are currently unclear. The latter are not photosynthetic (here called “heterotrophic” and hence require external sources of organic matter to sustain N2 fixation. Here we added the photosynthesis inhibitor 3-(3,4-dichlorophenyl-1,1-dimethylurea (DCMU to estimate the N2 fixation potential of heterotrophic diazotrophs as compared to autotrophic ones. Additionally, we explored the influence of dissolved organic matter (DOM on these diazotrophs along a coast to open ocean gradient in the surface waters of a subtropical coral lagoon (New Caledonia. Total N2 fixation (samples not amended with DCMU ranged from 0.66 to 1.32 nmol N L−1 d−1. The addition of DCMU reduced N2 fixation by >90%, suggesting that the contribution of heterotrophic diazotrophs to overall N2 fixation activity was minor in this environment. Higher contribution of heterotrophic diazotrophs occurred in stations closer to the shore and coincided with the decreasing lability of DOM, as shown by various colored DOM and fluorescent DOM (CDOM and FDOM indices. We tested the response of diazotrophs (in terms of nifH gene expression and bulk N2 fixation rates upon the addition of a mix of carbohydrates (“DOC” treatment, amino acids (“DON” treatment, and phosphonates and phosphomonesters (“DOP” treatment. While nifH expression increased significantly in Trichodesmium exposed to the DOC treatment, bulk N2 fixation rates increased significantly only in the DOP treatment. The lack of nifH expression by gammaproteobacteria, in any of the DOM addition treatments applied, questions the contribution of non

MtZIP6 is a novel metal transporter required for symbiotic nitrogen fixation in nodules of Medicago truncatula plants

OpenAIRE

Saez Somolinos, Ángela; Imperial Ródenas, Juan; Gonzalez Guerrero, Manuel

2015-01-01

Symbiotic nitrogen fixation (SNF) carried out by the interaction rhizobia-legumes takes place in legume root nodules. Many of the enzymes involved in SNF are metalloproteins that obtain their metal cofactor from the host plant. Metals reach the nodule through the vasculature, where they are released in the apoplast on the infection/differentiation zone (zone II) of the nodule (Rodriguez-Haas et al., 2013). From there, these oligonutrients have to cross a number of membranes to be used for met...

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

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

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.

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

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

Co-occurrence of methanogenesis and N2 fixation in oil sands tailings.

Science.gov (United States)

Collins, C E Victoria; Foght, Julia M; Siddique, Tariq

2016-09-15

Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N2 fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N2 headspace. Some cultures were further amended with citrate, which is used in oil sands processing, as a relevant carbon source, and/or with PAM. After an initial delay, N-deficient cultures with or without PAM produced methane (CH4) at the same rate as N-containing cultures, indicating a mechanism of overcoming apparent N-deficiency. Acetylene reduction and (15)N2 incorporation in all N-deficient cultures (with or without PAM) suggested active N2 fixation concurrently with methanogenesis but inability to use PAM as a N source. 16S rRNA gene pyrosequencing revealed little difference between archaeal populations regardless of N content. However, bacterial sequences in N-deficient cultures showed enrichment of Hyphomicrobiaceae and Clostridium members that might contain N2-fixing species. The results are important in understanding long-term production of biogenic greenhouse gases in oil sands tailings. Copyright © 2016 Elsevier B.V. All rights reserved.

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

Effect of planting patterns on dinitrogen fixation of alfalfa and transfer of N fixed

International Nuclear Information System (INIS)

Yao Yunyin; Chen Ming; Zhang Xizhong

1993-01-01

Contribution of symbiotic nitrogen fixation of alfalfa grown with different planting patterns was studied in a field experiment. %Ndfa and Ndfa in alfalfa and N transferred from alfalfa in meadow fescue were examined by 2 kinds of 15 N tracer techniques. The superiority of mixed culture of legumes with grasses to monoculture was influenced by planting patterns. Biomass in a mixed culture was related to proportion of alfalfa in it. The proportion of alfalfa was in close relationship not only with ratio of their seeds, but also with planting patterns. Row seeding in mixed seeds was better than broadcasting or intercropping in hay yield, total N yield and %Ndfa and Ndfa. It was also higher than the average of corresponding item of alfalfa and meadow fescue in monoculture each equal area. There was no significantly difference (P 15 N isotope dilution method and natural 1 '5N abundance method. N in meadow fescue transferred from alfalfa could be accurately determined by 15 N isotope diffusion method, but 15 N abundance method gave underestimates, even could not examined N in grasses transferred from associated legumes

Loss of the nodule-specific cysteine rich peptide, NCR169, abolishes symbiotic nitrogen fixation in the Medicago truncatula dnf7 mutant.

Science.gov (United States)

Horváth, Beatrix; Domonkos, Ágota; Kereszt, Attila; Szűcs, Attila; Ábrahám, Edit; Ayaydin, Ferhan; Bóka, Károly; Chen, Yuhui; Chen, Rujin; Murray, Jeremy D; Udvardi, Michael K; Kondorosi, Éva; Kaló, Péter

2015-12-08

Host compatible rhizobia induce the formation of legume root nodules, symbiotic organs within which intracellular bacteria are present in plant-derived membrane compartments termed symbiosomes. In Medicago truncatula nodules, the Sinorhizobium microsymbionts undergo an irreversible differentiation process leading to the development of elongated polyploid noncultivable nitrogen fixing bacteroids that convert atmospheric dinitrogen into ammonia. This terminal differentiation is directed by the host plant and involves hundreds of nodule specific cysteine-rich peptides (NCRs). Except for certain in vitro activities of cationic peptides, the functional roles of individual NCR peptides in planta are not known. In this study, we demonstrate that the inability of M. truncatula dnf7 mutants to fix nitrogen is due to inactivation of a single NCR peptide, NCR169. In the absence of NCR169, bacterial differentiation was impaired and was associated with early senescence of the symbiotic cells. Introduction of the NCR169 gene into the dnf7-2/NCR169 deletion mutant restored symbiotic nitrogen fixation. Replacement of any of the cysteine residues in the NCR169 peptide with serine rendered it incapable of complementation, demonstrating an absolute requirement for all cysteines in planta. NCR169 was induced in the cell layers in which bacteroid elongation was most pronounced, and high expression persisted throughout the nitrogen-fixing nodule zone. Our results provide evidence for an essential role of NCR169 in the differentiation and persistence of nitrogen fixing bacteroids in M. truncatula.

Estimate of symbiotically fixed nitrogen in field grown soybeans using variations in /sup 15/N natural abundance

Energy Technology Data Exchange (ETDEWEB)

Amarger, N; Durr, J C; Bourguignon, C; Lagacherie, B [INRA Centre de Recherches de Dijon, 21 (France). Lab. de Microbiologie des Sols; Mariotti, A; Mariotti, F [Paris-6 Univ., 75 (France). Lab. de Geologie Dynamique

1979-07-01

The use of variations in natural abundance of /sup 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 /sup 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/sub 2/H/sub 2/ reduction assay over the growing season. Estimates given by the /sup 15/N measurements were correlated with the C/sub 2/H/sub 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 /sup 15/N abundance should be reliable. The absence of correlation between estimates based on /sup 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.

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

African Journals Online (AJOL)

acer

[*Author of Correspondence: hyakubu2009@g-mail.com]. 229. ABSTRACT: ... Yusuf et al, (2006) reported that cowpea fixed. 16-34kgN/ha and ... fixation of legume crops (Michiels et al.,. 1994). ..... Robert, M.B. (1995). ... nitrogen fixation), John.

Symbiotic capability of calopo rhizobia from an agrisoil with different crops in Pernambuco

Directory of Open Access Journals (Sweden)

Altanys Silva Calheiros

2013-08-01

Full Text Available Biological nitrogen fixation by rhizobium-legume symbiosis represents one of the most important nitrogen sources for plants and depends strongly on the symbiotic efficiency of the rhizobium strain. This study evaluated the symbiotic capacity of rhizobial isolates from calopo (CALOPOGONIUM MUCUNOIDES taken from an agrisoil under BRACHIARIA DECUMBENS pasture, sabiá (MIMOSA CAESALPINIIFOLIA plantations and Atlantic Forest areas of the Dry Forest Zone of Pernambuco. A total of 1,575 isolates were obtained from 398 groups. A single random isolate of each group was authenticated, in randomized blocks with two replications. Each plant was inoculated with 1 mL of a bacterial broth, containing an estimated population of 10(8 rhizobial cells mL-1. Forty-five days after inoculation, the plants were harvested, separated into shoots, roots and nodules, oven-dried to constant mass, and weighed. Next, the symbiotic capability was tested with 1.5 kg of an autoclaved sand:vermiculite (1:1 mixture in polyethylene bags. The treatments consisted of 122 authenticated isolates, selected based on the shoot dry matter, five uninoculated controls (treated with 0, 50, 100, 150, or 200 kg ha-1 N and a control inoculated with SEMIA 6152 (=BR1602, a strain of BRADYRHIZOBIUM JAPONICUM The test was performed as described above. The shoot dry matter of the plants inoculated with the most effective isolates did not differ from that of plants treated with 150 kg ha-1 N. Shoot dry matter was positively correlated with all other variables. The proportion of effective isolates was highest among isolates from SABIÁ forests. There was great variation in nodule dry weight, as well as in N contents and total N.

Two isotopic methods for estimation of soybean nitrogen fixation

International Nuclear Information System (INIS)

Domenach, A.-M.; Chalamet, Alain; Pachiaudi, Christiane

1979-01-01

Measurements of rate of nitrogen symbiotic fixation by Soybean were determined by two different methods: variations in the natural abundance of 15 N in plants; use of 'A' value determined from labelled nitrogen applications to the soil. The results from both methods were in good agreement. Rates of fixed nitrogen were similar when using non nodulated Soybean or Ray-Grass as reference [fr

Two isotopic methods for estimation of soybean nitrogen fixation

Energy Technology Data Exchange (ETDEWEB)

Domenach, A M; Chalamet, A; Pachiaudi, C [Lyon-1 Univ., 69 - Villeurbanne (France)

1979-07-16

Measurements of rate of nitrogen symbiotic fixation by Soybean were determined by two different methods: variations in the natural abundance of /sup 15/N in plants; use of 'A' value determined from labelled nitrogen applications to the soil. The results from both methods were in good agreement. Rates of fixed nitrogen were similar when using non nodulated Soybean or Ray-Grass as reference.

15N enrichment of soil NH4+-N as an alternative non-N2-fixing reference for assessing varietal differences in N2 fixation of rice

International Nuclear Information System (INIS)

Shrestha, R.K.; Ladha, J.K.

1996-01-01

A pot experiment in the greenhouse was conducted to assess the usefulness of 15 N enrichment of soil NH 4 + -N as an alternative to a non-fixing reference plant to determine varietal differences in N 2 fixation among rice varieties. Diverse rice genotypes were grown in a 15 N stabilized soil obtained after 6 wk of application under flooded conditions. Atom % 15 N excess of soil NH 4 + -N was decreased exponentially with amount of N mineralized (r=99). Close agreement was observed between the 15 N enrichment of reference rice plant and 15 N enrichment of KCl extractable NH 4 + -N from unplanted pots maintained in the greenhouse. Whole plant atom % 15 N excess was inversely correlated within growth duration. Therefore, it was necessary to calculate Ndfa within growth duration. Ndfa estimated within the growth duration using 15 N enrichment of soil NH 4 + -N and reference rice genotype correlated almost perfectly (r=998). Thus the study demonstrated the potential of using 15 N enrichment of soil NH 4 + -N as a non-N 2 fixing reference for reliable estimate of biological nitrogen fixation by nonlegumes under flooded conditions. (author)

Attempt at estimating the rate of symbiotic fixation of nitrogen in the Lupine by natural isotopic tracing (/sup 15/N)

Energy Technology Data Exchange (ETDEWEB)

Amarger, Noelle [INRA Centre de Recherches de Dijon, 21 (France). Lab. de Microbiologie des Sols; Mariotti, Andre; Mariotti, Francoise [Paris-6 Univ., 75 (France)

1977-06-06

The rate of nitrogen fixation by a Rhizobium-Leguminous plant pair has been determined by natural isotopic tracing (/sup 15/N). After determining the isotopic fractionation coefficients between atmospheric nitrogen and plant nitrogen on the one hand (epsilon=-0.9) and nitrogen of the substrate and plant nitrogen on the other hand (epsilon=-1.1), the rate of nitrogen fixation by way of mixed nutrition cultures was calculated. The method is more accurate than standard methods.

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.

The Effects of SO2 on N2-Fixation, Carbon Partitioning, and Yield Components in Snapbean, Phaseolus Vulgaris L.

OpenAIRE

Griffith, Stephen M.

1983-01-01

The primary air pollutant sulfur dioxide has been shown to affect plant biochemistry and physiology, although very little is known about its effects on N2-fixation in legumes. This study was designed to determine if N2-fixation, carbon partitioning , and productivity are affected under short term low level, so2 exposures. Greenhouse grown snapbeans (P has eo lus vulgaris L. cv. Ear l iwax), 29 days from planting, were exposed to 0.0, 0.4, and 0.8 parts per million sulfur dioxide for 4 hour...

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

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.

Characterization of the Symbiotic Nitrogen-Fixing Common Bean Low Phytic Acid (lpa1) Mutant Response to Water Stress.

Science.gov (United States)

Chiozzotto, Remo; Ramírez, Mario; Talbi, Chouhra; Cominelli, Eleonora; Girard, Lourdes; Sparvoli, Francesca; Hernández, Georgina

2018-02-15

The common bean ( Phaseolus vulgaris L.) low phytic acid ( lpa1 ) biofortified genotype produces seeds with improved nutritional characteristics and does not display negative pleiotropic effects. Here we demonstrated that lpa1 plants establish an efficient nitrogen-fixing symbiosis with Rhizobium etli CE3. The lpa1 nodules showed a higher expression of nodule-function related genes than the nodules of the parental wild type genotype (BAT 93). We analyzed the response to water stress of lpa1 vs. BAT 93 plants grown under fertilized or under symbiotic N₂-fixation conditions. Water stress was induced by water withholding (up to 14% soil moisture) to fertilized or R. etli nodulated plants previously grown with normal irrigation. The fertilized lpa1 plants showed milder water stress symptoms during the water deployment period and after the rehydration recovery period when lpa1 plants showed less biomass reduction. The symbiotic water-stressed lpa1 plants showed decreased nitrogenase activity that coincides with decreased sucrose synthase gene expression in nodules; lower turgor weight to dry weight (DW) ratio, which has been associated with higher drought resistance index; downregulation of carbon/nitrogen (C/N)-related and upregulation of stress-related genes. Higher expression of stress-related genes was also observed in bacteroids of stressed lpa1 plants that also displayed very high expression of the symbiotic cbb ₃ oxidase ( fixN d).

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

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.

The Contamination of Commercial 15N2 Gas Stocks with 15N–Labeled Nitrate and Ammonium and Consequences for Nitrogen Fixation Measurements

Science.gov (United States)

Dabundo, Richard; Lehmann, Moritz F.; Treibergs, Lija; Tobias, Craig R.; Altabet, Mark A.; Moisander, Pia H.; Granger, Julie

2014-01-01

We report on the contamination of commercial 15-nitrogen (15N) N2 gas stocks with 15N-enriched ammonium, nitrate and/or nitrite, and nitrous oxide. 15N2 gas is used to estimate N2 fixation rates from incubations of environmental samples by monitoring the incorporation of isotopically labeled 15N2 into organic matter. However, the microbial assimilation of bioavailable 15N-labeled N2 gas contaminants, nitrate, nitrite, and ammonium, is liable to lead to the inflation or false detection of N2 fixation rates. 15N2 gas procured from three major suppliers was analyzed for the presence of these 15N-contaminants. Substantial concentrations of 15N-contaminants were detected in four Sigma-Aldrich 15N2 lecture bottles from two discrete batch syntheses. Per mole of 15N2 gas, 34 to 1900 µmoles of 15N-ammonium, 1.8 to 420 µmoles of 15N-nitrate/nitrite, and ≥21 µmoles of 15N-nitrous oxide were detected. One 15N2 lecture bottle from Campro Scientific contained ≥11 µmoles of 15N-nitrous oxide per mole of 15N2 gas, and no detected 15N-nitrate/nitrite at the given experimental 15N2 tracer dilutions. Two Cambridge Isotopes lecture bottles from discrete batch syntheses contained ≥0.81 µmoles 15N-nitrous oxide per mole 15N2, and trace concentrations of 15N-ammonium and 15N-nitrate/nitrite. 15N2 gas equilibrated cultures of the green algae Dunaliella tertiolecta confirmed that the 15N-contaminants are assimilable. A finite-differencing model parameterized using oceanic field conditions typical of N2 fixation assays suggests that the degree of detected 15N-ammonium contamination could yield inferred N2 fixation rates ranging from undetectable, detected in field assays. These results indicate that past reports of N2 fixation should be interpreted with caution, and demonstrate that the purity of commercial 15N2 gas must be ensured prior to use in future N2 fixation rate determinations. PMID:25329300

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.

The effect of different levels of fertilizer on nitrogen nutrient of pasture using 15N-isotope dilution method

International Nuclear Information System (INIS)

Wei Dongpu; Bai Lingyu; Hua Luo; Yao Yunyin

2000-01-01

A pot experiment was carried out to study the effect of different levels of fertilizer on N% of ryegrass in monoculture or mixed culture with white clover and symbiotic dinitrogen fixation of white clover by using 15 N-isotope dilution method. It showed that (1) N% of ryegrass in monoculture or mixed culture was the highest at 67 days after fertilizing (DAF) and decreased with time; (2) N% of white clover was the greatest at 67 DAF, slightly decreased at 92 DAF, and then increased at 137 DAF, related to the increasing of nitrogen fixation by white clover; (3) At 164 kg 15 NH 4 SO 4 /hm 2 , N% of ryegrass in mixed culture at different cutting time was greater than that in monoculture. It obviously occurred that fixed nitrogen was transferred from white clover to ryegrass in mixed; (4) During the whole growth period, the main nitrogen resource of white clover was symbiotic dinitrogen fixation and that of ryegrass was soil nitrogen; (5) Effect of different levels of applied N on N% of ryegrass and white clover was significant

Nitrogen fixation rates associated with the invasive macroalgae Sargassum horneri around Catalina Island, CA

Science.gov (United States)

DeLiberto, A.

2016-02-01

Nitrogen fixation is an important process which allows organisms access to biologically unavailable dinitrogen gas. Bacteria, known as diazotrophs use the enzyme nitrogenase to convert N2 to NH3. These bacteria, including certain species of heterotrophic bacteria and cyanobacteria, can be symbiotically associated with marine macroalgae, facilitating nutrient cycling in oligotrophic regions. As many species within the genera Sargassum are associated with nitrogen fixation, this study hypothesized that nitrogenase activity would be associated with the benthic invasive Sargassum horneri on Catalina Island. In the past decade, Sargassum horneri, an invasive from Japan, has spread throughout the waters around Catalina Island. Using the acetylene reduction procedure using flame ionization detection, initial nitrogenase activity of S. horneri sampled from Indian Rock was observed. Nitrogen fixation rates increased with decomposition, particularly in dark/anaerobic treatments, suggesting the presence of heterotrophic bacteria. In addition, acetate additions greatly increase nitrogen fixation rates, once again indicating heterotrophic nitrogen fixing bacteria.

Growth conditions determine the DNF2 requirement for symbiosis.

Directory of Open Access Journals (Sweden)

Fathi Berrabah

Full Text Available Rhizobia and legumes are able to interact in a symbiotic way leading to the development of root nodules. Within nodules, rhizobia fix nitrogen for the benefit of the plant. These interactions are efficient because spectacularly high densities of nitrogen fixing rhizobia are maintained in the plant cells. DNF2, a Medicago truncatula gene has been described as required for nitrogen fixation, bacteroid's persistence and to prevent defense-like reactions in the nodules. This manuscript shows that a Rhizobium mutant unable to differentiate is not sufficient to trigger defense-like reactions in this organ. Furthermore, we show that the requirement of DNF2 for effective symbiosis can be overcome by permissive growth conditions. The dnf2 knockout mutants grown in vitro on agarose or Phytagel as gelling agents are able to produce nodules fixing nitrogen with the same efficiency as the wild-type. However, when agarose medium is supplemented with the plant defense elicitor ulvan, the dnf2 mutant recovers the fix- phenotype. Together, our data show that plant growth conditions impact the gene requirement for symbiotic nitrogen fixation and suggest that they influence the symbiotic suppression of defense reactions in nodules.

Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields

Science.gov (United States)

Ariosa, Yoanna; Quesada, Antonio; Aburto, Juan; Carrasco, David; Carreres, Ramón; Leganés, Francisco; Fernández Valiente, Eduardo

2004-01-01

The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N2 fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N2 fixation rate associated with Chara was 27.53 kg of N ha−1 crop−1. The mean estimated N2 fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha−1 crop−1; submerged parts of rice plants, 3.93 kg of N ha−1 crop−1; and roots, 0.28 kg of N ha−1 crop−1. Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% ± 4.4% and 6.2% ± 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 ± 28.0 and 4.0 ± 3.8 μg mg [dry weight] of Chara−1 in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field

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

continues to increase) and allewiate world hunger is to increase the intensity of production in those ecosystems that lend themselves to sustainable intensification while decreasing the intensity of production in the more fragile ecologies (Reeves 1998). Most plants depend entirely for growth on fixed nitrogen absorbed from the soil, mainly as nitrate but also as ammonium. Therefore to the methods of crop production now dominant in the agricultural systems of many developed countries strongly depend upon a sustained input of N. Economic and environmental considerations surrounding fertilizer use then empasize the need to increase the efficiency of N- utilization by plants. On the other hand the biological nitrogen fixation (BNF) is important under all imput conditions to ensure an optimal supply of nitrogen to the farming system. A well-founded understanding of the mechanistic interactions between BNF and N limitations is presently lacking. Synbiotic nitrogen fixation by legumes makes a valuable contribution to N-inputs, especially in countries like Hungary where effective rhizobia-inoculation techniques have been developed in the context of the new sustainable agricultural system. It is widely known that soya bean -Glycine max (L.) Merr.-, is an important legume. This plant able to fix the atmospheric nitrogen (N2) it needs for growth through the agency of specific bacteria Rhizobium japonicum. Under field conditions fixation usually accounts for only 25-30% of the total nitrogen accumulated by these plants at harvest. Therefore to marginal yield have to optimalise the nitrogen supply of these legume by N-fertilization. Objectives for our experiments were to (1.) comparisons of the plant nutrition performance of different soil nitrogen supply levels by N- fertilization and N- fixation under Mediterranean climate conditions at Hungary, (2.) evaluates the potential for N2 fixation imputs by grain legume based on the soya bean as a means of improving soil fertility, (3

The importance of regulation of nitrogen fixation

Science.gov (United States)

Menge, D. N.

2012-12-01

I am not a proponent of including more detail in models simply because it makes them more realistic. More complexity increases the difficulty of model interpretation, so it only makes sense to include complexity if its benefit exceeds its costs. Biological nitrogen (N) fixation (BNF) is one process for which I feel the benefits of including greater complexity far outweigh the costs. I don't think that just because I work on BNF; I work on BNF because I think that. BNF, a microbial process carried out by free-living and symbiotic microbes, is the dominant N input to many ecosystems, the primary mechanism by which N deficiency can feed back to N inputs, and a main mechanism by which N surplus can develop. The dynamics of BNF, therefore, have huge implications for the rate of carbon uptake and the extent of CO2 fertilization, as well as N export to waterways and N2O emissions to the atmosphere. Unfortunately, there are serious deficiencies in our understanding of BNF. One main deficiency in our understanding is the extent to which various symbiotic N fixing organisms respond to imbalanced nutrition. Theory suggests that these responses, which I will call "strategies," have fundamental consequences for N fixer niches and ecosystem-level N and C cycling. Organisms that fix N regardless of whether they need it, a strategy that I will call "obligate," occupy post-disturbance niches and rapidly lead to N surplus. On the contrary, organisms that only fix as much N as they need, a "facultative" strategy, can occupy a wider range of successional niches, do not produce surplus N, and respond more rapidly to increased atmospheric CO2. In this talk I will show new results showing that consideration of these strategies could on its own explain the latitudinal distribution of symbiotic N fixing trees in North America. Specifically, the transition in N-fixing tree abundance from ~10% of basal area south of 35° latitude to ~1% of basal area north of 35° latitude that we observe

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

Nitrogen fixation by free-living organisms in rice soils. Studies with 15N

International Nuclear Information System (INIS)

Rao, V.R.; Charyulu, P.B.B.N.; Nayak, D.N.; Ramakrishna, C.

1979-01-01

Heterotrophic nitrogen fixation as influenced by water regime, organic matter, combined nitrogen and pesticides was investigated in several Indian rice soils by means of the 15 N 2 tracer technique. Soil submergence accelerated nitrogen fixation. Addition of cellulose to both non-flooded and flooded soils enhanced nitrogen fixation. Under submerged conditions, addition of sucrose, glucose and malate in that order stimulated nitrogen fixation in alluvial soil, while only sucrose enhanced nitrogen fixation in laterite soil. Nitrogen fixation in flooded alluvial and laterite soils decreased with increasing concentration of combined nitrogen. Nitrogen fixation was appreciable in acid sulphate and saline soils under both flooded and non-flooded conditions, despite high salinity and acidity. Application of certain pesticides at rates equivalent to recommended field level greatly influenced nitrogen fixation in flooded rice soils. Additions of benomyl (carbamate fungicide) and carbofuran (methyl carbamate insecticide) to alluvial and laterite soils resulted in significant stimulation of nitrogen fixation. Gamma-BHC stimulated nitrogen fixation only in alluvial soil, with considerable inhibition in a laterite soil. Nitrogen fixation by Azospirillum lipoferum was investigated by 15 N 2 . Large variations in 15 N 2 incorporation by A. lipoferum isolated from the roots of several rice cultivars was observed. Specific lines of rice harbouring A. lipoferum with high nitrogenase activity might be selected. Nitrogen fixed by heterotrophic organisms in a complex system such as soil could not be evaluated precisely. Indigenous nitrogen fixation in a flooded soil would be in the range of 5-10 kg N/ha, increasable 3 to 4-fold by appropriate fertilizers and cultural practices

Measurement of N2 fixation in Sesbania aculeata pers. and Sorghum bicolor L. grown in intercropping system, using sup 1 sup 5 N isotopic dilution technique. 1: Field evaluation under non-saline conditions

International Nuclear Information System (INIS)

Kurdali, F.; Khalifa, K.; Janat, M.

2002-01-01

A field experiment on Sesbania aculeata and Sorghum bicolor grown in mono cropping and in inter cropping systems was conducted under non-saline conditions (soil EC sub e 0.16, water EC sub w 1 ds/m/m) to evaluate dry matter production, total N yield, soil N uptake and N sub 2 -fixation using sup 1 sup 5 N isotope dilution method. Three different row ratios of sesbania (ses) and sorghum (sor) were subjected in the inter cropping system (2 ses: 1 sor; 1 ses: 1 sor and 1 ses: 2 sor row ratio). Dry matter yield of sole sorghum was higher than that of sole sesbania, and it was similar to that produced by the inter cropping treatments. However, total N yield of sole sorghum was significantly the lowest, with no differences being obtained between sole sesbania and inter cropping treatments. The LERs of total N yield were, in all cases, higher than 1, reflecting a greater advantage of inter cropping system in terms of land use efficiency. Percentages of N sub 2 fixation in the inter cropped sesbania were considerably enhanced compared with the pure stand of sesbania. This was mainly attributed to the depletion of soil N resulting from the greater apparent competitiveness of sorghum for soil N, and consequently, a greater dependence of sesbania on N sub 2 fixation. However, the degree of the intraspecific competition for soil N uptake was affected by the proportion of crops in the mixture, and it was considerably reduced in the 2 ses: 1 sor row ratio. This was demonstrated when an equal depletion of soil and fertilizer N uptake occurred for both crops. We excluded in all-inter cropping treatments the possibility of N transfer from sesbania to sorghum. Row inter cropping, with crops grown in alternation of two rows of sesbania with one row of sorghum, seemed to be the most adequate row ratio in terms of total N yield, LER, N sub 2 -fixation and soil N uptake balance of the component crops. (author)

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)

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.

Levels of daily light doses under changed day-night cycles regulate temporal segregation of photosynthesis and N2 Fixation in the cyanobacterium Trichodesmium erythraeum IMS101.

Science.gov (United States)

Cai, Xiaoni; Gao, Kunshan

2015-01-01

While the diazotrophic cyanobacterium Trichodesmium is known to display inverse diurnal performances of photosynthesis and N2 fixation, such a phenomenon has not been well documented under different day-night (L-D) cycles and different levels of light dose exposed to the cells. Here, we show differences in growth, N2 fixation and photosynthetic carbon fixation as well as photochemical performances of Trichodesmium IMS101 grown under 12L:12D, 8L:16D and 16L:8D L-D cycles at 70 μmol photons m-2 s-1 PAR (LL) and 350 μmol photons m-2 s-1 PAR (HL). The specific growth rate was the highest under LL and the lowest under HL under 16L:8D, and it increased under LL and decreased under HL with increased levels of daytime light doses exposed under the different light regimes, respectively. N2 fixation and photosynthetic carbon fixation were affected differentially by changes in the day-night regimes, with the former increasing directly under LL with increased daytime light doses and decreased under HL over growth-saturating light levels. Temporal segregation of N2 fixation from photosynthetic carbon fixation was evidenced under all day-night regimes, showing a time lag between the peak in N2 fixation and dip in carbon fixation. Elongation of light period led to higher N2 fixation rate under LL than under HL, while shortening the light exposure to 8 h delayed the N2 fixation peaking time (at the end of light period) and extended it to night period. Photosynthetic carbon fixation rates and transfer of light photons were always higher under HL than LL, regardless of the day-night cycles. Conclusively, diel performance of N2 fixation possesses functional plasticity, which was regulated by levels of light energy supplies either via changing light levels or length of light exposure.

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)

Measurement of nitrogen fixation in beam (Phaseolus vulgaris L.) cv. carioca, using a 15N2 low enrichment method

International Nuclear Information System (INIS)

Trivelin, P.C.O.; Matsui, E.; Saito, S.M.T.; Libardi, P.L.; Salati, E.

1984-01-01

A experimental work under field conditions to develop a method to measure atmospheric N 2 -fixation by leguminous plants, using a low enrichment 15 N 2 technique, is carried out. The experiment was developed using a N 2 -fixation measuring chamber on Terra Roxa Estruturada. The beam plants had their aereal part under normal conditions and the rooting system confined, through which a mixture of Ar, O 2 and N 2 labelled with 15 N (1.9% atom excess) was circulated from the 22nd to the 31st day from planting. Samples of the gaseous Ar, O 2 and N 2 mixture were analysed by mass spectrometry to determine 15 N concentrations and O 2 and CO 2 contents. The N 2 -fixed was measured by determination of total-N and isotopic concentration of nitrogen in the plants. (M.A.C.) [pt

SPARCHS: Symbiotic, Polymorphic, Automatic, Resilient, Clean-Slate, Host Security

Science.gov (United States)

2016-03-01

SPARCHS: SYMBIOTIC , POLYMORPHIC, AUTOMATIC, RESILIENT, CLEAN-SLATE, HOST SECURITY COLUMBIA UNIVERSITY MARCH 2016 FINAL... SYMBIOTIC , POLYMORPHIC, AUTOTOMIC, RESILIENT, CLEAN-SLATE, HOST SECURITY 5a. CONTRACT NUMBER N/A 5b. GRANT NUMBER FA8750-10-2-0253 5c. PROGRAM...17 4.2.3 SYMBIOTIC EMBEDDED MACHINES

Construction and simulation of the Bradyrhizobium diazoefficiens USDA110 metabolic network: a comparison between free-living and symbiotic states.

Science.gov (United States)

Yang, Yi; Hu, Xiao-Pan; Ma, Bin-Guang

2017-02-28

Bradyrhizobium diazoefficiens is a rhizobium able to convert atmospheric nitrogen into ammonium by establishing mutualistic symbiosis with soybean. It has been recognized as an important parent strain for microbial agents and is widely applied in agricultural and environmental fields. In order to study the metabolic properties of symbiotic nitrogen fixation and the differences between a free-living cell and a symbiotic bacteroid, a genome-scale metabolic network of B. diazoefficiens USDA110 was constructed and analyzed. The metabolic network, iYY1101, contains 1031 reactions, 661 metabolites, and 1101 genes in total. Metabolic models reflecting free-living and symbiotic states were determined by defining the corresponding objective functions and substrate input sets, and were further constrained by high-throughput transcriptomic and proteomic data. Constraint-based flux analysis was used to compare the metabolic capacities and the effects on the metabolic targets of genes and reactions between the two physiological states. The results showed that a free-living rhizobium possesses a steady state flux distribution for sustaining a complex supply of biomass precursors while a symbiotic bacteroid maintains a relatively condensed one adapted to nitrogen-fixation. Our metabolic models may serve as a promising platform for better understanding the symbiotic nitrogen fixation of this species.

Enzymology of biological nitrogen fixation. Final report, May 1, 1987--April 30, 1996

Energy Technology Data Exchange (ETDEWEB)

NONE

1997-05-01

Biological nitrogen fixation is of central importance in the earth`s nitrogen economy. Fixation of nitrogen is accomplished by a variety of microorganisms, all of them procaryotic. Some operate independently and some function symbiotically or associatively with photosynthesizing plants. Biological nitrogen fixation is accomplished via the reaction: N{sub 2} + 8H{sup +} + 8e{sup {minus}} {yields} 2NH{sub 3} + H{sub 2}. This reaction requires a minimum of 16 ATP under ideal laboratory conditions, so it is obvious that the energy demand of the reaction is very high. When certain nitrogen-fixing organisms are supplied fixed nitrogen (e.g., ammonium) the organisms use the fixed nitrogen and turn off their nitrogenase system, thus conserving energy. When the fixed nitrogen is exhausted, the organism reactivates its nitrogenase. The system is turned off by dinitrogenase reductase ADP-ribosyl transferase (DRAT) and turned back on by dinitrogenase reductase-activating glycohydrolase (DRAG). The authors have investigated the details of how DRAT and DRAG are formed, how they function, and the genetics of their formation and operation.

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)

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

Field effect of P fertilization on N$_{2}$ fixation rate of Ulex europaeus

OpenAIRE

Cavard , Xavier; Augusto , Laurent; Saur , Etienne; Trichet , Pierre

2007-01-01

European gorse (Ulex europaeus L.) N-2 fixation rate (% Ndfa) was studied in a maritime pine (Pinus pinaster Ait.) oligotrophic forest. Fertilization field trials were carried out on 5 sites with various inputs of phosphorus (0-240 kg P2O5. ha(-1)). Seven to ten years after pine planting, gorse were sampled to evaluate the effect of P fertilization on gorse % Ndfa, determined using the N-15 natural abundance method. One of the prerequisites of this method is the existence of a significant dif...

Evaluation for dinitrogen fixation of induced wheat nodules by 15N isotope dilution method

International Nuclear Information System (INIS)

Yao Yunyin; Zhen Ming; Chang Xizhong

1993-11-01

The results in pot experiments showed that the treating of 2,4-D and Azorhizobium caulinodans (2,4-D+A) could induce para-nodule formation on wheat roots. Plants treated grew normally. The plant height and dry weight are significantly higher than reference plants which are treated with 2,4-D+azorhizobium sterilized (2,4-D+AS). The nitrogenase activity is detected by ARA method. The N yield of most treated plants, especially in root systems, is higher than reference group that is measured by Kjeldahl method. The atom % 15 N excess in leaf and stem of treated plants measured by 15 N isotope dilution method is lower than that of reference group. Through four years experiments, it shows that para-nodules of wheat treated with 2,4-D+A could fix N 2 from air, but the ability of nitrogen fixation is lower and unstable. Although the nodulation efficiency could reach 100%, not each para-nodule induced can present activity of dinitrogen fixation. The amount of N fixed is 0.05∼18.1 mg/pot (0.01∼3.87 mg/plant). The net %Ndfa is 2.32%∼18.07%. The free-living N 2 fixing activity of azorhizobium is detected by 15 N isotope dilution method. The calculation of %Ndfa of nodulated wheat accurately is also discussed

Manganese toxicity effects on nodulation and nitrogen fixation of beans (Phaseolus vulgaris L. ), in acid soils

Energy Technology Data Exchange (ETDEWEB)

Doebereiner, J

1966-02-01

Three greenhouse experiments were conducted to study manganese toxicity effects on the nitrogen fixing symbiosis of beans (Phaseolus vulgaris). Addition of 40 ppm of manganese to two acid soils affected nodulation and nitrogen fixation. Dependent on the Rhizobion strain either nodule numbers or efficiency in nitrogen fixation were reduced; the efficiency of one Rhizobium-host combination was more affected than another. Under less severe conditions of manganese toxicity, reduction of nodule numbers or of efficiency in nitrogen fixation could be compensated by an increase of nodule size. In the absence of manganese toxicity nodulation and nitrogen fixation of beans were abundant in a soil with pH 4.4. Naturally occurring manganese toxicity in a gray hydromorphic soil was eliminated by liming. The total nitrogen content of bean plants which were dependent on symbiotic nitrogen fixation decreased linearly with the logarithm of the manganese concentration in the plants. This did not happen when the plants were grown with mineral nitrogen. The role of manganese toxicity in the well known sensitivity to acid soil conditions of certain legumes and the importance of selection of manganese tolerant Rhizobium strains for the inoculation of beans in acid tropical soils, are discussed. 25 references, 1 figure, 6 tables.

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.

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.

Alfalfa (Medicago sativa L.) forage production, tissue and soil nutrient concentration under three N based broiler litter regimes

Science.gov (United States)

Alfalfa (Medicago sativa L.) is considered as most important forage legume grown in Kentucky. Alfalfa supports many livestock production systems including the beef, dairy, and horse industries in Kentucky. Being a legume, alfalfa typically meets its N requirement through symbiotic N2 fixation, but h...

Inducible hydrogenase in cyanobacteria enhances N/sub 2/ fixation. [Nostoc, anabaena

Energy Technology Data Exchange (ETDEWEB)

Tel-Or, E.; Luijk, L.W.; Packer, L.

1977-06-01

Whether hydrogenase is activated or induced, we found no evidence for activation of either consumption or production of H/sub 2/ in aerobically-grown cultures but both of these activities increased 5--20-fold when cultures are grown under H/sub 2/ gas. On the other hand, hydrogenase-catalyzed consumption of H/sub 2/ is stimulated by light and/or light plus CO/sub 2/ in hydrogenase-induced cultures. Nitrogenase activity appears to be induced in cultures grown under H/sub 2/. Studies unambiguously establish that in H/sub 2/-induced cultures hydrogenase manifests a cooperativity with nitrogenase. In the presence of H/sub 2/ the activity of nitrogenase is stimulated 3--5-fold such that rates of about 3 ..mu..mol N/sub 2/ fixed/mg chlorophyll/h are obtained if the method of Peterson and Burris is used to convert acetylene reduction data to equivalents of /sup 15/N/sub 2/ fixation to ammonia.

Adaptation of the symbiotic Mesorhizobium-chickpea relationship to phosphate deficiency relies on reprogramming of whole-plant metabolism.

Science.gov (United States)

Nasr Esfahani, Maryam; Kusano, Miyako; Nguyen, Kien Huu; Watanabe, Yasuko; Ha, Chien Van; Saito, Kazuki; Sulieman, Saad; Herrera-Estrella, Luis; Tran, L S

2016-08-09

Low inorganic phosphate (Pi) availability is a major constraint for efficient nitrogen fixation in legumes, including chickpea. To elucidate the mechanisms involved in nodule acclimation to low Pi availability, two Mesorhizobium-chickpea associations exhibiting differential symbiotic performances, Mesorhizobium ciceri CP-31 (McCP-31)-chickpea and Mesorhizobium mediterranum SWRI9 (MmSWRI9)-chickpea, were comprehensively studied under both control and low Pi conditions. MmSWRI9-chickpea showed a lower symbiotic efficiency under low Pi availability than McCP-31-chickpea as evidenced by reduced growth parameters and down-regulation of nifD and nifK These differences can be attributed to decline in Pi level in MmSWRI9-induced nodules under low Pi stress, which coincided with up-regulation of several key Pi starvation-responsive genes, and accumulation of asparagine in nodules and the levels of identified amino acids in Pi-deficient leaves of MmSWRI9-inoculated plants exceeding the shoot nitrogen requirement during Pi starvation, indicative of nitrogen feedback inhibition. Conversely, Pi levels increased in nodules of Pi-stressed McCP-31-inoculated plants, because these plants evolved various metabolic and biochemical strategies to maintain nodular Pi homeostasis under Pi deficiency. These adaptations involve the activation of alternative pathways of carbon metabolism, enhanced production and exudation of organic acids from roots into the rhizosphere, and the ability to protect nodule metabolism against Pi deficiency-induced oxidative stress. Collectively, the adaptation of symbiotic efficiency under Pi deficiency resulted from highly coordinated processes with an extensive reprogramming of whole-plant metabolism. The findings of this study will enable us to design effective breeding and genetic engineering strategies to enhance symbiotic efficiency in legume crops.

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.

A proteomic network for symbiotic nitrogen fixation efficiency in Bradyrhizobium elkanii

Science.gov (United States)

Rhizobia bacteroids colonize legumes and reduce N2 to NH3 in root nodules. The current model is that bacteroids avoid assimilating this NH3. Instead, the legume forms glutamine from it, the nitrogen of which is returned to the bacteroid as leucine, isoleucine, valine, dicarboxylates, and peptides. I...

Use of Bio-Organic Fertilizers to Develop N Uptake Using 15N Technique

International Nuclear Information System (INIS)

Galal, Y.G.M.

2008-01-01

Experimental work either in field scale or in green house conditions were conducted using 15 N technique to evaluate the role of different bio fertilizers and different plant residues as organic amendments on enhancement of plant N nutrition. Nitrogen fixation by a symbiotic bacteria has been observed in greenhouse and field experiments under dry land cropping systems. Biological N 2 fixation associated with crop residues (legumes or cereals) was investigated in pot experiments with wheat and chickpea cultivars. In these experiments, labelled wheat and rice straw were used as organic N sources in comparison with either 15 N-labelled ammonium sulfate or ammonium nitrate as chemical nitrogen fertilizers. Rhizobium inoculation extended to be used with wheat gave the best results of N uptake and N 2 fixation when combined with Azospirillum brasilense as heterotrophic diazotrophs. The nitrogen uptake by wheat plants was significantly increased by application of soybean residues and inoculation with Azospirillum brasilense. From the field trial we can conclude that soybean residue as enriched N material, and Azospirillum brasilense inoculation enhanced N yields of wheat cultivars grown in poor fertile sandy soil

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)

Nitrogen cycling in the soil-plant system along a precipitation gradient in the Kalahari sands

CSIR Research Space (South Africa)

Aranibar, JN

2004-03-01

Full Text Available ). This and the fact that the driest savannas of the Kalahari sands are dominated by Mimosoideae species lead us to hypothe- size that symbiotic N2 fixation is more prevalent in drier sites of the Kalahari transect. Cyanobacteria are also capable of fixing atmospheric... enrichment for soils and plants; lower soil organic C and N; increased symbiotic and non-symbiotic N2 fixation; and de- creased NO losses from the system. The processes and pools analyzed are compared with the isotopic signatures along the precipitation...

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

) for the adjacent sea and creates different salinity and nutrient gradients over different seasons. River water (salinity 0), mesohaline waters (salinity 14-32), a transition zone with salinities between 32 and 33.5, and marine waters (salinity above 33.5) were sampled at different spatial resolutions in both......The influence of the Mekong River (South China Sea) on N2 fixation and phytoplankton distribution was investigated during the lowest- and highest-discharge seasons (April 2007 and September 2008, respectively). The river plays an essential role in providing nutrients (nitrate, phosphate, silicate...... cruises. High N2 fixation rates were measured during both seasons, with rates of up to 5.05 nmol N L-1 h -1 in surface waters under nitrogen-replete conditions, increasing to 22.77 nmol N L-1 h-1 in nitrogen-limited waters. Asymbiotic diatoms were found only close to the river mouth, and symbiotic diatoms...

Nitrogen fixation by legumes in retorted shale

Energy Technology Data Exchange (ETDEWEB)

Hersman, L E; Molitoris, E; Klein, D A

1981-01-01

Although a soil-shale mixture was employed as the growth medium in this experiment, the results presentd are applicable to the proposed method of disposal mentioned earlier. Under field conditions, when covering the retorted shale with topsoil, some mixing of these materials might occur in the plant root region. In addition, it has been demonstrated that buried shale negatively affects enzyme activities in overburden surface soil. The occurrence of either of those events could affect symbiotic N/sub 2/ fixation in a manner similar to that reported in this paper. Researchers conclude that due to the varied effects of retorted shale on the legumes tested, further evaluation of other legumes may be necessary. Additional research would be required to determine which legumes have potential use for reclamation of retorted shale.

Measurement of N2 fixation in Sesbania aculeata pers. and Sorghum bicolor L. grown in intercropping system, under saline conditions, using 15N isotopic dilution technique

International Nuclear Information System (INIS)

Kurdali, F.; Khalifa, K.; Janat, M.

2001-09-01

A field experiment was conducted under saline conditions (soil EC e 15, water EC w 8 dS/m/m) to evaluate the performance of sole crops and inter crops of Sesbania aculeata and Sorghum bicolor (1:1 row ratio) in terms of dry matter production, total N yield, soil N uptake and N 2 -fixation using 15 N isotope dilution method. Dry matter yield in sole crop of sesbania was significantly higher that that of sole sorghum; whereas, that of the inter cropping was significantly lower than sole sesbania, but was similar to that produced by sole sorghum. Total nitrogen yield in sole sesbania was four-fold than that accumulated in sole sorghum, whereas, that of mixed cropping was 2.6 fold compared to that of sole sorghum. The LER of total N yield was higher than 1 reflecting a greater advantage of inter cropping system in terms of land use efficiency. The proportion of N derived from N 2 fixation (%Ndfa) in the sesbania was increased from 63 to 79%, for sole and inter cropping system, respectively. There was no evidence of a significant transfer of N from the sesbania to the sorghum. Results on the relative growth of plants on saline soil compared with non-saline soil clearly demonstrated that sesbania was more salt tolerant than the sorghum. soil nitrogen uptake by plants, particularly in sorghum, was adversely affected by salinity. However, amounts of N 2 fixed by sole sesbania grown is saline soil was close or even higher than on non-saline soil. The use of inter cropping systems of legumes and non-legumes could be a promising agricultural approach to reutilize wasted lands, after a careful selection of appropriate tolerant genotypes to prevailing saline conditions. (author)

15N dilution technique of assessing the contribution of nitrogen fixation to rice plant

International Nuclear Information System (INIS)

Ventura, Wilbur; Watanabe, Iwao

1983-01-01

An attempt to correlate the positive nitrogen balance in rice-soil system with the 15 N dilution in rice plants was made to see if isotope dilution can be used to assess the contribution of nitrogen fixation to the nitrogen nutrition of rice. 15 N ammonium sulfate and sucrose were added to the moist soil in pots to label biomass nitrogen fraction. The rice-soil system with higher nitrogen gain had lower 15 N content in the rice plants. When the surface of pots was covered with black cloths to suppress photodependent N 2 fixation, no significant nitrogen gain was observed. Significant gain was found in the rice-flooded soil system exposed to light, and the 15 N content of plants decreased in allowing the photodependent N 2 fixation by blue-green algae symbiosis. The contribution of plant nitrogen derived from photodependent N 2 fixation was estimated to be 20-30 % of the positive nitrogen gain in the system by the 15 N dilution technique using the rice-covered soil as reference system. (Mori, K.)

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.

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.

Initial organic products of fixation of [13N]dinitrogen by root nodules of soybean (Glycine max)

International Nuclear Information System (INIS)

Meeks, J.C.; Wolk, C.P.; Schilling, N.; Shaffer, P.W.; Avissar, Y.; Chien, W.S.

1978-01-01

When detached soybean Glycine max (L.) Merr. cv. Hark, nodules assimilate ( 13 N)N 2 , the initial organic product of fixation is glutamine; glutamate becomes more highly radioactive than glutamine within 1 minute; 13 N in alanine becomes detectable at 1 minute of fixation and increases rapidly between 1 and 2 minutes. After 15 minutes of fixation, the major 13 N-labeled organic products in both detached and attached nodules are glutamate and alanine, plus, in the case of attached nodules, an unidentified substance, whereas ( 13 N)glutamine comprises only a small fraction of organic 13 N, and very little 13 N is detected in asparagine. The fixation of ( 13 N)N 2 into organic products was inhibited more than 99 percent by C 2 H 2 (10 percent, v/v). The results support the idea that the glutamine synthetase-glutamate synthase pathway is the primary route for assimilation of fixed nitrogen in soybean nodules

Heterotrophic N2-fixation contributes to nitrogen economy of a common wetland sedge, Schoenoplectus californicus.

Science.gov (United States)

Rejmánková, Eliška; Sirová, Dagmara; Castle, Stephanie T; Bárta, Jiří; Carpenter, Heather

2018-01-01

A survey of the ecological variability within 52 populations of Schoenoplectus californicus (C.A. Mey.) Soják across its distributional range revealed that it is commonly found in nitrogen (N) limited areas, but rarely in phosphorus limited soils. We explored the hypothesis that S. californicus supplements its nitrogen demand by bacterial N2-fixation processes associated with its roots and rhizomes. We estimated N2-fixation of diazotrophs associated with plant rhizomes and roots from several locations throughout the species' range and conducted an experiment growing plants in zero, low, and high N additions. Nitrogenase activity in rhizomes and roots was measured using the acetylene reduction assay. The presence of diazotrophs was verified by the detection of the nifH gene. Nitrogenase activity was restricted to rhizomes and roots and it was two orders of magnitude higher in the latter plant organs (81 and 2032 nmol C2H4 g DW-1 d-1, respectively). Correspondingly, 40x more nifH gene copies were found on roots compared to rhizomes. The proportion of the nifH gene copies in total bacterial DNA was positively correlated with the nitrogenase activity. In the experiment, the contribution of fixed N to the plant N content ranged from 13.8% to 32.5% among clones from different locations. These are relatively high values for a non-cultivated plant and justify future research on the link between N-fixing bacteria and S. californicus production.

Global climate change will increase the abundance of symbiotic nitrogen-fixing trees in much of North America.

Science.gov (United States)

Liao, Wenying; Menge, Duncan N L; Lichstein, Jeremy W; Ángeles-Pérez, Gregorio

2017-11-01

Symbiotic nitrogen (N)-fixing trees can drive N and carbon cycling and thus are critical components of future climate projections. Despite detailed understanding of how climate influences N-fixation enzyme activity and physiology, comparatively little is known about how climate influences N-fixing tree abundance. Here, we used forest inventory data from the USA and Mexico (>125,000 plots) along with climate data to address two questions: (1) How does the abundance distribution of N-fixing trees (rhizobial, actinorhizal, and both types together) vary with mean annual temperature (MAT) and precipitation (MAP)? (2) How will changing climate shift the abundance distribution of N-fixing trees? We found that rhizobial N-fixing trees were nearly absent below 15°C MAT, but above 15°C MAT, they increased in abundance as temperature rose. We found no evidence for a hump-shaped response to temperature throughout the range of our data. Rhizobial trees were more abundant in dry than in wet ecosystems. By contrast, actinorhizal trees peaked in abundance at 5-10°C MAT and were least abundant in areas with intermediate precipitation. Next, we used a climate-envelope approach to project how N-fixing tree relative abundance might change in the future. The climate-envelope projection showed that rhizobial N-fixing trees will likely become more abundant in many areas by 2080, particularly in the southern USA and western Mexico, due primarily to rising temperatures. Projections for actinorhizal N-fixing trees were more nuanced due to their nonmonotonic dependence on temperature and precipitation. Overall, the dominant trend is that warming will increase N-fixing tree abundance in much of the USA and Mexico, with large increases up to 40° North latitude. The quantitative link we provide between climate and N-fixing tree abundance can help improve the representation of symbiotic N fixation in Earth System Models. © 2017 John Wiley & Sons Ltd.

Comparative transcriptome analysis of nodules of two Mesorhizobium-chickpea associations with differential symbiotic efficiency under phosphate deficiency.

Science.gov (United States)

Nasr Esfahani, Maryam; Inoue, Komaki; Chu, Ha Duc; Nguyen, Kien Huu; Van Ha, Chien; Watanabe, Yasuko; Burritt, David J; Herrera-Estrella, Luis; Mochida, Keiichi; Tran, Lam-Son Phan

2017-09-01

Phosphate (Pi) deficiency is known to be a major limitation for symbiotic nitrogen fixation (SNF), and hence legume crop productivity globally. However, very little information is available on the adaptive mechanisms, particularly in the important legume crop chickpea (Cicer arietinum L.), which enable nodules to respond to low-Pi availability. Thus, to elucidate these mechanisms in chickpea nodules at molecular level, we used an RNA sequencing approach to investigate transcriptomes of the nodules in Mesorhizobium mediterraneum SWRI9-(MmSWRI9)-chickpea and M. ciceri CP-31-(McCP-31)-chickpea associations under Pi-sufficient and Pi-deficient conditions, of which the McCP-31-chickpea association has a better SNF capacity than the MmSWRI9-chickpea association during Pi starvation. Our investigation revealed that more genes showed altered expression patterns in MmSWRI9-induced nodules than in McCP-31-induced nodules (540 vs. 225) under Pi deficiency, suggesting that the Pi-starvation-more-sensitive MmSWRI9-induced nodules required expression change in a larger number of genes to cope with low-Pi stress than the Pi-starvation-less-sensitive McCP-31-induced nodules. The functional classification of differentially expressed genes (DEGs) was examined to gain an understanding of how chickpea nodules respond to Pi starvation, caused by soil Pi deficiency. As a result, more DEGs involved in nodulation, detoxification, nutrient/ion transport, transcriptional factors, key metabolic pathways, Pi remobilization and signalling were found in Pi-starved MmSWRI9-induced nodules than in Pi-starved McCP-31-induced nodules. Our findings have enabled the identification of molecular processes that play important roles in the acclimation of nodules to Pi deficiency, ultimately leading to the development of Pi-efficient chickpea symbiotic associations suitable for Pi-deficient soils. © 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.

Host-secreted antimicrobial peptide enforces symbiotic selectivity in Medicago truncatula.

Science.gov (United States)

Wang, Qi; Yang, Shengming; Liu, Jinge; Terecskei, Kata; Ábrahám, Edit; Gombár, Anikó; Domonkos, Ágota; Szűcs, Attila; Körmöczi, Péter; Wang, Ting; Fodor, Lili; Mao, Linyong; Fei, Zhangjun; Kondorosi, Éva; Kaló, Péter; Kereszt, Attila; Zhu, Hongyan

2017-06-27

Legumes engage in root nodule symbioses with nitrogen-fixing soil bacteria known as rhizobia. In nodule cells, bacteria are enclosed in membrane-bound vesicles called symbiosomes and differentiate into bacteroids that are capable of converting atmospheric nitrogen into ammonia. Bacteroid differentiation and prolonged intracellular survival are essential for development of functional nodules. However, in the Medicago truncatula - Sinorhizobium meliloti symbiosis, incompatibility between symbiotic partners frequently occurs, leading to the formation of infected nodules defective in nitrogen fixation (Fix - ). Here, we report the identification and cloning of the M. truncatula NFS2 gene that regulates this type of specificity pertaining to S. meliloti strain Rm41. We demonstrate that NFS2 encodes a nodule-specific cysteine-rich (NCR) peptide that acts to promote bacterial lysis after differentiation. The negative role of NFS2 in symbiosis is contingent on host genetic background and can be counteracted by other genes encoded by the host. This work extends the paradigm of NCR function to include the negative regulation of symbiotic persistence in host-strain interactions. Our data suggest that NCR peptides are host determinants of symbiotic specificity in M. truncatula and possibly in closely related legumes that form indeterminate nodules in which bacterial symbionts undergo terminal differentiation.

Energy Considerations for Plasma-Assisted N-Fixation Reactions

Directory of Open Access Journals (Sweden)

Aikaterini Anastasopoulou

2014-09-01

Full Text Available In a time of increasing concerns about the immense energy consumption and poor environmental performance of contemporary processes in the chemical industry, there is great need to develop novel sustainable technologies that enhance energy efficiency. There is abundant chemical literature on process innovations (laboratory-scale around the plasma reactor itself, which, naturally, is the essential part to be intensified to achieve a satisfactory process. In essence, a plasma process needs attention beyond reaction engineering towards the process integration side and also with strong electrical engineering focus. In this mini-review, we have detailed our future focus on the process and energy intensification of plasma-based N-fixation. Three focal points are mainly stressed throughout the review: (I the integration of renewable energy; (II the power supply system of plasma reactors and (III process design of industrial plasma-assisted nitrogen fixation. These different enabling strategies will be set in a holistic and synergetic picture so as to improve process performance.

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.

Dinitrogen fixation in aphotic oxygenated marine environments

Directory of Open Access Journals (Sweden)

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.

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)

Efficient Visible Light Nitrogen Fixation with BiOBr Nanosheets of Oxygen Vacancies on the Exposed {001} Facets.

Science.gov (United States)

Li, Hao; Shang, Jian; Ai, Zhihui; Zhang, Lizhi

2015-05-20

Even though the well-established Haber-Bosch process has been the major artificial way to "fertilize" the earth, its energy-intensive nature has been motivating people to learn from nitrogenase, which can fix atmospheric N2 to NH3 in vivo under mild conditions with its precisely arranged proteins. Here we demonstrate that efficient fixation of N2 to NH3 can proceed under room temperature and atmospheric pressure in water using visible light illuminated BiOBr nanosheets of oxygen vacancies in the absence of any organic scavengers and precious-metal cocatalysts. The designed catalytic oxygen vacancies of BiOBr nanosheets on the exposed {001} facets, with the availability of localized electrons for π-back-donation, have the ability to activate the adsorbed N2, which can thus be efficiently reduced to NH3 by the interfacial electrons transferred from the excited BiOBr nanosheets. This study might open up a new vista to fix atmospheric N2 to NH3 through the less energy-demanding photochemical process.

MtCAS31 Aids Symbiotic Nitrogen Fixation by Protecting the Leghemoglobin MtLb120-1 Under Drought Stress in Medicago truncatula

Directory of Open Access Journals (Sweden)

Xin Li

2018-05-01

Full Text Available Symbiotic nitrogen fixation (SNF in legume root nodules injects millions of tons of nitrogen into agricultural lands and provides ammonia to non-legume crops under N-deficient conditions. During plant growth and development, environmental stresses, such as drought, salt, cold, and heat stress are unavoidable. This raises an interesting question as to how the legumes cope with the environmental stress along with SNF. Under drought stress, dehydrin proteins are accumulated, which function as protein protector and osmotic substances. In this study, we found that the dehydrin MtCAS31 (cold-acclimation-specific 31 functions in SNF in Medicago truncatula during drought stress. We found that MtCAS31 is expressed in nodules and interacts with leghemoglobin MtLb120-1. The interaction between the two proteins protects MtLb120-1 from denaturation under thermal stress in vivo. Compared to wild type, cas31 mutants display a lower nitrogenase activity, a lower ATP/ADP ratio, higher expression of nodule senescence genes and higher accumulation of amyloplasts under dehydration conditions. The results suggested that MtCAS31 protects MtLb120-1 from the damage of drought stress. We identified a new function for dehydrins in SNF under drought stress, which enriches the understanding of the molecular mechanism of dehydrins.

Intracellular pH and its response to CO2-driven seawater acidification in symbiotic versus non-symbiotic coral cells.

Science.gov (United States)

Gibbin, Emma M; Putnam, Hollie M; Davy, Simon K; Gates, Ruth D

2014-06-01

Regulating intracellular pH (pHi) is critical for optimising the metabolic activity of corals, yet the mechanisms involved in pH regulation and the buffering capacity within coral cells are not well understood. Our study investigated how the presence of symbiotic dinoflagellates affects the response of pHi to PCO2-driven seawater acidification in cells isolated from Pocillopora damicornis. Using the fluorescent dye BCECF-AM, in conjunction with confocal microscopy, we simultaneously characterised the pHi response in host coral cells and their dinoflagellate symbionts, in symbiotic and non-symbiotic states under saturating light, with and without the photosynthetic inhibitor DCMU. Each treatment was run under control (pH 7.8) and CO2-acidified seawater conditions (decreasing pH from 7.8 to 6.8). After 105 min of CO2 addition, by which time the external pH (pHe) had declined to 6.8, the dinoflagellate symbionts had increased their pHi by 0.5 pH units above control levels when in the absence of DCMU. In contrast, in both symbiotic and non-symbiotic host coral cells, 15 min of CO2 addition (0.2 pH unit drop in pHe) led to cytoplasmic acidosis equivalent to 0.3-0.4 pH units irrespective of whether DCMU was present. Despite further seawater acidification over the duration of the experiment, the pHi of non-symbiotic coral cells did not change, though in host cells containing a symbiont cell the pHi recovered to control levels when photsynthesis was not inhibited. This recovery was negated when cells were incubated with DCMU. Our results reveal that photosynthetic activity of the endosymbiont is tightly coupled with the ability of the host cell to recover from cellular acidosis after exposure to high CO2/low pH. © 2014. Published by The Company of Biologists Ltd.

/sup 15/N dilution technique of assessing the contribution of nitrogen fixation to rice plant

Energy Technology Data Exchange (ETDEWEB)

Ventura, W; Watanabe, Iwao [International Rice Research Inst., College, Laguna (Phillippines)

1983-06-01

An attempt to correlate the positive nitrogen balance in rice-soil system with the /sup 15/N dilution in rice plants was made to see if isotope dilution can be used to assess the contribution of nitrogen fixation to the nitrogen nutrition of rice. /sup 15/N ammonium sulfate and sucrose were added to the moist soil in pots to label biomass nitrogen fraction. The rice-soil system with higher nitrogen gain had lower /sup 15/N content in the rice plants. When the surface of pots was covered with black cloths to suppress photodependent N/sub 2/ fixation, no significant nitrogen gain was observed. Significant gain was found in the rice-flooded soil system exposed to light, and the /sup 15/N content of plants decreased in allowing the photodependent N/sub 2/ fixation by blue-green algae symbiosis. The contribution of plant nitrogen derived from photodependent N/sub 2/ fixation was estimated to be 20-30 % of the positive nitrogen gain in the system by the /sup 15/N dilution technique using the rice-covered soil as reference system.

Delta.sup.15 ./sup.N as an indicator of N.sub.2./sub.-fixation by cyanobacterial mats in tropical marshes

Czech Academy of Sciences Publication Activity Database

Rejmánková, E.; Komárková, Jaroslava; Rejmánek, M.

2004-01-01

Roč. 67, č. 3 (2004), s. 353-368 ISSN 0168-2563 Grant - others:UC Davis Faculty(US) Research Grants Institutional research plan: CEZ:AV0Z6017912 Keywords : delta 15N * cyanobacteria * nitrogen fixation * wetlands Subject RIV: CE - Biochemistry Impact factor: 2.125, year: 2004

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.

Woody legume fallow productivity, biological N2-fixation and residual benefits to two successive maize crops in Zimbabwe

NARCIS (Netherlands)

Chikowo, R.; Mapfumo, P.; Nyamugafata, P.; Giller, K.E.

2004-01-01

Three woody legumes were planted as two-year 'improved fallows' to evaluate their residual nitrogen (N) effects on two subsequent maize crops under minimum and conventional tillage management. Maize monoculture and cowpea-maize-maize sequence treatments were included as controls. N-2-fixation was

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)

Improvement of Chickpea Growth and Biological N Fixation under Water Salinity Stress

International Nuclear Information System (INIS)

Gadalla, A. M.; Galal, Y. G. M.; Hamdy, A.

2004-01-01

This work had been carried out under greenhouse conditions of IAM-Bari, aimed at evaluating the effects of water and soil salinity on growth, yield and nitrogen fixation by chickpea plants inoculated with selected Rhizobium strains. Isotope dilution approach ( 15 N) was applied for quantification of biological N fixation and portions derived from fertilizer and soil (Ndff and Ndfs, respectively). Number of pods was decreased gradually with increasing water salinity levels. High levels of salinity negatively affected shoot, root dry matter, seed yield and N accumulated in shoots and roots. A slight difference in seed N was noticed between fresh water and 9 dS/m treatments. Nitrogen derived from fertilizer by shoots was slightly increased with 3, 6 and 9 dS/m treatments, while they were notably higher than the fresh water control. More than 80% and 70% of N accumulated in shoots and seeds, respectively were derived from fixation. Portions of N 2 -fixed in shoots was decreased with the level of 3 dS/m as compared to the fresh water, then tended to increase with both 6 and 9 dS/m treatments. Stability of %Ndfa with increasing salinity was noticed with seeds-N. Soil-N came next as a fraction of nitrogen demand, where it increased with increasing water salinity levels. Under adverse conditions of salinity, the plants offered some of their N requirements from the other two N sources. Application of the suitable Rhizobium bacteria strains could be profits for both of the plant growth and soil fertility via N 2 fixation. (Authors)

Measurement of N{sub 2} fixation in Sesbania aculeata pers. and Sorghum bicolor L. grown in intercropping system, under saline conditions, using {sup 15}N isotopic dilution technique

Energy Technology Data Exchange (ETDEWEB)

Kurdali, F; Khalifa, K; Janat, M [Atomic Energy Commission, Damascus (Syrian Arab Republic). Dept. of Agriculture

2001-09-01

A field experiment was conducted under saline conditions (soil EC{sub e} 15, water EC{sub w} 8 dS/m/m) to evaluate the performance of sole crops and inter crops of Sesbania aculeata and Sorghum bicolor (1:1 row ratio) in terms of dry matter production, total N yield, soil N uptake and N{sub 2}-fixation using {sup 15}N isotope dilution method. Dry matter yield in sole crop of sesbania was significantly higher that that of sole sorghum; whereas, that of the inter cropping was significantly lower than sole sesbania, but was similar to that produced by sole sorghum. Total nitrogen yield in sole sesbania was four-fold than that accumulated in sole sorghum, whereas, that of mixed cropping was 2.6 fold compared to that of sole sorghum. The LER of total N yield was higher than 1 reflecting a greater advantage of inter cropping system in terms of land use efficiency. The proportion of N derived from N{sub 2} fixation (%Ndfa) in the sesbania was increased from 63 to 79%, for sole and inter cropping system, respectively. There was no evidence of a significant transfer of N from the sesbania to the sorghum. Results on the relative growth of plants on saline soil compared with non-saline soil clearly demonstrated that sesbania was more salt tolerant than the sorghum. soil nitrogen uptake by plants, particularly in sorghum, was adversely affected by salinity. However, amounts of N{sub 2} fixed by sole sesbania grown is saline soil was close or even higher than on non-saline soil. The use of inter cropping systems of legumes and non-legumes could be a promising agricultural approach to reutilize wasted lands, after a careful selection of appropriate tolerant genotypes to prevailing saline conditions. (author)

Symbiotic Optimization of Behavior

Science.gov (United States)

2015-05-01

SYMBIOTIC OPTIMIZATION OF BEHAVIOR UNIVERSITY OF WASHINGTON MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED...2014 4. TITLE AND SUBTITLE SYMBIOTIC OPTIMIZATION OF BEHAVIOR 5a. CONTRACT NUMBER FA8750-12-1-0304 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT

Nitrogen fixation by free-living microorganisms in tropical rice soils using labelled fertilizer. Part of a coordinated programme on isotope techniques in studies of biological nitrogen fixation for the dual purpose of increasing crop production and decreasing nitrogen fertilizer use to conserve the environment

International Nuclear Information System (INIS)

Rao, V.R.

1981-11-01

Both acetylene-reduction and 15 N techniques were used to study heterotrophic N fixation in the rhizosphere of rice plants. Soils subjected to flooding in 4 soil types in both greenhouse and the field were found to stimulate greater heterotrophic nitrogen fixation than moist soils. The addition of organic materials, in particular, cellulose and rice straw, in general, enhanced nitrogen fixed by heterotrophic organisms living in the rhizosphere of rice plants. The highest amount of N fixed was 38 kg N/ha, and was obtained in a flooded lateritic soil to which had been added cellulose. Heterotrophic nitrogen fixation was influenced by soil type. In this study, the lowest value for fixed N was recorded in an acid sulphate soil of low pH. The addition of increasing amounts of inorganic nitrogen fertilizer in the form of ammonium sulphate suppressed rhizospheric nitrogen fixation in all soils, but the extent of suppression differed in the different soils. Benomyl fungicide and methyl carbamate insecticide had a stimulatory effect on heterotrophic nitrogen fixation in soils under rice roots. Different rice cultivars stimulated strains of Azospirillum to varying extent, and thus did not fix nitrogen to the same extent. It is thus possible that varieties of rice could be selected on the basis of their ability to support non-symbiotic N fixation in their rhizosphere

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.

Relevance of various nitrogen fixing microorganisms in ecology and plant productivity as a basis for evaluating their damage by environmental chemicals

Energy Technology Data Exchange (ETDEWEB)

Jagnow, G

1981-01-01

To evaluate detrimental side-effects of environmental chemicals on the biological N/sub 2/-fixation the relative importance of the N/sub 2/-fixation of legume and non-legume root nodules, of symbiotic and free living blue-green algae, of aerobic and facultatively anaerobic rhizosphere bacteria and of anaerobic bacteria is discussed on the basis of their fixation rate and their contribution to the conservation of ecosystems. From an agricultural and ecological point of view the symbiotic N/sub 2/-fixation of legumes and non-legumes takes the first place, being followed by that of blue-green algae and rhizosphere bacteria. Compared with these, the strictly anaerobic N/sub 2/-fixation has only a minor importance. Variable side-effects of herbicides on N/sub 2/-fixing bacteria are cited to stress the necessity of testing representatives of various ecological groups. Suitable test systems are proposed with soybeans, white clover, Rhizobium cultures, N/sub 2/-fixing blue-green algae and with Azospirillum species.

Nitrogen fixation in different chickpea cultivars as affected by iron application N-15 Technique

Energy Technology Data Exchange (ETDEWEB)

Gadalla, A M; Soliman, S M; Abdelmonem, M [Soil and Water Dept., Atomic Energy Authority, Cairo, (Egypt)

1995-10-01

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.

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

Taxonomically Different Co-Microsymbionts of a Relict Legume, Oxytropis popoviana, Have Complementary Sets of Symbiotic Genes and Together Increase the Efficiency of Plant Nodulation.

Science.gov (United States)

Safronova, Vera I; Belimov, Andrey A; Sazanova, Anna L; Chirak, Elizaveta R; Verkhozina, Alla V; Kuznetsova, Irina G; Andronov, Evgeny E; Puhalsky, Jan V; Tikhonovich, Igor A

2018-06-20

Ten rhizobial strains were isolated from root nodules of a relict legume Oxytropis popoviana Peschkova. For identification of the isolates, sequencing of rrs, the internal transcribed spacer region, and housekeeping genes recA, glnII, and rpoB was used. Nine fast-growing isolates were Mesorhizobium-related; eight strains were identified as M. japonicum and one isolate belonged to M. kowhaii. The only slow-growing isolate was identified as a Bradyrhizobium sp. Two strains, M. japonicum Opo-242 and Bradyrhizobium sp. strain Opo-243, were isolated from the same nodule. Symbiotic genes of these isolates were searched throughout the whole-genome sequences. The common nodABC genes and other symbiotic genes required for plant nodulation and nitrogen fixation were present in the isolate Opo-242. Strain Opo-243 did not contain the principal nod, nif, and fix genes; however, five genes (nodP, nodQ, nifL, nolK, and noeL) affecting the specificity of plant-rhizobia interactions but absent in isolate Opo-242 were detected. Strain Opo-243 could not induce nodules but significantly accelerated the root nodule formation after coinoculation with isolate Opo-242. Thus, we demonstrated that taxonomically different strains of the archaic symbiotic system can be co-microsymbionts infecting the same nodule and promoting the nodulation process due to complementary sets of symbiotic genes.

Au Sub-Nanoclusters on TiO2 toward Highly Efficient and Selective Electrocatalyst for N2 Conversion to NH3 at Ambient Conditions.

Science.gov (United States)

Shi, Miao-Miao; Bao, Di; Wulan, Ba-Ri; Li, Yong-He; Zhang, Yue-Fei; Yan, Jun-Min; Jiang, Qing

2017-05-01

As the NN bond in N 2 is one of the strongest bonds in chemistry, the fixation of N 2 to ammonia is a kinetically complex and energetically challenging reaction and, up to now, its synthesis is still heavily relying on energy and capital intensive Haber-Bosch process (150-350 atm, 350-550 °C), wherein the input of H 2 and energy are largely derived from fossil fuels and thus result in large amount of CO 2 emission. In this paper, it is demonstrated that by using Au sub-nanoclusters (≈0.5 nm ) embedded on TiO 2 (Au loading is 1.542 wt%), the electrocatalytic N 2 reduction reaction (NRR) is indeed possible at ambient condition. Unexpectedly, NRR with very high and stable production yield (NH 3 : 21.4 µg h -1 mg -1 cat. , Faradaic efficiency: 8.11%) and good selectivity is achieved at -0.2 V versus RHE, which is much higher than that of the best results for N 2 fixation under ambient conditions, and even comparable to the yield and activation energy under high temperatures and/or pressures. As isolated precious metal active centers dispersed onto oxide supports provide a well-defined system, the special structure of atomic Au cluster would promote other important reactions besides NRR for water splitting, fuel cells, and other electrochemical devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

He 2-104 - A symbiotic proto-planetary nebula?

International Nuclear Information System (INIS)

Schwarz, H.E.; Aspin, C.; Lutz, J.H.

1989-01-01

CCD observations are presented for He 2-104, an object previously classified as both PN and symbiotic star, which show that this is in fact a protoplanetary nebula (PPN) with a dynamical age of about 800 yr. The presence of highly collimated jets, extending over 75 arcsec on the sky, combined with an energy distribution showing a hot as well as a cool component, indicates that He 2-104 is a binary PPN. Since the primary is probably a Mira with a 400-d period (as reported by Whitelock, 1988), it is proposed that the system is a symbiotic PPN. 16 refs

Differential regulation of Rhizobium etli rpoN2 gene expression during symbiosis and free-living growth.

Science.gov (United States)

Michiels, J; Moris, M; Dombrecht, B; Verreth, C; Vanderleyden, J

1998-07-01

The Rhizobium etli rpoN1 gene, encoding the alternative sigma factor sigma54 (RpoN), was recently characterized and shown to be involved in the assimilation of several nitrogen and carbon sources during free-living aerobic growth (J. Michiels, T. Van Soom, I. D'hooghe, B. Dombrecht, T. Benhassine, P. de Wilde, and J. Vanderleyden, J. Bacteriol. 180:1729-1740, 1998). We identified a second rpoN gene copy in R. etli, rpoN2, encoding a 54.0-kDa protein which displays 59% amino acid identity with the R. etli RpoN1 protein. The rpoN2 gene is cotranscribed with a short open reading frame, orf180, which codes for a protein with a size of 20.1 kDa that is homologous to several prokaryotic and eukaryotic proteins of similar size. In contrast to the R. etli rpoN1 mutant strain, inactivation of the rpoN2 gene did not produce any phenotypic defects during free-living growth. However, symbiotic nitrogen fixation was reduced by approximately 90% in the rpoN2 mutant, whereas wild-type levels of nitrogen fixation were observed in the rpoN1 mutant strain. Nitrogen fixation was completely abolished in the rpoN1 rpoN2 double mutant. Expression of rpoN1 was negatively autoregulated during aerobic growth and was reduced during microaerobiosis and symbiosis. In contrast, rpoN2-gusA and orf180-gusA fusions were not expressed aerobically but were strongly induced at low oxygen tensions or in bacteroids. Expression of rpoN2 and orf180 was abolished in R. etli rpoN1 rpoN2 and nifA mutants under all conditions tested. Under free-living microaerobic conditions, transcription of rpoN2 and orf180 required the RpoN1 protein. In symbiosis, expression of rpoN2 and orf180 occurred independently of the rpoN1 gene, suggesting the existence of an alternative symbiosis-specific mechanism of transcription activation.

Effect of vanadium and tungsten on nitrogen fixation and the growth of Medicago sativa

Energy Technology Data Exchange (ETDEWEB)

Jha, K K

1969-01-01

In sand culture, it was found that vanadium had no stimulatory effect on nitrogen content or the growth of Medicago sativa inoculated with an effective strain of Rhizobium meliloti or supplied with ammonium nitrate. At the level of 500 ppm it reduced the plant growth, the inhibitory effect being particularly severe on the root. On the other hand tungsten increased nitrogen fixation and the dry matter yield of the inoculated plants. The results are suggestive of a direct role of tungsten in symbiotic nitrogen fixation. 4 references, 2 tables.

Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria

Science.gov (United States)

Kanno, Masahiro; Carroll, Austin L.; Atsumi, Shota

2017-03-01

Cyanobacteria have attracted much attention as hosts to recycle CO2 into valuable chemicals. Although cyanobacteria have been engineered to produce various compounds, production efficiencies are too low for commercialization. Here we engineer the carbon metabolism of Synechococcus elongatus PCC 7942 to improve glucose utilization, enhance CO2 fixation and increase chemical production. We introduce modifications in glycolytic pathways and the Calvin Benson cycle to increase carbon flux and redirect it towards carbon fixation. The engineered strain efficiently uses both CO2 and glucose, and produces 12.6 g l-1 of 2,3-butanediol with a rate of 1.1 g l-1 d-1 under continuous light conditions. Removal of native regulation enables carbon fixation and 2,3-butanediol production in the absence of light. This represents a significant step towards industrial viability and an excellent example of carbon metabolism plasticity.

Transcriptomic dissection of Bradyrhizobium sp. strain ORS285 in symbiosis with Aeschynomene spp. inducing different bacteroid morphotypes with contrasted symbiotic efficiency.

Science.gov (United States)

Lamouche, Florian; Gully, Djamel; Chaumeret, Anaïs; Nouwen, Nico; Verly, Camille; Pierre, Olivier; Sciallano, Coline; Fardoux, Joël; Jeudy, Christian; Szücs, Attila; Mondy, Samuel; Salon, Christophe; Nagy, István; Kereszt, Attila; Dessaux, Yves; Giraud, Eric; Mergaert, Peter; Alunni, Benoit

2018-06-19

To circumvent the paucity of nitrogen sources in the soil legume plants establish a symbiotic interaction with nitrogen-fixing soil bacteria called rhizobia. During symbiosis, the plants form root organs called nodules, where bacteria are housed intracellularly and become active nitrogen fixers known as bacteroids. Depending on their host plant, bacteroids can adopt different morphotypes, being either unmodified (U), elongated (E) or spherical (S). E- and S-type bacteroids undergo a terminal differentiation leading to irreversible morphological changes and DNA endoreduplication. Previous studies suggest that differentiated bacteroids display an increased symbiotic efficiency (E>U and S>U). In this study, we used a combination of Aeschynomene species inducing E- or S-type bacteroids in symbiosis with Bradyrhizobium sp. ORS285 to show that S-type bacteroids present a better symbiotic efficiency than E-type bacteroids. We performed a transcriptomic analysis on E- and S-type bacteroids formed by Aeschynomene afraspera and Aeschynomene indica nodules and identified the bacterial functions activated in bacteroids and specific to each bacteroid type. Extending the expression analysis in E- and S-type bacteroids in other Aeschynomene species by qRT-PCR on selected genes from the transcriptome analysis narrowed down the set of bacteroid morphotype-specific genes. Functional analysis of a selected subset of 31 bacteroid-induced or morphotype-specific genes revealed no symbiotic phenotypes in the mutants. This highlights the robustness of the symbiotic program but could also indicate that the bacterial response to the plant environment is partially anticipatory or even maladaptive. Our analysis confirms the correlation between differentiation and efficiency of the bacteroids and provides a framework for the identification of bacterial functions that affect the efficiency of bacteroids. This article is protected by copyright. All rights reserved. © 2018 Society for Applied

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...

Genetic diversity and symbiotic effectiveness of Bradyrhizobium strains nodulating selected annual grain legumes growing in Ethiopia.

Science.gov (United States)

Degefu, Tulu; Wolde-Meskel, Endalkachew; Rasche, Frank

2018-01-01

Vigna unguiculata, Vigna radiata and Arachis hypogaea growing in Ethiopia are nodulated by a genetically diverse group of Bradyrhizobium strains. To determine the genetic identity and symbiotic effectiveness of these bacteria, a collection of 36 test strains originating from the root nodules of the three hosts was investigated using multilocus sequence analyses (MLSA) of core genes including 16S rRNA, recA, glnII, gyrB, atpD and dnaK. Sequence analysis of nodA and nifH genes along with tests for symbiotic effectiveness using δ 15 N analysis were also carried out. The phylogenetic trees derived from the MLSA grouped most test strains into four well-supported distinct positions designated as genospecies I-IV. The maximum likelihood (ML) tree that was constructed based on the nodA gene sequences separated the entire test strains into two lineages, where the majority of the test strains were clustered on one of a well-supported large branch that comprise Bradyrhizobium species from the tropics. This clearly suggested the monophyletic origin of the nodA genes within the bradyrhizobia of tropical origin. The δ 15 N-based symbiotic effectiveness test of seven selected strains revealed that strains GN100 (δ 15 N=0.73) and GN102 (δ 15 N=0.79) were highly effective nitrogen fixers when inoculated to cowpea, thus can be considered as inoculants in cowpea production. It was concluded that Ethiopian soils are a hotspot for rhizobial diversity. This calls for further research to unravel as yet unknown bradyrhizobia nodulating legume host species growing in the country. In this respect, prospective research should also address the mechanisms of symbiotic specificity that could lead to high nitrogen fixation in target legumes.

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

KAUST Repository

Pogoreutz, Claudia; Radecker, Nils; Cardenas, Anny; Gä rdes, Astrid; Voolstra, Christian R.; Wild, Christian

2017-01-01

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.

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.

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

Evolutionary Dynamics of Nitrogen Fixation in the Legume–Rhizobia Symbiosis

Science.gov (United States)

Fujita, Hironori; Aoki, Seishiro; Kawaguchi, Masayoshi

2014-01-01

The stabilization of host–symbiont mutualism against the emergence of parasitic individuals is pivotal to the evolution of cooperation. One of the most famous symbioses occurs between legumes and their colonizing rhizobia, in which rhizobia extract nutrients (or benefits) from legume plants while supplying them with nitrogen resources produced by nitrogen fixation (or costs). Natural environments, however, are widely populated by ineffective rhizobia that extract benefits without paying costs and thus proliferate more efficiently than nitrogen-fixing cooperators. How and why this mutualism becomes stabilized and evolutionarily persists has been extensively discussed. To better understand the evolutionary dynamics of this symbiosis system, we construct a simple model based on the continuous snowdrift game with multiple interacting players. We investigate the model using adaptive dynamics and numerical simulations. We find that symbiotic evolution depends on the cost–benefit balance, and that cheaters widely emerge when the cost and benefit are similar in strength. In this scenario, the persistence of the symbiotic system is compatible with the presence of cheaters. This result suggests that the symbiotic relationship is robust to the emergence of cheaters, and may explain the prevalence of cheating rhizobia in nature. In addition, various stabilizing mechanisms, such as partner fidelity feedback, partner choice, and host sanction, can reinforce the symbiotic relationship by affecting the fitness of symbionts in various ways. This result suggests that the symbiotic relationship is cooperatively stabilized by various mechanisms. In addition, mixed nodule populations are thought to encourage cheater emergence, but our model predicts that, in certain situations, cheaters can disappear from such populations. These findings provide a theoretical basis of the evolutionary dynamics of legume–rhizobia symbioses, which is extendable to other single-host, multiple

Genetic Variability and Symbiotic Efficiency of Erythrina velutina Willd. Root Nodule Bacteria from the Semi-Arid Region in Northeastern Brazil

Directory of Open Access Journals (Sweden)

Kelly Alexsandra Souza Menezes

Full Text Available ABSTRACT Legume-rhizobia symbiosis is a cross-kingdom association that results in large amounts of nitrogen incorporated in food webs. For the Brazilian semi-arid region, data on genetic variability and symbiotic efficiency of Papilionoidae rhizobial communities are very scarce. The aim of this study was to evaluate the genetic variability and the symbiotic efficiency of eight rhizobial isolates obtained from “mulungu” (Erythrina velutina Willd. nodules. For 16S rRNA gene sequencing, the genomic DNA was extracted using a commercial kit, amplified with universal primers, and subjected to sequencing reactions. For the isolate ESA 71, PCR amplifications for nodC and nodA genes were attempted. Rhizobial efficiency was assessed by two greenhouse experiments. The first assay was carried out under gnotobiotic conditions, with sterile sand as a substrate; the second experiment was conducted in a non-sterile soil. For both experiments, the inoculation treatments consisted of a single inoculation of each isolate, in addition to a treatment with Bradyrhizobium elkanii BR 5609 as a reference strain. Furthermore, two non-inoculated control treatments, supplied and not supplied with mineral N, were also evaluated. Bacterial identification indicated that both α and β-rhizobia could be found in “mulungu” root nodules. Three isolates where classified within the Rhizobium genus, four bacteria belonged to Bradyrhizobium and one isolate clustered with Burkholderia. Positive amplification of an intragenic fragment of the nodA gene using a primer set to β-rhizobia could be found for ESA 71 (Burkholderia. All bacterial isolates were effective in colonizing “mulungu” roots. In the first experiment, all inoculated treatments and N fertilization increased the N concentration in “mulungu” shoot tissues. For total N in the shoots, the isolates ESA 70, ESA 72, and ESA 75 stood out. In the non-sterile substrate experiment, the isolates ESA 70, ESA 71, ESA

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%)

Methanotrophy induces nitrogen fixation during peatland development

Science.gov (United States)

Larmola, Tuula; Leppänen, Sanna M.; Tuittila, Eeva-Stiina; Aarva, Maija; Merilä, Päivi; Fritze, Hannu; Tiirola, Marja

2014-01-01

Nitrogen (N) accumulation rates in peatland ecosystems indicate significant biological atmospheric N2 fixation associated with Sphagnum mosses. Here, we show that the linkage between methanotrophic carbon cycling and N2 fixation may constitute an important mechanism in the rapid accumulation of N during the primary succession of peatlands. In our experimental stable isotope enrichment study, previously overlooked methane-induced N2 fixation explained more than one-third of the new N input in the younger peatland stages, where the highest N2 fixation rates and highest methane oxidation activities co-occurred in the water-submerged moss vegetation. PMID:24379382

Demography of Symbiotic Nitrogen-Fixing Trees Explains Their Rarity and Successional Decline in Temperate Forests in the United States.

Science.gov (United States)

Liao, Wenying; Menge, Duncan N L

2016-01-01

Symbiotic nitrogen (N) fixation is the major N input to many ecosystems. Although temperate forests are commonly N limited, symbiotic N-fixing trees ("N fixers") are rare and decline in abundance as succession proceeds-a challenging paradox that remains unexplained. Understanding demographic processes that underlie N fixers' rarity and successional decline would provide a proximate answer to the paradox. Do N fixers grow slower, die more frequently, or recruit less in temperate forests? We quantified demographic rates of N-fixing and non-fixing trees across succession using U.S. forest inventory data. We used an individual-based model to evaluate the relative contribution of each demographic process to community dynamics. Compared to non-fixers, N fixers had lower growth rates, higher mortality rates, and lower recruitment rates throughout succession. The mortality effect contributed more than the growth effect to N fixers' successional decline. Canopy and understory N fixers experienced these demographic disadvantages, indicating that factors in addition to light limitation likely contribute to N fixers' successional decline. We show that the rarity and successional decline of N-fixing trees in temperate forests is due more to their survival disadvantage than their growth disadvantage, and a recruitment disadvantage might also play a large role.

The influence of phosphorus deficiency on growth and nitrogen fixation of white clover plants

OpenAIRE

Høgh-Jensen, Dr Henning; Schjoerring, Dr Jan K.; Soussana, Dr Jean-Francois

2002-01-01

The effects of P deficiency on growth, N2‐fixation and photosynthesis in white clover (Trifolium repens L.) plants were investigated using three contrasting relative addition rates of P, or following abrupt withdrawal of the P supply. Responses to a constant below‐optimum P supply rate consisted of a decline in N2‐fixation per unit root weight and a small reduction in the efficiency with which electrons were allocated to the reduction of N2 in nodules. Abrupt removal of P arrested nodule grow...

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.

Breeding food and forge legumes for enhancement of nitrogen fixation: a review

International Nuclear Information System (INIS)

Ali, A.; Hussain, S.; Qamar, I.A.; Khan, B.R.

2000-01-01

Nitrogen fixation in legume - root nodules requires the functioning of genes present in the Rhizobia that induce nodule-formation. The plant produces the nodules and the energy required for respiration. Genes in both Rhizobium and the plant are responsible for the efficient use of photosynthesis for N/sub 2/ fixation and assimilation of nitrogen. Genes from Rhizobium and legume hosts that are involved in the symbiosis are being identified, isolated and cloned, to facilitate the manipulation of either partner. The amounts of nitrogen fixed by grain-legumes vary appreciably, between and within, species and are also influenced by environment. With few exceptions, most legumes fix insufficient N/sub 2/ to support substantial seed-yields. Deficits between required N and the combined amounts provide by soil and fertilizer help in estimating the improvements in N/sub 2/ fixation which is possible through breeding. Since the symbiosis is a complex process, heritability of traits is weak, and most methods which estimate fixation are destructive, a breeding method that allows selection of replicated families rather than single plants is preferred. (author)

Effects of Bean-Maize Intercropping,Phosphorus and Manure Additions on N2 fixation and Grain Yield of Phaseolus Vulgaris in the Central Kenya Highlands

International Nuclear Information System (INIS)

Kimani, S.K.; Mwangale, N.; Gathua, K.W.; Delve, R.; Cadisch, G.

1999-01-01

Sole bean and intercropped bean crops were studied for four seasons from 1996-1998. Addition of organic P at the recommended rate of 60 kg P 2 O 5 ha -1 increased bean standing biomass and grain yields during the first season. Cattle manure applied at the rate of 12 t ha -1 (25% moisture content), had a negative effect on bean yield during the first season, possibly due to short-term nutrient immobilisation induced by the high C:N ratio of manure. In subsequent seasons, manure additions resulted in higher grain yields compared to inorganic P. Intercropping bean with maize lowered grain yields by 10-100%. N 2 fixed on beans on average from 55 to 69%. Intercropping thus provides a strategy for a better N resource use where the maize competes efficiently for available soil mineral N and the legume replenishes part of the extracted N via atmospheric N 2 fixation. However, the amounts of N 2 fixed appear not to be enough to replenish whole systems N in grain crops and so additional N 2 are needed. Thus more attention needs to be given to manure management and its long-term impact on soil fertility

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.

Effect of sheep manure and phosphorus application on growth, yield, and N2 - fixation of inoculated soybean (Glycine max (L.) Merr) grown on Syrian arid soils using the 15N isotopic dilution technique

International Nuclear Information System (INIS)

Khalifa, Kh.; Al-Ain, F.; Al-Shamma'a, M.

2003-10-01

A field experiment was carried out in Syrian arid soils at Deir Al-Hajar research station to study the effect of different rates of sheep manure (0, 20, and 40 ton/ha) and levels of P- fertilizer (0, 40 and 80 kg P 2 O 5 /ha) on dry matter production and N 2 fixation by Soybean [(Glycine max) (SB171 variety)], of which seeds were inoculated by Bradyrhizobium japonicum-FA3 bacterial. Sorghum bicolor L. was employed as a reference crop ti evaluate N 2 -fixation using the 15 N-isotope dilution technique. In general, results indicated that, a positive effects were found to adding Sheep Manure or P-fertilizer on D.M production in different plants parts of soybean (shoots, roots, pods). This effect was more pronounced when adding sheep manure and phosphorus together especially under the optimum M40P80 treatment. Quantity of N-fixed by Soybean responds positively to sole application of Sheep Manure or P-fertilizer. Moreover, the optimum combined treatment showed significant increases in the quantity of nitrogen derived from the atmosphere (Qndfa), which were (3.29, 25.54, 53.49 kg N/ha) in roots, shoots, and pods respectively. P-fertilization resulted in a significant increase in the percentage of nitrogen use efficiency (NUE) with increasing phosphorus levels added to Sorghum plants; However, an adverse effect was noticed for the NUE when using sheep manure solely or in combination with P-fertilizer. (author)

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

Nitrogen fixation in legume trees: Measurement based on 15N techniques

International Nuclear Information System (INIS)

Sisworo, E.L.; Rasyid, H.; Sisworo, H.W.; Solahuddin, S.; Wemay, J.

2000-01-01

A field experiment has been conducted to measure the N2-fixation in six legume trees, namely Gliricidia sepium(F1), Sesbania sesban(F2), Caliandra tetragona(F3), Flemengia conges-7ta(F4), Acacia mangium(F5), and Leucena leucocephala (F6), using 15N techniques, e.g. the isotope dilution method. For this technique a reference tress, that is a non N2--fixing trees has to be used. In this experiment three reference trees were planted, but only one was used, which above ground growth was equal to the legyme trees. The reference tree chosen was Eucalyptus alba (R1). Data obtained from this experiment show that in general the legume trees have growth then the reference trees expressed, in dray weight of various plant parts and plants and total-N uptake (TN). At harvest some of the legume and reference tree have reached a 2.5 m height. The percentage of N2-fixation(%-fix) ranges from 50-70%. The highest %N-Fix was shown by Leucena leucocephala (F6) (70%N-Fix). High %N-Fix does not necessarily mean hgh N-Fix uptake(gn/tree)too. The N-Fix appears to be determined by the TN (gn/tree). The highest N-Fix was contributed by the leaves, which also has the highest percentage of total -N(%TN) compare to the other plant parts, i.e. roots, stem, and branches

Comparative symbiotic plasmid analysis indicates that symbiosis gene ancestor type affects plasmid genetic evolution.

Science.gov (United States)

Wang, X; Zhao, L; Zhang, L; Wu, Y; Chou, M; Wei, G

2018-07-01

Rhizobial symbiotic plasmids play vital roles in mutualistic symbiosis with legume plants by executing the functions of nodulation and nitrogen fixation. To explore the gene composition and genetic constitution of rhizobial symbiotic plasmids, comparison analyses of 24 rhizobial symbiotic plasmids derived from four rhizobial genera was carried out. Results illustrated that rhizobial symbiotic plasmids had higher proportion of functional genes participating in amino acid transport and metabolism, replication; recombination and repair; carbohydrate transport and metabolism; energy production and conversion and transcription. Mesorhizobium amorphae CCNWGS0123 symbiotic plasmid - pM0123d had similar gene composition with pR899b and pSNGR234a. All symbiotic plasmids shared 13 orthologous genes, including five nod and eight nif/fix genes which participate in the rhizobia-legume symbiosis process. These plasmids contained nod genes from four ancestors and fix genes from six ancestors. The ancestral type of pM0123d nod genes was similar with that of Rhizobium etli plasmids, while the ancestral type of pM0123d fix genes was same as that of pM7653Rb. The phylogenetic trees constructed based on nodCIJ and fixABC displayed different topological structures mainly due to nodCIJ and fixABC ancestral type discordance. The study presents valuable insights into mosaic structures and the evolution of rhizobial symbiotic plasmids. This study compared 24 rhizobial symbiotic plasmids that included four genera and 11 species, illuminating the functional gene composition and symbiosis gene ancestor types of symbiotic plasmids from higher taxonomy. It provides valuable insights into mosaic structures and the evolution of symbiotic plasmids. © 2018 The Society for Applied Microbiology.

Role of antimicrobial peptides in controlling symbiotic bacterial populations.

Science.gov (United States)

Mergaert, P

2018-04-25

Covering: up to 2018 Antimicrobial peptides (AMPs) have been known for well over three decades as crucial mediators of the innate immune response in animals and plants, where they are involved in the killing of infecting microbes. However, AMPs have now also been found to be produced by eukaryotic hosts during symbiotic interactions with bacteria. These symbiotic AMPs target the symbionts and therefore have a more subtle biological role: not eliminating the microbial symbiont population but rather keeping it in check. The arsenal of AMPs and the symbionts' adaptations to resist them are in a careful balance, which contributes to the establishment of the host-microbe homeostasis. Although in many cases the biological roles of symbiotic AMPs remain elusive, for a number of symbiotic interactions, precise functions have been assigned or proposed to the AMPs, which are discussed here. The microbiota living on epithelia in animals, from the most primitive ones to the mammals, are challenged by a cocktail of AMPs that determine the specific composition of the bacterial community as well as its spatial organization. In the symbiosis of legume plants with nitrogen-fixing rhizobium bacteria, the host deploys an extremely large panel of AMPs - called nodule-specific cysteine-rich (NCR) peptides - that drive the bacteria into a terminally differentiated state and manipulate the symbiont physiology to maximize the benefit for the host. The NCR peptides are used as tools to enslave the bacterial symbionts, limiting their reproduction but keeping them metabolically active for nitrogen fixation. In the nutritional symbiotic interactions of insects and protists that have vertically transmitted bacterial symbionts with reduced genomes, symbiotic AMPs could facilitate the integration of the endosymbiont and host metabolism by favouring the flow of metabolites across the symbiont membrane through membrane permeabilization.

Origin and Evolution of Nitrogen Fixation Genes on Symbiosis Islands and Plasmid in Bradyrhizobium

Science.gov (United States)

Okubo, Takashi; Piromyou, Pongdet; Tittabutr, Panlada; Teaumroong, Neung; Minamisawa, Kiwamu

2016-01-01

The nitrogen fixation (nif) genes of nodule-forming Bradyrhizobium strains are generally located on symbiosis islands or symbiosis plasmids, suggesting that these genes have been transferred laterally. The nif genes of rhizobial and non-rhizobial Bradyrhizobium strains were compared in order to infer the evolutionary histories of nif genes. Based on all codon positions, the phylogenetic tree of concatenated nifD and nifK sequences showed that nifDK on symbiosis islands formed a different clade from nifDK on non-symbiotic loci (located outside of symbiosis islands and plasmids) with elongated branches; however, these genes were located in close proximity, when only the 1st and 2nd codon positions were analyzed. The guanine (G) and cytosine (C) content of the 3rd codon position of nifDK on symbiosis islands was lower than that on non-symbiotic loci. These results suggest that nif genes on symbiosis islands were derived from the non-symbiotic loci of Bradyrhizobium or closely related strains and have evolved toward a lower GC content with a higher substitution rate than the ancestral state. Meanwhile, nifDK on symbiosis plasmids clustered with nifDK on non-symbiotic loci in the tree representing all codon positions, and the GC content of symbiotic and non-symbiotic loci were similar. These results suggest that nif genes on symbiosis plasmids were derived from the non-symbiotic loci of Bradyrhizobium and have evolved with a similar evolutionary pattern and rate as the ancestral state. PMID:27431195

St 2-22 - Another Symbiotic Star with High-Velocity Bipolar Jets

Science.gov (United States)

Tomov, T.; Zamanov, R.; Gałan, C.; Pietrukowicz, P.

2017-09-01

We report the detection of high-velocity components in the wings of Hα emission line in spectra of symbiotic binary star St 2-22 obtained in 2005. This finding encouraged us to start the present investigation in order to show that this poorly-studied object is a jet-producing system. We have used high-resolution optical and low-resolution near-infrared spectra, as well as available optical and infrared photometry, to evaluate some physical parameters of the St 2-22 components and characteristics of the jets. We confirm that St 2-22 is a S-type symbiotic star. Our results demonstrate that an unnoticed outburst, similar to those in classical symbiotic systems, occurred in the first half of 2005. During the outburst, collimated bipolar jets were ejected by the hot component of St 2-22 with an average velocity of about 1700 km/s.

Nonphotosynthetic CO2 fixation by alfalfa (Medicago sativa L.) roots and nodules

International Nuclear Information System (INIS)

Anderson, M.P.; Heichel, G.H.; Vance, C.P.

1987-01-01

The dependence of alfalfa (Medicago sativa L.) root and nodule nonphotosynthetic CO 2 fixation on the supply of currently produced photosynthate and nodule nitrogenase activity was examined a various times after phloem-girdling and exposure of nodules to Ar:O 2 . Phloem-girdling was effected 20 hours and exposure to Ar:O 2 was effected 2 to 3 hours before initiation of experiments. Nodule and root CO 2 fixation rates of phloem-girdled plants were reduced to 38 and 50%, respectively, of those of control plants. Exposure to Ar:O 2 decreased nodule CO 2 fixation rates to 45%, respiration rates to 55%, and nitrogenase activities to 51% of those of the controls. The products of nodule CO 2 fixation were exported through the xylem to the shoot mainly as amino acids within 30 to 60 minutes after exposure to 14 CO 2 . In contrast to nodules, roots exported very little radioactivity, and most of the 14 C was exported as organic acids. The nonphotosynthetic CO 2 fixation rate of roots and nodules averaged 26% of the gross respiration rate, i.e. the sum of net respiration and nonphotosynthetic CO 2 assimilation. Nodules fixed CO 2 at a rate 5.6 times that of roots, but since nodules comprised a small portion of root system mass, roots accounted for 76% of the nodulated roots system CO 2 fixation. The results indicate that nodule CO 2 fixation in alfalfa is associated with N assimilation

The symbiotic relationship between dominant canopy trees and soil microbes affects the nitrogen source utilization of co-existing understory trees

Science.gov (United States)

Iwaoka, C.; Hyodo, F.; Taniguchi, T.; Shi, W.; Du, S.; Yamanaka, N.; Tateno, R.

2017-12-01

The symbiotic relationship between dominant canopy trees and soil microbes such as mycorrhiza or nitrogen (N) fixer are important determinants of soil N dynamics of a forest. However, it is not known how and to what extent the symbiotic relationship of dominant canopy trees with soil microbes affect the N source of co-existing trees in forest. We measured the δ15N of surface soils (0-10 cm), leaves, and roots of the dominant canopy trees and common understory trees in an arbuscular mycorrhizal N-fixing black locust (Robinia pseudoacacia) plantation and an ectomycorrhizal oak (Quercus liaotungensis) natural forest in a China dryland. We also analyzed the soil dissolved N content in soil extracts and absorbed by ion exchange resin, and soil ammonia-oxidizer abundance using real-time PCR. The δ15N of soil and leaves were higher in the black locust forest than in the oak forest, although the δ15N of fine roots was similar in the two forests, in co-existing understory trees as well as dominant canopy trees. Accordingly, the δ15N of leaves was similar to or higher than that of fine roots in the black locust forest, whereas it was consistently lower than that of fine roots in the oak forest. In the black locust forest, the soil dissolved organic N and ammonium N contents were less abundant but the nitrate N contents in soils and absorbed by the ion exchange resin and ammonia-oxidizer abundance were greater, due to N fixation or less uptake of organic N from arbuscular mycorrhiza. In contrast, the soil dissolved organic N and ammonium N contents were more abundant in the oak forest, whereas the N content featured very low nitrate, due to ectomycorrhizal ability to access organic N. These results suggest that the main N source is nitrate N in the black locust forest, but dissolved organic N or ammonium N in the oak forest. N fixation or high N loss due to high N availability would cause high δ15N in soil and leaves in black locust forest. On the other hand, low soil N

The Importance of the Microbial N Cycle in Soil for Crop Plant Nutrition.

Science.gov (United States)

Hirsch, Penny R; Mauchline, Tim H

2015-01-01

Nitrogen is crucial for living cells, and prior to the introduction of mineral N fertilizer, fixation of atmospheric N2 by diverse prokaryotes was the primary source of N in all ecosystems. Microorganisms drive the N cycle starting with N2 fixation to ammonia, through nitrification in which ammonia is oxidized to nitrate and denitrification where nitrate is reduced to N2 to complete the cycle, or partially reduced to generate the greenhouse gas nitrous oxide. Traditionally, agriculture has relied on rotations that exploited N fixed by symbiotic rhizobia in leguminous plants, and recycled wastes and manures that microbial activity mineralized to release ammonia or nitrate. Mineral N fertilizer provided by the Haber-Bosch process has become essential for modern agriculture to increase crop yields and replace N removed from the system at harvest. However, with the increasing global population and problems caused by unintended N wastage and pollution, more sustainable ways of managing the N cycle in soil and utilizing biological N2 fixation have become imperative. This review describes the biological N cycle and details the steps and organisms involved. The effects of various agricultural practices that exploit fixation, retard nitrification, and reduce denitrification are presented, together with strategies that minimize inorganic fertilizer applications and curtail losses. The development and implementation of new technologies together with rediscovering traditional practices are discussed to speculate how the grand challenge of feeding the world sustainably can be met. Copyright © 2015 Elsevier Inc. All rights reserved.

Dinitrogen fixation estimates in Vetch-barley swards using {sup 15} N-methodology

Energy Technology Data Exchange (ETDEWEB)

Kurdali, F; Sharabi, N E [Atomic Energy Commission, P.O.Box 6091, Damascus, (Syrian Arab Republic)

1995-10-01

N 2- fixation in vetch (Vicia Sativa) grown alone and in mixture with barley (hordeum vulgare) in pots was evaluated using {sup 15} N isotope dilution method. Two harvests were made over the growing season. The proportion of the above-ground N, derived from atmospheric N 2 (% Ndfa) in mixed vetch was significantly higher than that of vetch in pure culture for the different harvests. However, this increase was not accompanied with the amount of N 2-fixation. On the other hand, no significant differences were observed in N-content or in N-derived from soil between barley grown in mixture and in monoculture, in spite of the difference in the number of plants between the tow cropping systems. These results indicate a high competing capacity of barley for soil nitrogen in mixed culture. Barley grown together with vetch had lower atom % 15 N excess than barley grown in mono-culture because it may have received some of their N from N-released by the legume in the second herbage but not in the first. Overall, results obtained from this experiment indicate the importance of mixed crops for forage production. Based on these results, further investigation must carried out in the field. 1 fig.

Nitrogen-use-efficiency: a biologically meaningful definition?

NARCIS (Netherlands)

Berendse, F.; Aerts, R.

1987-01-01

A parameter to measure the efficiency of nitrogen use should include 1) the mean residence time of the N in the plant, ie the period during which the absorbed N can be used for C-fixation; and 2) the instantaneous rate of C-fixation per unit of N in the plant. It is essential to distinguish between

Free amino acids exhibit anthozoan "host factor" activity: they induce the release of photosynthate from symbiotic dinoflagellates in vitro.

Science.gov (United States)

Gates, R D; Hoegh-Guldberg, O; McFall-Ngai, M J; Bil, K Y; Muscatine, L

1995-08-01

Reef-building corals and other tropical anthozoans harbor endosymbiotic dinoflagellates. It is now recognized that the dinoflagellates are fundamental to the biology of their hosts, and their carbon and nitrogen metabolisms are linked in important ways. Unlike free living species, growth of symbiotic dinoflagellates is unbalanced and a substantial fraction of the carbon fixed daily by symbiont photosynthesis is released and used by the host for respiration and growth. Release of fixed carbon as low molecular weight compounds by freshly isolated symbiotic dinoflagellates is evoked by a factor (i.e., a chemical agent) present in a homogenate of host tissue. We have identified this "host factor" in the Hawaiian coral Pocillopora damicornis as a set of free amino acids. Synthetic amino acid mixtures, based on the measured free amino acid pools of P. damicornis tissues, not only elicit the selective release of 14C-labeled photosynthetic products from isolated symbiotic dinoflagellates but also enhance total 14CO2 fixation.

Carbon sequestration in soybean crop soils: the role of hydrogen-coupled CO2 fixation

Science.gov (United States)

Graham, A.; Layzell, D. B.; Scott, N. A.; Cen, Y.; Kyser, T. K.

2011-12-01

Conversion of native vegetation to agricultural land in order to support the world's growing population is a key factor contributing to global climate change. However, the extent to which agricultural activities contribute to greenhouse gas emissions compared to carbon storage is difficult to ascertain, especially for legume crops, such as soybeans. Soybean establishment often leads to an increase in N2O emissions because N-fixation leads to increased soil available N during decomposition of the low C:N legume biomass. However, soybean establishment may also reduce net greenhouse gas emissions by increasing soil fertility, plant growth, and soil carbon storage. The mechanism behind increased carbon storage, however, remains unclear. One explanation points to hydrogen coupled CO2 fixation; the process by which nitrogen fixation releases H2 into the soil system, thereby promoting chemoautotrophic carbon fixation by soil microbes. We used 13CO2 as a tracer to track the amount and fate of carbon fixed by hydrogen coupled CO2 fixation during one-year field and laboratory incubations. The objectives of the research are to 1) quantify rates of 13CO2 fixation in soil collected from a field used for long-term soybean production 2) examine the impact of H2 gas concentration on rates of 13CO2 fixation, and 3) measure changes in δ13C signature over time in 3 soil fractions: microbial biomass, light fraction, and acid stable fraction. If this newly-fixed carbon is incorporated into the acid-stable soil C fraction, it has a good chance of contributing to long-term soil C sequestration under soybean production. Soil was collected in the field both adjacent to root nodules (nodule soil) and >3cm away (root soil) and labelled with 13CO2 (1% v/v) in the presence and absence of H2 gas. After a two week labelling period, δ13C signatures already revealed differences in the four treatments of bulk soil: -17.1 for root, -17.6 for nodule, -14.2 for root + H2, and -6.1 for nodule + H2

Exploring symbiotic nitrogen fixation and assimilation in pea root nodules by in vivo 15N nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry

DEFF Research Database (Denmark)

Scharff, A.M.; Egsgaard, H.; Hansen, P.E.

2003-01-01

Nitrogen (N) fixation and assimilation in pea (Pisum sativum) root nodules were studied by in vivo N-15 nuclear magnetic resonance (NMR) by exposing detached nodules to N-15, via a perfusion medium, while recording a time course of spectra. In vivo P-31 NMR spectroscopy was used to monitor...... the physiological state of the metabolically active nodules. The nodules were extracted after the NMR studies and analyzed for total soluble amino acid pools and N-15 labeling of individual amino acids by liquid chromatography-mass spectrometry. A substantial pool of free ammonium was observed by N-15 NMR...... labeling of Asn was observed by liquid chromatography-mass spectrometry, which is consistent with the generally accepted role of Asn as the end product of primary N assimilation in pea nodules. However, the Asn N-15 amino signal was absent in in vivo N-15 NMR spectra, which could be because...

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.

15N in biological nitrogen fixation studies

International Nuclear Information System (INIS)

Faust, H.

1986-05-01

A bibliography with 298 references on the use of the stable nitrogen isotope 15 N in the research on the biological fixation of dinitrogen is presented. The literature pertaining to this bibliography covers the period from 1975 to the middle of 1985. (author)

Effects of elevated carbon dioxide concentration on growth and N2 fixation of young Robinia pseudoacacia

International Nuclear Information System (INIS)

Feng, Z; Flessa, H.; Dyckmans, J.

2004-01-01

The effects of elevated carbon dioxide concentration on carbon and nitrogen uptake and nitrogen source partitioning were determined in one year-old locust trees using a dual 13 C and 15 N continuous labelling experiment. Elevated carbon dioxide increased the fraction of new carbon in total carbon, but it did not alter carbon partitioning among plant compartments. Elevated carbon dioxide also increased the fraction of new nitrogen in total nitrogen. This was coupled with a shift in nitrogen source partitioning toward nitrogen fixation. Soil nitrogen uptake was not affected, but nitrogen fixation was markedly increased by elevated carbon dioxide treatment. The increased nitrogen fixation tended to decrease the C/N ratio in the presence of elevated carbon dioxide. Total dry mass of root nodules doubled in response to elevated carbon dioxide, however, this effect was not considered significant because of the great variability in root nodule formation. Overall, it was concluded that the growth of locust trees in an elevated carbon dioxide environment will not primarily be limited by nitrogen availability, giving the R. pseudoacacia species a competitive advantage over non-nitrogen-fixing tree species. It was also suggested that the increase in nitrogen fixation observed in response to elevated carbon dioxide treatment may play a key role in the growth response of forest ecosystems to elevated carbon dioxide by improving nitrogen availability for non-nitrogen-fixing trees. 51 refs., 1 tab., 4 figs

Symbiotic Novae

OpenAIRE

Mikolajewska, Joanna

2010-01-01

The symbiotic novae are thermonuclear novae in symbiotic binary systems -- interacting binaries with evolved red giant donors, and the longest orbital periods. This paper aims at presenting physical characteristics of these objects and discussing their place among the whole family of symbiotic stars.

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.

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

Symbiotic Performance of Herbaceous Legumes in Tropical Cover Cropping Systems

Directory of Open Access Journals (Sweden)

Basil Ibewiro

2001-01-01

Full Text Available Increasing use of herbaceous legumes such as mucuna (Mucuna pruriens var. utilis [Wright] Bruck and lablab (Lablab purpureus [L.] Sweet in the derived savannas of West Africa can be attributed to their potential to fix atmospheric nitrogen (N2. The effects of management practices on N2 fixation in mucuna and lablab were examined using 15N isotope dilution technique. Dry matter yield of both legumes at 12 weeks was two to five times more in in situ mulch (IM than live mulch (LM systems. Land Equivalent Ratios, however, showed 8 to 30% more efficient utilization of resources required for biomass production under LM than IM systems. Live mulching reduced nodule numbers in the legumes by one third compared to values in the IM systems. Similarly, nodule mass was reduced by 34 to 58% under LM compared to the IM systems. The proportion of fixed N2 in the legumes was 18% higher in LM than IM systems. Except for inoculated mucuna, the amounts of N fixed by both legumes were greater in IM than LM systems. Rhizobia inoculation of the legumes did not significantly increase N2 fixation compared to uninoculated plots. Application of N fertilizer reduced N2 fixed in the legumes by 36 to 51% compared to inoculated or uninoculated systems. The implications of cover cropping, N fertilization, and rhizobia inoculation on N contributions of legumes into tropical low-input systems were discussed.

Using 32 P to evaluation of bio fertilizers symbiotic efficiency in wheat

International Nuclear Information System (INIS)

Ardakani, M.R.; Majd, F.; Nourmohammadi, G.

2004-01-01

In order to study the symbiotic efficiency of bio fertilizers in wheat specially Azospirillam, Mycorrhizal and streptomyces, an experiment have been carried out for 2 years by using 32p in greenhouse condition. The results showed that number of till/plant dry weight and activity/plant were increased in concordance with the increase of phosphorus amount. In addition, the application of Mycorrhizal in comparison with its non-application resulted in significant increase in entire above-mentioned measured characteristics, but its efficiency reduced by increasing phosphorous.Moreover, it was proven that there was a negative antagonistic effect by Streptomyces on Mycorrhizal, so that in all examined characteristics in which these two microorganisms were simultaneously used, a significant decrease was observed. Otherwise, study on phosphorus and mycorrhizal at different levels applications showed that phosphorus usage amount (0.40g/pot), in comparison with its more usage(0.60g/pot) had better effects on mycorrhizal. Application of Streptomyces had no significant on the examined characteristics. However, when applying both mycorrhizal and streptomyces, because of the sensitivity of mycorrhizal to Streptomyces presence, a decrease effect was observed. Application of Azospirillum, Mycorrhizal and specially organic fertilizer (manure), had positive and significant effects on the many of the measured characters

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; Endre, Gabriella; Kaló, Péter

2017-01-01

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. PMID:29240711

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

Directory of Open Access Journals (Sweden)

Ágota Domonkos

2017-12-01

Full Text Available 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.

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.

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.

{sup 15}N methodologies for quantifying the response of N{sub 2}-fixing associations to elevated [CO{sub 2}]: A review

Energy Technology Data Exchange (ETDEWEB)

Chalk, Phillip M., E-mail: chalkphillip@gmail.com; Lam, Shu K., E-mail: shukee.lam@unimelb.edu.au; Chen, Deli, E-mail: delichen@unimelb.edu.au

2016-11-15

Methodologies based on {sup 15}N enrichment (E) and {sup 15}N natural abundance (NA) have been used to obtain quantitative estimates of the response of biological N{sub 2} fixation (BNF) of legumes (woody, grain and forage) and actinorhizal plants grown in artificial media or in soil exposed to elevated atmospheric concentrations of carbon dioxide e[CO{sub 2}] for extended periods of time, in growth rooms, greenhouses, open top chambers or free-air CO{sub 2} enrichment (FACE) facilities. {sup 15}N{sub 2} has also been used to quantify the response of endophytic and free-living diazotrophs to e[CO{sub 2}]. The primary criterion of response was the proportional dependence of the N{sub 2}-fixing system on the atmosphere as a source of N. i.e. the symbiotic dependence (P{sub atm}). The unique feature of {sup 15}N-based methods is their ability to provide time-integrated and yield-independent estimates of P{sub atm}. In studies conducted in artificial media or in soil using the E methodology there was either no response or a positive response of P{sub atm} to e[CO{sub 2}]. The interpretation of results obtained in artificial media or with {sup 15}N{sub 2} is straight forward, not being subject to the assumptions on which the E and NA soil-cultured methods are based. A variety of methods have been used to estimate isotopic fractionation attendant on the NA technique, the so-called ‘B value’, which attaches a degree of uncertainty to the results obtained. Using the NA technique, a suite of responses of P{sub atm} to e[CO{sub 2}] has been published, from positive to neutral to sometimes negative effects. Several factors which interact with the response of N{sub 2}-fixing species to e[CO{sub 2}] were identified.

A mechanistic, globally-applicable model of plant nitrogen uptake, retranslocation and fixation

Science.gov (United States)

Fisher, J. B.; Tan, S.; Malhi, Y.; Fisher, R. A.; Sitch, S.; Huntingford, C.

2008-12-01

Nitrogen is one of the nutrients that can most limit plant growth, and nitrogen availability may be a controlling factor on biosphere responses to climate change. We developed a plant nitrogen assimilation model based on a) advective transport through the transpiration stream, b) retranslocation whereby carbon is expended to resorb nitrogen from leaves, c) active uptake whereby carbon is expended to acquire soil nitrogen, and d) biological nitrogen fixation whereby carbon is expended for symbiotic nitrogen fixers. The model relies on 9 inputs: 1) net primary productivity (NPP), 2) plant C:N ratio, 3) available soil nitrogen, 4) root biomass, 5) transpiration rate, 6) saturated soil depth,7) leaf nitrogen before senescence, 8) soil temperature, and 9) ability to fix nitrogen. A carbon cost of retranslocation is estimated based on leaf nitrogen and compared to an active uptake carbon cost based on root biomass and available soil nitrogen; for nitrogen fixers both costs are compared to a carbon cost of fixation dependent on soil temperature. The NPP is then allocated to optimize growth while maintaining the C:N ratio. The model outputs are total plant nitrogen uptake, remaining NPP available for growth, carbon respired to the soil and updated available soil nitrogen content. We test and validate the model (called FUN: Fixation and Uptake of Nitrogen) against data from the UK, Germany and Peru, and run the model under simplified scenarios of primary succession and climate change. FUN is suitable for incorporation into a land surface scheme of a General Circulation Model and will be coupled with a soil model and dynamic global vegetation model as part of a land surface model (JULES).

Fixation of Light Weight Polypropylene Mesh with n-Butyl-2-cyanocrylate in Pelvic Floor Surgery: Experimental Design Approach in Sheep for Effectiveness Evaluation

Directory of Open Access Journals (Sweden)

Sandra Barbosa

2015-01-01

Full Text Available Objective. The aim of this study was to find a proper experimental design and to evaluate n-butyl-2-cyanoacrylate (Histoacryl as a fixation method for a light-weight and large pore PP mesh (Synthetic PP Mesh-1 using the sheep as an animal model. Methods. Posterior vaginal implantation by means of episiotomy was used to implant 8 ewes which were evaluated macroscopically and histologically at 3 months (n=4 and 6 months (n=4 post-surgery. In previous pilot studies anterior vaginal implantation was evaluated, as well as different synthetic mesh materials, sizes and fixation methods (n=1 to 3 during three weeks. In all cases a clinical evaluation of the animal was performed. Results. A reduction in the mesh size (Synthetic PP Mesh-1 together with precise application of the surgical glue Histoacryl to fix the mesh yielded significantly better histocompatibility results (P<0.01 compared to larger size or other fixation methods. Conclusion. The combination of Synthetic PP Mesh-1 with Histoacryl offered a high degree of graft integration without vaginal ulceration and a minimal foreign body reaction, being the sheep a proper animal model to test these types of medical devices.

Quantitative analysis of an engineered CO2-fixing Escherichia coli reveals great potential of heterotrophic CO2 fixation.

Science.gov (United States)

Gong, Fuyu; Liu, Guoxia; Zhai, Xiaoyun; Zhou, Jie; Cai, Zhen; Li, Yin

2015-01-01

Production of fuels from the abundant and wasteful CO2 is a promising approach to reduce carbon emission and consumption of fossil fuels. Autotrophic microbes naturally assimilate CO2 using energy from light, hydrogen, and/or sulfur. However, their slow growth rates call for investigation of the possibility of heterotrophic CO2 fixation. Although preliminary research has suggested that CO2 fixation in heterotrophic microbes is feasible after incorporation of a CO2-fixing bypass into the central carbon metabolic pathway, it remains unclear how much and how efficient that CO2 can be fixed by a heterotrophic microbe. A simple metabolic flux index was developed to indicate the relative strength of the CO2-fixation flux. When two sequential enzymes of the cyanobacterial Calvin cycle were incorporated into an E. coli strain, the flux of the CO2-fixing bypass pathway accounts for 13 % of that of the central carbon metabolic pathway. The value was increased to 17 % when the carbonic anhydrase involved in the cyanobacterial carbon concentrating mechanism was introduced, indicating that low intracellular CO2 concentration is one limiting factor for CO2 fixation in E. coli. The engineered CO2-fixing E. coli with carbonic anhydrase was able to fix CO2 at a rate of 19.6 mg CO2 L(-1) h(-1) or the specific rate of 22.5 mg CO2 g DCW(-1) h(-1). This CO2-fixation rate is comparable with the reported rates of 14 autotrophic cyanobacteria and algae (10.5-147.0 mg CO2 L(-1) h(-1) or the specific rates of 3.5-23.7 mg CO2 g DCW(-1) h(-1)). The ability of CO2 fixation was created and improved in E. coli by incorporating partial cyanobacterial Calvin cycle and carbon concentrating mechanism, respectively. Quantitative analysis revealed that the CO2-fixation rate of this strain is comparable with that of the autotrophic cyanobacteria and algae, demonstrating great potential of heterotrophic CO2 fixation.

Novel European free-living, non-diazotrophic Bradyrhizobium isolates from contrasting soils that lack nodulation and nitrogen fixation genes - a genome comparison

Science.gov (United States)

Jones, Frances Patricia; Clark, Ian M.; King, Robert; Shaw, Liz J.; Woodward, Martin J.; Hirsch, Penny R.

2016-05-01

The slow-growing genus Bradyrhizobium is biologically important in soils, with different representatives found to perform a range of biochemical functions including photosynthesis, induction of root nodules and symbiotic nitrogen fixation and denitrification. Consequently, the role of the genus in soil ecology and biogeochemical transformations is of agricultural and environmental significance. Some isolates of Bradyrhizobium have been shown to be non-symbiotic and do not possess the ability to form nodules. Here we present the genome and gene annotations of two such free-living Bradyrhizobium isolates, named G22 and BF49, from soils with differing long-term management regimes (grassland and bare fallow respectively) in addition to carbon metabolism analysis. These Bradyrhizobium isolates are the first to be isolated and sequenced from European soil and are the first free-living Bradyrhizobium isolates, lacking both nodulation and nitrogen fixation genes, to have their genomes sequenced and assembled from cultured samples. The G22 and BF49 genomes are distinctly different with respect to size and number of genes; the grassland isolate also contains a plasmid. There are also a number of functional differences between these isolates and other published genomes, suggesting that this ubiquitous genus is extremely heterogeneous and has roles within the community not including symbiotic nitrogen fixation.

Farmers' agronomic and social evaluation of productivity yield and N2-fixation in different cowpea varieties and their subsequent residual N effects on a succeeding maize crop

NARCIS (Netherlands)

Adjei-Nsiah, S.; Kuyper, T.W.; Leeuwis, C.; Abekoe, M.K.; Cobbinah, J.; Sakyi-Dawson, O.; Giller, K.E.

2008-01-01

Cowpea-maize rotations form an important component of the farming systems of smallholder farmers in the forest/savannah transitional agro-ecological zone of Ghana. We evaluated five cowpea varieties for grain yield, N-2-fixation, biomass production, and contribution to productivity of subsequent

SIMULTANEOUS OBSERVATIONS OF SiO AND H2O MASERS TOWARD SYMBIOTIC STARS

International Nuclear Information System (INIS)

Cho, Se-Hyung; Kim, Jaeheon

2010-01-01

We present the results of simultaneous observations of SiO v = 1, 2, J = 1-0, 29 SiO v = 0, J = 1-0, and H 2 O 6 16 -5 23 maser lines performed with the KVN Yonsei 21 m radio telescope from 2009 November to 2010 January. We searched for these masers in 47 symbiotic stars and detected maser emission from 21 stars, giving the first time detection from 19 stars. Both SiO and H 2 O masers were detected from seven stars of which six were D-type symbiotic stars and one was an S-type star, WRAY 15-1470. In the SiO maser emission, the 28 SiO v = 1 maser was detected from 10 stars, while the v = 2 maser was detected from 15 stars. In particular, the 28 SiO v = 2 maser emission without the v = 1 maser detection was detected from nine stars with a detection rate of 60%, which is much higher than that of isolated Miras/red giants. The 29 SiO v = 0 maser emission was also detected from two stars, H 2-38 and BF Cyg, together with the 28 SiO v = 2 maser. We conclude that these different observational results between isolated Miras/red giants and symbiotic stars may be related with the presence of hot companions in a symbiotic binary system.

Symbiotic stars

International Nuclear Information System (INIS)

Boyarchuk, A.A.

1975-01-01

There are some arguments that the symbiotic stars are binary, where one component is a red giant and the other component is a small hot star which is exciting a nebula. The symbiotic stars belong to the old disc population. Probably, symbiotic stars are just such an evolutionary stage for double stars as planetary nebulae for single stars. (Auth.)

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

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.

Elevated Atmospheric CO2 and Warming Stimulates Growth and Nitrogen Fixation in a Common Forest Floor Cyanobacterium under Axenic Conditions

Directory of Open Access Journals (Sweden)

Zoë Lindo

2017-03-01

Full Text Available The predominant input of available nitrogen (N in boreal forest ecosystems originates from moss-associated cyanobacteria, which fix unavailable atmospheric N2, contribute to the soil N pool, and thereby support forest productivity. Alongside climate warming, increases in atmospheric CO2 concentrations are expected in Canada’s boreal region over the next century, yet little is known about the combined effects of these factors on N fixation by forest floor cyanobacteria. Here we assess changes in N fixation in a common forest floor, moss-associated cyanobacterium, Nostoc punctiforme Hariot, under elevated CO2 conditions over 30 days and warming combined with elevated CO2 over 90 days. We measured rates of growth and changes in the number of specialized N2 fixing heterocyst cells, as well as the overall N fixing activity of the cultures. Elevated CO2 stimulated growth and N fixation overall, but this result was influenced by the growth stage of the cyanobacteria, which in turn was influenced by our temperature treatments. Taken together, climate change factors of warming and elevated CO2 are expected to stimulate N2 fixation by moss-associated cyanobacteria in boreal forest systems.

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.

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

experimentalmente. El manejo de bosque afectó la composición florística de la hojarasca, pero no hubo diferencias su relación C/N, ni en los contenidos de N o P totales.Nitrogen input to evergreen températe forests of Chiloé Island, Chile occurs predominantly via non-symbiotic fixation (NSF. Because this is a bacterial-mediated process (diazotrophs, in addition to environmental factors (e.g., temperature and moisture, phosphorous availability and energy supply from carbón in the substrate may influence the rates of N fixation. Our hypothesis is that if both phosphorous and carbón are limiting NSF, this limitation would be greater in logged forests, where additions of labile P and C would stimulate microbial activity. Our objectives are to assess the effects of inorganic phosphorus and labile carbón (as glucose additions (0 mmol P/L, 0.645 mmol P/L, 3.23 mmol P/L y 6.45 mmol P/L and 0 mmol P/L, 23.3 mmol C/L, 46.6 mmol C/L y 70 mmol C/L, respectively on the rates of NSF measured in the litter layer of each forest in laboratory assays, under controlled temperature and moisture and using homogeneous litter samples. We studied lowland evergreen rainforests (100-200 m of altitude, located in the Chonchi district, in Chiloé Island. Two forest stands were logged, subjected to industrial and non-industrial selective logging, and the third stand was unlogged (control. The NSF of nitrogen was assessed by the acetylene reduction assay. Two-way ANOVAs showed that phosphorous addition had no effect on acetylene reduction rates (ARR in the litter of logged or unlogged forests, but the addition of labile carbón in the form of glucose negatively affected ARR when applied at the máximum level to the litter of unlogged forest. In all treatments the factor forest accounted for the differences in ARR, which was higher in unlogged forest. These differences were not explained by any of the variables experimentally manipulated in this study. The main difference among forests was floristic

The use of 15N-labelled dinitrogen in the study of nitrogen fixation by blue-green algae

International Nuclear Information System (INIS)

Jones, J.

1985-01-01

Prior to the development of the acetylene reduction technique 15 N was used as the main qualitative and quantitative measure of nitrogen fixation by free-living cyanobacteria in a variety of aquatic and terrestrial habitats. Despite its expense and the technical difficulty, 15 N is a major tool in the study of cyanobacteria, for example, incorporation of 15 N 2 is the definitive test for nitrogen fixation; it is used in the determination of the correct ratio of acetylene reduction to nitrogen fixation, in in situ nitrogen fixation assays, in tracing the formation and fate of extra-cellular nitrogen and in measuring the turnover and grazing rates of cyanobacterial intra-cellular nitrogen. These latter studies show that 15 N-labelled extra-cellular nitrogen can serve as nitrogen sources for a variety of bacteria, fungi, algae and higher plants, and that cyanobacteria are graced and digested by a variety of animals. The turnover rates of cyanobacterial 15 N-labelled cells are dependent on the type of cell, species, environmental conditions and the availability of degrading organisms. The breakdown products are rapidly mineralised and used as nitrogen sources by higher plants. (author)

The Effect of Land-use Change and Management on Free-living N2 fixation in the Brazilian Atlantic Forest

Science.gov (United States)

De Oliveira Bomfim, B.; Silva, L. C. R.; Horwath, W. R.; Hello, J.; Doane, T. A.

2016-12-01

Globally, primary tropical forests are increasingly disturbed by deforestation, urbanization, agriculture, and cattle ranching. It has been recognized that the resulting (secondary) forests now play a key role in global biogeochemical cycles; however, little is known about alterations in forest function caused by the combination of disturbance and land use change. Fire, deforestation, and forest-to-monocrop conversion are all likely to affect biotic N inputs, yet our understanding of how free-living N2 fixation influences ecosystem response after disturbance remains poorly understood. Our research is assessing the role of asymbiotic (free-living) biological nitrogen fixation (BNF), a microbially-mediated process responsible for providing N inputs across terrestrial ecosystems and modulating the effect of fire and land cover in secondary forest succession. Free-living BNF is being quantified through incubations using stable isotope (15N2 labeling experiment) in different substrates (soil and leaf litter) under contrasting land use and management in the Brazilian Atlantic Forest, the most deforested Biome in Brazil with only 7% of its original cover. Soil and litter samples were collected in primary forests, 12-year secondary forests, Eucalyptus spp. plantations and 10-year Brachiaria brizantha pastures. Preliminary results indicate that free-living BNF rates did not vary significantly between either secondary land use (0.02 to 0.46 µg N2 fixed gDW-1 h-1), but rates were significantly higher in the litter layer (0.32 to 3.8 µg N2 fixed gDW-1 h-1) than in the surface soil (0 - 10 cm and 10 - 30 cm). Free-living BNF in this stretch of the Brazilian Atlantic Forest seems not to be significantly affected by contrasting land use and management.

Comparative Effects of Cowpea and Soybean Genotypes on N2 ...

African Journals Online (AJOL)

acer

ABSTRACT:A field trial was conducted to asses N2 - fixation and N balance in five cultivars each of soybean (TGX 1945 – 1F, ... Key words: Legume genotype, N2 fixation, N balance and Nitrogen Harvest Index (NHI) ..... subsequent maize grain yield in the guinea savanna ... On-farm evaluation of biological nitrogen fixation.

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. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

Optimized breeding strategies for multiple trait integration: II. Process efficiency in event pyramiding and trait fixation.

Science.gov (United States)

Peng, Ting; Sun, Xiaochun; Mumm, Rita H

2014-01-01

Multiple trait integration (MTI) is a multi-step process of converting an elite variety/hybrid for value-added traits (e.g. transgenic events) through backcross breeding. From a breeding standpoint, MTI involves four steps: single event introgression, event pyramiding, trait fixation, and version testing. This study explores the feasibility of marker-aided backcross conversion of a target maize hybrid for 15 transgenic events in the light of the overall goal of MTI of recovering equivalent performance in the finished hybrid conversion along with reliable expression of the value-added traits. Using the results to optimize single event introgression (Peng et al. Optimized breeding strategies for multiple trait integration: I. Minimizing linkage drag in single event introgression. Mol Breed, 2013) which produced single event conversions of recurrent parents (RPs) with ≤8 cM of residual non-recurrent parent (NRP) germplasm with ~1 cM of NRP germplasm in the 20 cM regions flanking the event, this study focused on optimizing process efficiency in the second and third steps in MTI: event pyramiding and trait fixation. Using computer simulation and probability theory, we aimed to (1) fit an optimal breeding strategy for pyramiding of eight events into the female RP and seven in the male RP, and (2) identify optimal breeding strategies for trait fixation to create a 'finished' conversion of each RP homozygous for all events. In addition, next-generation seed needs were taken into account for a practical approach to process efficiency. Building on work by Ishii and Yonezawa (Optimization of the marker-based procedures for pyramiding genes from multiple donor lines: I. Schedule of crossing between the donor lines. Crop Sci 47:537-546, 2007a), a symmetric crossing schedule for event pyramiding was devised for stacking eight (seven) events in a given RP. Options for trait fixation breeding strategies considered selfing and doubled haploid approaches to achieve homozygosity

Promoting helix pitch and trichome length to improve biomass harvesting efficiency and carbon dioxide fixation rate by Spirulina sp. in 660 m2 raceway ponds under purified carbon dioxide from a coal chemical flue gas.

Science.gov (United States)

Cheng, Jun; Guo, Wangbiao; Ameer Ali, Kubar; Ye, Qing; Jin, Guiyong; Qiao, Zhanshan

2018-08-01

The helix pitch and trichome length of Spirulina sp. were promoted to improve the biomass harvesting efficiency and CO 2 fixation rate in 660 m 2 raceway ponds aerated with food-grade CO 2 purified from a coal chemical flue gas. The CO 2 fixation rate was improved with increased trichome length of the Spirulina sp. in a raceway pond with double paddlewheels, baffles, and CO 2 aerators (DBA raceway pond). The trichome length has increased by 33.3 μm, and CO 2 fixation rate has increased by 42.3% and peaked to 51.3 g/m 2 /d in a DBA raceway pond. Biomass harvesting efficiency was increased with increased helix pitch. When the day-average greenhouse temperature was 33 °C and day-average sunlight intensity was 72,100 lu×, the helix pitch of Spirulina sp. was increased to 56.2 μm. Hence the biomass harvesting efficiency was maximized to 75.6% and biomass actual yield was increased to 35.9 kg in a DBA raceway pond. Copyright © 2018 Elsevier Ltd. All rights reserved.

Modification of bifunctional epoxy resin using CO2 fixation process and nanoclay

International Nuclear Information System (INIS)

Khoshkish, Morteza; Bouhendi, Hosein; Vafayan, Mehdi

2014-01-01

A bifunctional epoxy resin was modified by using a CO 2 fixation solution process in the presence of tetra n-butyl ammonium bromide (TBAB) as catalyst and the modified treated resin was treated by cloisite 30B as nano additive. The Unmodified epoxy resin (UME), CO 2 fixated modified epoxy resin (CFME), and CFME/clay nano composite (CFMEN), were cured by diethylenetriamine (DETA). A cycloaliphatic compound as a reactive diluent was used to control the viscosity of high viscose CFME. The exfoliation of organoclay in UME and CFME was investigated by X-ray diffraction and activation energy was computed using the advanced integral isoconversional method. The activation energy dependency demonstrated that the mechanism of UME curing did not change in the presence of nanoclay. In contrast, the CO 2 fixation results showed a significant change in the activation energy dependency. The Thermal stability parameters include the initial degradation temperature (IDT), the temperature at the maximum rate of weight loss (T max ), and the decomposition activation energy (E d ) were determined by thermal gravimetry analysis. Dynamic mechanical thermal analysis measurements showed that the presence of organoclay in CFME increases the T g of nano composite in contrast to UME. The fracture roughness of UME, CFME and CFNE were determined by scanning electron microscope. The exfoliated UME/1%clay nanocomposite was confirmed by TEM image. - Highlights: • A new epoxy resin was synthesized using CO 2 fixation reaction. • The synthesized epoxy resin was modified by an organo nano-clay. • CO 2 fixation noticeably changed the curing mechanism. • CO 2 fixation reaction consumes CO 2 which is a harmful greenhouse gas

Disturbance and topography shape nitrogen availability and δ15 N over long-term forest succession

Science.gov (United States)

Perakis, Steven; Tepley, Alan J.; Compton, Jana

2015-01-01

Forest disturbance and long-term succession towards old-growth are thought to increase nitrogen (N) availability and N loss, which should increase soil δ15N values. We examined soil and foliar patterns in N and δ15N, and soil N mineralization, across 800 years of forest succession in a topographically complex montane landscape influenced by human logging and wildfire. In contrast to expectations, we found that disturbance caused declines in surface mineral soil δ15N values, both in logged forests measured 40–50 years after disturbance, and in unlogged forests disturbed by severe wildfire within the last 200 years. Both symbiotic N fixation and N transfers from disturbed vegetation and detritus could lower soil δ15N values after disturbance. A more important role for symbiotic N fixation is suggested by lower soil δ15N values in slow-successional sites with slow canopy closure, which favors early-successional N fixers. Soil δ15N values increased only marginally throughout 800 years of succession, reflecting soil N uptake by vegetation and strong overall N retention. Although post-disturbance N inputs lowered surface soil δ15N values, steady-state mass balance calculations suggest that wildfire combustion of vegetation and detritus can dominate long-term N loss and increase whole-ecosystem δ15N. On steeper topography, declining soil δ15N values highlight erosion and accelerated soil turnover as an additional abiotic control on N balances. We conclude for N-limited montane forests that soil δ15N and N availability are less influenced by nitrate leaching and denitrification loss than by interactions between disturbance, N fixation, and erosion.

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.

Mechanism of CO 2 Fixation by Ir I -X Bonds (X = OH, OR, N, C)

KAUST Repository

Vummaleti, Sai V. C.; Talarico, Giovanni; Nolan, Steven P.; Cavallo, Luigi; Poater, Albert

2015-01-01

Density functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5-cyclooctadiene; IiPr = 1,3-diisopropylimidazol-2-ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate-limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir-OR1 (R1 = H, methyl, and phenyl) and Ir-N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0-23.0 kcal/mol. Substantially higher values (35.0-50.0 kcal/mol) are reported for analogous Ir-C bonds. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanism of CO 2 Fixation by Ir I -X Bonds (X = OH, OR, N, C)

KAUST Repository

Vummaleti, Sai V. C.

2015-09-08

Density functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5-cyclooctadiene; IiPr = 1,3-diisopropylimidazol-2-ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate-limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir-OR1 (R1 = H, methyl, and phenyl) and Ir-N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0-23.0 kcal/mol. Substantially higher values (35.0-50.0 kcal/mol) are reported for analogous Ir-C bonds. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

Evolutionary signals of symbiotic persistence in the legume-rhizobia mutualism.

Science.gov (United States)

Werner, Gijsbert D A; Cornwell, William K; Cornelissen, Johannes H C; Kiers, E Toby

2015-08-18

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they "lock" the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships.

Evolutionary signals of symbiotic persistence in the legume–rhizobia mutualism

Science.gov (United States)

Werner, Gijsbert D. A.; Cornwell, William K.; Cornelissen, Johannes H. C.; Kiers, E. Toby

2015-01-01

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they “lock” the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships. PMID:26041807

The infrared variability and nature of symbiotic stars

International Nuclear Information System (INIS)

Feast, M.W.; Catchpole, R.M.; Whitelock, P.A.; Carter, B.S.; Roberts, G.

1983-01-01

Infrared variability and spectra show that the symbiotic systems (He 2-106, He 2-38, He 2-34) contain Mira variable components. The first two also show a longer term infrared variability. It is suggested that this is due to variable dust obscuration (as in R Aqr). The phenomenon is then too frequent for the dust clouds to be confined to the orbital planes of the binary systems. Seven Miras in symbiotics have known periods which range from 370 to 580 days, suggesting a greater frequency of long-period Miras in symbiotics than in the general field. Symbiotic Miras have dust excesses with colour temperatures near 1000 K. Observations of four other symbiotic systems (Pe 2-3, He 2-87, H 2-5, AG Peg) are consistent with their containing non-variable or low amplitude M-type components. (author)

14CO2 fixation pattern of cyanobacteria

International Nuclear Information System (INIS)

Erdmann, N.; Schiewer, U.

1985-01-01

The 14 CO 2 fixation pattern of three cyanobacteria in the light and dark were studied. Two different chromatographic methods widely used for separating labelled photosynthetic intermediates were compared. After ethanolic extraction, a rather uniform fixation pattern reflecting mainly the β-carboxylation pathway is obtained for all 3 species. Of the intermediates, glucosylglycerol is specific and high citrulline and low malate contents are fairly specific to cyanobacteria. The composition of the 14 CO 2 fixation pattern is hardly affected by changes in temperature or light intensity, but it is severely affected by changes in the water potential of the medium. (author)