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Sample records for nitrogen fixation island

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Large-scale impact of the island mass effect through nitrogen fixation in the western South Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Shiozaki, Takuhei; Kodama, Taketoshi; Furuya, Ken

    2014-04-01

    We describe a new mechanism for the island mass effect fueled by nitrogen fixation. The nitrogen fixation activities and δ15N of suspended particles in the surface water in the South Pacific were examined. Active nitrogen fixation and abundant Trichodesmium spp. were observed near islands in the western subtropical region, which was attributable to the material supplied by land runoff. High primary production was extensively centered around the islands and was characterized by low δ15N of suspended particles and a reduction in phosphate concentrations at the surface compared with the subtropical gyre and eastern equatorial upwelling. This suggested that Trichodesmium spp. were advected to areas remote from these islands, and consequently, the elevated primary production fueled by nitrogen fixation extended over a large area around them. Because the proposed island mass effect is triggered by a terrigenous nutrient supply, this ecosystem is potentially vulnerable to human activity on small islands.

  3. Interspecies Transfer and Regulation of Pseudomonas stutzeri A1501 Nitrogen Fixation Island in Escherichia coli.

    PubMed

    Han, Yunlei; Lu, Na; Chen, Qinghua; Zhan, Yuhua; Liu, Wei; Lu, Wei; Zhu, Baoli; Lin, Min; Yang, Zhirong; Yan, Yongliang

    2015-08-01

    Until now, considerable effort has been made to engineer novel nitrogen-fixing organisms through the transfer of nif genes from various diazotrophs to non-nitrogen fixers; however, regulatory coupling of the heterologous nif genes with the regulatory system of the new host is still not well understood. In this work, a 49 kb nitrogen fixation island from P. stutzeri A1501 was transferred into E. coli using a novel and efficient transformation strategy, and a series of recombinant nitrogen-fixing E. coli strains were obtained. We found that the nitrogenase activity of the recombinant E. coli strain EN-01, similar to the parent strain P. stutzeri A1501, was dependent on external ammonia concentration, oxygen tension, and temperature. We further found that there existed a regulatory coupling between the E. coli general nitrogen regulatory system and the heterologous P. stutzeri nif island in the recombinant E. coli strain. We also provided evidence that the E. coli general nitrogen regulator GlnG protein was involved in the activation of the nif-specific regulator NifA via a direct interaction with the NifA promoter. To the best of our knowledge, this work plays a groundbreaking role in increasing understanding of the regulatory coupling of the heterologous nitrogen fixation system with the regulatory system of the recipient host. Furthermore, it will shed light on the structure and functional integrity of the nif island and will be useful for the construction of novel and more robust nitrogen-fixing organisms through biosynthetic engineering.

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

    PubMed

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

    2016-09-29

    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.

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

    PubMed Central

    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

  6. Nitrogen fixation island and rhizosphere competence traits in the genome of root-associated Pseudomonas stutzeri A1501.

    PubMed

    Yan, Yongliang; Yang, Jian; Dou, Yuetan; Chen, Ming; Ping, Shuzhen; Peng, Junping; Lu, Wei; Zhang, Wei; Yao, Ziying; Li, Hongquan; Liu, Wei; He, Sheng; Geng, Lizhao; Zhang, Xiaobing; Yang, Fan; Yu, Haiying; Zhan, Yuhua; Li, Danhua; Lin, Zhanglin; Wang, Yiping; Elmerich, Claudine; Lin, Min; Jin, Qi

    2008-05-27

    The capacity to fix nitrogen is widely distributed in phyla of Bacteria and Archaea but has long been considered to be absent from the Pseudomonas genus. We report here the complete genome sequencing of nitrogen-fixing root-associated Pseudomonas stutzeri A1501. The genome consists of a single circular chromosome with 4,567,418 bp. Comparative genomics revealed that, among 4,146 protein-encoding genes, 1,977 have orthologs in each of the five other Pseudomonas representative species sequenced to date. The genome contains genes involved in broad utilization of carbon sources, nitrogen fixation, denitrification, degradation of aromatic compounds, biosynthesis of polyhydroxybutyrate, multiple pathways of protection against environmental stress, and other functions that presumably give A1501 an advantage in root colonization. Genetic information on synthesis, maturation, and functioning of nitrogenase is clustered in a 49-kb island, suggesting that this property was acquired by lateral gene transfer. New genes required for the nitrogen fixation process have been identified within the nif island. The genome sequence offers the genetic basis for further study of the evolution of the nitrogen fixation property and identification of rhizosphere competence traits required in the interaction with host plants; moreover, it opens up new perspectives for wider application of root-associated diazotrophs in sustainable agriculture.

  7. Update: Biological Nitrogen Fixation.

    ERIC Educational Resources Information Center

    Wiseman, Alan; And Others

    1985-01-01

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

  8. The Fixation of Nitrogen.

    ERIC Educational Resources Information Center

    Andrew, S. P. S.

    1978-01-01

    Discusses the fixation of atmospheric nitrogen in the form of ammonia as one of the foundations of modern chemical industry. The article describes ammonia production and synthesis, purifying the hydrogen-nitrogen mix, nitric acid production, and its commericial plant. (HM)

  9. The Fixation of Nitrogen.

    ERIC Educational Resources Information Center

    Andrew, S. P. S.

    1978-01-01

    Discusses the fixation of atmospheric nitrogen in the form of ammonia as one of the foundations of modern chemical industry. The article describes ammonia production and synthesis, purifying the hydrogen-nitrogen mix, nitric acid production, and its commericial plant. (HM)

  10. Trichodesmium and nitrogen fixation in the Kuroshio

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Takeda, S.; Itoh, S.; Kodama, T.; Liu, X.; Hashihama, F.; Furuya, K.

    2015-07-01

    Nitrogen fixation in the Kuroshio influences nitrogen balance in the North Pacific Ocean. The genus Trichodesmium is recognized as a major diazotroph in the Kuroshio. Although its abundance is higher in the Kuroshio than in adjacent waters, the reason for this difference remains unclear. The present study investigated the abundance of Trichodesmium spp. and nitrogen fixation together with concentrations of dissolved iron and phosphate, whose availabilities potentially control diazotrophy, in the Kuroshio and its marginal seas. We performed the observations near the Miyako Islands, which form part of the Ryukyu Islands, situated along the Kuroshio, since satellite analysis suggested that material transport could occur from the islands to the Kuroshio. Trichodesmium spp. bloomed (> 20 000 filaments L-1) near the Miyako Islands, and the abundance was high in the Kuroshio and the Kuroshio bifurcation region of the East China Sea, but was low in the Philippine Sea. The abundance of Trichodesmium spp. was significantly correlated with the total nitrogen fixation activity. The surface concentrations of dissolved iron (0.19-0.89 nM) and phosphate (< 3-36 nM) were similar for all of the study areas, indicating that the nutrient distribution could not explain the spatial differences in Trichodesmium spp. abundance and nitrogen fixation. We used a numerical model to simulate the transportation of water around the Ryukyu Islands to the Kuroshio. Our results indicate that Trichodesmium growing around the islands situated along the Kuroshio is potentially important for determining diazotrophy in this region.

  11. Molecular Biology of Nitrogen Fixation

    ERIC Educational Resources Information Center

    Shanmugam, K. T.; Valentine, Raymond C.

    1975-01-01

    Reports that as a result of our increasing knowledge of the molecular biology of nitrogen fixation it might eventually be possible to increase the biological production of nitrogenous fertilizer from atmospheric nitrogen. (GS)

  12. Molecular Biology of Nitrogen Fixation

    ERIC Educational Resources Information Center

    Shanmugam, K. T.; Valentine, Raymond C.

    1975-01-01

    Reports that as a result of our increasing knowledge of the molecular biology of nitrogen fixation it might eventually be possible to increase the biological production of nitrogenous fertilizer from atmospheric nitrogen. (GS)

  13. Nitrogen fixation apparatus

    DOEpatents

    Chen, Hao-Lin

    1984-01-01

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

  14. Eighth international congress on nitrogen fixation

    SciTech Connect

    Not Available

    1990-01-01

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

  15. Understanding Nitrogen Fixation

    SciTech Connect

    Paul J. Chirik

    2012-05-25

    synthesis of ammonia, NH{sub 3}, from its elements, H{sub 2} and N{sub 2}, via the venerable Haber-Bosch process is one of the most significant technological achievements of the past century. Our research program seeks to discover new transition metal reagents and catalysts to disrupt the strong N {triple_bond} N bond in N{sub 2} and create new, fundamental chemical linkages for the construction of molecules with application as fuels, fertilizers and fine chemicals. With DOE support, our group has discovered a mild method for ammonia synthesis in solution as well as new methods for the construction of nitrogen-carbon bonds directly from N{sub 2}. Ideally these achievements will evolve into more efficient nitrogen fixation schemes that circumvent the high energy demands of industrial ammonia synthesis. Industrially, atmospheric nitrogen enters the synthetic cycle by the well-established Haber-Bosch process whereby N{sub 2} is hydrogenated to ammonia at high temperature and pressure. The commercialization of this reaction represents one of the greatest technological achievements of the 20th century as Haber-Bosch ammonia is responsible for supporting approximately 50% of the world's population and serves as the source of half of the nitrogen in the human body. The extreme reaction conditions required for an economical process have significant energy consequences, consuming 1% of the world's energy supply mostly in the form of pollution-intensive coal. Moreover, industrial H{sub 2} synthesis via the water gas shift reaction and the steam reforming of methane is fossil fuel intensive and produces CO{sub 2} as a byproduct. New synthetic methods that promote this thermodynamically favored transformation ({Delta}G{sup o} = -4.1 kcal/mol) under milder conditions or completely obviate it are therefore desirable. Most nitrogen-containing organic molecules are derived from ammonia (and hence rely on the Haber-Bosch and H{sub 2} synthesis processes) and direct synthesis from

  16. Missing nitrogen fixation in the Benguela region

    NASA Astrophysics Data System (ADS)

    Wasmund, Norbert; Struck, Ulrich; Hansen, Anja; Flohr, Anita; Nausch, Günther; Grüttmüller, Annett; Voss, Maren

    2015-12-01

    Opposing opinions on the importance of nitrogen fixation in the northern Benguela upwelling region provoked us to investigate the magnitude of nitrogen fixation in front of northern Namibia and southern Angola. Measurements of nitrogen fixation rates using the 15N method at 66 stations during seven cruises from 2008 to 2014 showed that, in general, the 15N content in the biomass did not increase after tracer incubation with 15N2, indicating that no nitrogen fixation occurred. Correspondingly, the filamentous nitrogen-fixing cyanobacterium Trichodesmium was almost not present. The abundant picocyanobacteria did obviously not perform nitrogen fixation to a significant degree. The artificial improvement of conditions for nitrogen fixation in mesocosm experiments, including phosphate and iron additions and a warmer temperature, failed to induce nitrogen fixation. A plausible explanation of these findings is a lack of conditioned cells for nitrogen fixation in the Benguela region.

  17. Nitrogen fixation by marine cyanobacteria.

    PubMed

    Zehr, Jonathan P

    2011-04-01

    Discrepancies between estimates of oceanic N(2) fixation and nitrogen (N) losses through denitrification have focused research on identifying N(2)-fixing cyanobacteria and quantifying cyanobacterial N(2) fixation. Previously unrecognized cultivated and uncultivated unicellular cyanobacteria have been discovered that are widely distributed, and some have very unusual properties. Uncultivated unicellular N(2)-fixing cyanobacteria (UCYN-A) lack major metabolic pathways including the tricarboxylic acid cycle and oxygen-evolving photosystem II. Genomes of the oceanic N(2)-fixing cyanobacteria are highly conserved at the DNA level, and genetic diversity is maintained by genome rearrangements. The major cyanobacterial groups have different physiological and ecological constraints that result in highly variable geographic distributions, with implications for the marine N-cycle budget.

  18. Biochemical Approaches to Improved Nitrogen Fixation

    USDA-ARS?s Scientific Manuscript database

    Improving symbiotic nitrogen fixation by legumes has emerged again as an important topic on the world scene due to the energy crisis and lack of access to nitrogen fertilizer in developing countries. We have taken a biochemical genomics approach to improving symbiotic nitrogen fixation in legumes. L...

  19. Nitrogen fixation method and apparatus

    DOEpatents

    Chen, H.L.

    1983-08-16

    A method and apparatus for achieving nitrogen fixation includes a volumetric electric discharge chamber. The volumetric discharge chamber provides an even distribution of an electron beam, and enables the chamber to be maintained at a controlled energy to pressure (E/p) ratio. An E/p ratio of from 5 to 15 kV/atm of O[sub 2]/cm promotes the formation of vibrationally excited N[sub 2]. Atomic oxygen interacts with vibrationally excited N[sub 2] at a much quicker rate than unexcited N[sub 2], greatly improving the rate at which NO is formed. 1 fig.

  20. Nitrogen fixation method and apparatus

    DOEpatents

    Chen, Hao-Lin

    1983-01-01

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

  1. The Nitrogen-Fixation Island Insertion Site Is Conserved in Diazotrophic Pseudomonas stutzeri and Pseudomonas sp. Isolated from Distal and Close Geographical Regions

    PubMed Central

    Venieraki, Anastasia; Dimou, Maria; Vezyri, Eleni; Vamvakas, Alexandros; Katinaki, Pagona-Artemis; Chatzipavlidis, Iordanis; Tampakaki, Anastasia; Katinakis, Panagiotis

    2014-01-01

    The presence of nitrogen fixers within the genus Pseudomonas has been established and so far most isolated strains are phylogenetically affiliated to Pseudomonas stutzeri. A gene ortholog neighborhood analysis of the nitrogen fixation island (NFI) in four diazotrophic P. stutzeri strains and Pseudomonas azotifigens revealed that all are flanked by genes coding for cobalamin synthase (cobS) and glutathione peroxidise (gshP). The putative NFIs lack all the features characterizing a mobilizable genomic island. Nevertheless, bioinformatic analysis P. stutzeri DSM 4166 NFI demonstrated the presence of short inverted and/or direct repeats within both flanking regions. The other P. stutzeri strains carry only one set of repeats. The genetic diversity of eleven diazotrophic Pseudomonas isolates was also investigated. Multilocus sequence typing grouped nine isolates along with P. stutzeri and two isolates are grouped in a separate clade. A Rep-PCR fingerprinting analysis grouped the eleven isolates into four distinct genotypes. We also provided evidence that the putative NFI in our diazotrophic Pseudomonas isolates is flanked by cobS and gshP genes. Furthermore, we demonstrated that the putative NFI of Pseudomonas sp. Gr65 is flanked by inverted repeats identical to those found in P. stutzeri DSM 4166 and while the other P. stutzeri isolates harbor the repeats located in the intergenic region between cobS and glutaredoxin genes as in the case of P. stutzeri A1501. Taken together these data suggest that all putative NFIs of diazotrophic Pseudomonas isolates are anchored in an intergenic region between cobS and gshP genes and their flanking regions are designated by distinct repeats patterns. Moreover, the presence of almost identical NFIs in diazotrophic Pseudomonas strains isolated from distal geographical locations around the world suggested that this horizontal gene transfer event may have taken place early in the evolution. PMID:25251496

  2. The nitrogen-fixation island insertion site is conserved in diazotrophic Pseudomonas stutzeri and Pseudomonas sp. isolated from distal and close geographical regions.

    PubMed

    Venieraki, Anastasia; Dimou, Maria; Vezyri, Eleni; Vamvakas, Alexandros; Katinaki, Pagona-Artemis; Chatzipavlidis, Iordanis; Tampakaki, Anastasia; Katinakis, Panagiotis

    2014-01-01

    The presence of nitrogen fixers within the genus Pseudomonas has been established and so far most isolated strains are phylogenetically affiliated to Pseudomonas stutzeri. A gene ortholog neighborhood analysis of the nitrogen fixation island (NFI) in four diazotrophic P. stutzeri strains and Pseudomonas azotifigens revealed that all are flanked by genes coding for cobalamin synthase (cobS) and glutathione peroxidise (gshP). The putative NFIs lack all the features characterizing a mobilizable genomic island. Nevertheless, bioinformatic analysis P. stutzeri DSM 4166 NFI demonstrated the presence of short inverted and/or direct repeats within both flanking regions. The other P. stutzeri strains carry only one set of repeats. The genetic diversity of eleven diazotrophic Pseudomonas isolates was also investigated. Multilocus sequence typing grouped nine isolates along with P. stutzeri and two isolates are grouped in a separate clade. A Rep-PCR fingerprinting analysis grouped the eleven isolates into four distinct genotypes. We also provided evidence that the putative NFI in our diazotrophic Pseudomonas isolates is flanked by cobS and gshP genes. Furthermore, we demonstrated that the putative NFI of Pseudomonas sp. Gr65 is flanked by inverted repeats identical to those found in P. stutzeri DSM 4166 and while the other P. stutzeri isolates harbor the repeats located in the intergenic region between cobS and glutaredoxin genes as in the case of P. stutzeri A1501. Taken together these data suggest that all putative NFIs of diazotrophic Pseudomonas isolates are anchored in an intergenic region between cobS and gshP genes and their flanking regions are designated by distinct repeats patterns. Moreover, the presence of almost identical NFIs in diazotrophic Pseudomonas strains isolated from distal geographical locations around the world suggested that this horizontal gene transfer event may have taken place early in the evolution.

  3. Eighth international congress on nitrogen fixation. Final program

    SciTech Connect

    Not Available

    1990-12-31

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

  4. Methanotrophy induces nitrogen fixation during peatland development.

    PubMed

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

    2014-01-14

    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.

  5. Methanotrophy induces nitrogen fixation during peatland development

    PubMed Central

    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

  6. Carbon consequences of a nitrogen fixation feedback

    NASA Astrophysics Data System (ADS)

    Levy, J.; Medvigy, D.; Hedin, L.; Batterman, S. A.; Xu, X.

    2014-12-01

    Tropical forests constitute a globally important carbon sink but it is unclear how their productivity and carbon storage depend upon nutrients. There is increasing evidence of an ecosystem carbon-nitrogen feedback mechanism, by which symbiotic dinitrogen (N2) fixing trees can provide the nitrogen needed to maintain high rates of forest biomass growth following disturbance. Field-based evaluation of this feedback is difficult, however, as the expected effects on forest carbon stores would emerge very slowly, over decades to centuries of ecological succession. Moreover, there is no known way to inhibit the fixation process in trees without causing structural damage and perturbing the carbon cycle. Coupled land biogeochemistry-vegetation models offer a way to examine the role of feedbacks that unfold over successional time. However, it is unclear how the process of nitrogen fixation ought to be represented in models so that they can capture the potential effect of fixation on the long-term forest carbon sink. In this study, we integrate a newly developed individual-based model with field observations across Panamanian tropical forests to address: 1) whether N2 fixation enhances tropical forest carbon storage; 2) whether models must resolve fixation at the individual plant level to capture the fixation feedback; and 3) whether fixation interacts with plant functional types (i.e., early, mid, vs. late succession) to determine the carbon sink? We find that forests that have fixation recover faster and store more carbon in the long term than forests without fixation. This results in 94-118% more plant carbon stored by 30 years and an additional 13 tons C ha -1 stored over 300 years when compared to forests without fixation. Additionally, resolving fixation at the individual plant level is necessary to capture nitrogen dynamics over time and is particularly important for modeling succession and disturbance events. Finally, we find that the overall fixation effect is the

  7. Nitrogen Inputs via Nitrogen Fixation in Northern Plants and Soils

    NASA Astrophysics Data System (ADS)

    Thorp, N. R.; Wieder, R. K.; Vile, M. A.

    2015-12-01

    Dominated by cold and often acidic water logged environments, mineralization of organic matter is slow in the majority of northern ecosystems. Measures of extractable ammonium and nitrate are generally low and can be undetectable in peat pore waters. Despite this apparent nitrogen limitation, many of these environments produce deep deposits of soil organic matter. Biological nitrogen fixation carried out by autotrophic and heterotrophic diazotrophs associated with cryptograms provides the majority of known nitrogen inputs in these northern ecosystems. Nitrogen fixation was assessed in a variety of northern soils within rhizospheres of dominant plant communities. We investigated the availability of this newly fixed nitrogen to the vascular plant community in nitrogen limited northern plant communities. We tracked nitrogen flow from 15N2 gas fixed in Sphagnum mosses into tissues of two native vascular plant species, boreal cranberry (Vaccinium oxycoccus) and black spruce (Picea mariana). 15N-labeled Sphagnum microcosms were grown within variable mesh size exclusion/inclusion fabrics in a nitrogen addition experiment in situ in order to investigate the role of mycorrhizal fungi in the uptake of newly fixed nitrogen. Up to 24% of daily fixed 15N label was transferred to vascular plant tissues during 2 months. Nitrogen addition resulted in decreased N2 fixation rates; however, with higher nitrogen availability there was a higher rate of 15N label uptake into the vascular plants, likely the result of increased production of dissolved organic nitrogen. Reliance on mycorrhizal networks for nitrogen acquisition was indicated by nitrogen isotope fractionation patterns. Moreover, N2 fixation activities in mosses were stimulated when vascular plants were grown in moss microcosms versus "moss only" treatments. Results indicate that bog vascular plants may derive considerable nitrogen from atmospheric N2 biologically fixed within Sphagnum mosses. This work demonstrates that

  8. Nitrogen fixation in a coral reef community.

    PubMed

    Wiebe, W J; Johannes, R E; Webb, K L

    1975-04-18

    Algal reef flats at Enewetak Atoll, Marshall Islands, fix atmospheric nitrogen at rates comparable to those in managed agriculture. The dominant nitrogen fixer appears to be the blue-green alga Calothrix crustacea. Since this nutrient enrichment contributes to the high productivity of adjacent coral reefs and undoubtedly to atoll lagoons, it is recommended that the algal reef flats receive increased conservation priority.

  9. Biological nitrogen fixation in Louisiana sugarcane

    USDA-ARS?s Scientific Manuscript database

    Nitrogen (N) is a major input for sugarcane with crops in Louisiana receiving between 90 and 180 kg/ha with the cost of N increasing 75% in the last decade. Biological N fixation (BNF) may be a viable alternative to fertilizer N. The process relies on endophytic bacteria (bacteria that live among th...

  10. Methanotrophy Induces Nitrogen Fixation in Boreal Mosses

    NASA Astrophysics Data System (ADS)

    Tiirola, M. A.

    2014-12-01

    Many methanotrophic bacterial groups fix nitrogen in laboratory conditions. Furthermore, nitrogen (N) is a limiting nutrient in many environments where methane concentrations are highest. Despite these facts, methane-induced N fixation has previously been overlooked, possibly due to methodological problems. To study the possible link between methanotrophy and diazotrophy in terrestrial and aquatic habitats, we measured the co-occurrence of these two processes in boreal forest, peatland and stream mosses using a stable isotope labeling approach (15 N2 and 13 CH4 double labeling) and sequencing of the nifH gene marker. N fixation associated with forest mosses was dependent on the annual N deposition, whereas methane stimulate N fixation neither in high (>3 kg N ha -1 yr -1) nor low deposition areas, which was in accordance with the nifH gene sequencing showing that forest mosses (Pleurozium schreberi and Hylocomium splendens ) carried mainly cyanobacterial N fixers. On the other extreme, in stream mosses (Fontinalis sp.) methane was actively oxidized throughout the year, whereas N fixation showed seasonal fluctuation. The co-occurrence of the two processes in single cell level was proven by co-localizing both N and methane-carbon fixation with the secondary ion mass spectrometry (SIMS) approach. Methanotrophy and diazotrophy was also studied in peatlands of different primary successional stages in the land-uplift coast of Bothnian Bay, in the Siikajoki chronosequence, where N accumulation rates in peat profiles indicate significant N fixation. Based on experimental evidence it was counted that methane-induced N fixation explained over one-third of the new N input in the younger peatland successional stages, where the highest N fixation rates and highest methane oxidation activities co-occurred in the water-submerged Sphagnum moss vegetation. The linkage between methanotrophic carbon cycling and N fixation may therefore constitute an important mechanism in the rapid

  11. Nitrogen Fixation: An Interdisciplinary Frontier

    ERIC Educational Resources Information Center

    Schneller, Stewart W.

    1972-01-01

    Research has progressed from three major directions--biological, chemical, and non-enzymatic. Hopefully all three will converge and will explain not only the process, but also introduce new means for modifying the molecule to meet the nutritional needs of man in areas now incapable of self support without fixed nitrogen. (DF)

  12. Nitrogen Fixation: An Interdisciplinary Frontier

    ERIC Educational Resources Information Center

    Schneller, Stewart W.

    1972-01-01

    Research has progressed from three major directions--biological, chemical, and non-enzymatic. Hopefully all three will converge and will explain not only the process, but also introduce new means for modifying the molecule to meet the nutritional needs of man in areas now incapable of self support without fixed nitrogen. (DF)

  13. Variable Nitrogen Fixation in Wild Populus

    PubMed Central

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

    2016-01-01

    The microbiome of plants is diverse, and like that of animals, is important for overall health and nutrient acquisition. In legumes and actinorhizal plants, a portion of essential nitrogen (N) is obtained through symbiosis with nodule-inhabiting, N2-fixing microorganisms. However, a variety of non-nodulating plant species can also thrive in natural, low-N settings. Some of these species may rely on endophytes, microorganisms that live within plants, to fix N2 gas into usable forms. Here we report the first direct evidence of N2 fixation in the early successional wild tree, Populus trichocarpa, a non-leguminous tree, from its native riparian habitat. In order to measure N2 fixation, surface-sterilized cuttings of wild poplar were assayed using both 15N2 incorporation and the commonly used acetylene reduction assay. The 15N label was incorporated at high levels in a subset of cuttings, suggesting a high level of N-fixation. Similarly, acetylene was reduced to ethylene in some samples. The microbiota of the cuttings was highly variable, both in numbers of cultured bacteria and in genetic diversity. Our results indicated that associative N2-fixation occurred within wild poplar and that a non-uniformity in the distribution of endophytic bacteria may explain the variability in N-fixation activity. These results point to the need for molecular studies to decipher the required microbial consortia and conditions for effective endophytic N2-fixation in trees. PMID:27196608

  14. Variable Nitrogen Fixation in Wild Populus.

    PubMed

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

    2016-01-01

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

  15. Nitrogen fixation and nitrogen transformations in marine symbioses.

    PubMed

    Fiore, Cara L; Jarett, Jessica K; Olson, Nathan D; Lesser, Michael P

    2010-10-01

    Many marine organisms have coevolved symbiotic relationships with nitrogen-fixing bacteria in nitrogen limited environments such as coral reefs. In addition, some of these organisms also harbor microbes that carry out nitrification and denitrification. Prokaryotes involved in nitrogen fixation and other nitrogen transformations are symbionts in a range of eukaryotic hosts in the marine environment including shipworms, diatoms, corals and sponges. Molecular genetic approaches, and other analytical techniques, have provided exciting new insights into symbiont diversity and the relationship between host and symbiont. We review the current state of knowledge of these symbioses and highlight important avenues for future studies. Copyright © 2010 Elsevier Ltd. All rights reserved.

  16. Nitrogen fixation associated with grasses in Oregon.

    PubMed

    Nelson, A D; Barber, L E; Tjepkema, J; Russell, S A; Powelson, R; Evans, H J

    1976-04-01

    Nitrogen fixation associated with both natural grasslands and grain crops of Oregon was studied using the acetylene-reduction assay. A number of the grasses collected has some acetylene-reducing activity. Agrostis tenuis Sibth. had substantially greater activity than any of the other species, with a mean rate estimated at 37 g N2 fixed per hectare per day. Assuming 100 days of activity, about 3 kg of N2 would be fixed per hectare per year. This quantity of nitrogen may be important in the maintenance of this species under natural conditions. Nitrogen-fixing microorganisms were isolated from the root surfaces of some of the grasses. Cultures of Bacillus macerans, Bacillus polymyxa, and Enterobacter cloacoa were isolated from wheat roots as were two cultures which have not been assigned a specific taxonomic classification. Strains of N2-fixing Bacillus species and Gram-negative aerobic bacteria were isolated from Festuca and Agrostis.

  17. Genetic regulation of nitrogen fixation in rhizobia.

    PubMed Central

    Fischer, H M

    1994-01-01

    This review presents a comparison between the complex genetic regulatory networks that control nitrogen fixation in three representative rhizobial species, Rhizobium meliloti, Bradyrhizobium japonicum, and Azorhizobium caulinodans. Transcription of nitrogen fixation genes (nif and fix genes) in these bacteria is induced primarily by low-oxygen conditions. Low-oxygen sensing and transmission of this signal to the level of nif and fix gene expression involve at least five regulatory proteins, FixL, FixJ, FixK, NifA, and RpoN (sigma 54). The characteristic features of these proteins and their functions within species-specific regulatory pathways are described. Oxygen interferes with the activities of two transcriptional activators, FixJ and NifA. FixJ activity is modulated via phosphorylation-dephosphorylation by the cognate sensor hemoprotein FixL. In addition to the oxygen responsiveness of the NifA protein, synthesis of NifA is oxygen regulated at the level of transcription. This type of control includes FixLJ in R. meliloti and FixLJ-FixK in A. caulinodans or is brought about by autoregulation in B. japonicum. NifA, in concert with sigma 54 RNA polymerase, activates transcription from -24/-12-type promoters associated with nif and fix genes and additional genes that are not directly involved in nitrogen fixation. The FixK proteins constitute a subgroup of the Crp-Fnr family of bacterial regulators. Although the involvement of FixLJ and FixK in nifA regulation is remarkably different in the three rhizobial species discussed here, they constitute a regulatory cascade that uniformly controls the expression of genes (fixNOQP) encoding a distinct cytochrome oxidase complex probably required for bacterial respiration under low-oxygen conditions. In B. japonicum, the FixLJ-FixK cascade also controls genes for nitrate respiration and for one of two sigma 54 proteins. Images PMID:7968919

  18. Denitrification and Nitrogen Fixation in Alaskan Continental Shelf Sediments

    PubMed Central

    Haines, John R.; Atlas, Ronald M.; Griffiths, Robert P.; Morita, Richard Y.

    1981-01-01

    Rates of nitrogen fixation and denitrification were measured in Alaskan continental shelf sediments. In some regions, rates of nitrogen fixation and denitrification appeared to be equal; in other areas, rates were significantly different. Potential rates of denitrification were found to be limited primarily by the available nitrate substrate. Major regional differences in rates of denitrification were not statistically significant, but significant differences were found for nitrogen fixation rates in different regions of the Alaskan continental shelf. Estimated net losses of nitrogen from Bering Sea sediments were calculated as 1.8 × 1012 g of N/yr. Experimental exposure of continental shelf sediments to petroleum hydrocarbons reduced rates of nitrogen fixation and denitrification in some cases but not others. Long-term exposure was necessary before a reduction in nitrogen fixation rates was observed; unamended rates of denitrification but not potential denitrification rates (NO3− added) were depressed after exposure to hydrocarbons. PMID:16345716

  19. Cultivar effects on nitrogen fixation in peas and lentils

    USDA-ARS?s Scientific Manuscript database

    Increasing nitrogen fixation in legume crops could increase cropping productivity and reduce nitrogen fertilizer use. Studies have found that crop genotype, rhizobial strain, and occasionally genotype-specific interactions affect N fixation, but this knowledge has not yet been used to evaluate or br...

  20. Nitrogen fixation in a chemoautotrophic lucinid symbiosis.

    PubMed

    König, Sten; Gros, Olivier; Heiden, Stefan E; Hinzke, Tjorven; Thürmer, Andrea; Poehlein, Anja; Meyer, Susann; Vatin, Magalie; Mbéguié-A-Mbéguié, Didier; Tocny, Jennifer; Ponnudurai, Ruby; Daniel, Rolf; Becher, Dörte; Schweder, Thomas; Markert, Stephanie

    2016-10-24

    The shallow water bivalve Codakia orbicularis lives in symbiotic association with a sulfur-oxidizing bacterium in its gills. The endosymbiont fixes CO2 and thus generates organic carbon compounds, which support the host's growth. To investigate the uncultured symbiont's metabolism and symbiont-host interactions in detail we conducted a proteogenomic analysis of purified bacteria. Unexpectedly, our results reveal a hitherto completely unrecognized feature of the C. orbicularis symbiont's physiology: the symbiont's genome encodes all proteins necessary for biological nitrogen fixation (diazotrophy). Expression of the respective genes under standard ambient conditions was confirmed by proteomics. Nitrogenase activity in the symbiont was also verified by enzyme activity assays. Phylogenetic analysis of the bacterial nitrogenase reductase NifH revealed the symbiont's close relationship to free-living nitrogen-fixing Proteobacteria from the seagrass sediment. The C. orbicularis symbiont, here tentatively named 'Candidatus Thiodiazotropha endolucinida', may thus not only sustain the bivalve's carbon demands. C. orbicularis may also benefit from a steady supply of fixed nitrogen from its symbiont-a scenario that is unprecedented in comparable chemoautotrophic symbioses.

  1. Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

    PubMed Central

    Bothe, Hermann; Schmitz, Oliver; Yates, M. Geoffrey; Newton, William E.

    2010-01-01

    Summary: This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N2 fixation and/or H2 formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H2 as a source of combustible energy. To enhance the rates of H2 production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H2 formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy. PMID:21119016

  2. Molybdenum limitation of asymbiotic nitrogen fixation in tropical forest soils

    NASA Astrophysics Data System (ADS)

    Barron, Alexander R.; Wurzburger, Nina; Bellenger, Jean Phillipe; Wright, S. Joseph; Kraepiel, Anne M. L.; Hedin, Lars O.

    2009-01-01

    Nitrogen fixation, the biological conversion of di-nitrogen to plant-available ammonium, is the primary natural input of nitrogen to ecosystems, and influences plant growth and carbon exchange at local to global scales. The role of this process in tropical forests is of particular concern, as these ecosystems harbour abundant nitrogen-fixing organisms and represent one third of terrestrial primary production. Here we show that the micronutrient molybdenum, a cofactor in the nitrogen-fixing enzyme nitrogenase, limits nitrogen fixation by free-living heterotrophic bacteria in soils of lowland Panamanian forests. We measured the fixation response to long-term nutrient manipulations in intact forests, and to short-term manipulations in soil microcosms. Nitrogen fixation increased sharply in treatments of molybdenum alone, in micronutrient treatments that included molybdenum by design and in treatments with commercial phosphorus fertilizer, in which molybdenum was a `hidden' contaminant. Fixation did not respond to additions of phosphorus that were not contaminated by molybdenum. Our findings show that molybdenum alone can limit asymbiotic nitrogen fixation in tropical forests and raise new questions about the role of molybdenum and phosphorus in the tropical nitrogen cycle. We suggest that molybdenum limitation may be common in highly weathered acidic soils, and may constrain the ability of some forests to acquire new nitrogen in response to CO2 fertilization.

  3. Uncertainties of Nitrogen Fixation in a Dynamic Global Vegetation Model

    NASA Astrophysics Data System (ADS)

    Steinkamp, Joerg; Werner, Christian; Weber, Bettina; Hickler, Thomas

    2015-04-01

    Nitrogen is an essential nutrient for life on earth. However, most of it is in the form of dinitrogen (N2) unutilizable to life and only few organisms are able to break the triple bond, fix the nitrogen and thus make it available for cycling in the biosphere through "fixation". In most state-of-the-art dynamic global vegetation models (DGVMs) including a nitrogen cycle, N fixation is simulated by the Cleveland et al. (1999) algorithm (O-CN, LPJ-GUESS, CLM), that correlates annual N fixation to evapotranspiration rates or net primary production. Nevertheless, this algorithm has two major uncertainties, which are investigated by us: 1. The algorithm is based on annual fixation rates that are then applied uniformly throughout the year. However, in nature nitrogen fixation is an expensive process, which occurs only under favorable conditions. Here we compare the annual fixation values evenly distributed over the year with daily-derived fixation values based on a modified version of the Cleveland algorithm. We postulate that in higher latitudinal regions with seasonal climate as well as in regions with a distinct dry/wet season, modeled growth is enhanced by daily derived values compared to evenly distributed values, whereas in tropical regions hardly any difference will be visible. 2. One distinguishes between symbiotic and unsymbiotic nitrogen fixation, where the first one is associated with higher plants as symbionts supplying the fixers with carbohydrates, whereas the second, unsymbiotic is performed by so-called cryptogamic covers (CC). We found that the fixation by CC is underrepresented by the Cleveland algorithm, and a correction thus leads to enhanced growth in forested regions of higher latitudes that feature substantial CC fractions. Overall, the improvements of the algorithm proposed by us are expected to better reflect the reality of nitrogen fixation and cause an increased growth of vegetation, especially in higher northern latitudes.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  5. Nitrogen fixation and carbon metabolism in legume nodules.

    PubMed

    Garg, Neera; Singla, Ranju; Geetanjali

    2004-02-01

    A large amount of energy is utilized by legume nodules for the fixation of nitrogen and assimilation of fixed nitrogen (ammonia) into organic compounds. The source of energy is provided in the form of photosynthates by the host plant. Phosphoenol pyruvate carboxylase (PEPC) enzyme, which is responsible for carbon dioxide fixation in C4 and crassulacean acid metabolism plants, has also been found to play an important role in carbon metabolism in legume root nodule. PEPC-mediated CO2 fixation in nodules results in the synthesis of C4 dicarboxylic acids, viz. aspartate, malate, fumarate etc. which can be transported into bacteroids with the intervention of dicarboxylate transporter (DCT) protein. PEPC has been purified from the root nodules of few legume species. Information on the relationship between nitrogen fixation and carbon metabolism through PEPC in leguminous plants is scanty and incoherent. This review summarizes the various aspects of carbon and nitrogen metabolism in legume root nodules.

  6. THE FREE ENERGY OF NITROGEN FIXATION BY LIVING FORMS.

    PubMed

    Burk, D

    1927-03-20

    Fixation of nitrogen even with liberation of energy or free energy, will take place if either oxygen gas or hydrogen gas, or other substances, especially gases, whose standard free energies are close to zero, are involved to form either nitrates, ammonia, or cyanide, not to speak of still other compounds. It has been pointed out that there are two and only two general conditions where nitrogen fixation can require energy. These are, first, if nitrogen reacts with some compound like water with an already high negative free energy of formation and where negligible oxidation of nitrogen would occur; second, if the plant does not take advantage of working at concentrations where the process would yield free energy. If nitrogen fixation is exothermic and free energy-yielding, how is the carbohydrate requirement of nitrogen-fixing organisms to be interpreted? Are the experimental determinations of the carbon to nitrogen ratio purely circumstantial? Is further hope given to those who may experimentally try to narrow this ratio to where the carbon used is only for the carbon requirements of general metabolism, exclusive of fixation? Do not hypotheses concerning the fixation of nitrogen in the evolutionary process, which are based on the conception that energy is required, lose some of their significance? Does it not suggest that perhaps fixation is far more universal than is supposed among living forms, particularly among the higher green plants, and thereby give encouragement to those who may wish to demonstrate this experimentally? Does it not indicate that perhaps the function of fixation is often to obtain energy for use in general metabolism? Is the general carbohydrate metabolism of the fixation forms to be regarded as being merely extremely inefficient? Or most suggestive of all, is the carbohydrate serving some unobserved function?

  7. Molecular biology and genetic engineering in nitrogen fixation.

    PubMed

    Dos Santos, Patricia C

    2011-01-01

    Biological nitrogen fixation is a complex and tightly regulated process limited to a group of prokaryotic species known as diazotrophs. Among well-studied diazotrophs, Azotobacter vinelandii is the best studied for its convenience of aerobic growth, its high levels of nitrogenase expression, and its genetic tractability. This chapter includes protocols and strategies in the molecular biology and genetic engineering of A. vinelandii that have been used as valuable tools for advancing studies on the biosynthesis, mechanism, and regulation of nitrogen fixation.

  8. Nutrient feedbacks to soil heterotrophic nitrogen fixation in forests

    USGS Publications Warehouse

    Perakis, Steven; Pett-Ridge, Julie C.; Catricala, Christina E.

    2017-01-01

    Multiple nutrient cycles regulate biological nitrogen (N) fixation in forests, yet long-term feedbacks between N-fixation and coupled element cycles remain largely unexplored. We examined soil nutrients and heterotrophic N-fixation across a gradient of 24 temperate conifer forests shaped by legacies of symbiotic N-fixing trees. We observed positive relationships among mineral soil pools of N, carbon (C), organic molybdenum (Mo), and organic phosphorus (P) across sites, evidence that legacies of symbiotic N-fixing trees can increase the abundance of multiple elements important to heterotrophic N-fixation. Soil N accumulation lowered rates of heterotrophic N-fixation in organic horizons due to both N inhibition of nitrogenase enzymes and declines in soil organic matter quality. Experimental fertilization of organic horizon soil revealed widespread Mo limitation of heterotrophic N-fixation, especially at sites where soil Mo was scarce relative to C. Fertilization also revealed widespread absence of P limitation, consistent with high soil P:Mo ratios. Responses of heterotrophic N-fixation to added Mo (positive) and N (negative) were correlated across sites, evidence that multiple nutrient controls of heterotrophic N-fixation were more common than single-nutrient effects. We propose a conceptual model where symbiotic N-fixation promotes coupled N, C, P, and Mo accumulation in soil, leading to positive feedback that relaxes nutrient limitation of overall N-fixation, though heterotrophic N-fixation is primarily suppressed by strong negative feedback from long-term soil N accumulation.

  9. A Mathematic Approach to Nitrogen Fixation Through Earth History

    NASA Astrophysics Data System (ADS)

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

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

  10. Changes in North Atlantic nitrogen fixation controlled by ocean circulation.

    PubMed

    Straub, Marietta; Sigman, Daniel M; Ren, Haojia; Martínez-García, Alfredo; Meckler, A Nele; Hain, Mathis P; Haug, Gerald H

    2013-09-12

    In the ocean, the chemical forms of nitrogen that are readily available for biological use (known collectively as 'fixed' nitrogen) fuel the global phytoplankton productivity that exports carbon to the deep ocean. Accordingly, variation in the oceanic fixed nitrogen reservoir has been proposed as a cause of glacial-interglacial changes in atmospheric carbon dioxide concentration. Marine nitrogen fixation, which produces most of the ocean's fixed nitrogen, is thought to be affected by multiple factors, including ocean temperature and the availability of iron and phosphorus. Here we reconstruct changes in North Atlantic nitrogen fixation over the past 160,000 years from the shell-bound nitrogen isotope ratio ((15)N/(14)N) of planktonic foraminifera in Caribbean Sea sediments. The observed changes cannot be explained by reconstructed changes in temperature, the supply of (iron-bearing) dust or water column denitrification. We identify a strong, roughly 23,000-year cycle in nitrogen fixation and suggest that it is a response to orbitally driven changes in equatorial Atlantic upwelling, which imports 'excess' phosphorus (phosphorus in stoichiometric excess of fixed nitrogen) into the tropical North Atlantic surface. In addition, we find that nitrogen fixation was reduced during glacial stages 6 and 4, when North Atlantic Deep Water had shoaled to become glacial North Atlantic intermediate water, which isolated the Atlantic thermocline from excess phosphorus-rich mid-depth waters that today enter from the Southern Ocean. Although modern studies have yielded diverse views of the controls on nitrogen fixation, our palaeobiogeochemical data suggest that excess phosphorus is the master variable in the North Atlantic Ocean and indicate that the variations in its supply over the most recent glacial cycle were dominated by the response of regional ocean circulation to the orbital cycles.

  11. Nitrogen fixation potential in global chickpea mini-core collection

    USDA-ARS?s Scientific Manuscript database

    Biological nitrogen fixation (BNF) is a sustainable alternative for nitrogen supply to agriculture worldwide. One approach to increasing BNF in agriculture is to breed and use legumes with greater BNF capacity. To assess the capacity for BNF in chickpea (Cicer arietinum) global germplasm, a genetica...

  12. Variability for Biological Nitrogen Fixation Capacity in Beans

    USDA-ARS?s Scientific Manuscript database

    As legumes, common beans have the capacity to form a symbiotic relationship with soil bacteria called rhizobia and fix nitrogen from the atmosphere. Common beans however are considered to be poor nitrogen fixers as compared to other legumes. Identification of genetic variability for N fixation capac...

  13. The importance of regulation of nitrogen fixation

    NASA Astrophysics Data System (ADS)

    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

  14. Nitrogen fixation by the diazotroph Cylindrospermopsis raciborskii (Cyanophyceae).

    PubMed

    Willis, Anusuya; Chuang, Ann W; Burford, Michele A

    2016-10-01

    Nitrogen fixation has been proposed as a mechanism that allows the diazotrophic cyanobacterium, Cylindrospermopsis raciborskii, to bloom in nitrogen-limited freshwater systems. However, it is unclear whether dinitrogen fixation (N2 fixation) can supplement available dissolved inorganic nitrogen (DIN) for growth, or only provides minimum nitrogen (N) for cell maintenance under DIN deplete conditions. Additionally, the rate at which cells can switch between DIN use and N2 fixation is unknown. This study investigated N2 fixation under a range of nitrate concentrations. Cultures were grown with pretreatments of nitrate replete (single dose 941 μmol NO3- · L(-1) ) and N-free conditions and then either received a single dose of 941 μmol NO3- · L(-1) (N941), 118 μmol NO3- · L(-1) (N118) or 0 N. Heterocysts appeared from days 3 to 5 when treatments of high NO3- were transferred to N free media (N941:N0), and from day 5 in N941 transferred to N118 treatments. Conversely, transferring cells from N0 to N941 resulted in heterocysts being discarded from day 3 and day 5 for N0:N118. Heterocyst appearance correlated with a detectable rate of N2 fixation and up-regulation of nifH gene expression, the discard of heterocysts occurred after sequential reduction of nifH expression and N2 fixation. Nitrate uptake rates were not affected by pretreatment, suggesting no regulation or saturation of this uptake pathway. These data demonstrate that for C. raciborskii, N2 fixation is regulated by the production or discard of heterocysts. In conclusion, this study has shown that N2 fixation only provides enough N to support relatively low growth under N-limited conditions, and does not supplement available nitrate to increase growth rates.

  15. Low Carbon Costs of Nitrogen Fixation in Tropical Dry Forests

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Legume tree species with the ability to fix nitrogen (N) are highly diverse and widespread across tropical forests but in particular in the dry tropics. Their ecological success in lower latitudes has been called a "paradox": soil N in the tropics is thought to be high, while acquiring N through fixation incurs high energetic costs. However, the long held assumptions that N fixation is limited by photosynthate and that N fixation penalizes plant productivity have rarely been tested, particularly in legume tree species. We show results from three different experiments where we grew eleven species of tropical dry forest legumes. We quantified plant biomass and N fixation using nodulation and the 15N natural isotope abundance (Ndfa or nitrogen derived from fixation). These data show little evidence for costs of N fixation in seedlings grown under different soil fertility, light regimes, and with different microbial communities. Seedling productivity did not incur major costs because of N fixation: indeed, the average slope between Ndfa and biomass was positive (range in slopes: -0.03 to 0.3). Moreover, foliar N, which varied among species, was tightly constrained and not correlated with Ndfa. This finding implies that legume species have a target N that does not change depending on N acquisition strategies. The process of N fixation in tropical legumes may be more carbon efficient than previously thought. This view is more consistent with the hyperabundance of members of this family in tropical ecosystems.

  16. Fixation of nitrogen in the presence of water vapor

    DOEpatents

    Harteck, Paul

    1984-01-01

    A process for the fixation of nitrogen is disclosed which comprises combining a mixture of nitrogen, oxygen, metal oxide and water vapor, initially heating the combination to initiate a reaction which forms nitrate, but at a temperature and pressure range below the dissociation pressure of the nitrate. With or without the water component, the yield of fixed nitrogen is increased by the use of a Linde Molecular Sieve Catalyst.

  17. Biogeochemical processing of nitrogen transformation including nitrogen fixation and nitrification in the western part of the South China Sea

    NASA Astrophysics Data System (ADS)

    Wu, M., Sr.

    2016-02-01

    Based on in situ observations made in summer, 2009 along one transect near Xisha Islands, South China Sea (SCS), this study aims at understanding factors controlling nutrient biogeochemical cycling, especially on nitrogen cycling. The weak cold eddy may have important influence on supplies of nutrients in water column in Xisha islands. Nitrite reaches 0.49 μmol L-1 at the depth of 50m. It is significant relationship between NO2- and Chl a (R2=0.58, p=0.00). Phytoplankton excretion had an important influence on primary nitrite maximum formation and maintenance in euphotic layer. In addition, the positive values of N* indicate that nitrogen fixation may occur in the surface water in the studying area. Our results indicate that cold eddy near Xisha Islands play a significant role in regulating biogeochemistry.

  18. Biome-scale nitrogen fixation strategies selected by climatic constraints on nitrogen cycle.

    PubMed

    Sheffer, Efrat; Batterman, Sarah A; Levin, Simon A; Hedin, Lars O

    2015-11-23

    Dinitrogen fixation by plants (in symbiosis with root bacteria) is a major source of new nitrogen for land ecosystems(1). A long-standing puzzle(2) is that trees capable of nitrogen fixation are abundant in nitrogen-rich tropical forests, but absent or restricted to early successional stages in nitrogen-poor extra-tropical forests. This biome-scale pattern presents an evolutionary paradox(3), given that the physiological cost(4) of nitrogen fixation predicts the opposite pattern: fixers should be out-competed by non-fixers in nitrogen-rich conditions, but competitively superior in nitrogen-poor soils. Here we evaluate whether this paradox can be explained by the existence of different fixation strategies in tropical versus extra-tropical trees: facultative fixers (capable of downregulating fixation(5,6) by sanctioning mutualistic bacteria(7)) are common in the tropics, whereas obligate fixers (less able to downregulate fixation) dominate at higher latitudes. Using a game-theoretic approach, we assess the ecological and evolutionary conditions under which these fixation strategies emerge, and examine their dependence on climate-driven differences in the nitrogen cycle. We show that in the tropics, transient soil nitrogen deficits following disturbance and rapid tree growth favour a facultative strategy and the coexistence of fixers and non-fixers. In contrast, sustained nitrogen deficits following disturbance in extra-tropical forests favour an obligate fixation strategy, and cause fixers to be excluded in late successional stages. We conclude that biome-scale differences in the abundance of nitrogen fixers can be explained by the interaction between individual plant strategies and climatic constraints on the nitrogen cycle over evolutionary time.

  19. Nitrogen fixation rates in algal turf communities of a degraded versus less degraded coral reef

    NASA Astrophysics Data System (ADS)

    den Haan, Joost; Visser, Petra M.; Ganase, Anjani E.; Gooren, Elfi E.; Stal, Lucas J.; van Duyl, Fleur C.; Vermeij, Mark J. A.; Huisman, Jef

    2014-12-01

    Algal turf communities are ubiquitous on coral reefs in the Caribbean and are often dominated by N2-fixing cyanobacteria. However, it is largely unknown (1) how much N2 is actually fixed by turf communities and (2) which factors affect their N2 fixation rates. Therefore, we compared N2 fixation activity by turf communities at different depths and during day and night-time on a degraded versus a less degraded coral reef site on the island of Curaçao. N2 fixation rates measured with the acetylene reduction assay were slightly higher in shallow (5-10-m depth) than in deep turf communities (30-m depth), and N2 fixation rates during the daytime significantly exceeded those during the night. N2 fixation rates by the turf communities did not differ between the degraded and less degraded reef. Both our study and a literature survey of earlier studies indicated that turf communities tend to have lower N2 fixation rates than cyanobacterial mats. However, at least in our study area, turf communities were more abundant than cyanobacterial mats. Our results therefore suggest that turf communities play an important role in the nitrogen cycle of coral reefs. N2 fixation by turfs may contribute to an undesirable positive feedback that promotes the proliferation of algal turf communities while accelerating coral reef degradation.

  20. Vascular plant removal effects on biological N fixation vary across a boreal forest island gradient.

    PubMed

    Gundale, Michael J; Wardle, David A; Nilsson, Marie-Charlotte

    2010-06-01

    There is currently much interest in understanding how biodiversity loss affects the functioning of ecosystems, but few studies have evaluated how ecosystem processes change in response to one another following biodiversity loss. We focused on a well-described gradient of 30 forested lake islands in northern Sweden, where island size determines the occurrence of lightning-ignited wildfire, which in turn determines successional stage, plant species composition, and productivity. We investigated the effect of biodiversity loss on biological nitrogen fixation by feathermosses through an experiment consisting of factorial removals of three understory shrub species (Vaccinium myrtillis, Vaccinium vitis-idaea, and Empetrum hermaphroditum) and two plant functional groups (shrubs and tree roots). We tested the hypothesis that, following vascular plant species loss, N fixation rates would be impaired by changes in pools or processes that increase extractable soil N, because changes in the supply rate of N to feathermosses should influence their demand for newly fixed N. Further, we hypothesized that the effects of removals on N fixation would depend on environmental context (i.e., island size), because it has been previously demonstrated that the effect of vascular plant species removal on N recycling pools and processes was strongest on productive islands. The data demonstrated that removal of two shrub species (V. vitis-idaea and E. hermaphroditum) negatively aflected the N fixation of Hylocomium splendens, but positively affected Pleurozium schreberi, resulting in unchanged areal N fixation rates. In the functional removal experiment, tree root removal resulted in a significant negative effect on N fixation. The effects of shrub and root removals on N fixation occurred only on small islands and thus were context dependent. This pattern did not correspond to the effect of shrub and root removal treatments on N-recycling pools or processes, which only occurred in response

  1. Nitrogen fixation by intact colonies of the termite Nasutitermes corniger.

    PubMed

    Prestwich, G D; Bentley, B L

    1981-05-01

    Whole colonies of the arboreal termite Nasutitermes corniger (lsoptera, Termitidae, Nasutitermitinae) from a Costa Rican rainforest were assayed for nitrogen fixation by the acetylene reduction method, using a 21-1 test chamber. Nitrogenase activity was positively correlated with termite biomass for the nexts examined, providing the experiment was performed within 2 h of removal of the colony from the field. Total colony fixation rates of 0.25-1.0 mg N per colony per hour indicate a nitrogen doubling time of 200-600 days, thereby making possible complete replacement of the nest population 1-2 times per year.

  2. Microbial community shifts influence patterns in tropical forest nitrogen fixation.

    PubMed

    Reed, Sasha C; Townsend, Alan R; Cleveland, Cory C; Nemergut, Diana R

    2010-10-01

    The role of biodiversity in ecosystem function receives substantial attention, yet despite the diversity and functional relevance of microorganisms, relationships between microbial community structure and ecosystem processes remain largely unknown. We used tropical rain forest fertilization plots to directly compare the relative abundance, composition and diversity of free-living nitrogen (N)-fixer communities to in situ leaf litter N fixation rates. N fixation rates varied greatly within the landscape, and 'hotspots' of high N fixation activity were observed in both control and phosphorus (P)-fertilized plots. Compared with zones of average activity, the N fixation 'hotspots' in unfertilized plots were characterized by marked differences in N-fixer community composition and had substantially higher overall diversity. P additions increased the efficiency of N-fixer communities, resulting in elevated rates of fixation per nifH gene. Furthermore, P fertilization increased N fixation rates and N-fixer abundance, eliminated a highly novel group of N-fixers, and increased N-fixer diversity. Yet the relationships between diversity and function were not simple, and coupling rate measurements to indicators of community structure revealed a biological dynamism not apparent from process measurements alone. Taken together, these data suggest that the rain forest litter layer maintains high N fixation rates and unique N-fixing organisms and that, as observed in plant community ecology, structural shifts in N-fixing communities may partially explain significant differences in system-scale N fixation rates.

  3. Nitrogen fixation by hydrogen-utilizing bacteria.

    PubMed

    De Bont, J A; Leijten, M W

    1976-04-01

    Seventeen strains of nitrogen-fixing bacteria, isolated from different habitats on hydrogen and carbon dioxide as well as on other substrates, morphologically resembled each other. All strains, including Mycobacterium flavum 301, grew autotrophically with hydrogen. The isolate strain 6 was sensitive to oxygen when dependent on N2 as nitrogen source, a consequence of the sensitivity of its nitrogenase towards oxygen. At the same time, strain 6 was sensitive to hydrogen when growing autotrophically on N2 as nitrogen source, but hydrogen did not affect acetylene reduction by these cells.

  4. Biological nitrogen fixation and habitat of running buffalo clover

    Treesearch

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

    2002-01-01

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

  5. A possible nitrogen crisis for Archaean life due to reduced nitrogen fixation by lightning.

    PubMed

    Navarro-González, R; McKay, C P; Mvondo, D N

    2001-07-05

    Nitrogen is an essential element for life and is often the limiting nutrient for terrestrial ecosystems. As most nitrogen is locked in the kinetically stable form, N2, in the Earth's atmosphere, processes that can fix N2 into biologically available forms-such as nitrate and ammonia-control the supply of nitrogen for organisms. On the early Earth, nitrogen is thought to have been fixed abiotically, as nitric oxide formed during lightning discharge. The advent of biological nitrogen fixation suggests that at some point the demand for fixed nitrogen exceeded the supply from abiotic sources, but the timing and causes of the onset of biological nitrogen fixation remain unclear. Here we report an experimental simulation of nitrogen fixation by lightning over a range of Hadean (4.5-3.8 Gyr ago) and Archaean (3.8-2.5 Gyr ago) atmospheric compositions, from predominantly carbon dioxide to predominantly dinitrogen (but always without oxygen). We infer that, as atmospheric CO2 decreased over the Archaean period, the production of nitric oxide from lightning discharge decreased by two orders of magnitude until about 2.2 Gyr. After this time, the rise in oxygen (or methane) concentrations probably initiated other abiotic sources of nitrogen. Although the temporary reduction in nitric oxide production may have lasted for only 100 Myr or less, this was potentially long enough to cause an ecological crisis that triggered the development of biological nitrogen fixation.

  6. Fixation of nitrogen in the prebiotic atmosphere

    NASA Technical Reports Server (NTRS)

    Yung, Y. L.; Mcelroy, M. B.

    1979-01-01

    Reactions between nitrogen and water in the air surrounding lightning discharges can provide an important source of nitric oxide even under conditions where oxygen is a minor atmospheric constituent. Estimates are given for the associated source of soluble nitrite and nitrate. It is shown that lightning and subsequent atmospheric chemistry can provide a source of nitrate for the primitive ocean as large as one million tons of nitrogen per year, sufficient to fill the ocean to its present level of nitrate in less than one million years.

  7. Fixation of nitrogen in the prebiotic atmosphere

    NASA Technical Reports Server (NTRS)

    Yung, Y. L.; Mcelroy, M. B.

    1979-01-01

    Reactions between nitrogen and water in the air surrounding lightning discharges can provide an important source of nitric oxide even under conditions where oxygen is a minor atmospheric constituent. Estimates are given for the associated source of soluble nitrite and nitrate. It is shown that lightning and subsequent atmospheric chemistry can provide a source of nitrate for the primitive ocean as large as one million tons of nitrogen per year, sufficient to fill the ocean to its present level of nitrate in less than one million years.

  8. Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

    NASA Technical Reports Server (NTRS)

    Klingler, J. M.; Mancinelli, R. L.; White, M. R.

    1989-01-01

    One of the most striking differences between the conditions on early Mars and earth was a low (18 mb) partial pressure of N2 (pN2) on early Mars, as opposed to 780 mb N2 on earth. To investigate the possibility of biological nitrogen fixation under conditions of early Mars, experiments were carried out on the growth of Azotobacter vinelandii and Azomonas agilis in nitrogen-free synthetic medium under various partial pressures of N2 (ranging from 780 to 0 mb). It was found that, although the biomass, cell number, and growth rate of these bacteria decreased with decreasing pN2 values below pN2 of 400 mb, both microorganisms were capable of growing at pN2 as low as 5 mb (but not at of below 1 mb), indicating that biological fixation of nitrogen could have occurred on primordial Mars.

  9. Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

    NASA Technical Reports Server (NTRS)

    Klingler, J. M.; Mancinelli, R. L.; White, M. R.

    1989-01-01

    One of the most striking differences between the conditions on early Mars and earth was a low (18 mb) partial pressure of N2 (pN2) on early Mars, as opposed to 780 mb N2 on earth. To investigate the possibility of biological nitrogen fixation under conditions of early Mars, experiments were carried out on the growth of Azotobacter vinelandii and Azomonas agilis in nitrogen-free synthetic medium under various partial pressures of N2 (ranging from 780 to 0 mb). It was found that, although the biomass, cell number, and growth rate of these bacteria decreased with decreasing pN2 values below pN2 of 400 mb, both microorganisms were capable of growing at pN2 as low as 5 mb (but not at of below 1 mb), indicating that biological fixation of nitrogen could have occurred on primordial Mars.

  10. Oxygen relations of nitrogen fixation in cyanobacteria.

    PubMed Central

    Fay, P

    1992-01-01

    The enigmatic coexistence of O2-sensitive nitrogenase and O2-evolving photosynthesis in diazotrophic cyanobacteria has fascinated researchers for over two decades. Research efforts in the past 10 years have revealed a range of O2 sensitivity of nitrogenase in different strains of cyanobacteria and a variety of adaptations for the protection of nitrogenase from damage by both atmospheric and photosynthetic sources of O2. The most complex and apparently most efficient mechanisms for the protection of nitrogenase are incorporated in the heterocysts, the N2-fixing cells of cyanobacteria. Genetic studies indicate that the controls of heterocyst development and nitrogenase synthesis are closely interrelated and that the expression of N2 fixation (nif) genes is regulated by pO2. Images PMID:1620069

  11. "Cold" Fixation: Reconciliation of Nitrogen Fixation Rates and Diazotroph Assemblages in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Fong, A. A.; Waite, A.; Rost, B.; Richter, K. U.

    2016-02-01

    Measurements of biological nitrogen fixation are typically conducted in oligotrophic subtropical and tropical marine environments where concentrations of fixed inorganic nitrogen are low. To date, only a handful of nitrogen fixation studies have been conducted in high latitude marine environments, but further investigation is needed to resolve the distribution of cold ocean diazotrophic assemblages. Nitrogen fixation rates and nifH gene distributions were measured at seven stations from 5°E to 20°E, north of 81°N in the Arctic Ocean at the onset of summer 2015. Discrete water samples in ice-covered regions were collected from the sea surface to 200 m for 15N2-tracer additions and targeted nifH gene and transcript analyses. Previous work suggests that heterotrophic bacteria dominate diazotrophic communities in the Arctic Ocean. Therefore, additional nifH gene surveys of sinking particles were conducted to test for enrichment on organic matter-rich microenvironments. Together, these measurements aim to reconcile diazotrophic activity with microbial community composition, further elucidating how nitrogen fixers could impact current concepts in polar carbon and nutrient cycling.

  12. Effect of ruthenium on nitrogen fixation by some nitrogen fixers.

    PubMed

    Bahadur, K; Gaur, N

    1979-01-01

    The effect of ruthenium chloride in the culture media on the nitrogen-fixing ability of the three nitrogen fixers (unidentified species of Azotobacter, designated here as D3, B3, and B), isolated from Allahabad soil, was studied. It was observed that the nitrogen-fixing ability of the organisms is much increased in presence of 25-75 micro M concentration of ruthenium chloride in the culture media, while sugar consumption remains more or less steady. Also, if mg nitrogen fixed/g carbon consumed in two culture media with successive increasing concentrations of ruthenium chloride is compared by calculating the difference in increase of the amount of nitrogen fixed and carbon consumed in these two culture media, it was observed that high amounts of nitrogen are fixed by B3 and B between 25-50 micro M, and between 50-75 micro M concentration of ruthenium chloride by D3.

  13. Ecosystem feedbacks and nitrogen fixation in boreal forests.

    PubMed

    DeLuca, Thomas H; Zackrisson, Olle; Gundale, Michael J; Nilsson, Marie-Charlotte

    2008-05-30

    Biological feedback mechanisms regulate fundamental ecosystem processes and potentially regulate ecosystem productivity. To date, no studies have documented the down-regulation of terrestrial nitrogen (N) fixation via an ecosystem-level feedback mechanism. Herein, we demonstrate such a feedback in boreal forests. Rapid cycling of N in early secondary succession forests yielded greater throughfall N deposition, which in turn decreased N fixation by cyanobacterial associates in feather moss carpets that reside on the forest floor. The forest canopy exerts a tight control on biotic N input at a period of high productivity.

  14. Heterotrophic organisms dominate nitrogen fixation in the South Pacific Gyre.

    PubMed

    Halm, Hannah; Lam, Phyllis; Ferdelman, Timothy G; Lavik, Gaute; Dittmar, Thorsten; LaRoche, Julie; D'Hondt, Steven; Kuypers, Marcel M M

    2012-06-01

    Oceanic subtropical gyres are considered biological deserts because of the extremely low availability of nutrients and thus minimum productivities. The major source of nutrient nitrogen in these ecosystems is N(2)-fixation. The South Pacific Gyre (SPG) is the largest ocean gyre in the world, but measurements of N(2)-fixation therein, or identification of microorganisms involved, are scarce. In the 2006/2007 austral summer, we investigated nitrogen and carbon assimilation at 11 stations throughout the SPG. In the ultra-oligotrophic waters of the SPG, the chlorophyll maxima reached as deep as 200 m. Surface primary production seemed limited by nitrogen, as dissolved inorganic carbon uptake was stimulated upon additions of (15)N-labeled ammonium and leucine in our incubation experiments. N(2)-fixation was detectable throughout the upper 200 m at most stations, with rates ranging from 0.001 to 0.19 nM N h(-1). N(2)-fixation in the SPG may account for the production of 8-20% of global oceanic new nitrogen. Interestingly, comparable (15)N(2)-fixation rates were measured under light and dark conditions. Meanwhile, phylogenetic analyses for the functional gene biomarker nifH and its transcripts could not detect any common photoautotrophic diazotrophs, such as, Trichodesmium, but a prevalence of γ-proteobacteria and the unicellular photoheterotrophic Group A cyanobacteria. The dominance of these likely heterotrophic diazotrophs was further verified by quantitative PCR. Hence, our combined results show that the ultra-oligotrophic SPG harbors a hitherto unknown heterotrophic diazotrophic community, clearly distinct from other oceanic gyres previously visited.

  15. Nitrogen Fixation (Acetylene Reduction) by Epiphytes of Freshwater Macrophytes

    PubMed Central

    Finke, Linda R.; Seeley, H. W.

    1978-01-01

    The involvement of epiphytic microorganisms in nitrogen fixation was investigated in a shallow freshwater pond near Ithaca, N.Y. The acetylene reduction technique was used to follow diel and seasonal cycles of nitrogen fixation by epiphytes of Myriophyllum spicatum. Acetylene-reducing activity was maximal between noon and 6 p.m., but substantial levels of activity relative to daytime rates continued through the night. Experiments with the seasonal course of activity showed a gradual decline during the autumn months and no activity in January or February. Activity commenced in May, with an abrupt increase to levels between 0.45 and 0.95 nmol of ethylene formed per mg (dry weight) of plant per h. Through most of the summer months, mean rates of acetylene reduction remained between 0.15 and 0.60 nmol/mg (dry weight) per h. It was calculated from diel and seasonal cycles that, in the pond areas studied, epiphytes were capable of adding from 7.5 to 12.5 μg of N per mg of plant per year to the pond. This amount is significant relative to the total amount of nitrogen incorporated into the plant. Blue-green algae (cyanobacteria), particularly Gloeotrichia, appeared to bear prime responsibility for nitrogen fixation, but photosynthetic bacteria of the genus Rhodopseudomonas were isolated from M. spicatum and shown to support high rates of acetylene reduction. PMID:16345301

  16. Transcriptional profiling of nitrogen fixation in Azotobacter vinelandii.

    PubMed

    Hamilton, Trinity L; Ludwig, Marcus; Dixon, Ray; Boyd, Eric S; Dos Santos, Patricia C; Setubal, João C; Bryant, Donald A; Dean, Dennis R; Peters, John W

    2011-09-01

    Most biological nitrogen (N(2)) fixation results from the activity of a molybdenum-dependent nitrogenase, a complex iron-sulfur enzyme found associated with a diversity of bacteria and some methanogenic archaea. Azotobacter vinelandii, an obligate aerobe, fixes nitrogen via the oxygen-sensitive Mo nitrogenase but is also able to fix nitrogen through the activities of genetically distinct alternative forms of nitrogenase designated the Vnf and Anf systems when Mo is limiting. The Vnf system appears to replace Mo with V, and the Anf system is thought to contain Fe as the only transition metal within the respective active site metallocofactors. Prior genetic analyses suggest that a number of nif-encoded components are involved in the Vnf and Anf systems. Genome-wide transcription profiling of A. vinelandii cultured under nitrogen-fixing conditions under various metal amendments (e.g., Mo or V) revealed the discrete complement of genes associated with each nitrogenase system and the extent of cross talk between the systems. In addition, changes in transcript levels of genes not directly involved in N(2) fixation provided insight into the integration of central metabolic processes and the oxygen-sensitive process of N(2) fixation in this obligate aerobe. The results underscored significant differences between Mo-dependent and Mo-independent diazotrophic growth that highlight the significant advantages of diazotrophic growth in the presence of Mo.

  17. Transcriptional Profiling of Nitrogen Fixation in Azotobacter vinelandii▿†

    PubMed Central

    Hamilton, Trinity L.; Ludwig, Marcus; Dixon, Ray; Boyd, Eric S.; Dos Santos, Patricia C.; Setubal, João C.; Bryant, Donald A.; Dean, Dennis R.; Peters, John W.

    2011-01-01

    Most biological nitrogen (N2) fixation results from the activity of a molybdenum-dependent nitrogenase, a complex iron-sulfur enzyme found associated with a diversity of bacteria and some methanogenic archaea. Azotobacter vinelandii, an obligate aerobe, fixes nitrogen via the oxygen-sensitive Mo nitrogenase but is also able to fix nitrogen through the activities of genetically distinct alternative forms of nitrogenase designated the Vnf and Anf systems when Mo is limiting. The Vnf system appears to replace Mo with V, and the Anf system is thought to contain Fe as the only transition metal within the respective active site metallocofactors. Prior genetic analyses suggest that a number of nif-encoded components are involved in the Vnf and Anf systems. Genome-wide transcription profiling of A. vinelandiicultured under nitrogen-fixing conditions under various metal amendments (e.g., Mo or V) revealed the discrete complement of genes associated with each nitrogenase system and the extent of cross talk between the systems. In addition, changes in transcript levels of genes not directly involved in N2fixation provided insight into the integration of central metabolic processes and the oxygen-sensitive process of N2fixation in this obligate aerobe. The results underscored significant differences between Mo-dependent and Mo-independent diazotrophic growth that highlight the significant advantages of diazotrophic growth in the presence of Mo. PMID:21724999

  18. Nitrogen fixation (acetylene reduction) by epiphytes of freshwater macrophytes.

    PubMed

    Finke, L R; Seeley, H W

    1978-07-01

    The involvement of epiphytic microorganisms in nitrogen fixation was investigated in a shallow freshwater pond near Ithaca, N.Y. The acetylene reduction technique was used to follow diel and seasonal cycles of nitrogen fixation by epiphytes of Myriophyllum spicatum. Acetylene-reducing activity was maximal between noon and 6 p.m., but substantial levels of activity relative to daytime rates continued through the night. Experiments with the seasonal course of activity showed a gradual decline during the autumn months and no activity in January or February. Activity commenced in May, with an abrupt increase to levels between 0.45 and 0.95 nmol of ethylene formed per mg (dry weight) of plant per h. Through most of the summer months, mean rates of acetylene reduction remained between 0.15 and 0.60 nmol/mg (dry weight) per h. It was calculated from diel and seasonal cycles that, in the pond areas studied, epiphytes were capable of adding from 7.5 to 12.5 mug of N per mg of plant per year to the pond. This amount is significant relative to the total amount of nitrogen incorporated into the plant. Blue-green algae (cyanobacteria), particularly Gloeotrichia, appeared to bear prime responsibility for nitrogen fixation, but photosynthetic bacteria of the genus Rhodopseudomonas were isolated from M. spicatum and shown to support high rates of acetylene reduction.

  19. Biological nitrogen fixation in non-legume plants

    PubMed Central

    Santi, Carole; Bogusz, Didier; Franche, Claudine

    2013-01-01

    Background Nitrogen is an essential nutrient in plant growth. The ability of a plant to supply all or part of its requirements from biological nitrogen fixation (BNF) thanks to interactions with endosymbiotic, associative and endophytic symbionts, confers a great competitive advantage over non-nitrogen-fixing plants. Scope Because BNF in legumes is well documented, this review focuses on BNF in non-legume plants. Despite the phylogenic and ecological diversity among diazotrophic bacteria and their hosts, tightly regulated communication is always necessary between the microorganisms and the host plant to achieve a successful interaction. Ongoing research efforts to improve knowledge of the molecular mechanisms underlying these original relationships and some common strategies leading to a successful relationship between the nitrogen-fixing microorganisms and their hosts are presented. Conclusions Understanding the molecular mechanism of BNF outside the legume–rhizobium symbiosis could have important agronomic implications and enable the use of N-fertilizers to be reduced or even avoided. Indeed, in the short term, improved understanding could lead to more sustainable exploitation of the biodiversity of nitrogen-fixing organisms and, in the longer term, to the transfer of endosymbiotic nitrogen-fixation capacities to major non-legume crops. PMID:23478942

  20. Biological nitrogen fixation in non-legume plants.

    PubMed

    Santi, Carole; Bogusz, Didier; Franche, Claudine

    2013-05-01

    Nitrogen is an essential nutrient in plant growth. The ability of a plant to supply all or part of its requirements from biological nitrogen fixation (BNF) thanks to interactions with endosymbiotic, associative and endophytic symbionts, confers a great competitive advantage over non-nitrogen-fixing plants. Because BNF in legumes is well documented, this review focuses on BNF in non-legume plants. Despite the phylogenic and ecological diversity among diazotrophic bacteria and their hosts, tightly regulated communication is always necessary between the microorganisms and the host plant to achieve a successful interaction. Ongoing research efforts to improve knowledge of the molecular mechanisms underlying these original relationships and some common strategies leading to a successful relationship between the nitrogen-fixing microorganisms and their hosts are presented. Understanding the molecular mechanism of BNF outside the legume-rhizobium symbiosis could have important agronomic implications and enable the use of N-fertilizers to be reduced or even avoided. Indeed, in the short term, improved understanding could lead to more sustainable exploitation of the biodiversity of nitrogen-fixing organisms and, in the longer term, to the transfer of endosymbiotic nitrogen-fixation capacities to major non-legume crops.

  1. Nitrogen Fixation (Acetylene Reduction) Associated with Duckweed (Lemnaceae) Mats

    PubMed Central

    Zuberer, D. A.

    1982-01-01

    Duckweed (Lemnaceae) mats in Texas and Florida were investigated, using the acetylene reduction assay, to determine whether nitrogen fixation occurred in these floating aquatic macrophyte communities. N2-fixing microorganisms were enumerated by plating or most-probable-number techniques, using appropriate N-free media. Results of the investigations indicated that substantial N2-fixation (C2H2) was associated with duckweed mats in Texas and Florida. Acetylene reduction values ranged from 1 to 18 μmol of C2H4 g (dry weight)−1 day−1 for samples incubated aerobically in light. Dark N2 fixation was always two- to fivefold lower. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (7 to 10 μM) reduced acetylene reduction to levels intermediate between light and dark incubation. Acetylene reduction was generally greatest for samples incubated anaerobically in the light. It was estimated that 15 to 20% of the N requirement of the duckweed could be supplied through biological nitrogen fixation. N2-fixing heterotrophic bacteria (105 cells g [wet weight]−1 and cyanobacteria (105 propagules g [wet weight]−1 were associated with the duckweed mats. Azotobacter sp. was not detected in these investigations. One diazotrophic isolate was classified as Klebsiella. PMID:16345992

  2. Physiological limitations and the genetic improvement of symbiotic nitrogen fixation

    SciTech Connect

    Gara, F.O.; Manian, S. ); Drevon, J.J. )

    1988-01-01

    The rhizobium legume symbiosis continues to be of strategic importance particularly in the context of food production. As the world population grows, it is necessary that new developments take place in crop improvement. The development and application of new technologies in biological sciences over past years has made the entire area of plant-microbial interaction an exciting and challenging research area to be involved in. In view of the importance of symbiotic nitrogen fixation, it is not surprising that it still represents one of the priority areas for commercial development in agricultural biotechnology. Since this symbiosis involves an association between procaryotic and eucaryhotic partners, it requires of necessity a coordinated and interdisciplinary approach. This book focuses on physiological limitations affecting symbiotic nitrogen fixation and the potential for overcoming such limitations by using genetic technologies.

  3. QTL analysis of symbiotic nitrogen fixation in a black bean RIL population

    USDA-ARS?s Scientific Manuscript database

    Dry bean (Phaseolus vulgaris L) acquires nitrogen (N) from the atmosphere through symbiotic nitrogen fixation (SNF) but it has a low efficiency to fix nitrogen. The objective of this study is to map the genes controlling nitrogen fixation in common bean. A mapping population consisting of 122 recomb...

  4. Nitrogen fixation (nif) genes and large plasmids of Rhizobium japonicum.

    PubMed Central

    Masterson, R V; Russell, P R; Atherly, A G

    1982-01-01

    The location of structural nitrogen-fixation genes was determined for the slow- and fast-growing types of Rhizobium japonicum. Slow-growing R. japonicum strains do not harbor structural nif genes, homologous to nifD and nifH, on large plasmids (100 to 200 megadaltons). In contrast, all fast-growing R. japonicum strains, except PRC194, contain structural nif genes on large plasmids. Images PMID:7130134

  5. Enhanced symbiotic nitrogen fixation with P. syringae pv tabaci

    SciTech Connect

    Langston-Unkefer, P.J.; Knight, T.J. New Mexico State Univ., Las Cruces ); Sengupta-Gopalan, C. )

    1989-04-01

    Infestation of legumes such as alfalfa and soybeans with the plant pathogen Pseudomonas syringae pv. tabaci is accompanied by increased plant growth, nodulation, overall nitrogen fixation, and total assimilated nitrogen. These effects are observed only in plants infested with Tox{sup +} pathogen; the toxin is tabtoxinine-{beta}-lactam, an active site-directed irreversible inhibitor of glutamine synthetase. The key to the legumes survival of this treatment is the insensitivity of the nodule-specific form of glutamine synthetase to the toxin. As expected, significant changes are observed in ammonia assimilation in these plants. The biochemical and molecular biological consequences of this treatment are being investigated.

  6. Nitrogen fixation rates in the eastern Arabian Sea

    NASA Astrophysics Data System (ADS)

    Ahmed, Ayaz; Gauns, Mangesh; Kurian, Siby; Bardhan, Pratirupa; Pratihary, Anil; Naik, Hema; Shenoy, Damodar M.; Naqvi, S. W. A.

    2017-05-01

    The Arabian Sea experiences bloom of the diazotroph Trichodesmium during certain times of the year when optimal sea surface temperature and oligotrophic condition favour their growth. We measured nitrogen fixation rates in the euphotic zone during one such event in the Eastern Arabian Sea using 15N2 tracer gas dissolution method. The measured rates varied between 0.8 and 225 μmol N m-3 d-1 and were higher than those reported from most other oceanic regions. The highest rates (1739 μmol N m-2 d-1; 0-10 m) coincided with the growth phase of Trichodesmium and led to low δ15N (<2‰) of particulate organic matter. At stations not experiencing Trichodesmium bloom nitrogen fixation rates were low (0.9-1.5 μmol N m-3 d-1). Due to episodic events of diazotroph bloom, contribution of N2 fixation to the total nitrogen pool may vary in space and time.

  7. Significant nonsymbiotic nitrogen fixation in Patagonian ombrotrophic bogs.

    PubMed

    Knorr, Klaus-Holger; Horn, Marcus A; Borken, Werner

    2015-06-01

    Nitrogen (N) nutrition in pristine peatlands relies on the natural input of inorganic N through atmospheric deposition or biological dinitrogen (N2 ) fixation. However, N2 fixation and its significance for N cycling, plant productivity, and peat buildup are mostly associated with the presence of Sphagnum mosses. Here, we report high nonsymbiotic N2 -fixation rates in two pristine Patagonian bogs with diversified vegetation and natural N deposition. Nonsymbiotic N2 fixation was measured in samples from 0 to 10, 10 to 20, and 40 to 50 cm depth using the (15) N2 assay as well as the acetylene reduction assay (ARA). The ARA considerably underestimated N2 fixation and can thus not be recommended for peatland studies. Based on the (15) N2 assay, high nonsymbiotic N2 -fixation rates of 0.3-1.4 μmol N2  g(-1)  day(-1) were found down to 50 cm under micro-oxic conditions (2 vol.%) in samples from plots covered by Sphagnum magellanicum or by vascular cushion plants, latter characterized by dense and deep aerenchyma roots. Peat N concentrations point to greater potential of nonsymbiotic N2 fixation under cushion plants, likely because of the availability of easily decomposable organic compounds and oxic conditions in the rhizosphere. In the Sphagnum plots, high N2 fixation below 10 cm depth rather reflects the potential during dry periods or low water level when oxygen penetrates the top peat layer and triggers peat mineralization. Natural abundance of the (15) N isotope of live Sphagnum (5.6 δ‰) from 0 to 10 cm points to solely N uptake from atmospheric deposition and nonsymbiotic N2 fixation. A mean (15) N signature of -0.7 δ‰ of peat from the cushion plant plots indicates additional N supply from N mineralization. Our findings suggest that nonsymbiotic N2 fixation overcomes N deficiency in different vegetation communities and has great significance for N cycling and peat accumulation in pristine peatlands. © 2014 John Wiley & Sons Ltd.

  8. Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

    NASA Astrophysics Data System (ADS)

    Klingler, J. M.; Mancinelli, R. L.; White, M. R.

    Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 <= 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.

  9. Solar Water Splitting and Nitrogen Fixation with Layered Bismuth Oxyhalides.

    PubMed

    Li, Jie; Li, Hao; Zhan, Guangming; Zhang, Lizhi

    2017-01-17

    Hydrogen and ammonia are the chemical molecules that are vital to Earth's energy, environmental, and biological processes. Hydrogen with renewable, carbon-free, and high combustion-enthalpy hallmarks lays the foundation of next-generation energy source, while ammonia furnishes the building blocks of fertilizers and proteins to sustain the lives of plants and organisms. Such merits fascinate worldwide scientists in developing viable strategies to produce hydrogen and ammonia. Currently, at the forefronts of hydrogen and ammonia syntheses are solar water splitting and nitrogen fixation, because they go beyond the high temperature and pressure requirements of methane stream reforming and Haber-Bosch reaction, respectively, as the commercialized hydrogen and ammonia production routes, and inherit the natural photosynthesis virtues that are green and sustainable and operate at room temperature and atmospheric pressure. The key to propelling such photochemical reactions lies in searching photocatalysts that enable water splitting into hydrogen and nitrogen fixation to make ammonia efficiently. Although the past 40 years have witnessed significant breakthroughs using the most widely studied TiO2, SrTiO3, (Ga1-xZnx)(N1-xOx), CdS, and g-C3N4 for solar chemical synthesis, two crucial yet still unsolved issues challenge their further progress toward robust solar water splitting and nitrogen fixation, including the inefficient steering of electron transportation from the bulk to the surface and the difficulty of activating the N≡N triple bond of N2. This Account details our endeavors that leverage layered bismuth oxyhalides as photocatalysts for efficient solar water splitting and nitrogen fixation, with a focus on addressing the above two problems. We first demonstrate that the layered structures of bismuth oxyhalides can stimulate an internal electric field (IEF) that is capable of efficiently separating electrons and holes after their formation and of precisely channeling

  10. Screening Prosopis (mesquite) germplasm for biomass production and nitrogen fixation

    SciTech Connect

    Felker, P.; Cannell, G.H.; Clark, P.R.; Osborn, J.F.

    1980-01-01

    The nitrogen-fixing trees of the genus Prosopis (mesquite or algaroba) are well adapted to the semi-arid and often saline regions of the world. These trees may produce firewood or pods for livestock food, they may stabilize sand dunes and they may enrich the soil by production of leaf litter supported by nitrogen fixation. A collection of nearly 500 Prosopis accessions representing North and South American and African germplasm has been established. Seventy of these accessions representing 14 taxa are being grown under field conditions where a 30-fold range in biomass productivity among accessions has been estimated. In a greehouse experiment, 13 Prosopis taxa grew on nitrogen-free medium nodulated, and had a 10-fold difference in nitrogen fixation (acetylene reduction). When Prosopis is propagated by seed the resulting trees are extremely variable in growth rate and presence or absence of thorns. Propagation of 6 Prosopis taxa by stem cuttings has been achieved with low success (1 to 10%) in field-grown plants and with higher success (50 to 100%) with young actively growing greenhouse plants.

  11. Nitrogen Fixation by White Lupin under Phosphorus Deficiency

    PubMed Central

    SCHULZE, JOACHIM; TEMPLE, GLENA; TEMPLE, STEPHEN J.; BESCHOW, HEIDRUN; VANCE, CARROLL P.

    2006-01-01

    • Background and Aims White lupin is highly adapted to growth in a low-P environment. The objective of the present study was to evaluate whether white lupin grown under P-stress has adaptations in nodulation and N2 fixation that facilitate continued functioning. • Methods Nodulated plants were grown in silica sand supplied with N-free nutrient solution containing 0 to 0·5 mm P. At 21 and 37 d after inoculation (DAI) growth, nodulation, P and N concentration, N2 fixation (15N2 uptake and H2 evolution), root/nodule net CO2 evolution and CO2 fixation (14CO2 uptake) were measured. Furthermore, at 21 DAI in-vitro activities and transcript abundance of key enzymes of the C and N metabolism in nodules were determined. Moreover, nodulation in cluster root zones was evaluated. • Key Results Treatment without P led to a lower P concentration in shoots, roots, and nodules. In both treatments, with or without P, the P concentration in nodules was greater than that in the other organs. At 21 DAI nitrogen fixation rates did not differ between treatments and the plants displayed no symptoms of P or N deficiency on their shoots. Although nodule number at 21 DAI increased in response to P-deficiency, total nodule mass remained constant. Increased nodule number in P-deficient plants was associated with cluster root formation. A higher root/nodule CO2 fixation in the treatment without P led to a lower net CO2 release per unit fixed N, although the total CO2 released per unit fixed N was higher in the treatment without P. The higher CO2 fixation was correlated with increased transcript abundance and enzyme activities of phosphoenolpyruvate carboxylase and malate dehydrogenase in nodules. Between 21 and 37 DAI, shoots of plants grown without P developed symptoms of N- and P-deficiency. By 37 DAI the P concentration had decreased in all organs of the plants treated with no P. At 37 DAI, nitrogen fixation in the treatment without P had almost ceased. • Conclusions Enhanced

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

    PubMed Central

    González-Guerrero, Manuel; Matthiadis, Anna; Sáez, Áez;ngela; Long, Terri A.

    2014-01-01

    Symbiotic nitrogen fixation is one of the most promising and immediate alternatives to the overuse of polluting nitrogen fertilizers for improving plant nutrition. At the core of this process are a number of metalloproteins that catalyze and provide energy for the conversion of atmospheric nitrogen to ammonia, eliminate free radicals produced by this process, and create the microaerobic conditions required by these reactions. In legumes, metal cofactors are provided to endosymbiotic rhizobia within root nodule cortical cells. However, low metal bioavailability is prevalent in most soils types, resulting in widespread plant metal deficiency and decreased nitrogen fixation capabilities. As a result, renewed efforts have been undertaken to identify the mechanisms governing metal delivery from soil to the rhizobia, and to determine how metals are used in the nodule and how they are recycled once the nodule is no longer functional. This effort is being aided by improved legume molecular biology tools (genome projects, mutant collections, and transformation methods), in addition to state-of-the-art metal visualization systems. PMID:24592271

  13. Factors influencing dark nitrogen fixation in a blue-green alga.

    PubMed

    Fay, P

    1976-03-01

    Nitrogen-fixing activity declines first rapidly and then more gradually when Anabaenopsis circularis is transferred from light into dark conditions. The rate and duration of dark acetylene reduction (nitrogen fixation) depend upon conditions prevailing during the preceding light period. Factors (such as light intensity, CO2 concentration, and supply of glucose), which in the light affect photosynthesis and the accumulation of reserve carbon, have a profound effect on dark nitrogen fixation. Glucose greatly promotes nitrogen fixation in the light and supports prolonged nitrogenase activity in the dark. The results suggest that heterotrophic nitrogen fixation by blue-green algae in the field may be important both under light and dark conditions.

  14. Evolutionary tradeoffs can select against nitrogen fixation and thereby maintain nitrogen limitation.

    PubMed

    Menge, Duncan N L; Levin, Simon A; Hedin, Lars O

    2008-02-05

    Symbiotic nitrogen (N) fixing trees are absent from old-growth temperate and boreal ecosystems, even though many of these are N-limited. To explore mechanisms that could select against N fixation in N-limited, old-growth ecosystems, we developed a simple resource-based evolutionary model of N fixation. When there are no costs of N fixation, increasing amounts of N fixation will be selected for until N no longer limits production. However, tradeoffs between N fixation and plant mortality or turnover, plant uptake of available soil N, or N use efficiency (NUE) can select against N fixation in N-limited ecosystems and can thereby maintain N limitation indefinitely (provided that there are losses of plant-unavailable N). Three key traits influence the threshold that determines how large these tradeoffs must be to select against N fixation. A low NUE, high mortality (or turnover) rate and low losses of plant-unavailable N all increase the likelihood that N fixation will be selected against, and a preliminary examination of published data on these parameters shows that these mechanisms, particularly the tradeoff with NUE, are quite feasible in some systems. Although these results are promising, a better characterization of these parameters in multiple ecosystems is necessary to determine whether these mechanisms explain the lack of symbiotic N fixers-and thus the maintenance of N limitation-in old-growth forests.

  15. Evolutionary tradeoffs can select against nitrogen fixation and thereby maintain nitrogen limitation

    PubMed Central

    Menge, Duncan N. L.; Levin, Simon A.; Hedin, Lars O.

    2008-01-01

    Symbiotic nitrogen (N) fixing trees are absent from old-growth temperate and boreal ecosystems, even though many of these are N-limited. To explore mechanisms that could select against N fixation in N-limited, old-growth ecosystems, we developed a simple resource-based evolutionary model of N fixation. When there are no costs of N fixation, increasing amounts of N fixation will be selected for until N no longer limits production. However, tradeoffs between N fixation and plant mortality or turnover, plant uptake of available soil N, or N use efficiency (NUE) can select against N fixation in N-limited ecosystems and can thereby maintain N limitation indefinitely (provided that there are losses of plant-unavailable N). Three key traits influence the threshold that determines how large these tradeoffs must be to select against N fixation. A low NUE, high mortality (or turnover) rate and low losses of plant-unavailable N all increase the likelihood that N fixation will be selected against, and a preliminary examination of published data on these parameters shows that these mechanisms, particularly the tradeoff with NUE, are quite feasible in some systems. Although these results are promising, a better characterization of these parameters in multiple ecosystems is necessary to determine whether these mechanisms explain the lack of symbiotic N fixers—and thus the maintenance of N limitation—in old-growth forests. PMID:18223153

  16. Nitrogen fixation in the mucus of Red Sea corals.

    PubMed

    Grover, Renaud; Ferrier-Pagès, Christine; Maguer, Jean-François; Ezzat, Leila; Fine, Maoz

    2014-11-15

    Scleractinian corals are essential constituents of tropical reef ecological diversity. They live in close association with diazotrophs [dinitrogen (N2)-fixing microbes], which can fix high rates of N2. Whether corals benefit from this extrinsic nitrogen source is still under debate. Until now, N2 fixation rates have been indirectly estimated using the acetylene reduction assay, which does not permit assessment of the amount of nitrogen incorporated into the different compartments of the coral holobiont. In the present study, the (15)N2 technique was applied for the first time on three Red Sea coral species. Significant (15)N enrichment was measured in particles released by corals to the surrounding seawater. N2 fixation rates were species specific and as high as 1.6-2 ng N day(-1) l(-1). However, no significant enrichment was measured in the symbiotic dinoflagellates or the coral host tissues, suggesting that corals do not benefit from diazotrophic N2 fixation. © 2014. Published by The Company of Biologists Ltd.

  17. Local versus basin-scale limitation of marine nitrogen fixation

    PubMed Central

    Weber, Thomas; Deutsch, Curtis

    2014-01-01

    Nitrogen (N) fixation by diazotrophic plankton is the primary source of this crucial nutrient to the ocean, but the factors limiting its rate and distribution are controversial. According to one view, the ecological niche of diazotrophs is primarily controlled by the ocean through internally generated N deficits that suppress the growth of their competitors. A second view posits an overriding limit from the atmosphere, which restricts diazotrophs to regions where dust deposition satisfies their high iron (Fe) requirement, thus separating N sources from sinks at a global scale. Here we use multiple geochemical signatures of N2 fixation to show that the Fe limitation of diazotrophs is strong enough to modulate the regional distribution of N2 fixation within ocean basins—particularly the Fe-poor Pacific—but not strong enough to influence its partition between basins, which is instead governed by rates of N loss. This scale-dependent limitation of N2 fixation reconciles local observations of Fe stress in diazotroph communities with an inferred spatial coupling of N sources and sinks. Within this regime of intermediate Fe control, the oceanic N reservoir would respond only weakly to enhanced dust fluxes during glacial climates, but strongly to the reduced fluxes hypothesized under anthropogenic climate warming. PMID:24889607

  18. Limited role of biochars in nitrogen fixation through nitrate adsorption.

    PubMed

    Yang, Jing; Li, Hao; Zhang, Di; Wu, Min; Pan, Bo

    2017-08-15

    Nitrate cycling is essential in sustaining soil systems. Excessive application of N-fertilizers and the associated underground water contamination have attracted a great deal of research attention. Sorption is efficient and environmentally friendly in nitrate fixation. A debate was noted in literature regarding whether biochars have potential to fix nitrate through sorption. In this study, biochars produced from different biomasses as well as biomass compositions were chosen as the absorbents to evaluate their potential efficiencies in nitrate fixation. Increased sorption to nitrate was observed for biochars with increased pyrolysis temperature, but the increasing extent varied with biomass. The surface base functional groups and surface charges of biochars could not well explain nitrate sorption. The significant positive correlation between nitrate sorption and biochar surface areas suggested that surface area was the controlling parameter for nitrate sorption. The pre-coating of tannic acid (TA) on biochars decreased but did not completely inhibit nitrate sorption. This observation suggested that nitrate sorption on biochars may be further decreased after their interactions with natural organic matter. Nitrate sorption was compared among various adsorbents, including biochars, soil particles, clay minerals, engineered particles, as well as humic substances. Soil particles generally showed high sorption to nitrate over biochars. This result suggested that biochars investigated in this work may play a limited role in nitrate fixation through sorption after their massive application. Nitrogen fixation through nitrate adsorption on biochars should be carefully evaluated taking into consideration of biochar feedstocks and properties.

  19. Local versus basin-scale limitation of marine nitrogen fixation.

    PubMed

    Weber, Thomas; Deutsch, Curtis

    2014-06-17

    Nitrogen (N) fixation by diazotrophic plankton is the primary source of this crucial nutrient to the ocean, but the factors limiting its rate and distribution are controversial. According to one view, the ecological niche of diazotrophs is primarily controlled by the ocean through internally generated N deficits that suppress the growth of their competitors. A second view posits an overriding limit from the atmosphere, which restricts diazotrophs to regions where dust deposition satisfies their high iron (Fe) requirement, thus separating N sources from sinks at a global scale. Here we use multiple geochemical signatures of N2 fixation to show that the Fe limitation of diazotrophs is strong enough to modulate the regional distribution of N2 fixation within ocean basins--particularly the Fe-poor Pacific--but not strong enough to influence its partition between basins, which is instead governed by rates of N loss. This scale-dependent limitation of N2 fixation reconciles local observations of Fe stress in diazotroph communities with an inferred spatial coupling of N sources and sinks. Within this regime of intermediate Fe control, the oceanic N reservoir would respond only weakly to enhanced dust fluxes during glacial climates, but strongly to the reduced fluxes hypothesized under anthropogenic climate warming.

  20. New insights into the evolutionary history of biological nitrogen fixation

    PubMed Central

    Boyd, Eric S.; Peters, John W.

    2013-01-01

    Nitrogenase, which catalyzes the ATP-dependent reduction of dinitrogen (N2) to ammonia (NH3), accounts for roughly half of the bioavailable nitrogen supporting extant life. The fundamental requirement for fixed forms of nitrogen for life on Earth, both at present and in the past, has led to broad and significant interest in the origin and evolution of biological N2 fixation. One key question is whether the limited availability of fixed nitrogen was a factor in life's origin or whether there were ample sources of fixed nitrogen produced by abiotic processes or delivered through the weathering of bolide impact materials to support this early life. If the latter, the key questions become what were the characteristics of the environment that precipitated the evolution of this oxygen sensitive process, when did this occur, and how was its subsequent evolutionary history impacted by the advent of oxygenic photosynthesis and the rise of oxygen in the Earth's biosphere. Since the availability of fixed sources of nitrogen capable of supporting early life is difficult to glean from the geologic record, there are limited means to get direct insights into these questions. Indirect insights, however, can be gained through phylogenetic studies of nitrogenase structural gene products and additional gene products involved in the biosynthesis of the complex metal-containing prosthetic groups associated with this enzyme complex. Insights gained from such studies, as reviewed herein, challenge traditional models for the evolution of biological nitrogen fixation and provide the basis for the development of new conceptual models that explain the stepwise evolution of this highly complex life sustaining process. PMID:23935594

  1. Extensive hydrogen supersaturations in the western South Atlantic Ocean suggest substantial underestimation of nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Moore, Robert M.; Kienast, Markus; Fraser, Michael; Cullen, John J.; Deutsch, Curtis; Dutkiewicz, Stephanie; Follows, Michael J.; Somes, Christopher J.

    2014-07-01

    The nitrogen cycle is fundamental to Earth's biogeochemistry. Yet major uncertainties of quantification remain, particularly regarding the global oceanic nitrogen fixation rate. Hydrogen is produced during nitrogen fixation and will become supersaturated in surface waters if there is net release from diazotrophs. Ocean surveys of hydrogen supersaturation thus have the potential to illustrate the spatial and temporal distribution of nitrogen fixation and to guide the far more onerous but quantitative methods for measuring it. Here we present the first transect of high resolution measurements of hydrogen supersaturations in surface waters along a meridional 10,000 km cruise track through the Atlantic. We compare measured saturations with published measurements of nitrogen fixation rates and also with model-derived values. If the primary source of excess hydrogen is nitrogen fixation and has a hydrogen release ratio similar to Trichodesmium, our hydrogen measurements would point to similar rates of fixation in the North and South Atlantic, roughly consistent with modeled fixation rates but not with measured rates, which are lower in the south. Possible explanations would include any substantial nitrogen fixation by newly discovered diazotrophs, particularly any having a hydrogen release ratio similar to or exceeding that of Trichodesmium; undersampling of nitrogen fixation south of the equator related to excessive focus on Trichodesmium; and methodological shortcomings of nitrogen fixation techniques that cause a bias toward colonial diazotrophs relative to unicellular forms. Alternatively, our data are affected by an unknown hydrogen source that is greater in the southern half of the cruise track than the northern.

  2. Biological nitrogen fixation in the context of global change.

    PubMed

    Olivares, José; Bedmar, Eulogio J; Sanjuán, Juan

    2013-05-01

    The intensive application of fertilizers during agricultural practices has led to an unprecedented perturbation of the nitrogen cycle, illustrated by the growing accumulation of nitrates in soils and waters and of nitrogen oxides in the atmosphere. Besides increasing use efficiency of current N fertilizers, priority should be given to value the process of biological nitrogen fixation (BNF) through more sustainable technologies that reduce the undesired effects of chemical N fertilization of agricultural crops. Wider legume adoption, supported by coordinated legume breeding and inoculation programs are approaches at hand. Also available are biofertilizers based on microbes that help to reduce the needs of N fertilization in important crops like cereals. Engineering the capacity to fix nitrogen in cereals, either by themselves or in symbiosis with nitrogen-fixing microbes, are attractive future options that, nevertheless, require more intensive and internationally coordinated research efforts. Although nitrogen-fixing plants may be less productive, at some point, agriculture must significantly reduce the use of warming (chemically synthesized) N and give priority to BNF if it is to sustain both food production and environmental health for a continuously growing human population.

  3. Marine oscillatoria (Trichodesmium): explanation for aerobic nitrogen fixation without heterocysts.

    PubMed

    Carpenter, E J; Price, C C

    1976-03-26

    Nitrogen fixation in marine Oscillatoria appears to be associated with differentiated cells located in the center of the colony. These central cells exhibit reduced pigmentation relative to peripherally located cells and do not incorporate 14CO2 in photosynthesis. Central cells apparently do not produce O2 which would deactivate nitrogenase. When central cells are exposed to O2 via disruption of the colonies, N2 fixation (acetylene reduction) decreases sharply even though individual trichomes remain intact. Disruption of colonies in the absence of O2 does not cause reduced nitrogenase activity. In the sea, turbulence from wave action apparently separates trichomes allowing O2 to enter thus decreasing nitrogenase activity. These observations explain how Oscillatoria is able to fix N2 without heterocysts in an aerobic environment and why it blooms virtually always occur in calm seas.

  4. The cyanobacterial nitrogen fixation paradox in natural waters.

    PubMed

    Paerl, Hans

    2017-01-01

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

  5. The cyanobacterial nitrogen fixation paradox in natural waters

    PubMed Central

    Paerl, Hans

    2017-01-01

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

  6. The effects of acid rain on nitrogen fixation in Western Washington coniferous forests

    Treesearch

    Robert Denison; Bruce Caldwell; Bernard Bormann; Lindell Eldred; Cynthia Swanberg; Steven Anderson

    1976-01-01

    We investigated both the current status of nitrogen fixation in Western Washington forests, and the potential effects of acid rain on this vital process. Even the low concentrations of sulfur dioxide presently found in the Northwest are thought to have an adverse effect on nitrogen fixation by limiting the distribution of the epiphytic nitrogen-fixing lichen, ...

  7. Nitrogen fixation on early Mars and other terrestrial planets: experimental demonstration of abiotic fixation reactions to nitrite and nitrate.

    PubMed

    Summers, David P; Khare, Bishun

    2007-04-01

    Understanding the abiotic fixation of nitrogen is critical to understanding planetary evolution and the potential origin of life on terrestrial planets. Nitrogen, an essential biochemical element, is certainly necessary for life as we know it to arise. The loss of atmospheric nitrogen can result in an incapacity to sustain liquid water and impact planetary habitability and hydrological processes that shape the surface. However, our current understanding of how such fixation may occur is almost entirely theoretical. This work experimentally examines the chemistry, in both gas and aqueous phases, that would occur from the formation of NO and CO by the shock heating of a model carbon dioxide/nitrogen atmosphere such as is currently thought to exist on early terrestrial planets. The results show that two pathways exist for the abiotic fixation of nitrogen from the atmosphere into the crust: one via HNO and another via NO(2). Fixation via HNO, which requires liquid water, could represent fixation on a planet with liquid water (and hence would also be a source of nitrogen for the origin of life). The pathway via NO(2) does not require liquid water and shows that fixation could occur even when liquid water has been lost from a planet's surface (for example, continuing to remove nitrogen through NO(2) reaction with ice, adsorbed water, etc.).

  8. An Alternative Path for the Evolution of Biological Nitrogen Fixation

    PubMed Central

    Boyd, Eric S.; Hamilton, Trinity L.; Peters, John W.

    2011-01-01

    Nitrogenase catalyzed nitrogen fixation is the process by which life converts dinitrogen gas into fixed nitrogen in the form of bioavailable ammonia. The most common form of nitrogenase today requires a complex metal cluster containing molybdenum (Mo), although alternative forms exist which contain vanadium (V) or only iron (Fe). It has been suggested that Mo-independent forms of nitrogenase (V and Fe) were responsible for N2 fixation on early Earth because oceans were Mo-depleted and Fe-rich. Phylogenetic- and structure-based examinations of multiple nitrogenase proteins suggest that such an evolutionary path is unlikely. Rather, our results indicate an evolutionary path whereby Mo-dependent nitrogenase emerged within the methanogenic archaea and then gave rise to the alternative forms suggesting that they arose later, perhaps in response to local Mo limitation. Structural inferences of nitrogenase proteins and related paralogs suggest that the ancestor of all nitrogenases had an open cavity capable of binding metal clusters which conferred reactivity. The evolution of the nitrogenase ancestor and its associated bound metal cluster was controlled by the availability of fixed nitrogen in combination with local environmental factors that influenced metal availability until a point in Earth’s geologic history where the most desirable metal, Mo, became sufficiently bioavailable to bring about and refine the solution (Mo-nitrogenase) we see perpetuated in extant biology. PMID:22065963

  9. Nitrogen Fixation by Anaerobes is Stimulated by Low Oxygen and Insensitive to Combined Nitrogen in Coastal Sediments

    NASA Astrophysics Data System (ADS)

    Jenkins, B. D.; Spinette, R.; Jones, A.; Puggioni, G.; Ehrlich, A.; Brown, S. M.

    2016-02-01

    Coastal sediments are typically zones of nitrogen removal via coupled nitrification-denitrification pathways. Increasingly, there are reports of nitrogen fixation in anthropogenically impacted sediments containing ample combined nitrogen. In previous work in the estuarine sediments of Narragansett Bay, we found that anaerobes related to Desulfovibrio spp. and in the Desulfuromonadales express genes for nitrogen fixation (nifH). We also determined that nitrogen fixation rates and gene expression are elevated during periods of seasonal hypoxia. Statistical modeling shows that a combination of elevated phytoplankton biomass as with a duration of hypoxia for a week or longer lead to conditions that promote nitrogen fixation as measured by acetylene reduction. Interestingly, diazotrophs closely related to those identified in Narragansett Bay are present and active in other low oxygen systems, suggesting that expansion of hypoxic events may lead to unanticipated consequences for the benthic nitrogen cycle in many ecosystems. To determine controls on diazotrophy on the organismal level, we isolated and sequenced the genomes of two Narragansett Bay members of the Desulfovibrio. We found that these organisms are insensitive to nitrate and urea, as they are missing the genes to assimilate these nitrogen sources. However, their nitrogen fixation is suppressed by increasing concentrations of ammonium, indicating that they may be sensitive to this nitrogen source in the environment. The paradox of detectable nitrogen fixation in the background of measurable ammonium in estuarine systems is a newly emergent theme and suggests that there are complex microbial interactions and/or structure to the nutrient regimes allowing for fixation.

  10. Evaluation of kidney bean yield and nitrogen fixation under low soil nitrogen

    USDA-ARS?s Scientific Manuscript database

    U.S. Kidney bean cultivars as a group have limited genetic diversity. They also require more intensive crop management than most other bean market classes. The objective of this study was to evaluate biological nitrogen fixation and seed yield in a diverse group of kidney lines. A 250 line Andean be...

  11. Symbiotic Nitrogen Fixation in Legume Nodules: Metabolism and Regulatory Mechanisms

    PubMed Central

    Sulieman, Saad; Tran, Lam-Son Phan

    2014-01-01

    The special issue “Symbiotic Nitrogen Fixation in Legume Nodules: Metabolism and Regulatory Mechanisms” aims to investigate the physiological and biochemical advances in the symbiotic process with an emphasis on nodule establishment, development and functioning. The original research articles included in this issue provide important information regarding novel aspects of nodule metabolism and various regulatory pathways, which could have important future implications. This issue also included one review article that highlights the importance of using legume trees in the production of renewable biofuels. PMID:25347276

  12. Redox regulation of differentiation in symbiotic nitrogen fixation.

    PubMed

    Ribeiro, Carolina Werner; Alloing, Geneviève; Mandon, Karine; Frendo, Pierre

    2015-08-01

    Nitrogen-fixing symbiosis between Rhizobium bacteria and legumes leads to the formation of a new organ, the root nodule. The development of the nodule requires the differentiation of plant root cells to welcome the endosymbiotic bacterial partner. This development includes the formation of an efficient vascular tissue which allows metabolic exchanges between the root and the nodule, the formation of a barrier to oxygen diffusion necessary for the bacterial nitrogenase activity and the enlargement of cells in the infection zone to support the large bacterial population. Inside the plant cell, the bacteria differentiate into bacteroids which are able to reduce atmospheric nitrogen to ammonia needed for plant growth in exchange for carbon sources. Nodule functioning requires a tight regulation of the development of plant cells and bacteria. Nodule functioning requires a tight regulation of the development of plant cells and bacteria. The importance of redox control in nodule development and N-fixation is discussed in this review. The involvement of reactive oxygen and nitrogen species and the importance of the antioxidant defense are analyzed. Plant differentiation and bacterial differentiation are controlled by reactive oxygen and nitrogen species, enzymes involved in the antioxidant defense and antioxidant compounds. The establishment and functioning of nitrogen-fixing symbiosis involve a redox control important for both the plant-bacteria crosstalk and the consideration of environmental parameters. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. Seabird modulations of isotopic nitrogen on islands.

    PubMed

    Caut, Stéphane; Angulo, Elena; Pisanu, Benoit; Ruffino, Lise; Faulquier, Lucie; Lorvelec, Olivier; Chapuis, Jean-Louis; Pascal, Michel; Vidal, Eric; Courchamp, Franck

    2012-01-01

    The transport of nutrients by migratory animals across ecosystem boundaries can significantly enrich recipient food webs, thereby shaping the ecosystems' structure and function. To illustrate the potential role of islands in enabling the transfer of matter across ecosystem boundaries to be gauged, we investigated the influence of seabirds on nitrogen input on islands. Basing our study on four widely differing islands in terms of their biogeography and ecological characteristics, sampled at different spatial and temporal intervals, we analyzed the nitrogen isotopic values of the main terrestrial ecosystem compartments (vascular plants, arthropods, lizards and rodents) and their relationship to seabird values. For each island, the isotopic values of the ecosystem were driven by those of seabirds, which ultimately corresponded to changes in their marine prey. First, terrestrial compartments sampled within seabird colonies were the most enriched in δ(15)N compared with those collected at various distances outside colonies. Second, isotopic values of the whole terrestrial ecosystems changed over time, reflecting the values of seabirds and their prey, showing a fast turnover throughout the ecosystems. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystems and trophic webs, but also modulate their isotopic values locally and temporally on these islands. The wealth of experimental possibilities in insular ecosystems justifies greater use of these model systems to further our understanding of the modalities of trans-boundary nutrient transfers.

  14. Seabird Modulations of Isotopic Nitrogen on Islands

    PubMed Central

    Caut, Stéphane; Angulo, Elena; Pisanu, Benoit; Ruffino, Lise; Faulquier, Lucie; Lorvelec, Olivier; Chapuis, Jean-Louis; Pascal, Michel; Vidal, Eric; Courchamp, Franck

    2012-01-01

    The transport of nutrients by migratory animals across ecosystem boundaries can significantly enrich recipient food webs, thereby shaping the ecosystems’ structure and function. To illustrate the potential role of islands in enabling the transfer of matter across ecosystem boundaries to be gauged, we investigated the influence of seabirds on nitrogen input on islands. Basing our study on four widely differing islands in terms of their biogeography and ecological characteristics, sampled at different spatial and temporal intervals, we analyzed the nitrogen isotopic values of the main terrestrial ecosystem compartments (vascular plants, arthropods, lizards and rodents) and their relationship to seabird values. For each island, the isotopic values of the ecosystem were driven by those of seabirds, which ultimately corresponded to changes in their marine prey. First, terrestrial compartments sampled within seabird colonies were the most enriched in δ15N compared with those collected at various distances outside colonies. Second, isotopic values of the whole terrestrial ecosystems changed over time, reflecting the values of seabirds and their prey, showing a fast turnover throughout the ecosystems. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystems and trophic webs, but also modulate their isotopic values locally and temporally on these islands. The wealth of experimental possibilities in insular ecosystems justifies greater use of these model systems to further our understanding of the modalities of trans-boundary nutrient transfers. PMID:22723945

  15. Variation in moss-associated nitrogen fixation in boreal forest stands.

    PubMed

    Markham, John H

    2009-08-01

    Traditionally it has been thought that most boreal forest communities lack a significant input of biologically fixed nitrogen. Recent discoveries of nitrogen fixation by cyanobacteria associated with mosses have resulted in a re-evaluation of this view. While it is recognized that rates of nitrogen fixation in mosses can be highly variable, there is little understanding as to why this occurs. I monitored nitrogen fixation, using acetylene reduction, in wet lowland and dry upland boreal forest communities, in central Canada, over a growing season. At the peak of nitrogen fixation in mid summer, Sphagnum capillifolium had an 11 times higher rate of fixation than Pleurozium schreberi. Variation in canopy openness and precipitation had no effect on rates of fixation over the growing season. In P. schreberi fixation rates did not vary between sites. Temperature had a positive effect on fixation rates in both S. capillifolium and P. schreberi, but the effect was 4 times more pronounced in S. capillifolium. Seasonal rates of nitrogen fixation were estimated at 193 mg N m(-2) for S. capillifolium and 23 mg N m(-2) for P. schreberi. With moderate increases in climate warming, predicted increases in nitrogen fixation in S. capillifolium are sufficient to raise its decomposition rate. Increased temperatures may therefore act synergistically to change boreal systems from a sink to a source of carbon.

  16. Regulation of Development and Nitrogen Fixation in Anabaena

    SciTech Connect

    James W Golden

    2004-08-05

    because all cells differentiate a few days after nitrogen step-down. Our continued analysis of these genes will provide a better understanding of how a simple prokaryotic organism can perform both photosynthetic carbon fixation and nitrogen fixation simultaneously by separating these processes in different cell types.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  18. Influence of sewage discharge on nitrogen fixation and nitrogen flux from coral reefs in Kaneohe Bay, Hawaii.

    PubMed Central

    Hanson, R B; Gundersen, K

    1976-01-01

    Nitrogen fixation was investigated in Kaneohe Bay, Oahu, Hawaii, a subtropical eutrophic estuary, by using the acetylene reduction technique on algal samples. No active, planktonic, N2-fixing blue-green algae or bacteria were observed. However, Calothrix and Nostoc capable of fixing N2 were cultured from navigational buoys and dead coral heads. Nitrogen fixation associated with these structures was greater in the middle sector than in the south and north sectors of the estuary. Experiments demonstrated that the fixation was photosynthetically dependent. Examination of the data showed that there was no significant correlation between rates of nitrogen fixation and concentration of combined nitrogen compounds in the Bay water. Fixation was significantly correlated to the inorganic N/P (atomic) ratio in the south and middle sectors but not in the north sector. The nutrient data indicate there was a flux of combined nitrogen, but not phosphate, from the reef flats. PMID:7198

  19. Nitrogen fixation strategies can explain the latitudinal shift in nitrogen-fixing tree abundance.

    PubMed

    Menge, Duncan N L; Lichstein, Jeremy W; Angeles-Pérez, Gregorio

    2014-08-01

    The rarity of symbiotic nitrogen-fixing trees in higher-latitude compared to lower-latitude forests is paradoxical because higher-latitude soils are relatively N poor. Using national-scale forest inventories from the United States and Mexico, we show that the latitudinal abundance distribution of N-fixing trees (more than 10 times less abundant poleward of 35 degrees N) coincides with a latitudinal transition in symbiotic N-fixation type: rhizobial N-fixing trees (which are typically facultative, regulating fixation to meet nutritional demand) dominate equatorward of 35 degrees N, whereas actinorhizal N-fixing trees (typically obligate, maintaining fixation regardless of soil nutrition) dominate to the north. We then use theoretical and statistical models to show that a latitudinal shift in N-fixation strategy (facultative vs. obligate) near 35 degrees N can explain the observed change in N-fixing tree abundance, even if N availability is lower at higher latitudes, because facultative fixation leads to much higher landscape-scale N-fixing tree abundance than obligate fixation.

  20. Nitrogen fixation in boreal peatlands: the effects of increased N deposition on N2-fixation

    NASA Astrophysics Data System (ADS)

    Popma, J. M.; Wieder, R.; Lamers, L.; Vile, M. A.

    2013-12-01

    Boreal peatlands are of great importance to global carbon and nitrogen cycling. While covering only 3-4 % of the terrestrial surface, they account for 25-30 % of the world's soil C and 9-15 % of the world's soil N. In Western Canada atmospheric dry deposition rates are extremely low: approximately 1 kg N ha-1 yr-1. Though these systems have been functioning as net sinks over the past 11,000 years, natural and anthropogenic disturbances might compromise the historical balance of C and N. Biological N2-fixation has recently been shown to represent a very significant input of N into these systems, contributing to 62% of total N in Western Canada. Interactions between N deposition and biological N2-fixation are as yet, unknown, but the impact of elevated deposition of N-compounds from increased industrial expansion of oil sands mining to peatlands, is concerning. Given that nitrogenase, the enzyme responsible for catalyzing N2-fixation, is energetically costly when active, enhanced inputs of atmospheric N deposition could be a major determinant for enzyme activity and rates of biological N input to these bogs. Understanding interactions between N deposition and N2 fixation in boreal peatlands can aid in predicting the consequences of increased N deposition and setting critical loads. We conducted a field-fertilization experiment in a poor fen in Alberta, Canada, to determine the effects of enhanced N deposition on a dominant fen species Sphagnum angustifolium. The experiment consisted of seven N treatments: Control, 0, 5, 10, 15, 20 and 25 kg N ha-1 y1, n=3. N2-fixation was measured during summer 2012 and 2013 using the acetylene reduction assay (ARA). ARA rates were converted to rates of N2-fixation by calibrating ARA with paired 15N2-incubations. In both 2012 and 2013, with increasing N deposition from 0 kg N ha-1 yr-1 to 25 kg N ha-1 yr-1, rates of N2 fixation decreased, with highest rates in the 0 kg N ha-1 yr-1 treatment mosses (54.2 × 1.40; 48.58 × 7.12 kg N ha

  1. Temporal Variability in Nitrogen Fixation and Particulate Nitrogen Export at Station ALOHA

    NASA Astrophysics Data System (ADS)

    Dore, J. E.; Böttjer, D.; Karl, D. M.; Letelier, R. M.; Mahaffey, C.; Wilson, S. T.; Zehr, J. P.; Church, M. J.

    2016-02-01

    In order to constrain biological N2 fixation rates in the North Pacific Subtropical Gyre we present 9 years (2005-2013) of near-monthly rates of upper-ocean N2 fixation (0 - 125 m), coupled with the isotopic composition of particulate nitrogen (PN) export (150 m) at Station ALOHA (22˚ 45'N, 158˚ 00'W). Between June 2005 and June 2012, N2 fixation rates were derived based on adding the 15N2 tracer as a gas bubble. Beginning in August 2012, 15N2 was first dissolved into filtered seawater and the 15N2-enriched water was subsequently added to N2 fixation incubations. Direct comparisons between both methodologies revealed a robust relationship, with the addition of 15N2-enriched seawater resulting in 2-fold greater rates of N2 fixation than those derived from adding a 15N2 gas bubble. The correction of the initial period of measurements (2005 - 2012) based on this relationship resulted in rates of N2 fixation that averaged 236 ± 107 µmol N m-2 d-1 for the full period of study. Furthermore, the analysis of the 15N isotopic composition of sinking PN, together with an isotope mass balance model, provided additional constraint on N2 fixation rates. These model derived N2 fixation rates varied from 70 to 128 mmol N m-2 d-1, representing 26 - 47% of the PN export. The resulting total N export derived from this analysis ranged between 506 and 921 µmol N m-2 d-1, equivalent to a net community production rate that ranged between 1.4 and 2.5 mol C m-2 yr-1, consistent with previous independent estimates at this site.

  2. Nitrogen Fixation and Molecular Oxygen: Comparative Genomic Reconstruction of Transcription Regulation in Alphaproteobacteria.

    PubMed

    Tsoy, Olga V; Ravcheev, Dmitry A; Čuklina, Jelena; Gelfand, Mikhail S

    2016-01-01

    Biological nitrogen fixation plays a crucial role in the nitrogen cycle. An ability to fix atmospheric nitrogen, reducing it to ammonium, was described for multiple species of Bacteria and Archaea. The transcriptional regulatory network for nitrogen fixation was extensively studied in several representatives of the class Alphaproteobacteria. This regulatory network includes the activator of nitrogen fixation NifA, working in tandem with the alternative sigma-factor RpoN as well as oxygen-responsive regulatory systems, one-component regulators FnrN/FixK and two-component system FixLJ. Here we used a comparative genomics approach for in silico study of the transcriptional regulatory network in 50 genomes of Alphaproteobacteria. We extended the known regulons and proposed the scenario for the evolution of the nitrogen fixation transcriptional network. The reconstructed network substantially expands the existing knowledge of transcriptional regulation in nitrogen-fixing microorganisms and can be used for genetic experiments, metabolic reconstruction, and evolutionary analysis.

  3. The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input

    PubMed Central

    Rousk, Kathrin; Michelsen, Anders

    2016-01-01

    Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha-1 yr-1) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha-1 yr-1, and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha-1 yr-1). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha-1 yr-1. Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold. PMID:26731691

  4. The Sensitivity of Moss-Associated Nitrogen Fixation towards Repeated Nitrogen Input.

    PubMed

    Rousk, Kathrin; Michelsen, Anders

    2016-01-01

    Nitrogen (N2) fixation is a major source of available N in ecosystems that receive low amounts of atmospheric N deposition. In boreal forest and subarctic tundra, the feather moss Hylocomium splendens is colonized by N2 fixing cyanobacteria that could contribute fundamentally to increase the N pool in these ecosystems. However, N2 fixation in mosses is inhibited by N input. Although this has been shown previously, the ability of N2 fixation to grow less sensitive towards repeated, increased N inputs remains unknown. Here, we tested if N2 fixation in H. splendens can recover from increased N input depending on the N load (0, 5, 20, 80, 320 kg N ha(-1) yr(-1)) after a period of N deprivation, and if sensitivity towards increased N input can decrease after repeated N additions. Nitrogen fixation in the moss was inhibited by the highest N addition, but was promoted by adding 5 kg N ha(-1) yr(-1), and increased in all treatments during a short period of N deprivation. The sensitivity of N2 fixation towards repeated N additions seem to decrease in the 20 and 80 kg N additions, but increased in the highest N addition (320 kg N ha(-1) yr(-1)). Recovery of N in leachate samples increased with increasing N loads, suggesting low retention capabilities of mosses if N input is above 5 kg N ha(-1) yr(-1). Our results demonstrate that the sensitivity towards repeated N additions is likely to decrease if N input does not exceed a certain threshold.

  5. Nitrogen fixation by corona discharge on the early precambrian Earth.

    PubMed

    Nna-Mvondo, Delphine; Navarro-González, Rafael; Raulin, François; Coll, Patrice

    2005-10-01

    We report the first experimental study of nitrogen fixation by corona discharge on the anoxic primitive Earth. The energy yields of nitric oxide (NO) and nitrous oxide (N(2)O) were experimentally determined over a wide range of CO(2)-N(2) mixtures simulating the evolution of the Earth's atmosphere during the Hadean and Archean eras (from 4.5 ba to 2.5 ba). NO, the principal form of fixed nitrogen in lightning and coronal discharge in early Earth, is produced ten times less efficiently in the latter type of electrical discharge with an estimated maximum annual production rate of the order of 10(10) g yr(-1). For N(2)O the maximum production rate was estimated to be approximately 10(9) g yr(-1). These low rates of syntheses indicate that corona discharges as point discharges on the clouds and ground did not play a significant role in the overall pool of reactive nitrogen needed for the emergence and sustainability of life.

  6. Nitrogen fixation may enrich phosphorus availability under elevated CO2

    NASA Astrophysics Data System (ADS)

    Houlton, B. Z.; Vitousek, P. M.; Field, C. B.; Michael, A.

    2006-12-01

    The ability of N2 fixers to effectively colonize new terrestrial landscapes has major implications for CO2 uptake, storage, and climate change. As part of the Jasper Ridge Global Change Experiment, we have initiated a manipulation to explore how nutrients, particularly nitrogen N and P, interact with elevated CO2 in controlling rates of N2 fixation and the persistence of symbiotic N2 fixers. Here we report that N2-fixing plants employ an N-rich strategy of P acquisition that enables them to successfully compete for soil P at ambient and elevated CO2 concentrations. Across all treatments (N, P, CO2), the N2 fixer releases large quantities of N-rich phosphatases (organic-P "weathering" enzymes) into the soil, whereas N appears to substantially limit phosphatase production by non-fixers. This investment in phosphatases increases significantly and linearly with biomass N:P ratios, is only slightly affected by elevated CO2, and can explain the very high P contents of N fixing organisms observed. Using a simulation model of C, N, and P cycles to explore this mechanism further, we find that the ability of N fixers to invest N into P liberation can accelerate the P cycle and enrich P availability at the ecosystem level. Consequently, such interactions between N2 fixation and the P cycle may provide a path by which even P-limited terrestrial environments can take up and store additional CO2 in the future. Our findings suggest that P may not represent a constraint on the ability of fixers to colonize new terrestrial environments, though N2 fixation rates are limited by P.

  7. Nutrient constraints on terrestrial carbon fixation: The role of nitrogen.

    PubMed

    Coskun, Devrim; Britto, Dev T; Kronzucker, Herbert J

    2016-09-20

    Carbon dioxide (CO2) concentrations in the earth's atmosphere are projected to rise from current levels near 400ppm to over 700ppm by the end of the 21st century. Projections over this time frame must take into account the increases in total net primary production (NPP) expected from terrestrial plants, which result from elevated CO2 (eCO2) and have the potential to mitigate the impact of anthropogenic CO2 emissions. However, a growing body of evidence indicates that limitations in soil nutrients, particularly nitrogen (N), the soil nutrient most limiting to plant growth, may greatly constrain future carbon fixation. Here, we review recent studies about the relationships between soil N supply, plant N nutrition, and carbon fixation in higher plants under eCO2, highlighting key discoveries made in the field, particularly from free-air CO2 enrichment (FACE) technology, and relate these findings to physiological and ecological mechanisms. Copyright © 2016 Elsevier GmbH. All rights reserved.

  8. A new perspective on environmental controls of marine nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Landolfi, A.; Koeve, W.; Dietze, H.; Kähler, P.; Oschlies, A.

    2015-06-01

    Growing slowly, marine N2 fixers are generally expected to be competitive only where nitrogen (N) supply is low relative to that of phosphorus (P) with respect to the cellular N:P ratio (R) of nonfixing phytoplankton. This is at odds with observed high N2 fixation rates in the oligotrophic North Atlantic where the ratio of nutrients supplied to the surface is elevated in N relative to the average R (16:1). In this study, we investigate several mechanisms to solve this puzzle: iron limitation, phosphorus enhancement by preferential remineralization or stoichiometric diversity of phytoplankton, and dissolved organic phosphorus (DOP) utilization. Combining resource competition theory and a global coupled ecosystem-circulation model, we find that the additional N and energy investments required for exoenzymatic breakdown of DOP give N2 fixers a competitive advantage in oligotrophic P-starved regions. Accounting for this mechanism expands the ecological niche of N2 fixers also to regions where the nutrient supply is high in N relative to R, yielding, in our model, a pattern consistent with the observed high N2 fixation rates in the oligotrophic North Atlantic.

  9. Mechanistic insights into nitrogen fixation by nitrogenase enzymes.

    PubMed

    Varley, J B; Wang, Y; Chan, K; Studt, F; Nørskov, J K

    2015-11-28

    Biological nitrogen fixation by nitrogenase enzymes is a process that activates dinitrogen (N2) one of the most inert molecules in nature, within the confines of a living organism and at ambient conditions. Despite decades of study, there are still no complete explanations as to how this is possible. Here we describe a model of N2 reduction using the Mo-containing nitrogenase (FeMoco) that can explain the reactivity of the active site via a series of electrochemical steps that reversibly unseal a highly reactive Fe edge site. Our model can explain the 8 proton-electron transfers involved in biological ammonia synthesis within the kinetic scheme of Lowe and Thorneley, the obligatory formation of one H2 per N2 reduced, and the behavior of known inhibitors.

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

    PubMed Central

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

    2016-01-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixation and prospects for increasing its importance in an agricultural setting. Biological nitrogen fixation is the conversion of atmospheric N2 to NH3, a form that can be used by plants. However, the process is restricted to bacteria and archaea and does not occur in eukaryotes. Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. This process is restricted mainly to legumes in agricultural systems, and there is considerable interest in exploring whether similar symbioses can be developed in nonlegumes, which produce the bulk of human food. We are at a juncture at which the fundamental understanding of biological nitrogen fixation has matured to a level that we can think about engineering symbiotic relationships using synthetic biology approaches. This minireview highlights the fundamental advances in our understanding of biological nitrogen fixation in the context of a blueprint for expanding symbiotic nitrogen fixation to a greater diversity of crop plants through synthetic biology. PMID:27084023

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

    PubMed

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

    2016-07-01

    Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world. There are significant potential gains to be had from reducing dependence on nitrogenous fertilizers in agriculture in the developed world and in developing countries, and there is significant interest in research on biological nitrogen fixation and prospects for increasing its importance in an agricultural setting. Biological nitrogen fixation is the conversion of atmospheric N2 to NH3, a form that can be used by plants. However, the process is restricted to bacteria and archaea and does not occur in eukaryotes. Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. This process is restricted mainly to legumes in agricultural systems, and there is considerable interest in exploring whether similar symbioses can be developed in nonlegumes, which produce the bulk of human food. We are at a juncture at which the fundamental understanding of biological nitrogen fixation has matured to a level that we can think about engineering symbiotic relationships using synthetic biology approaches. This minireview highlights the fundamental advances in our understanding of biological nitrogen fixation in the context of a blueprint for expanding symbiotic nitrogen fixation to a greater diversity of crop plants through synthetic biology.

  12. Role of boron nutrient in nodules growth and nitrogen fixation rates in soybean genotypes under water stress conditions

    USDA-ARS?s Scientific Manuscript database

    Although boron has a stimulatory effect on nodule growth and nitrogen fixation, mechanisms of how boron affects nodules growth and nitrogen fixation, especially under water stress, are still unknown. The stimulatory effect of boron (B) on nodules and nitrogen fixation (NF) is influenced by biotic (s...

  13. Microbial fixation of nitrogen in presence of lanthanum sulphate with sodium molybdate.

    PubMed

    Bahadur, K; Prakash, S; Jyotishmati, U

    1978-01-01

    The effect of lanthanum sulphate together with 100 micrometer of sodium molybdate show that there is considerable increase in nitrogen fixation and carbon consumption in the culture medium of nitrogen-fixing Azotobacter species A1 and A2, isolated from Allahabad soil. But these combination decrease the nitrogen fixation and carbon consumption in case of another species, Azotobacter A3, of the same soil.

  14. Regulation of Development and Nitrogen Fixation in Anabaena

    SciTech Connect

    James W. Golden

    2008-10-17

    The regulation of development and cellular differentiation is important for all multicellular organisms. The nitrogen-fixing filamentous cyanobacterium Anabaena (also Nostoc) sp. PCC 7120 (hereafter Anabaena) provides a model of multicellular microbial development and pattern formation. Anabaena reduces N2 to ammonia in specialized terminally differentiated cells called heterocysts. A one-dimensional developmental pattern of single heterocysts regularly spaced along filaments of photosynthetic vegetative cells is established to form a multicellular organism composed of these two interdependent cell types. This multicellular growth pattern, the distinct phylogeny of cyanobacteria, and the suspected antiquity of heterocyst development make this an important model system. Our long-term goal is to understand the regulatory network required for heterocyst development and nitrogen fixation. This project is focused on two key aspects of heterocyst regulation: one, the mechanism by which HetR controls the initiation of differentiation, and two, the cis and trans acting factors required for expression of the nitrogen-fixation (nif) genes. HetR is thought to be a central regulator of heterocyst development but the partners and mechanisms involved in this regulation are unknown. Our recent results indicate that PatS and other signals that regulate heterocyst pattern cannot interact, directly or indirectly, with a R223W mutant of HetR. We plan to use biochemical and genetic approaches to identify proteins that interact with the HetR protein, which will help reveal the mechanisms underlying its regulation of development. Our second goal is to determine how the nif genes are expressed. It is important to understand the mechanisms controlling nif genes since they represent the culmination of the differentiation process and the essence of heterocyst function. The Anabaena genome lacks the genes required for expression of nif genes present in other organisms such as rpoN (sigma 54

  15. Accounting for nitrogen fixation in simple models of lake nitrogen loading/export.

    PubMed

    Ruan, Xiaodan; Schellenger, Frank; Hellweger, Ferdi L

    2014-05-20

    Coastal eutrophication, an important global environmental problem, is primarily caused by excess nitrogen and management efforts consequently focus on lowering watershed N export (e.g., by reducing fertilizer use). Simple quantitative models are needed to evaluate alternative scenarios at the watershed scale. Existing models generally assume that, for a specific lake/reservoir, a constant fraction of N loading is exported downstream. However, N fixation by cyanobacteria may increase when the N loading is reduced, which may change the (effective) fraction of N exported. Here we present a model that incorporates this process. The model (Fixation and Export of Nitrogen from Lakes, FENL) is based on a steady-state mass balance with loading, output, loss/retention, and N fixation, where the amount fixed is a function of the N/P ratio of the loading (i.e., when N/P is less than a threshold value, N is fixed). Three approaches are used to parametrize and evaluate the model, including microcosm lab experiments, lake field observations/budgets and lake ecosystem model applications. Our results suggest that N export will not be reduced proportionally with N loading, which needs to be considered when evaluating management scenarios.

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

    SciTech Connect

    Johnson, G.V. )

    1990-05-01

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

  17. Chemosynthetic symbionts of marine invertebrate animals are capable of nitrogen fixation.

    PubMed

    Petersen, Jillian M; Kemper, Anna; Gruber-Vodicka, Harald; Cardini, Ulisse; van der Geest, Matthijs; Kleiner, Manuel; Bulgheresi, Silvia; Mußmann, Marc; Herbold, Craig; Seah, Brandon K B; Antony, Chakkiath Paul; Liu, Dan; Belitz, Alexandra; Weber, Miriam

    2016-10-24

    Chemosynthetic symbioses are partnerships between invertebrate animals and chemosynthetic bacteria. The latter are the primary producers, providing most of the organic carbon needed for the animal host's nutrition. We sequenced genomes of the chemosynthetic symbionts from the lucinid bivalve Loripes lucinalis and the stilbonematid nematode Laxus oneistus. The symbionts of both host species encoded nitrogen fixation genes. This is remarkable as no marine chemosynthetic symbiont was previously known to be capable of nitrogen fixation. We detected nitrogenase expression by the symbionts of lucinid clams at the transcriptomic and proteomic level. Mean stable nitrogen isotope values of Loripes lucinalis were within the range expected for fixed atmospheric nitrogen, further suggesting active nitrogen fixation by the symbionts. The ability to fix nitrogen may be widespread among chemosynthetic symbioses in oligotrophic habitats, where nitrogen availability often limits primary productivity.

  18. Novel regulatory cascades controlling expression of nitrogen-fixation genes in Geobacter sulfurreducens.

    PubMed

    Ueki, Toshiyuki; Lovley, Derek R

    2010-11-01

    Geobacter species often play an important role in bioremediation of environments contaminated with metals or organics and show promise for harvesting electricity from waste organic matter in microbial fuel cells. The ability of Geobacter species to fix atmospheric nitrogen is an important metabolic feature for these applications. We identified novel regulatory cascades controlling nitrogen-fixation gene expression in Geobacter sulfurreducens. Unlike the regulatory mechanisms known in other nitrogen-fixing microorganisms, nitrogen-fixation gene regulation in G. sulfurreducens is controlled by two two-component His-Asp phosphorelay systems. One of these systems appears to be the master regulatory system that activates transcription of the majority of nitrogen-fixation genes and represses a gene encoding glutamate dehydrogenase during nitrogen fixation. The other system whose expression is directly activated by the master regulatory system appears to control by antitermination the expression of a subset of the nitrogen-fixation genes whose transcription is activated by the master regulatory system and whose promoter contains transcription termination signals. This study provides a new paradigm for nitrogen-fixation gene regulation.

  19. Novel regulatory cascades controlling expression of nitrogen-fixation genes in Geobacter sulfurreducens

    PubMed Central

    Ueki, Toshiyuki; Lovley, Derek R.

    2010-01-01

    Geobacter species often play an important role in bioremediation of environments contaminated with metals or organics and show promise for harvesting electricity from waste organic matter in microbial fuel cells. The ability of Geobacter species to fix atmospheric nitrogen is an important metabolic feature for these applications. We identified novel regulatory cascades controlling nitrogen-fixation gene expression in Geobacter sulfurreducens. Unlike the regulatory mechanisms known in other nitrogen-fixing microorganisms, nitrogen-fixation gene regulation in G. sulfurreducens is controlled by two two-component His–Asp phosphorelay systems. One of these systems appears to be the master regulatory system that activates transcription of the majority of nitrogen-fixation genes and represses a gene encoding glutamate dehydrogenase during nitrogen fixation. The other system whose expression is directly activated by the master regulatory system appears to control by antitermination the expression of a subset of the nitrogen-fixation genes whose transcription is activated by the master regulatory system and whose promoter contains transcription termination signals. This study provides a new paradigm for nitrogen-fixation gene regulation. PMID:20660485

  20. Can we trust current estimates for biological nitrogen fixation?

    NASA Astrophysics Data System (ADS)

    Bellenger, Jean-Philippe; Kraepiel, Anne

    2016-04-01

    Biological nitrogen fixation (BNF) consists on the reduction of atmospheric dinitrogen (N2) into bioavailable ammonium. This reaction accounts for up to 97% of nitrogen (N) input in unmanaged terrestrial ecosystems. Closing the N budget is a long standing challenge in many ecosystems. Recent studies have highlighted that current methods used to assess BNF are affected by critical biases. These findings challenge our confidence in many N budgets and call for a profound reconsideration of our methodological approaches. Beside these methodological issues, our ability to properly assess BNF might be further altered as a result of a misconception regarding the importance of BNF enzymatic diversity in nature. BNF is catalyzed by the enzyme nitrogenase (Nase) for which three isoforms have been identified so far; the molybdenum (Mo), vanadium (V) and iron-only (Fe) isoforms. Currently BNF is mostly considered to primarily depend on the Mo isoform. The contribution of the alternative Nases (V and Fe isoforms) to BNF in natural habitats has been mostly overlooked. However, recent findings have challenged this traditional view of the Nases hierarchy (Mo isoform predominance) with deep implications for BNF assessment in the field. Here, I will present an overview of recent findings, provided by various research groups, challenging current methods used to assess BNF. I will also present a summary of recent studies highlighting the importance of alternative Nases in nature. I will finally illustrate how altering our view on the Mo-Nase predominance can deeply affect our confidence in current BNF estimates. I will conclude by presenting new methodological approaches that will contribute to significantly improve our ability to understand and estimate BNF in the field by improving our capacity to access BNF spatio-temporal variability and enzymatic diversity.

  1. Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh

    PubMed Central

    Huang, Jingxin; Xu, Xiao; Wang, Min; Nie, Ming; Qiu, Shiyun; Wang, Qing; Quan, Zhexue; Xiao, Ming; Li, Bo

    2016-01-01

    Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. alterniflora community had a higher soil N-fixation rate but a lower diversity of the nifH gene in comparison with the native community. The S. alterniflora community with N addition had the highest soil N-fixation rate and the nifH gene abundance across all treatments. Our results suggest that S. alterniflora invasion can increase soil N fixation in the high N-loading estuarine ecosystem, and thus may further mediate soil N availability. PMID:26869197

  2. Responses of soil nitrogen fixation to Spartina alterniflora invasion and nitrogen addition in a Chinese salt marsh.

    PubMed

    Huang, Jingxin; Xu, Xiao; Wang, Min; Nie, Ming; Qiu, Shiyun; Wang, Qing; Quan, Zhexue; Xiao, Ming; Li, Bo

    2016-02-12

    Biological nitrogen fixation (BNF) is the major natural process of nitrogen (N) input to ecosystems. To understand how plant invasion and N enrichment affect BNF, we compared soil N-fixation rates and N-fixing microbes (NFM) of an invasive Spartina alterniflora community and a native Phragmites australis community in the Yangtze River estuary, with and without N addition. Our results indicated that plant invasion relative to N enrichment had a greater influence on BNF. At each N level, the S. alterniflora community had a higher soil N-fixation rate but a lower diversity of the nifH gene in comparison with the native community. The S. alterniflora community with N addition had the highest soil N-fixation rate and the nifH gene abundance across all treatments. Our results suggest that S. alterniflora invasion can increase soil N fixation in the high N-loading estuarine ecosystem, and thus may further mediate soil N availability.

  3. Nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Nagata, T.; Ijichi, M.; Furuya, K.

    2015-08-01

    Nitrogen fixation in temperate oceans is a potentially important, but poorly understood process that may influence the marine nitrogen budget. This study determined seasonal variations in nitrogen fixation and the diazotroph community within the euphotic zone in the temperate coastal region of the northwestern North Pacific. Nitrogen fixation as high as 13.6 nmol N L-1 d-1 was measured from early summer to fall when the surface temperature exceeded 14.2 °C (but was lower than 24.3 °C) and the surface nitrate concentration was low (≤ 0.30 μM), although we also detected nitrogen fixation in subsurface layers (42-62 m) where nitrate concentrations were high (> 1 μM). Clone library analysis results indicated that nifH gene sequences were omnipresent throughout the investigation period. During the period when nitrogen fixation was detected (early summer to fall), the genes affiliated with UCYN-A, Trichodesmium, and γ-proteobacterial phylotype γ-24774A11 were frequently recovered. In contrast, when nitrogen fixation was undetectable (winter to spring), many sequences affiliated with Cluster III diazotrophs (putative anaerobic bacteria) were recovered. Quantitative PCR analysis revealed that UCYN-A was relatively abundant from early to late summer compared with Trichodesmium and γ-24774A11, whereas Trichodesmium abundance was the highest among the three groups during fall.

  4. Rhizobium japonicum mutants defective in symbiotic nitrogen fixation.

    PubMed Central

    Noel, K D; Stacey, G; Tandon, S R; Silver, L E; Brill, W J

    1982-01-01

    Rhizobium japonicum strains 3I1b110 and 61A76 were mutagenized to obtain 25 independently derived mutants that produced soybean nodules defective in nitrogen fixation, as assayed by acetylene reduction. The proteins of both the bacterial and the plant portions of the nodules were analyzed by two-dimensional polyacrylamide gel electrophoresis. All of the mutants had lower-than-normal levels of the nitrogenase components, and all but four contained a prominent bacteroid protein not observed in wild-type bacteroids. Experiments with bacteria grown ex planta suggested that this protein was derepressed by the absence of ammonia. Nitrogenase component II of one mutant was altered in isoelectric point. The soluble plant fraction of the nodules of seven mutants had very low levels of heme, yet the nodules of five of these seven mutants contained the polypeptide of leghemoglobin. Thus, the synthesis of the globin may not be coupled to the content of available heme in soybean nodules. The nodules of the other two of these seven mutants lacked not only leghemoglobin but most of the other normal plant and bacteroid proteins. Ultrastructural examination of nodules formed by these two mutants indicated normal ramification of infection threads but suggested a problem in subsequent survival of the bacteria and their release from the infection threads. Images PMID:6956566

  5. Seasonal patterns of climate controls over nitrogen fixation by Alnus viridis subsp

    Treesearch

    Jennifer S. Mitchell; Roger W. Ruess

    2009-01-01

    Patterns of and controls over N2 fixation by green alder were studied in post-fire, mid-succession, and white spruce upland forests in interior Alaska, focusing on the hypothesis that ecosystem-level nitrogen (N) inputs decrease with successional development. N2-fixation rates tracked plant phenology during the 1997 (...

  6. Effects of drought on characters related to nitrogen fixation in peanut

    USDA-ARS?s Scientific Manuscript database

    Twelve peanut genotypes were tested under three water regimes in two greenhouses to investigate the effects of drought on biomass production and N2 fixation. Drought reduced biomass production from 36.5 to 56.0% and reduced nitrogen fixation from 26.8 to 68.8%. Most genotypes with high biomass produ...

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

    PubMed

    Wurzburger, Nina; Bellenger, Jean Philippe; Kraepiel, Anne M L; Hedin, Lars O

    2012-01-01

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

  8. Nitrogen Fixation Control under Drought Stress. Localized or Systemic?1[OA

    PubMed Central

    Marino, Daniel; Frendo, Pierre; Ladrera, Ruben; Zabalza, Ana; Puppo, Alain; Arrese-Igor, Cesar; González, Esther M.

    2007-01-01

    Legume-Rhizobium nitrogen fixation is dramatically affected under drought and other environmental constraints. However, it has yet to be established as to whether such regulation of nitrogen fixation is only exerted at the whole-plant level (e.g. by a systemic nitrogen feedback mechanism) or can also occur at a local nodule level. To address this question, nodulated pea (Pisum sativum) plants were grown in a split-root system, which allowed for half of the root system to be irrigated at field capacity, while the other half was water deprived, thus provoking changes in the nodule water potential. Nitrogen fixation only declined in the water-deprived, half-root system and this result was correlated with modifications in the activities of key nodule's enzymes such as sucrose synthase and isocitrate dehydrogenase and in nodular malate content. Furthermore, the decline in nodule water potential resulted in a cell redox imbalance. The results also indicate that systemic nitrogen feedback signaling was not operating in these water-stressed plants, since nitrogen fixation activity was maintained at control values in the watered half of the split-root plants. Thus, the use of a partially droughted split-root system provides evidence that nitrogen fixation activity under drought stress is mainly controlled at the local level rather than by a systemic nitrogen signal. PMID:17416644

  9. Probing the evolution of biological nitrogen fixation by examining phylogenetic relationships of nitrogen fixation genes related by gene duplication

    NASA Astrophysics Data System (ADS)

    Peters, J.; Boyd, E. S.; Hamilton, T.

    2011-12-01

    Mounting evidence indicates the presence of a near complete biological nitrogen cycle in redox stratified oceans during the late Archean to early Proterozoic (~2.5 to 2.0 Ga). It has been suggested that the iron (Fe)-only or vanadium (V)-dependent alternative forms of nitrogenase rather than molybdenum (Mo)-dependent form was responsible for dinitrogen (N2) fixation during this time because oceans were depleted in Mo and rich in Fe. However, the only extant nitrogen fixing organisms that harbor alternative nitrogenases also harbor a Mo-dependent nitrogenase. Furthermore, our recent global gene expression analysis revealed that the alternative enzymes rely on genes encoding biosynthetic machinery to assemble active enzymes that are associated with the Mo-dependent nitrogenase. In our recent work we conducted an in-depth phylogenetic analysis of the proteins required for molybdenum (Mo)-nitrogenase that arose from gene fusion and duplication, expanding on previous analyses of single gene loci and multiple gene loci. The results of this analysis are highly suggestive that Mo-nitrogenase is unlikely to have been associated with the last universal common ancestor (LUCA). Rather, the oldest extant organisms harboring Mo-nitrogenase can be traced to hydrogenotrophic methanogens with acquisition in the bacterial domain via lateral gene transfer involving an anaerobic member of the Firmicutes. An origin and ensuing proliferation of Mo-nitrogenase under anoxic conditions would likely have occurred in an environment where anaerobic methanogens and Firmicutes coexisted and where Mo was at least episodically available, such as in a redox stratified Proterozoic ocean basin. In more recent work we have examined the hypothesis that the alternative forms predate the Mo-dependent nitrogenase by examining the phylogenetic relationships of the genetically distinct structural proteins of the Fe-only, V-, and Mo-nitrogenase that are required for activity. As a result, a clear and

  10. Respiration , nitrogen fixation, and mineralizable nitrogen spatial and temporal patterns within two Oregon Douglas-fir stands.

    Treesearch

    Sharon M. Hope; Ching-Yan. Li

    1997-01-01

    Substrate respiration, mineralizable nitrogen, and nitrogen fixation rates, substrate moisture,content, and temperature were measured in trenched and undisturbed plots within two western Oregon Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands. The stands represent two different environments and ages. Woods Creek, the site of the lower...

  11. EFFECT OF NITROGEN AND METAL ADDITIONS ON NITROGEN FIXATION ACTIVITY IN BIOLOGICAL SOIL CRUSTS

    NASA Astrophysics Data System (ADS)

    Alexander, K.; Lui, D.; Anbar, A. D.; Garcia-Pichel, F.; Hartnett, H. E.

    2009-12-01

    Biological soil crusts (BSCs) are diverse consortia of microorganisms that live in intimate association with soils in arid environments. Also called cryptogamic or microbiotic crusts, these communities can include cyanobacteria, algae, heterotrophic bacteria, fungi, lichens, and mosses. Together, these organisms provide many services to their surrounding ecosystems, including reduction of water runoff, promotion of water infiltration, and prevention of soil erosion. The cyanobacteria and algae also provide fixed carbon (C) to the soil through photosynthesis, and because atmospheric deposition of nitrogen (N) in arid environments is low, the major input of biologically available N comes from cyanobacteria capable of converting nitrogen gas (N2) to ammonium (NH4+). Biological soil crusts are easily destroyed by livestock grazing, motor vehicle travel, and many forms of recreational and agricultural land use. Loss of BSC cover can leave the soil vulnerable to intense erosion that can remove the nutrients necessary to sustain plant and animal life, thus accelerating the process of desertification. In order to preserve existing crusts and encourage the development of new crusts, it is crucial to understand the nutrient requirements of metabolism and growth in these microbial communities. This study investigated the affect of nitrogen and metal additions on N2-fixation activity in cyanobacterially-dominated crusts from the Colorado Plateau near Moab, Utah. Although N2-fixation has been studied in this system before, the affect of nutrient additions on N2-fixation activity has not been documented. The goal of this work was to understand how N and metal supplementation affects crust N metabolism. Three experiments were conducted to observe how N2-fixation activity changed with the addition of N, molybdenum (Mo), and vanadium (V). Molybdenum and vanadium were chosen because they are most commonly found at the active site of the enzyme nitrogenase, the molecule responsible

  12. Low rates of nitrogen fixation in eastern tropical South Pacific surface waters

    PubMed Central

    Knapp, Angela N.; Casciotti, Karen L.; Berelson, William M.; Prokopenko, Maria G.; Capone, Douglas G.

    2016-01-01

    An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2 fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2 fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2 fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m−2 d−1 based on sediment trap fluxes. Whereas the fractional importance of N2 fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2 fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m−2 d−1, and detected N2 fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2 fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2 fixation in the ETSP. PMID:26976587

  13. Low rates of nitrogen fixation in eastern tropical South Pacific surface waters.

    PubMed

    Knapp, Angela N; Casciotti, Karen L; Berelson, William M; Prokopenko, Maria G; Capone, Douglas G

    2016-04-19

    An extensive region of the Eastern Tropical South Pacific (ETSP) Ocean has surface waters that are nitrate-poor yet phosphate-rich. It has been proposed that this distribution of surface nutrients provides a geochemical niche favorable for N2fixation, the primary source of nitrogen to the ocean. Here, we present results from two cruises to the ETSP where rates of N2fixation and its contribution to export production were determined with a suite of geochemical and biological measurements. N2fixation was only detectable using nitrogen isotopic mass balances at two of six stations, and rates ranged from 0 to 23 µmol N m(-2)d(-1)based on sediment trap fluxes. Whereas the fractional importance of N2fixation did not change, the N2-fixation rates at these two stations were several-fold higher when scaled to other productivity metrics. Regardless of the choice of productivity metric these N2-fixation rates are low compared with other oligotrophic locations, and the nitrogen isotope budgets indicate that N2fixation supports no more than 20% of export production regionally. Although euphotic zone-integrated short-term N2-fixation rates were higher, up to 100 µmol N m(-2)d(-1), and detected N2fixation at all six stations, studies of nitrogenase gene abundance and expression from the same cruises align with the geochemical data and together indicate that N2fixation is a minor source of new nitrogen to surface waters of the ETSP. This finding is consistent with the hypothesis that, despite a relative abundance of phosphate, iron may limit N2fixation in the ETSP.

  14. Nitrogen isotope simulations show the importance of atmospheric iron deposition for nitrogen fixation across the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Somes, Christopher J.; Schmittner, Andreas; Altabet, Mark A.

    2010-12-01

    Nitrogen (N) fixation by specialized microorganisms (diazotrophs) influences global plankton productivity because it provides the ocean with most of its bio-available N. However, its global rate and large-scale spatial distribution is still regarded with considerable uncertainty. Here we use a global ocean nitrogen isotope model, in comparison with δ15NO3- observations, to constrain the pattern of N2 fixation across the Pacific Ocean. N2 fixation introduces isotopically light atmospheric N2 from to the ocean (δ15N = 0‰) relative to the oceanic average near 5‰, which makes nitrogen isotopes suitable to infer patterns of N2 fixation. Including atmospheric iron limitation of diazotrophy in the model shifts the pattern of simulated N2 fixation from the South Pacific to the North Pacific and from the East Pacific westward. These changes considerably improve the agreement with meridional transects of available δ15NO3- observations, as well as excess P (PO43- - NO3-/16), suggesting that atmospheric iron deposition is indeed important for N fixation in the Pacific Ocean. This study highlights the potential for using δ15N observations and model simulations to constrain patterns and rates of N fixation in the ocean.

  15. Towards understanding the effects of crop production practices on soil nitrogen fixation and denitrification

    NASA Astrophysics Data System (ADS)

    Pereg, Lily; McMillan, Mary; Renz, Katrin

    2014-05-01

    Soil productivity can be highly influenced by the composition and activity of its microbial communities. Certain crop production practices suppress microbial processes, e.g. nitrogen fixation is suppressed due to excessive application of chemical supplements of N (ammonium, nitrate), whereas removal of nitrogen by denitrification may be enhanced by such conditions. We optimise and use PCR-based techniques to analyse the soil potential for nitrogen fixation and denitrification and seek ways to enhance microbial nitrogen fixation by managing the amount and form of N applied to the soil. These techniques are being optimised for Australian cotton production soils and will also be useful for determining the effects of different crop production strategies on microbial nitrogen cycling in such soils.

  16. Refactoring the nitrogen fixation gene cluster from Klebsiella oxytoca.

    PubMed

    Temme, Karsten; Zhao, Dehua; Voigt, Christopher A

    2012-05-01

    Bacterial genes associated with a single trait are often grouped in a contiguous unit of the genome known as a gene cluster. It is difficult to genetically manipulate many gene clusters because of complex, redundant, and integrated host regulation. We have developed a systematic approach to completely specify the genetics of a gene cluster by rebuilding it from the bottom up using only synthetic, well-characterized parts. This process removes all native regulation, including that which is undiscovered. First, all noncoding DNA, regulatory proteins, and nonessential genes are removed. The codons of essential genes are changed to create a DNA sequence as divergent as possible from the wild-type (WT) gene. Recoded genes are computationally scanned to eliminate internal regulation. They are organized into operons and placed under the control of synthetic parts (promoters, ribosome binding sites, and terminators) that are functionally separated by spacer parts. Finally, a controller consisting of genetic sensors and circuits regulates the conditions and dynamics of gene expression. We applied this approach to an agriculturally relevant gene cluster from Klebsiella oxytoca encoding the nitrogen fixation pathway for converting atmospheric N(2) to ammonia. The native gene cluster consists of 20 genes in seven operons and is encoded in 23.5 kb of DNA. We constructed a "refactored" gene cluster that shares little DNA sequence identity with WT and for which the function of every genetic part is defined. This work demonstrates the potential for synthetic biology tools to rewrite the genetics encoding complex biological functions to facilitate access, engineering, and transferability.

  17. Genetic regulation of nitrogen fixation in Rhizobium meliloti.

    PubMed

    Cebolla, A; Palomares, A J

    1994-12-01

    The soil bacterium Rhizobium meliloti fixes dinitrogen when associated with root nodules formed on its plant host, Medicago sativa (alfalfa). The expression of most of the known genes required for nitrogen fixation (nif and fix genes), including the structural genes for nitrogenase, is induced in response to a decrease in oxygen concentration. Induction of nif and fix gene expression by low oxygen is physiologically relevant because a low-oxygen environment is maintained in root nodules to prevent inactivation of the highly oxygen-sensitive nitrogenase enzyme. The genes responsible for sensing and transducing the low oxygen signal, fixL and fixJ, encode proteins (FixL and FixJ, respectively) that are homologous to a large family of bacterial proteins involved in signal transduction, the two component regulatory system proteins. The two components consist of a sensor protein, to which FixL is homologous, and a response regulator protein, to which FixJ is homologous. The sensor protein respond to an activating signal by autophosphorylating and then transferring the phosphate to its cognate response regulator protein. The phosphorylated response regulator, which is often a transcriptional activator, is then able to activate its target. A cascade model of nif and fix gene regulation in R. meliloti has been proposed, whereby FixL acts as an oxygen sensor as the initial event in the cascade and transmits this information to FixJ. FixJ, which possesses a putative helix-turn-helix DNA-binding motif, then activates transcription of the nifA and fixK genes. The nifA and fixK gene products, are transcriptional activators of at least 14 other nif and fix genes.

  18. Stimulation of nitrogen fixation in soddy-podzolic soils with fungi

    NASA Astrophysics Data System (ADS)

    Kurakov, A. V.; Prokhorov, I. S.; Kostina, N. V.; Makhova, E. G.; Sadykova, V. S.

    2006-09-01

    Stimulation of nitrogen fixation in soddy-podzolic soils is related to the hydrolytic activity of fungi decomposing plant polymers. It was found that the rate of nitrogen fixation upon the simultaneous inoculation of the strains of nitrogen-fixing bacteria Bacillus cereus var. mycoides and the cellulolytic fungus Trichoderma asperellum into a sterile soil enriched with cellulose or Jerusalem artichoke residues is two to four times higher than upon the inoculation of the strains of Bacillus cereus var. mycoides L1 only. The increase in the nitrogen fixation depended on the resistance of the substrates added into the soil to fungal hydrolysis. The biomass of the fungi decomposing plant polymers increased by two-four times. The nitrogen-fixing activity of the soil decreased when the growth of the fungi was inhibited with cycloheximide, which attested to a close correlation between the intensity of the nitrogen fixation and the decomposition of the plant polymers by fungi. The introduction of an antifungal antibiotic, together with starch or with plant residues, significantly (by 60-90%) decreased the rate of nitrogen fixation in the soll.

  19. Hydrologic Control on Bacterial Nitrogen Fixation in the Holocene Black Sea

    NASA Astrophysics Data System (ADS)

    Fulton, J. M.; Arthur, M. A.; Freeman, K. H.

    2008-12-01

    Stratified oceans of the Phanerozoic Oceanic Anoxic Events apparently were dominated by bacterial nitrogen fixation. Decreased marine N:P nutrient ratios resulting from increased denitrification and decreased phosphate burial efficiency under anoxic waters drove this nutrient regime. This model is upheld by the presence of cyanobacterial hopanoid biomarkers in sedimentary records and δ15N values indicative of nitrogen fixation. However, in the largest modern redox-stratified marine basin, the Black Sea, bacterial nitrogen fixation seems to be only a minor contributor to the nitrogen cycle. In this study, we use geochemical proxies to evaluate the role of bacterial nitrogen fixation during the deposition of the Holocene Black Sea sapropel, starting 7.8 ka. We report compound-specific nitrogen and carbon stable isotope values of pyropheophytin a, a chlorophyll degradation product, and bacteriochlorophyll e produced by green sulfur bacteria. We also present the surprising finding of scytonemin, a pigment produced only by filamentous cyanobacteria exposed to ultraviolet radiation, in certain intervals in these sediments. In the Holocene, nitrogen fixation in the Black Sea is most prominent during times of reduced river water influx. This directly decreases the external flux of nitrate into the surface waters. Reduced freshwater influx also decreases the volume of low salinity water dispersed around the sea by the Rim Current, allowing the chemocline to shoal along the margins. Previous geochemical studies have described this changing chemocline geometry. The exposure of shallow water sediments to anoxic waters further stimulates nitrogen fixation by releasing more phosphorus to the system. Nitrogen fixation is recorded in the sediments as bulk and compound-specific pyropheophytin a δ15N values near 0 ‰ and -5 ‰, respectively. We have also detected scytonemin in two intervals characterized by especially low δ15N values. This compound suggests abundant filamentous

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

    USDA-ARS?s Scientific Manuscript database

    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 ...

  1. Regional and national significance of biological nitrogen fixation by crops in the United States

    EPA Science Inventory

    Background/Questions/Methods Biological nitrogen fixation by crops (C-BNF) represents one of the largest anthropogenic inputs of reactive nitrogen (N) to land surfaces around the world. In the United States (US), existing estimates of C-BNF are uncertain because of incomplete o...

  2. Nitrogen fixation by microbial cultures with sodium salt of organic acids as carbon source.

    PubMed

    Bahadur, K; Tripathi, P

    1976-01-01

    The best source of carbon, when used as the sodium salt of organic acids, is sodium salicylate which shows highest nitrogen fixation and also appreciably large amounts of nitrogen fixed per g carbon consumed. Next in order is sodium benzoate, then oxalate. Sodium citrate is followed by sowium acetate in the order of decreasing efficiency.

  3. Regional and national significance of biological nitrogen fixation by crops in the United States

    EPA Science Inventory

    Background/Questions/Methods Biological nitrogen fixation by crops (C-BNF) represents one of the largest anthropogenic inputs of reactive nitrogen (N) to land surfaces around the world. In the United States (US), existing estimates of C-BNF are uncertain because of incomplete o...

  4. 15N discrimination and the sensitivity of nitrogen fixation to changes in dietary nitrogen in Reticulitermes flavipes (Isoptera: Rhinotermitidae).

    PubMed

    Meuti, Megan E; Jones, Susan C; Curtis, Peter S

    2010-12-01

    Xylophagous termites possess symbiotic bacteria that fix atmospheric nitrogen (N(2)). Although symbiotic N(2) fixation is central to termite nutrition and ecologically important, it is energetically costly. Using stable isotopes, we tested the hypothesis that symbiotic N(2) fixation would decrease in workers of the eastern subterranean termite, Reticulitermes flavipes Kollar, which were exposed to high nitrogen diets. To calculate the isotope discrimination factor occurring as a result of digestion, Δ(dig), and which occurs as the result of N(2) fixation, Δ(fix), symbiotic N(2) fixation was inhibited via force feeding termites the antibiotic kanamycin. Antibiotic-treated termites and control (N(2)-fixing) termites were exposed to different concentrations of dietary N (0, 0.21, and 0.94% N), their (15)N signatures were obtained, and the percent nitrogen derived from the atmosphere within termite samples was calculated. As we hypothesized, symbiotic N(2) fixation rates were negatively correlated with dietary N, suggesting that high concentrations of dietary N suppressed symbiotic N(2) fixation in R. flavipes. A comparison of the (15)N isotope signatures of antibiotic-treated termites with their food sources demonstrated that Δ(dig) = 2.284‰, and a comparison of the (15)N isotope signatures of antibiotic-treated termites with control termites indicated that Δ(fix) = -1.238‰. These are the first estimates of Δ(dig) for R. flavipes, and the first estimate of Δ(fix) for any N(2)-fixing termite species.

  5. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    PubMed Central

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-01-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C−C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion. PMID:23877200

  6. Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion

    NASA Astrophysics Data System (ADS)

    Jeon, In-Yup; Choi, Hyun-Jung; Ju, Myung Jong; Choi, In Taek; Lim, Kimin; Ko, Jaejung; Kim, Hwan Kyu; Kim, Jae Cheon; Lee, Jae-Joon; Shin, Dongbin; Jung, Sun-Min; Seo, Jeong-Min; Kim, Min-Jung; Park, Noejung; Dai, Liming; Baek, Jong-Beom

    2013-07-01

    Nitrogen fixation is essential for the synthesis of many important chemicals (e.g., fertilizers, explosives) and basic building blocks for all forms of life (e.g., nucleotides for DNA and RNA, amino acids for proteins). However, direct nitrogen fixation is challenging as nitrogen (N2) does not easily react with other chemicals. By dry ball-milling graphite with N2, we have discovered a simple, but versatile, scalable and eco-friendly, approach to direct fixation of N2 at the edges of graphene nanoplatelets (GnPs). The mechanochemical cracking of graphitic C-C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs) with superb catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional Pt-based catalysts for energy conversion.

  7. The Role of Symbiotic Nitrogen Fixation in Sustainable Production of Biofuels

    PubMed Central

    Biswas, Bandana; Gresshoff, Peter M.

    2014-01-01

    With the ever-increasing population of the world (expected to reach 9.6 billion by 2050), and altered life style, comes an increased demand for food, fuel and fiber. However, scarcity of land, water and energy accompanied by climate change means that to produce enough to meet the demands is getting increasingly challenging. Today we must use every avenue from science and technology available to address these challenges. The natural process of symbiotic nitrogen fixation, whereby plants such as legumes fix atmospheric nitrogen gas to ammonia, usable by plants can have a substantial impact as it is found in nature, has low environmental and economic costs and is broadly established. Here we look at the importance of symbiotic nitrogen fixation in the production of biofuel feedstocks; how this process can address major challenges, how improving nitrogen fixation is essential, and what we can do about it. PMID:24786096

  8. Symbiotic nitrogen fixation in the fungus gardens of leaf-cutter ants.

    PubMed

    Pinto-Tomás, Adrián A; Anderson, Mark A; Suen, Garret; Stevenson, David M; Chu, Fiona S T; Cleland, W Wallace; Weimer, Paul J; Currie, Cameron R

    2009-11-20

    Bacteria-mediated acquisition of atmospheric N2 serves as a critical source of nitrogen in terrestrial ecosystems. Here we reveal that symbiotic nitrogen fixation facilitates the cultivation of specialized fungal crops by leaf-cutter ants. By using acetylene reduction and stable isotope experiments, we demonstrated that N2 fixation occurred in the fungus gardens of eight leaf-cutter ant species and, further, that this fixed nitrogen was incorporated into ant biomass. Symbiotic N2-fixing bacteria were consistently isolated from the fungus gardens of 80 leaf-cutter ant colonies collected in Argentina, Costa Rica, and Panama. The discovery of N2 fixation within the leaf-cutter ant-microbe symbiosis reveals a previously unrecognized nitrogen source in neotropical ecosystems.

  9. Climatic controls of moss-associated nitrogen fixation in the Subarctic

    NASA Astrophysics Data System (ADS)

    Rousk, Kathrin; Michelsen, Anders

    2017-04-01

    Nitrogen (N2) fixation performed by moss-associated cyanobacteria is one of the main sources of new N input in pristine, high latitude ecosystems like boreal forests and subarctic tundra. However, N2 fixation in mosses is strongly influenced by climatic conditions, in particular, moisture and temperature. Previous attempts to temporally scaling up N2 fixation in mosses from low frequency in situ measurements to several weeks, months or even the entire growing season without taking into account changes in abiotic conditions could not capture the variation in moss-associated N2 fixation. We therefore aimed to estimate moss-associated N2 fixation throughout the snow-free period in subarctic tundra in field experiments simulating climate change: willow (Salix myrsinifolia) and birch (Betula pubescens spp. tortuosa) litter addition, and warming. The litter additions were sought to simulate shrub expansion in high latitude ecosystems. We established relationships between measured in situ N2 fixation rates and soil moisture and soil temperature and used high-resolution measurements of soil moisture and soil temperature (hourly from May - October) to model N2 fixation. The modelled N2 fixation rates were highest in the warmed (2.8 ±0.3 kg N ha-1) and birch litter addition plots (2.8 ±0.2 kg N ha-1), and lowest in the plots receiving willow litter (1.6 ±0.2 kg N ha-1). The control plots had intermediate rates (2.2 ±0.2 kg N ha-1). Our findings suggest that a longer snow-free period and increased temperatures in a future climate will likely lead to higher N2 fixation rates in mosses. Yet, the consequences of increased litter fall on moss-associated N2 fixation due to shrub expansion in the Arctic will depend on the shrub species' litter traits. To follow up on the strong dependence of moss-associated N2 fixation on moisture and temperature, we collected mosses along a precipitation gradient in subarctic tundra, Northern Sweden and exposed the mosses to different

  10. Molecular evidence for sediment nitrogen fixation in a temperate New England estuary.

    PubMed

    Newell, Silvia E; Pritchard, Kaitlyn R; Foster, Sarah Q; Fulweiler, Robinson W

    2016-01-01

    Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at three sites in a temperate New England estuary (Waquoit Bay, Massachusetts, USA) and compared our results to net sediment N2 fluxes previously measured at these sites. We observed nifH expression at all sites, including a site heavily impacted by anthropogenic N. At this N impacted site, we also observed mean net sediment N2-fixation, linking the geochemical rate measurement with nifH expression. This same site also had the lowest diversity (non-parametric Shannon = 2.75). At the two other sites, we also detected nifH transcripts, however, the mean N2 flux indicated net denitrification. These results suggest that N2-fixation and denitrification co-occur in these sediments. Of the unique sequences in this study, 67% were most closely related to uncultured bacteria from various marine environments, 17% to Cluster III, 15% to Cluster I, and only 1% to Cluster II. These data add to the growing body of literature that sediment heterotrophic N2-fixation, even under high inorganic nitrogen concentrations, may be an important yet overlooked source of N in coastal systems.

  11. Molecular evidence for sediment nitrogen fixation in a temperate New England estuary

    PubMed Central

    Newell, Silvia E.; Pritchard, Kaitlyn R.; Foster, Sarah Q.

    2016-01-01

    Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at three sites in a temperate New England estuary (Waquoit Bay, Massachusetts, USA) and compared our results to net sediment N2 fluxes previously measured at these sites. We observed nifH expression at all sites, including a site heavily impacted by anthropogenic N. At this N impacted site, we also observed mean net sediment N2-fixation, linking the geochemical rate measurement with nifH expression. This same site also had the lowest diversity (non-parametric Shannon = 2.75). At the two other sites, we also detected nifH transcripts, however, the mean N2 flux indicated net denitrification. These results suggest that N2-fixation and denitrification co-occur in these sediments. Of the unique sequences in this study, 67% were most closely related to uncultured bacteria from various marine environments, 17% to Cluster III, 15% to Cluster I, and only 1% to Cluster II. These data add to the growing body of literature that sediment heterotrophic N2-fixation, even under high inorganic nitrogen concentrations, may be an important yet overlooked source of N in coastal systems. PMID:26977375

  12. Nitrogen Fixation and Molecular Oxygen: Comparative Genomic Reconstruction of Transcription Regulation in Alphaproteobacteria

    PubMed Central

    Tsoy, Olga V.; Ravcheev, Dmitry A.; Čuklina, Jelena; Gelfand, Mikhail S.

    2016-01-01

    Biological nitrogen fixation plays a crucial role in the nitrogen cycle. An ability to fix atmospheric nitrogen, reducing it to ammonium, was described for multiple species of Bacteria and Archaea. The transcriptional regulatory network for nitrogen fixation was extensively studied in several representatives of the class Alphaproteobacteria. This regulatory network includes the activator of nitrogen fixation NifA, working in tandem with the alternative sigma-factor RpoN as well as oxygen-responsive regulatory systems, one-component regulators FnrN/FixK and two-component system FixLJ. Here we used a comparative genomics approach for in silico study of the transcriptional regulatory network in 50 genomes of Alphaproteobacteria. We extended the known regulons and proposed the scenario for the evolution of the nitrogen fixation transcriptional network. The reconstructed network substantially expands the existing knowledge of transcriptional regulation in nitrogen-fixing microorganisms and can be used for genetic experiments, metabolic reconstruction, and evolutionary analysis. PMID:27617010

  13. Simultaneous measurement of denitrification and nitrogen fixation using isotope pairing with membrane inlet mass spectrometry analysis.

    PubMed

    An, S; Gardner, W S; Kana, T

    2001-03-01

    A method for estimating denitrification and nitrogen fixation simultaneously in coastal sediments was developed. An isotope-pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N(2) gas species ((28)N(2), (29)N(2), and (30)N(2)) were monitored during incubation experiments after the addition of (15)NO(3)(-). Formulas were developed to estimate the production (denitrification) and consumption (N(2) fixation) of N(2) gas from the fluxes of the different isotopic forms of N(2). Proportions of the three isotopic forms produced from (15)NO(3)(-) and (14)NO(3)(-) agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Nitrogen fixation rates from an algal mat measured with intact sediment cores ranged from 32 to 390 microg-atoms of N m(-2) h(-1). They were enhanced by light and organic matter enrichment. In this environment of high nitrogen fixation, low N(2) production rates due to denitrification could be separated from high N(2) consumption rates due to nitrogen fixation. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas sea grass bed (Laguna Madre). Denitrification rates (average, 20 microg-atoms of N m(-2) h(-1)) were lower than nitrogen fixation rates (average, 60 microg-atoms of N m(-2) h(-1)). The developed method benefits from simple and accurate dissolved-gas measurement by the MIMS system. By adding the N(2) isotope capability, it was possible to do isotope-pairing experiments with the MIMS system.

  14. Simultaneous Measurement of Denitrification and Nitrogen Fixation Using Isotope Pairing with Membrane Inlet Mass Spectrometry Analysis†

    PubMed Central

    An, Soonmo; Gardner, Wayne S.; Kana, Todd

    2001-01-01

    A method for estimating denitrification and nitrogen fixation simultaneously in coastal sediments was developed. An isotope-pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N2 gas species (28N2, 29N2, and 30N2) were monitored during incubation experiments after the addition of 15NO3−. Formulas were developed to estimate the production (denitrification) and consumption (N2 fixation) of N2 gas from the fluxes of the different isotopic forms of N2. Proportions of the three isotopic forms produced from 15NO3− and 14NO3− agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Nitrogen fixation rates from an algal mat measured with intact sediment cores ranged from 32 to 390 μg-atoms of N m−2 h−1. They were enhanced by light and organic matter enrichment. In this environment of high nitrogen fixation, low N2 production rates due to denitrification could be separated from high N2 consumption rates due to nitrogen fixation. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas sea grass bed (Laguna Madre). Denitrification rates (average, 20 μg-atoms of N m−2 h−1) were lower than nitrogen fixation rates (average, 60 μg-atoms of N m−2 h−1). The developed method benefits from simple and accurate dissolved-gas measurement by the MIMS system. By adding the N2 isotope capability, it was possible to do isotope-pairing experiments with the MIMS system. PMID:11229907

  15. Potential for Nitrogen Fixation in the Fungus-Growing Termite Symbiosis

    PubMed Central

    Sapountzis, Panagiotis; de Verges, Jane; Rousk, Kathrin; Cilliers, Magdeleen; Vorster, Barend J.; Poulsen, Michael

    2016-01-01

    Termites host a gut microbiota of diverse and essential symbionts that enable specialization on dead plant material; an abundant, but nutritionally imbalanced food source. To supplement the severe shortage of dietary nitrogen (N), some termite species make use of diazotrophic bacteria to fix atmospheric nitrogen (N2). Fungus-growing termites (subfamily Macrotermitinae) host a fungal exosymbiont (genus Termitomyces) that provides digestive services and the main food source for the termites. This has been thought to obviate the need for N2-fixation by bacterial symbionts. Here, we challenge this notion by performing acetylene reduction assays of live colony material to show that N2 fixation is present in two major genera (Macrotermes and Odontotermes) of fungus-growing termites. We compare and discuss fixation rates in relation to those obtained from other termites, and suggest avenues of research that may lead to a better understanding of N2 fixation in fungus-growing and other termites. PMID:28018322

  16. Potential for Nitrogen Fixation in the Fungus-Growing Termite Symbiosis.

    PubMed

    Sapountzis, Panagiotis; de Verges, Jane; Rousk, Kathrin; Cilliers, Magdeleen; Vorster, Barend J; Poulsen, Michael

    2016-01-01

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

  17. Chemical Conversion of PON to Nitrous Oxide for Nitrogen Isotopic Analysis : High- Sensitivity Tracer Assay for Nitrogen Fixation

    NASA Astrophysics Data System (ADS)

    Tsunogai, U.; Kido, T.; Hirota, A.; Ohkubo, S.; Komatsu, D. D.; Nakagawa, F.

    2006-12-01

    We present a method for high-sensitivity nitrogen isotopic analysis of particulate organic nitrogen (PON) in seawater and freshwater, for the aim of measuring the rate of nitrogen fixation through 15N2 tracer technique for samples that contain low numeric abundance of organisms. The method composed of the traditional oxidation/reduction methods: such as oxidation of PON to nitrate using persulfate, the reduction of nitrate to nitrite using spongy cadmium, and further reduction of nitrite to nitrous oxide using sodium azide in an acetic acid buffer. Then, Nitrous oxide is purged from the water and trapped cryogenically with subsequent release into a gas chromatography column to analyze stable nitrogen isotopic compositions using a continuous-flow isotope ratio mass spectrometer. A standard deviation less than 0.3 ‰ for nitrogen was found for PON samples containing more than 80 nmolN, with a blank nitrogen of 20 nmolN. Nitrogen isotopic fractionation were consistent within each batch of analysis. Besides, we found that we can also determine nitrogen isotopic compositions of total dissolved nitrogen (TDN, sum of NO3-, NO2-, ammonium, and DON), by applying the method for filtrate samples. Our method may prove to obtain isotopic information for lower quantities of PON and TDN than other methods, so that we can reduce quantities of water samples needed for incubation to determine the nitrogen fixation rate in both seawater and freshwater. Besides, the method is also useful to determine the rate of nitrogen fixation by the small size fraction in ocean. We will also present the results obtained at western subtropical North Pacific to support our conclusions.

  18. Effect of insecticides and phenolics on nitrogen fixation by Nostoc linckia

    SciTech Connect

    Megharaj, M.; Venkateswarlu, K.; Rao, A.S.

    1988-08-01

    The nitrogen-fixing blue-green algae (cyanobacteria) significantly influence the nitrogen economy of temperate and tropical soils. Although the genera Nostoc and Tolypothrix have been particularly implicated in the fixation of significantly large amounts of atmospheric nitrogen, these diazotrophs received little attention in relation to insecticide treatment and the available few reports do not indicate a permanent deleterious effect of insecticides on their nitrogenase activity. As it has been well established that the effect of insecticides on nitrogen fixation by cyanobacteria is independent of that on growth, an attempt was, therefore, made to determine the influence of four insecticides (monocrotophos, quinalphos, cypermethrin and fenvalerate) and four phenolics (p-nitrophenol (PNP), m-nitrophenol (MNP), 2,4-dinitrophenol (DNP) and catechol) on nitrogen-fixing capacity of N.linckia, isolated from a black soil.

  19. Biotic nitrogen fixation in the bryosphere is inhibited more by drought than warming.

    PubMed

    Whiteley, Jonathan A; Gonzalez, Andrew

    2016-08-01

    The boreal forest is of particular interest to climate change research due to its large circumpolar distribution and accumulated soil carbon pool. Carbon uptake in this ecosystem is nitrogen (N)-limited, therefore factors affecting carbon or nitrogen dynamics in the boreal forest can have consequences for global climate. We used a 2-year field experiment to investigate the response of biotic nitrogen fixation by cyanobacteria associated with boreal forest bryophytes, in a factorial experiment combining simulated climate change with habitat fragmentation treatments. We simulated climate change conditions using open-top greenhouse chambers in the field, which increased mean and maximum temperatures, and created a precipitation gradient from ambient levels in the center to extreme drought conditions at the periphery of the chamber. The dry patches near the chamber walls exhibited almost no N-fixation, despite having similar densities of cyanobacteria (predominantly Stigonema sp.) as other patches. Rates of N-fixation were best explained by a model containing moisture, fragmentation, cyanobacteria density and time; warming was not a significant variable affecting N-fixation. There was no significant interaction between warming and fragmentation. These results suggest that cyanobacteria responded physiologically to drought by reducing N-fixation activity long before any changes in density. Ecosystem processes, such as N-fixation, can respond in the short term to environmental change much more rapidly than changes in the underlying community structure. Such rapid physiological responses may occur faster than demographic insurance effects of biodiversity.

  20. Enhancement of root growth and nitrogen fixation in Trigonella by UV-exclusion from solar radiation.

    PubMed

    Sharma, Sonika; Guruprasad, K N

    2012-12-01

    A field experiment was conducted to study the impact of solar UV on root growth and nitrogen fixation in Trigonella foenum-graecum. Plants were grown in iron mesh cages covered with polyester filters that could specifically cut off UV-B (280-315 nm) or UV-A + B (280-400 nm) part of the solar spectrum. The control plants were grown under a polythene filter transmissible to UV. Root biomass, number of nodules and nodule fresh weight were enhanced after exclusion of solar UV. Nitrogenase activity was significantly enhanced by 120% and 80% in the UV-B and UV-A + B excluded plants respectively. Along with nitrogenase there was concomitant increase in leghemoglobin and hemechrome content in the nodules after exclusion of solar UV. These components of sunlight limits nitrogen fixation and their elimination can enhance nitrogen fixation with agricultural advantages like reduction in the use of fertilizers. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

  1. Diel nitrogen fixation pattern of Trichodesmium: the interactive control of light and Ni

    PubMed Central

    Rodriguez, Irene B.; Ho, Tung-Yuan

    2014-01-01

    Trichodesmium, a nonheterocystous cyanobacterium widely abundant in the surface water of the tropical and subtropical ocean, fixes dinitrogen under high light conditions while concurrently undergoing photosynthesis. The new production considerably influences the cycling of nitrogen and carbon in the ocean. Here, we investigated how light intensity and nickel (Ni) availability interplay to control daily rates and diel patterns of N2 fixation in Trichodesmium. We found that increasing Ni concentration increased N2 fixation rates by up to 30-fold in the high light treatment. Cultures subjected to high Ni and light levels fixed nitrogen throughout most of the 24 H light:dark regime with the highest rate coinciding with the end of the 12 H light period. Our study demonstrates the importance of Ni on nitrogen fixation rates for Trichodesmium under high light conditions. PMID:24658259

  2. Diel nitrogen fixation pattern of Trichodesmium: the interactive control of light and Ni

    NASA Astrophysics Data System (ADS)

    Rodriguez, Irene B.; Ho, Tung-Yuan

    2014-03-01

    Trichodesmium, a nonheterocystous cyanobacterium widely abundant in the surface water of the tropical and subtropical ocean, fixes dinitrogen under high light conditions while concurrently undergoing photosynthesis. The new production considerably influences the cycling of nitrogen and carbon in the ocean. Here, we investigated how light intensity and nickel (Ni) availability interplay to control daily rates and diel patterns of N2 fixation in Trichodesmium. We found that increasing Ni concentration increased N2 fixation rates by up to 30-fold in the high light treatment. Cultures subjected to high Ni and light levels fixed nitrogen throughout most of the 24 H light:dark regime with the highest rate coinciding with the end of the 12 H light period. Our study demonstrates the importance of Ni on nitrogen fixation rates for Trichodesmium under high light conditions.

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

    SciTech Connect

    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.

  4. Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs.

    PubMed

    Karlson, Agnes M L; Duberg, Jon; Motwani, Nisha H; Hogfors, Hedvig; Klawonn, Isabell; Ploug, Helle; Barthel Svedén, Jennie; Garbaras, Andrius; Sundelin, Brita; Hajdu, Susanna; Larsson, Ulf; Elmgren, Ragnar; Gorokhova, Elena

    2015-06-01

    Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.

  5. Nitrogen limitation and nitrogen fixation during alkane biodegradation in a sandy soil.

    PubMed Central

    Toccalino, P L; Johnson, R L; Boone, D R

    1993-01-01

    We investigated nutrient limitations during hydrocarbon degradation in a sandy soil and found that fixed nitrogen was initially a limiting nutrient but that N limitation could sometimes be overcome by N2 fixation. Hydrocarbon biodegradation was examined in an unsaturated sandy soil incubated aerobically at 20 degrees C with propane or butane and various added nutrients. Propane and butane degradation proceeded similarly during the first 3 months of incubation. That is, bacteria in soil amended with N oxidized these hydrocarbons more rapidly than in controls without nutrient additions or in soil with added phosphate or trace minerals. Both propane- and butane-amended soil apparently became N limited after the initial available inorganic N was utilized, as indicated by a decrease in the rates of hydrocarbon degradation. After 3 months, propane and butane degradation proceeded differently. Bacteria in propane-degrading soil apparently remained N limited because propane degradation rates stayed low unless more N was added. In contrast, bacteria in butane-degrading soil appeared to overcome their N limitation because butane degradation rates later increased regardless of whether more N was added. Analyses of total N and acetylene reduction assays supported this apparent surplus of N in butane-amended soil. Total N was significantly (P < 0.01) higher in soil incubated with butane and no N amendments than in soil incubated with propane, even when the latter was amended with N. Acetylene reduction occurred only in butane-amended soil. These results indicate that N2 fixation occurred in butane-amended soil but not in propane-amended soil. PMID:8215369

  6. [Nitrogen fixation potential of biological soil crusts in southeast edge of Tengger Desert, Northwest China].

    PubMed

    Zhang, Peng; Li, Xin-Rong; Zhang, Zhi-Shan; Pan, Yan-Xia; Liu, Yan-Mei; Su, Jie-Qiong

    2012-08-01

    Taking three typical types of biological soil crusts (BSCs), i.e., cyanobacterial-algal crust, lichen crust, and moss crust, in the southeast fringe of Tengger Desert as test objects, this paper studied their nitrogen fixation potential, seasonal fluctuation, and responses to the environmental factors from June 2010 to May 2011. During the whole study period, the nitrogenase activity (NA) of the cyanobacterial-algal, lichen, and moss crusts had significant difference, being 14-133, 20-101, and 4-28 micromol x m(-2) x h(-1), respectively, which indicated the critical role of the species composition of BSCs in nitrogen fixation. The NA of the three crust types had similar response characteristics to environmental factors. The NA had less correlation with the precipitation during the study period, but was positively correlated to the < 3 mm precipitation in the former 3 days of the experiment, indicating that the three types of BSCs could reach the maximum rate of nitrogen fixation under 3 mm precipitation. The NA of the three crust types had a significant quadratic functional relationship with air temperature, i.e., decreased after an initial increase. The NA of cyanobacterial-algal and lichen crusts declined rapidly when the temperature exceeded 30 degrees C, while the NA of moss crust began to decline when the temperature exceeded 25 degrees C, suggesting that different types of BSCs had different optimal temperature range of nitrogen fixation. The seasonal change of the NA of the three crust types was in the order of autumn > spring > summer > winter. The high air temperature in summer and the low air temperature (< 0 degrees C) in winter inhibited the NA of the crusts, while the suitable water and heat conditions in late spring and early autumn promoted the NA, which implied that the seasonal fluctuation of the NA was mainly controlled by the joint effect of the water and heat conditions. Under humid condition, the BSCs in the temperate desert zone had nitrogen

  7. Engineering Pseudomonas protegens Pf-5 for Nitrogen Fixation and its Application to Improve Plant Growth under Nitrogen-Deficient Conditions

    PubMed Central

    Setten, Lorena; Soto, Gabriela; Mozzicafreddo, Matteo; Fox, Ana Romina; Lisi, Christian; Cuccioloni, Massimiliano; Angeletti, Mauro; Pagano, Elba; Díaz-Paleo, Antonio; Ayub, Nicolás Daniel

    2013-01-01

    Nitrogen is the second most critical factor for crop production after water. In this study, the beneficial rhizobacterium Pseudomonas protegens Pf-5 was genetically modified to fix nitrogen using the genes encoding the nitrogenase of Pseudomonas stutzeri A1501 via the X940 cosmid. Pf-5 X940 was able to grow in L medium without nitrogen, displayed high nitrogenase activity and released significant quantities of ammonium to the medium. Pf-5 X940 also showed constitutive expression and enzymatic activity of nitrogenase in ammonium medium or in nitrogen-free medium, suggesting a constitutive nitrogen fixation. Similar to Pseudomonas protegens Pf-5, Pseudomonas putida, Pseudomonas veronii and Pseudomonas taetrolens but not Pseudomonas balearica and Pseudomonas stutzeri transformed with cosmid X940 showed constitutive nitrogenase activity and high ammonium production, suggesting that this phenotype depends on the genome context and that this technology to obtain nitrogen-fixing bacteria is not restricted to Pf-5. Interestingly, inoculation of Arabidopsis, alfalfa, tall fescue and maize with Pf-5 X940 increased the ammonium concentration in soil and plant productivity under nitrogen-deficient conditions. In conclusion, these results open the way to the production of effective recombinant inoculants for nitrogen fixation on a wide range of crops. PMID:23675499

  8. Nitrogen fixation dynamics of two diazotrophic communities in Mono Lake, California

    USGS Publications Warehouse

    Oremland, R.S.

    1990-01-01

    Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by O2, nitrate, and ammonia. The second community consisted of a ball-shaped association of a filamentous chlorophyte (Ctenocladus circinnatus) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria (Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and by propanil [N-(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N2 fixation were measured seasonally, using chambers. Highest rates (~29.3 ??mol of C2H4 m-2 h-1) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N2 fixation has the potential to be a significant nitrogen source in Mono Lake.

  9. Nitrogen Fixation Dynamics of Two Diazotrophic Communities in Mono Lake, California †

    PubMed Central

    Oremland, Ronald S.

    1990-01-01

    Two types of diazotrophic microbial communities were found in the littoral zone of alkaline hypersaline Mono Lake, California. One consisted of anaerobic bacteria inhabiting the flocculent surface layers of sediments. Nitrogen fixation (acetylene reduction) by flocculent surface layers occurred under anaerobic conditions, was not stimulated by light or by additions of organic substrates, and was inhibited by O2, nitrate, and ammonia. The second community consisted of a ball-shaped association of a filamentous chlorophyte (Ctenocladus circinnatus) with diazotrophic, nonheterocystous cyanobacteria, as well as anaerobic bacteria (Ctenocladus balls). Nitrogen fixation by Ctenocladus balls was usually, but not always, stimulated by light. Rates of anaerobic dark fixation equaled those in the light under air. Fixation in the light was stimulated by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and by propanil [N-(3,4-dichlorophenyl)propanamide]. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea-elicited nitrogenase activity was inhibited by ammonia (96%) and nitrate (65%). Fixation was greatest when Ctenocladus balls were incubated anaerobically in the light with sulfide. Dark anaerobic fixation was not stimulated by organic substrates in short-term (4-h) incubations, but was in long-term (67-h) ones. Areal estimates of benthic N2 fixation were measured seasonally, using chambers. Highest rates (∼29.3 μmol of C2H4 m−2 h−1) occurred under normal diel regimens of light and dark. These estimates indicate that benthic N2 fixation has the potential to be a significant nitrogen source in Mono Lake. Images PMID:16348136

  10. Identifying Regulatory Changes to Facilitate Nitrogen Fixation in the Nondiazotroph Synechocystis sp. PCC 6803.

    PubMed

    Mueller, Thomas J; Welsh, Eric A; Pakrasi, Himadri B; Maranas, Costas D

    2016-03-18

    The incorporation of biological nitrogen fixation into a nondiazotrophic photosynthetic organism provides a promising solution to the increasing fixed nitrogen demand, but is accompanied by a number of challenges for accommodating two incompatible processes within the same organism. Here we present regulatory influence networks for two cyanobacteria, Synechocystis PCC 6803 and Cyanothece ATCC 51142, and evaluate them to co-opt native transcription factors that may be used to control the nif gene cluster once it is transferred to Synechocystis. These networks were further examined to identify candidate transcription factors for other metabolic processes necessary for temporal separation of photosynthesis and nitrogen fixation, glycogen catabolism and cyanophycin synthesis. Two transcription factors native to Synechocystis, LexA and Rcp1, were identified as promising candidates for the control of the nif gene cluster and other pertinent metabolic processes, respectively. Lessons learned in the incorporation of nitrogen fixation into a nondiazotrophic prokaryote may be leveraged to further progress the incorporation of nitrogen fixation in plants.

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

    PubMed

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

    2016-08-01

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

  12. Quantitative trait locus analysis of symbiotic nitrogen fixation activity in the model legume Lotus japonicus.

    PubMed

    Tominaga, Akiyoshi; Gondo, Takahiro; Akashi, Ryo; Zheng, Shao-Hui; Arima, Susumu; Suzuki, Akihiro

    2012-05-01

    Many legumes form nitrogen-fixing root nodules. An elevation of nitrogen fixation in such legumes would have significant implications for plant growth and biomass production in agriculture. To identify the genetic basis for the regulation of nitrogen fixation, quantitative trait locus (QTL) analysis was conducted with recombinant inbred lines derived from the cross Miyakojima MG-20 × Gifu B-129 in the model legume Lotus japonicus. This population was inoculated with Mesorhizobium loti MAFF303099 and grown for 14 days in pods containing vermiculite. Phenotypic data were collected for acetylene reduction activity (ARA) per plant (ARA/P), ARA per nodule weight (ARA/NW), ARA per nodule number (ARA/NN), NN per plant, NW per plant, stem length (SL), SL without inoculation (SLbac-), shoot dry weight without inoculation (SWbac-), root length without inoculation (RLbac-), and root dry weight (RWbac-), and finally 34 QTLs were identified. ARA/P, ARA/NN, NW, and SL showed strong correlations and QTL co-localization, suggesting that several plant characteristics important for symbiotic nitrogen fixation are controlled by the same locus. QTLs for ARA/P, ARA/NN, NW, and SL, co-localized around marker TM0832 on chromosome 4, were also co-localized with previously reported QTLs for seed mass. This is the first report of QTL analysis for symbiotic nitrogen fixation activity traits.

  13. Nitrogen fixation (acetylene reduction) by annual winter legumes on a coal surface mine

    SciTech Connect

    Gabrielson, F.C.

    1982-01-01

    The winter annuals, crimson clover, rose clover, subterranean clover and hairy vetch, were evaluated for their ability to fix nitrogen on coal surface mine substrates by measuring their ability to reduce acetylene to ethylene. The effects of fertilizer, Abruzzi ryegrass, Kentucky 31 fescue grass and a phytotoxic plant Chenopodium album on nitrogen fixation was also assessed. Crimson clover was recommended as the best legume to use on topsoil and shale in the South. Hairy vetch gave good results on shale and subterranean clover did well on topsoil. The use of these species for revegetation is discussed. Overall, no correlation between substrate pH and ethylene levels was found and effects of substrate depended upon the legume species. Super phosphate fertilizer supported less nitrogen fixation than 13-13-13. Abruzzi ryegrass in some unknown way inhibited plant density and nitrogen fixation by legumes but not by free living substrate micro-organisms. Shale from under dead Chenopodium plants in both field and greenhouse experiments did not inhibit nitrogen fixation. 11 references, 7 tables.

  14. Nitrogen fixation (Acetylene Reduction) by annual winter legumes on a coal surface mine

    SciTech Connect

    Gabrielson, F.C.

    1982-01-01

    The winter annuals, crimson clover, rose clover, subterranean clover and hairy vetch, were evaluated for nitrogen fixing capacity on coal surface mine substrates by measuring their ability to reduce acetylene to ethylene. The effects of fertilizer, Abruzzi rye, Kentucky 31 fescue grass and a phytotoxic plant Chenopodium album on nitrogen fixation were also assessed. Crimson clover was recommended as the best legume to use on topsoil and shale in the south. Hairy vetch gave good results on shale and subterranean clover did well on topsoil. The use of these species for revegetation is discussed. Overall, no correlation between substrate pH and ethylene levels was found and effects of substrate depended upon the legume species. Super phosphate fertilizer supported less nitrogen fixation than 13-13-13. Abruzzi rye in some unknown way inhibited plant density and nitrogen fixation by legumes but not by free living substrate micro-organisms. Shale from under dead Chenopodium plants in both field and greehouse experiments did not inhibit nitrogen fixation. 7 tables.

  15. Iron and phosphorus co-limit nitrogen fixation in the eastern tropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Mills, Matthew M.; Ridame, Celine; Davey, Margaret; La Roche, Julie; Geider, Richard J.

    2004-05-01

    The role of iron in enhancing phytoplankton productivity in high nutrient, low chlorophyll oceanic regions was demonstrated first through iron-addition bioassay experiments and subsequently confirmed by large-scale iron fertilization experiments. Iron supply has been hypothesized to limit nitrogen fixation and hence oceanic primary productivity on geological timescales, providing an alternative to phosphorus as the ultimate limiting nutrient. Oceanographic observations have been interpreted both to confirm and refute this hypothesis, but direct experimental evidence is lacking. We conducted experiments to test this hypothesis during the Meteor 55 cruise to the tropical North Atlantic. This region is rich in diazotrophs and strongly impacted by Saharan dust input. Here we show that community primary productivity was nitrogen-limited, and that nitrogen fixation was co-limited by iron and phosphorus. Saharan dust addition stimulated nitrogen fixation, presumably by supplying both iron and phosphorus. Our results support the hypothesis that aeolian mineral dust deposition promotes nitrogen fixation in the eastern tropical North Atlantic.

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

    PubMed Central

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

    2016-01-01

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

  17. Genome-wide transcriptome profiling of nitrogen fixation in Paenibacillus sp. WLY78.

    PubMed

    Shi, Hao-wen; Wang, Li-ying; Li, Xin-xin; Liu, Xiao-meng; Hao, Tian-yi; He, Xiao-juan; Chen, San-feng

    2016-03-01

    Diazotrophic (nitrogen-fixing) Gram-positive and endospore-formed Paenibacillus spp. have potential uses as a bacterial fertilizer in agriculture. The transcriptional analysis of nitrogen fixation in Paenibacillus is lacking, although regulation mechanisms of nitrogen fixation have been well studied in Gram-negative diazotrophs. Here we report a global transcriptional profiling analysis of nitrogen fixation in Paenibacillus sp. WLY78 cultured under N2-fixing condition (without O2 and NH4(+)) and non-N2-fixing condition (air and 100 mM NH4(+)). The nif (nitrogen fixation) gene operon composed of 9 genes (nifBHDKENXhesAnifV) in this bacterium was significantly up-regulated in N2-fixing condition compared to non-N2-fixing condition, indicating that nif gene transcription is strictly controlled by NH4(+) and O2. qRT-PCR confirmed that these nif genes were differently expressed. Non-nif genes specifically required in nitrogen fixation, such as mod, feoAB and cys encoding transporters of Mo, Fe and S atoms, were coordinately transcribed with nif genes in N2-fixing condition. The transcript abundance of suf operon specific for synthesis of Fe-S cluster was up-regulated in N2-fixing condition, suggesting that Sul system, which takes place of nifS and nifU, plays important role in the synthesis of nitrogenase. We discover potential specific electron transporters which might provide electron from Fe protein to MoFe protein of nitrogenase. The glnR whose predicted protein might mediate nif transcription regulation by NH4(+) is significantly up-regulated in N2-fixing condition. The transcription levels of nitrogen metabolism and anaerobic respiration were also analyzed. The nif gene operon (nifBHDKENXhesAnifV) in Paenibacillus sp. WLY78 is significantly up-regulated in N2-fixing condition compared to non-N2-fixing condition. Non-nif genes specifically required in nitrogen fixation were also significantly up-regulated in N2-fixing condition. Fur and Fnr which are involved in

  18. Variability in nitrogen uptake and fixation in the oligotrophic waters off the south west coast of Australia

    NASA Astrophysics Data System (ADS)

    Twomey, L. J.; Waite, A. M.; Pez, V.; Pattiaratchi, C. B.

    2007-04-01

    The results presented in this study provide the first broad-scale regional characterisation of the phytoplankton-nitrogen dynamics across the continental shelf between the Abrolhos Islands and Cape Leeuwin, Western Australia. We demonstrate key features of N-uptake, including nitrate and ammonium uptake and N fixation, across the dominant current systems of the west coast of Australia during a 2-week period in spring-summer. The surface waters of the region were N impoverished with low phytoplankton biomass. Nitrate and ammonium uptake rates were among the lowest on record, and f-ratios were high compared to other oligotrophic systems ( f-ratio ˜0.5 throughout), indicating an equal preference for nitrate and ammonium uptake. Areas of high phytoplankton biomass were most likely fuelled by nitrate transported into the euphotic zone during temporally short bursts of upwelling on ˜weekly, rather than monthly time scales. When upwelling had relaxed, phytoplankton productivity was largely maintained by microbial regeneration in the euphotic zone. A large proportion (20-60%) of the phytoplankton biomass was comprised of picoplankton and nanoplankton cyanobacteria. However, rates of N 2 fixation were 2 orders of magnitude lower than dissolved inorganic N uptake, indicating that N 2-fixation did not significantly contribute to phytoplankton productivity during the study.

  19. Methane-Stimulated Benthic Marine Nitrogen Fixation at Deep-Sea Methane Seeps

    NASA Astrophysics Data System (ADS)

    Dekas, A. E.; Orphan, V.

    2011-12-01

    Biological nitrogen fixation (the conversion of N2 to NH3) is a critical process in the oceans, counteracting the production of N2 gas by dissimilatory bacterial metabolisms and providing a source of bioavailable nitrogen to many nitrogen-limited ecosystems. Although current measurements of N2 production and consumption in the oceans indicate that the nitrogen cycle is not balanced, recent findings on the limits of nitrogen fixation suggest that the perceived imbalance is an artifact of an incomplete assessment of marine diazotrophy. One currently poorly studied and potentially underappreciated habitat for diazotrophic organisms is the sediments of the deep-sea. In the present study we investigate the distribution and magnitude of benthic marine diazotrophy at several active deep-sea methane seeps (Mound 12, Costa Rica; Eel River Basin, CA, USA; Hydrate Ridge, OR, USA; and Monterey Canyon, CA, USA). Using 15N2 and 15NH4 sediment incubation experiments followed by single-cell (FISH-NanoSIMS) and bulk isotopic analysis (EA-IRMS), we observed total protein synthesis (15N uptake from 15NH4) and nitrogen fixation (15N update from 15N2). The highest rates of nitrogen fixation observed in the methane seep sediment incubation experiments were over an order of magnitude greater than those previously published from non-seep deep-sea sediments (Hartwig and Stanley, Deep-Sea Research, 1978, 25:411-417). However, methane seep diazotrophy appears to be highly spatially variable, with sediments exhibiting no nitrogen fixation originating only centimeters away from sediments actively incorporating 15N from 15N2. The greatest spatial variability in diazotrophy was observed with depth in the sediment, and corresponded to steep gradients in sulfate and methane. The maximum rates of nitrogen fixation were observed within the methane-sulfate transition zone, where organisms mediating the anaerobic oxidation of methane are typically in high abundance. Additionally, incubation

  20. Transcriptomic Analysis of Sinorhizobium meliloti and Medicago truncatula Symbiosis Using Nitrogen Fixation-Deficient Nodules.

    PubMed

    Lang, Claus; Long, Sharon R

    2015-08-01

    The bacterium Sinorhizobium meliloti interacts symbiotically with legume plant hosts such as Medicago truncatula to form nitrogen-fixing root nodules. During symbiosis, plant and bacterial cells differentiate in a coordinated manner, resulting in specialized plant cells that contain nitrogen-fixing bacteroids. Both plant and bacterial genes are required at each developmental stage of symbiosis. We analyzed gene expression in nodules formed by wild-type bacteria on six plant mutants with defects in nitrogen fixation. We observed differential expression of 482 S. meliloti genes with functions in cell envelope homeostasis, cell division, stress response, energy metabolism, and nitrogen fixation. We simultaneously analyzed gene expression in M. truncatula and observed differential regulation of host processes that may trigger bacteroid differentiation and control bacterial infection. Our analyses of developmentally arrested plant mutants indicate that plants use distinct means to control bacterial infection during early and late symbiotic stages.

  1. Increasing Nitrogen Fixation and Seed Development in Soybean Requires Complex Adjustments of Nodule Nitrogen Metabolism and Partitioning Processes.

    PubMed

    Carter, Amanda M; Tegeder, Mechthild

    2016-08-08

    Legumes are able to access atmospheric di-nitrogen (N2) through a symbiotic relationship with rhizobia that reside within root nodules. In soybean, following N2 fixation by the bacteroids, ammonia is finally reduced in uninfected cells to allantoin and allantoic acid [1]. These ureides present the primary long-distance transport forms of nitrogen (N), and are exported from nodules via the xylem for shoot N supply. Transport of allantoin and allantoic acid out of nodules requires the function of ureide permeases (UPS1) located in cells adjacent to the vasculature [2, 3]. We expressed a common bean UPS1 transporter in cortex and endodermis cells of soybean nodules and found that delivery of N from nodules to shoot, as well as seed set, was significantly increased. In addition, the number of transgenic nodules was increased and symbiotic N2 fixation per nodule was elevated, indicating that transporter function in nodule N export is a limiting step in bacterial N acquisition. Further, the transgenic nodules showed considerable increases in nodule N assimilation, ureide synthesis, and metabolite levels. This suggests complex adjustments of nodule N metabolism and partitioning processes in support of symbiotic N2 fixation. We propose that the transgenic UPS1 plants display metabolic and allocation plasticity to overcome N2 fixation and seed yield limitations. Overall, it is demonstrated that transporter function in N export from nodules is a key step for enhancing atmospheric N2 fixation and nodule function and for improving shoot N nutrition and seed development in legumes.

  2. Nitrogen fixation and nifH diversity in human gut microbiota

    PubMed Central

    Igai, Katsura; Itakura, Manabu; Nishijima, Suguru; Tsurumaru, Hirohito; Suda, Wataru; Tsutaya, Takumi; Tomitsuka, Eriko; Tadokoro, Kiyoshi; Baba, Jun; Odani, Shingo; Natsuhara, Kazumi; Morita, Ayako; Yoneda, Minoru; Greenhill, Andrew R.; Horwood, Paul F.; Inoue, Jun-ichi; Ohkuma, Moriya; Hongoh, Yuichi; Yamamoto, Taro; Siba, Peter M.; Hattori, Masahira; Minamisawa, Kiwamu; Umezaki, Masahiro

    2016-01-01

    It has been hypothesized that nitrogen fixation occurs in the human gut. However, whether the gut microbiota truly has this potential remains unclear. We investigated the nitrogen-fixing activity and diversity of the nitrogenase reductase (NifH) genes in the faecal microbiota of humans, focusing on Papua New Guinean and Japanese individuals with low to high habitual nitrogen intake. A 15N2 incorporation assay showed significant enrichment of 15N in all faecal samples, irrespective of the host nitrogen intake, which was also supported by an acetylene reduction assay. The fixed nitrogen corresponded to 0.01% of the standard nitrogen requirement for humans, although our data implied that the contribution in the gut in vivo might be higher than this value. The nifH genes recovered in cloning and metagenomic analyses were classified in two clusters: one comprising sequences almost identical to Klebsiella sequences and the other related to sequences of Clostridiales members. These results are consistent with an analysis of databases of faecal metagenomes from other human populations. Collectively, the human gut microbiota has a potential for nitrogen fixation, which may be attributable to Klebsiella and Clostridiales strains, although no evidence was found that the nitrogen-fixing activity substantially contributes to the host nitrogen balance. PMID:27554344

  3. Nitrogen fixation and nifH diversity in human gut microbiota.

    PubMed

    Igai, Katsura; Itakura, Manabu; Nishijima, Suguru; Tsurumaru, Hirohito; Suda, Wataru; Tsutaya, Takumi; Tomitsuka, Eriko; Tadokoro, Kiyoshi; Baba, Jun; Odani, Shingo; Natsuhara, Kazumi; Morita, Ayako; Yoneda, Minoru; Greenhill, Andrew R; Horwood, Paul F; Inoue, Jun-Ichi; Ohkuma, Moriya; Hongoh, Yuichi; Yamamoto, Taro; Siba, Peter M; Hattori, Masahira; Minamisawa, Kiwamu; Umezaki, Masahiro

    2016-08-24

    It has been hypothesized that nitrogen fixation occurs in the human gut. However, whether the gut microbiota truly has this potential remains unclear. We investigated the nitrogen-fixing activity and diversity of the nitrogenase reductase (NifH) genes in the faecal microbiota of humans, focusing on Papua New Guinean and Japanese individuals with low to high habitual nitrogen intake. A (15)N2 incorporation assay showed significant enrichment of (15)N in all faecal samples, irrespective of the host nitrogen intake, which was also supported by an acetylene reduction assay. The fixed nitrogen corresponded to 0.01% of the standard nitrogen requirement for humans, although our data implied that the contribution in the gut in vivo might be higher than this value. The nifH genes recovered in cloning and metagenomic analyses were classified in two clusters: one comprising sequences almost identical to Klebsiella sequences and the other related to sequences of Clostridiales members. These results are consistent with an analysis of databases of faecal metagenomes from other human populations. Collectively, the human gut microbiota has a potential for nitrogen fixation, which may be attributable to Klebsiella and Clostridiales strains, although no evidence was found that the nitrogen-fixing activity substantially contributes to the host nitrogen balance.

  4. Selection and breeding of corn to enhance associative bacterial nitrogen fixation

    SciTech Connect

    Ela, S.W.; Anderson, M.A.; Brill, W.J.

    1980-01-01

    We have increased, through screening and breeding, the ability of corn (maize, Zea mays L.) to support bacterial nitrogen fixation in or on corn roots. Isotopic N fixed from /sup 15/N/sub 2/ was found on the roots. Even though the nitrogen-fixing association depends on germ plasm from tropical corn, the activity can be bred into corn currently used in midwestern United States agriculture.

  5. Low temperature delays timing and enhances the cost of nitrogen fixation in the unicellular cyanobacterium Cyanothece

    PubMed Central

    Brauer, Verena S; Stomp, Maayke; Rosso, Camillo; van Beusekom, Sebastiaan AM; Emmerich, Barbara; Stal, Lucas J; Huisman, Jef

    2013-01-01

    Marine nitrogen-fixing cyanobacteria are largely confined to the tropical and subtropical ocean. It has been argued that their global biogeographical distribution reflects the physiologically feasible temperature range at which they can perform nitrogen fixation. In this study we refine this line of argumentation for the globally important group of unicellular diazotrophic cyanobacteria, and pose the following two hypotheses: (i) nitrogen fixation is limited by nitrogenase activity at low temperature and by oxygen diffusion at high temperature, which is manifested by a shift from strong to weak temperature dependence of nitrogenase activity, and (ii) high respiration rates are required to maintain very low levels of oxygen for nitrogenase, which results in enhanced respiratory cost per molecule of fixed nitrogen at low temperature. We tested these hypotheses in laboratory experiments with the unicellular cyanobacterium Cyanothece sp. BG043511. In line with the first hypothesis, the specific growth rate increased strongly with temperature from 18 to 30 °C, but leveled off at higher temperature under nitrogen-fixing conditions. As predicted by the second hypothesis, the respiratory cost of nitrogen fixation and also the cellular C:N ratio rose sharply at temperatures below 21 °C. In addition, we found that low temperature caused a strong delay in the onset of the nocturnal nitrogenase activity, which shortened the remaining nighttime available for nitrogen fixation. Together, these results point at a lower temperature limit for unicellular nitrogen-fixing cyanobacteria, which offers an explanation for their (sub)tropical distribution and suggests expansion of their biogeographical range by global warming. PMID:23823493

  6. Nitrogen fixation in acidophile iron-oxidizing bacteria: the nif regulon of Leptospirillum ferrooxidans.

    PubMed

    Parro, Víctor; Moreno-Paz, Mercedes

    2004-11-01

    The Gram-negative iron-oxidizing bacterium Leptospirillum ferrooxidans contains all genes necessary for nitrogen fixation, from genes encoding the Mo-Fe nitrogenase, the specific regulator (nifA), global regulators like glnB and ntrC like genes, to other sensors and transport systems somehow related to nitrogen assimilation. We review current knowledge about the nif regulon and its connection with other metabolic functions in L. ferrooxidans.

  7. Low temperature delays timing and enhances the cost of nitrogen fixation in the unicellular cyanobacterium Cyanothece.

    PubMed

    Brauer, Verena S; Stomp, Maayke; Rosso, Camillo; van Beusekom, Sebastiaan A M; Emmerich, Barbara; Stal, Lucas J; Huisman, Jef

    2013-11-01

    Marine nitrogen-fixing cyanobacteria are largely confined to the tropical and subtropical ocean. It has been argued that their global biogeographical distribution reflects the physiologically feasible temperature range at which they can perform nitrogen fixation. In this study we refine this line of argumentation for the globally important group of unicellular diazotrophic cyanobacteria, and pose the following two hypotheses: (i) nitrogen fixation is limited by nitrogenase activity at low temperature and by oxygen diffusion at high temperature, which is manifested by a shift from strong to weak temperature dependence of nitrogenase activity, and (ii) high respiration rates are required to maintain very low levels of oxygen for nitrogenase, which results in enhanced respiratory cost per molecule of fixed nitrogen at low temperature. We tested these hypotheses in laboratory experiments with the unicellular cyanobacterium Cyanothece sp. BG043511. In line with the first hypothesis, the specific growth rate increased strongly with temperature from 18 to 30 °C, but leveled off at higher temperature under nitrogen-fixing conditions. As predicted by the second hypothesis, the respiratory cost of nitrogen fixation and also the cellular C:N ratio rose sharply at temperatures below 21 °C. In addition, we found that low temperature caused a strong delay in the onset of the nocturnal nitrogenase activity, which shortened the remaining nighttime available for nitrogen fixation. Together, these results point at a lower temperature limit for unicellular nitrogen-fixing cyanobacteria, which offers an explanation for their (sub)tropical distribution and suggests expansion of their biogeographical range by global warming.

  8. [Effect of nitrogen-containing compounds on hydrogen light emission and nitrogen fixation by purple bacteria].

    PubMed

    Kondrat'eva, E N; Gogotov, I N; Gruzinskiĭ, I V

    1979-01-01

    The cells of Rhodospirillum rubrum and Thiocapsa roseopersicina grown in media containing glutamate and arginine, respectively, as well as under conditions of nitrogen fixation evolve H2 in the light. If the cultures were grown in media with NH4+, NO3-, urea, glutamine or asparagine, hydrogen photoevolution by the cells and acetylene reduction started after the lag-phase and proceeded at a low rate. Extracts of such cells did not display the activity of nitrogenase which could be assayed by the ATP-dependent evolution of H2 from dithionite. The data obtained confirm the fact that hydrogen photoevolution by purple bacteria involves nitrogenase whose synthesis is regulated (according to the action of glutamine) with the participation of glutamine synthetase. NH4+, glutamine and asparagine inhibit also hydrogen photoproduction by purple bacteria and acetylene photoreduction. However, they have no effect on hydrogen evolution in the dark by the cells of R. rubrum and T. roseopersicina in the presence of formiate or pyruvate, respectively, whereas carbon monoxide inhibits hydrogen production. Therefore, hydrogen production by purple bacteria in the dark must be catalyzed by hydrogenase.

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

    PubMed

    Pogoreutz, Claudia; Rädecker, Nils; Cárdenas, Anny; Gärdes, Astrid; Voolstra, Christian R; Wild, Christian

    2017-09-01

    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. © 2017 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  11. Nitrogen Fixation by Vibrio parahaemolyticus and Its Implications for a New Ecological Niche▿

    PubMed Central

    Criminger, J. D.; Hazen, T. H.; Sobecky, P. A.; Lovell, C. R.

    2007-01-01

    A Vibrio parahaemolyticus strain isolated from the rhizosphere of the ecosystem dominant estuarine grass, Spartina alterniflora, was characterized and shown to carry nifH, the gene encoding the nitrogenase iron protein, and to fix N2. Nitrogen fixation may contribute substantially to the adaptability, niche breadth, and ecological significance of V. parahaemolyticus. PMID:17675440

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

    USDA-ARS?s Scientific Manuscript database

    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...

  13. Nitrogen Fixation Tolerance to Soil Water Deficit Among Commercial Cultivars and breeding Lines of Peanut

    USDA-ARS?s Scientific Manuscript database

    Peanut is often grown in the U.S. on sandy soil with limited water holding capacity. Since nitrogen fixation activity of other grain legume species, and some peanut cultivars, has been found to be especially sensitive to soil drying, this study was undertaken to examine a possible limitation in U.S...

  14. Application of 15N-enrichment methodologies to estimate nitrogen fixation in Casuarina equisetifolia

    Treesearch

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

    1994-01-01

    The 15N-enrichment technique for estimating biological nitrogen fixation in Casuarina equisetifolia J.R. & G. Forst. was evaluated under field conditions in single-species and mixed-species plantings (with a nonfixing reference species, Eucalyptus X robusta J.E. Smith) between...

  15. Estimation of nitrogen fixation in Leucaena leucocephala using 15N-enrichment methodologies

    Treesearch

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

    1994-01-01

    An estimation of biological nitrogen fixation by Leucaena leucocephala (Lam.) de Wit in monoculture and mixed-species plantations (with Casuarina equisetifolia L. ex J.R. & G. Forst., and Eucalyptus robusta Sm.) was undertaken over a two-year period in Puerto Rico using the 15N-enrichment...

  16. Ammonia fixation by humic substances: A nitrogen-15 and carbon-13 NMR study

    USGS Publications Warehouse

    Thorn, K.A.; Mikita, M.A.

    1992-01-01

    The process of ammonia fixation has been studied in three well characterized and structurally diverse fulvic and humic acid samples. The Suwannee River fulvic acid, and the IHSS peat and leonardite humic acids, were reacted with 15N-labelled ammonium hydroxide, and analyzed by liquid phase 15N NMR spectrometry. Elemental analyses and liquid phase 13C NMR spectra also were recorded on the samples before and after reaction with ammonium hydroxide. The largest increase in percent nitrogen occurred with the Suwannee River fulvic acid, which had a nitrogen content of 0.88% before fixation and 3.17% after fixation. The 15N NMR spectra revealed that ammonia reacted similarly with all three samples, indicating that the functional groups which react with ammonia exist in structural configurations common to all three samples. The majority of nitrogcn incorporated into the samples appears to be in the form of indole and pyrrole nitrogen, followed by pyridine, pyrazine, amide and aminohydroquinone nitrogen. Chemical changes in the individual samples upon fixation could not be discerned from the 13C NMR spectra.

  17. Assessment of free-living nitrogen fixing microorganisms for commercial nitrogen fixation. [economic analysis of ammonia production

    NASA Technical Reports Server (NTRS)

    Stokes, B. O.; Wallace, C. J.

    1978-01-01

    Ammonia production by Klebsiella pneumoniae is not economical with present strains and improving nitrogen fixation to its theoretical limits in this organism is not sufficient to achieve economic viability. Because the value of both the hydrogen produced by this organism and the methane value of the carbon source required greatly exceed the value of the ammonia formed, ammonia (fixed nitrogen) should be considered the by-product. The production of hydrogen by KLEBSIELLA or other anaerobic nitrogen fixers should receive additional study, because the activity of nitrogenase offers a significant improvement in hydrogen production. The production of fixed nitrogen in the form of cell mass by Azotobacter is also uneconomical and the methane value of the carbon substrate exceeds the value of the nitrogen fixed. Parametric studies indicate that as efficiencies approach the theoretical limits the economics may become competitive. The use of nif-derepressed microorganisms, particularly blue-green algae, may have significant potential for in situ fertilization in the environment.

  18. The interactive effects of temperature and light on biological nitrogen fixation in boreal forests.

    PubMed

    Gundale, Michael J; Nilsson, Madeleine; Bansal, Sheel; Jäderlund, Anders

    2012-04-01

    Plant productivity is predicted to increase in northern latitudes as a result of climate warming; however, this may depend on whether biological nitrogen (N)-fixation also increases. We evaluated how the variation in temperature and light affects N-fixation by two boreal feather mosses, Pleurozium schreberi and Hylocomium splendens, which are the primary source of N-fixation in most boreal environments. We measured N-fixation rates 2 and 4 wk after exposure to a factorial combination of environments of normal, intermediate and high temperature (16.3, 22.0 and 30.3°C) and light (148.0, 295.7 and 517.3 μmol m(-2) s(-1)). Our results showed that P. schreberi achieved higher N-fixation rates relative to H. splendens in response to warming treatments, but that the highest warming treatment eventually caused N-fixation to decline for both species. Light strongly interacted with warming treatments, having positive effects at low or intermediate temperatures and damaging effects at high temperatures. These results suggest that climate warming may increase N-fixation in boreal forests, but that increased shading by the forest canopy or the occurrence of extreme temperature events could limit increases. They also suggest that P. schreberi may become a larger source of N in boreal forests relative to H. splendens as climate warming progresses.

  19. Nitrogen fixation in sediments along a depth transect through the Peruvian oxygen minimum zone

    NASA Astrophysics Data System (ADS)

    Gier, Jessica; Sommer, Stefan; Löscher, Carolin R.; Dale, Andrew W.; Schmitz, Ruth A.; Treude, Tina

    2016-07-01

    The potential coupling of nitrogen (N2) fixation and sulfate reduction (SR) was explored in sediments of the Peruvian oxygen minimum zone (OMZ). Sediment samples were retrieved by a multiple corer at six stations along a depth transect (70-1025 m water depth) at 12° S, covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation, determined by the acetylene reduction assay, was detected at all sites, with highest rates between 70 and 253 m and lower rates at greater depth. SR rates decreased with increasing water depth. N2 fixation and SR overlapped in sediments, suggesting a potential coupling of both processes. However, a weak positive correlation of their activity distribution was detected by principle component analysis. A potential link between N2 fixation and sulfate-reducing bacteria was indicated by the molecular analysis of nifH genes. Detected nifH sequences clustered with the sulfate-reducing bacteria Desulfonema limicola at the 253 m station. However, nifH sequences of other stations clustered with uncultured organisms, Gammaproteobacteria, and Firmicutes (Clostridia) rather than with known sulfate reducers. The principle component analysis revealed that benthic N2 fixation in the Peruvian OMZ is controlled by organic matter (positive) and free sulfide (negative). No correlation was found between N2 fixation and ammonium concentrations (even at levels > 2022 µM). N2 fixation rates in the Peruvian OMZ sediments were in the same range as those measured in other organic-rich sediments.

  20. Diversity of Ammonia Oxidation (amoA) and Nitrogen Fixation (nifH) Genes in Lava Caves of Terceira, Azores, Portugal

    PubMed Central

    Hathaway, Jennifer J. Marshall; Sinsabaugh, Robert L.; Dapkevicius, Maria De Lurdes N. E.; Northup, Diana E.

    2015-01-01

    Lava caves are an understudied ecosystem in the subterranean world, particularly in regard to nitrogen cycling. The diversity of ammonia oxidation (amoA) and nitrogen fixation (nifH) genes in bacterial mats collected from lava cave walls on the island of Terceira (Azores, Portugal) was investigated using denaturing gradient gel electrophoresis (DGGE). A total of 55 samples were collected from 11 lava caves that were selected with regard to surface land use. Land use types above the lava caves were categorized into pasture, forested, and sea/urban, and used to determine if land use influenced the ammonia oxidizing and nitrogen fixing bacterial communities within the lava caves. The soil and water samples from each lava cave were analyzed for total organic carbon, inorganic carbon, total nitrogen, ammonium, nitrate, phosphate and sulfate, to determine if land use influences either the nutrient content entering the lava cave or the nitrogen cycling bacteria present within the cave. Nitrosospira-like sequences dominated the ammonia-oxidizing bacteria (AOB) community, and the majority of the diversity was found in lava caves under forested land. The nitrogen fixation community was dominated by Klebsiella pneumoniae-like sequences, and diversity was evenly distributed between pasture and forested land, but very little overlap in diversity was observed. The results suggest that land use is impacting both the AOB and the nitrogen fixing bacterial communities. PMID:26778867

  1. Diversity of Ammonia Oxidation (amoA) and Nitrogen Fixation (nifH) Genes in Lava Caves of Terceira, Azores, Portugal.

    PubMed

    Hathaway, Jennifer J Marshall; Sinsabaugh, Robert L; Dapkevicius, Maria De Lurdes N E; Northup, Diana E

    Lava caves are an understudied ecosystem in the subterranean world, particularly in regard to nitrogen cycling. The diversity of ammonia oxidation (amoA) and nitrogen fixation (nifH) genes in bacterial mats collected from lava cave walls on the island of Terceira (Azores, Portugal) was investigated using denaturing gradient gel electrophoresis (DGGE). A total of 55 samples were collected from 11 lava caves that were selected with regard to surface land use. Land use types above the lava caves were categorized into pasture, forested, and sea/urban, and used to determine if land use influenced the ammonia oxidizing and nitrogen fixing bacterial communities within the lava caves. The soil and water samples from each lava cave were analyzed for total organic carbon, inorganic carbon, total nitrogen, ammonium, nitrate, phosphate and sulfate, to determine if land use influences either the nutrient content entering the lava cave or the nitrogen cycling bacteria present within the cave. Nitrosospira-like sequences dominated the ammonia-oxidizing bacteria (AOB) community, and the majority of the diversity was found in lava caves under forested land. The nitrogen fixation community was dominated by Klebsiella pneumoniae-like sequences, and diversity was evenly distributed between pasture and forested land, but very little overlap in diversity was observed. The results suggest that land use is impacting both the AOB and the nitrogen fixing bacterial communities.

  2. Pyruvate is synthesized by two pathways in pea bacteroids with different efficiencies for nitrogen fixation.

    PubMed

    Mulley, Geraldine; Lopez-Gomez, Miguel; Zhang, Ye; Terpolilli, Jason; Prell, Jurgen; Finan, Turlough; Poole, Philip

    2010-10-01

    Nitrogen fixation in legume bacteroids is energized by the metabolism of dicarboxylic acids, which requires their oxidation to both oxaloacetate and pyruvate. In alfalfa bacteroids, production of pyruvate requires NAD+ malic enzyme (Dme) but not NADP+ malic enzyme (Tme). However, we show that Rhizobium leguminosarum has two pathways for pyruvate formation from dicarboxylates catalyzed by Dme and by the combined activities of phosphoenolpyruvate (PEP) carboxykinase (PckA) and pyruvate kinase (PykA). Both pathways enable N2 fixation, but the PckA/PykA pathway supports N2 fixation at only 60% of that for Dme. Double mutants of dme and pckA/pykA did not fix N2. Furthermore, dme pykA double mutants did not grow on dicarboxylates, showing that they are the only pathways for the production of pyruvate from dicarboxylates normally expressed. PckA is not expressed in alfalfa bacteroids, resulting in an obligate requirement for Dme for pyruvate formation and N2 fixation. When PckA was expressed from a constitutive nptII promoter in alfalfa dme bacteroids, acetylene was reduced at 30% of the wild-type rate, although this level was insufficient to prevent nitrogen starvation. Dme has N-terminal, malic enzyme (Me), and C-terminal phosphotransacetylase (Pta) domains. Deleting the Pta domain increased the peak acetylene reduction rate in 4-week-old pea plants to 140 to 150% of the wild-type rate, and this was accompanied by increased nodule mass. Plants infected with Pta deletion mutants did not have increased dry weight, demonstrating that there is not a sustained change in nitrogen fixation throughout growth. This indicates a complex relationship between pyruvate synthesis in bacteroids, nitrogen fixation, and plant growth.

  3. Soil spatial variability and symbiotic nitrogen fixation by legumes

    SciTech Connect

    Reichardt, K. )

    1990-09-01

    The isotope dilution method for the estimation of N{sub 2} fixation by legumes is analyzed, comparing the application of {sup 15}N-enriched fertilizer with {sup 15}N-labeled soil. Soil variability of other dynamic processes in the soil are discussed in light of the distribution of the {sup 15}N label in the system. Field data were collected along six transects, 45 m long, with 30 plots (replicates) each. The legume (Vicia faba L.) was used as a fixing crop, barley (Hordeum vulgare L.) and oil radish (Raphinus sativus L.) as nonfixing standard crops. Isotope methods were also compared with the yield difference method. Results show that isotope methods were very sensitive to the distribution of the label in the soil and that dynamic processes involving N can significantly affect this distribution over a whole field. Best results were obtained with {sup 15}N-labeled soil. The particular site used, having been farmed for more than 20 years with {sup 15}N trials, showed a homogeneous residual {sup 15}N label that made it possible to estimate N{sub 2} fixation without the application of extra label. Estimates of N{sub 2} fixation with the isotope method were well correlated with the yield difference method when fertilizer use efficiency of the fixing and nonfixing crops were similar. Results also indicate that a good reference crop for one method might not be the best for the other method, and one reason for this is the variability of soil parameters and of dynamic processes occurring in the soil.

  4. Ureide Assay for Measuring Nitrogen Fixation by Nodulated Soybean Calibrated by 15N Methods 1

    PubMed Central

    Herridge, David F.; Peoples, Mark B.

    1990-01-01

    We report experiments to quantify the relationships between the relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap, and hot water extracts of stems and petioles of nodulated soybean (Glycine max [L.] Merrill cv Bragg) and the proportion of plant N derived from nitrogen fixation. Additional experiments examined the effects of plant genotype and strain of rhizobia on these relationships. In each of the five experiments reported, plants of cv Bragg (experiment 1), cv Lincoln (experiments 3, 4, 5), or six cultivars/genotypes (experiment 2) were grown in a sand:vermiculite mixture in large pots in a naturally lit, temperature-controlled glasshouse during summer. Pots were inoculated at sowing with effective Bradyrhizobium japonicum CB1809 (USDA 136) or with one of 21 different strains of rhizobia. The proportions of plant N derived from nitrogen fixation were determined using 15N dilution. In one experiment with CB1809, plants were supplied throughout growth with either N-free nutrients or with nutrients supplemented with 1, 2, 4, or 8 millimolar 15N-nitrate and harvested on eight occasions between V6 and R7 for root-bleeding sap, vacuum-extracted sap, stems (including petioles), and whole plant dry matter. Analyses of the saps and stem extracts for ureides (allantoin plus allantoic acid), α-amino-N, and nitrate, and of dry matter for N and 15N, indicated a positive effect of nitrate supply on concentrations of nitrate in saps and extracts and a negative effect on ureides and on the proportion of plant N derived from nitrogen fixation. The relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap (100 [ureide-N]/[ureide-N+ α-amino-N + nitrate-N]) and stem extracts (100 [ureide-N]/[ureide-N + nitrate-N]) and the proportion of plant N, derived from nitrogen fixation between successive samplings were highly correlated (r = 0.97-1.00). For each variable, two standard curves were prepared to account for the shifts in the compositions

  5. Abiotic nitrogen fixation on terrestrial planets: reduction of NO to ammonia by FeS.

    PubMed

    Summers, David P; Basa, Ranor C B; Khare, Bishun; Rodoni, David

    2012-02-01

    Understanding the abiotic fixation of nitrogen and how such fixation can be a supply of prebiotic nitrogen is critical for understanding both the planetary evolution of, and the potential origin of life on, terrestrial planets. As nitrogen is a biochemically essential element, sources of biochemically accessible nitrogen, especially reduced nitrogen, are critical to prebiotic chemistry and the origin of life. Loss of atmospheric nitrogen can result in loss of the ability to sustain liquid water on a planetary surface, which would impact planetary habitability and hydrological processes that shape the surface. It is known that NO can be photochemically converted through a chain of reactions to form nitrate and nitrite, which can be subsequently reduced to ammonia. Here, we show that NO can also be directly reduced, by FeS, to ammonia. In addition to removing nitrogen from the atmosphere, this reaction is particularly important as a source of reduced nitrogen on an early terrestrial planet. By converting NO directly to ammonia in a single step, ammonia is formed with a higher product yield (~50%) than would be possible through the formation of nitrate/nitrite and subsequent conversion to ammonia. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface that converts NO to NO₂ and N₂O. The NO₂ is then converted to ammonia, while the N₂O is released back in the gas phase, which provides an abiotic source of nitrous oxide.

  6. Nitrogen fixation in distinct microbial niches within a chemoautotrophy-driven cave ecosystem.

    PubMed

    Desai, Mahesh S; Assig, Karoline; Dattagupta, Sharmishtha

    2013-12-01

    Microbial sulfur and carbon cycles in ecosystems driven by chemoautotrophy-present at deep-sea hydrothermal vents, cold seeps and sulfidic caves-have been studied to some extent, yet little is known about nitrogen fixation in these systems. Using a comprehensive approach comprising of (15)N2 isotope labeling, acetylene reduction assay and nitrogenase gene expression analyses, we investigated nitrogen fixation in the sulfide-rich, chemoautotrophy-based Frasassi cave ecosystem (Italy). Nitrogen fixation was examined in three different microbial niches within the cave waters: (1) symbiotic bacterial community of Niphargus amphipods, (2) Beggiatoa-dominated biofilms, which occur at the sulfide-oxygen interface, and (3) sulfidic sediment. We found evidence for nitrogen fixation in all the three niches, and the nitrogenase gene (homologs of nifH) expression data clearly show niche differentiation of diazotrophic Proteobacteria within the water streams. The nifH transcript originated from the symbiotic community of Niphargus amphipods might belong to the Thiothrix ectosymbionts. Two abundantly expressed nifH genes in the Beggiatoa-dominated biofilms are closely related to those from Beggiatoa- and Desulfovibrio-related bacteria. These two diazotrophs were consistently found in Beggiatoa-dominated biofilms collected at various time points, thus illustrating species-specific associations of the diazotrophs in biofilm formation, and micron-scale niche partitioning of sulfur-oxidizing and sulfate-reducing bacteria driven by steep redox gradients within the biofilm. Finally, putative heterotrophs (Geobacter, Azoarcus and Desulfovibrio related) were the active diazotrophs in the sulfidic sediment. Our study is the first to shed light on nitrogen fixation in permanently dark caves and suggests that diazotrophy may be widespread in chemosynthetic communities.

  7. Simulating interactive effects of symbiotic nitrogen fixation, carbon dioxide elevation, and climatic change on legume growth.

    PubMed

    Yu, Mei; Gao, Q; Shaffer, M J

    2002-01-01

    The underlying mechanisms of interaction between the symbiotic nitrogen-fixation process and main physiological processes, such as assimilation, nutrient allocation, and structural growth, as well as effects of nitrogen fixation on plant responses to global change, are important and still open to more investigation. Appropriate models have not been adequately developed. A dynamic ecophysiological model was developed in this study for a legume plant [Glycine max (L.) Merr.] growing in northern China. The model synthesized symbiotic nitrogen fixation and the main physiological processes under variable atmospheric CO2 concentration and climatic conditions, and emphasized the interactive effects of these processes on seasonal biomass dynamics of the plant. Experimental measurements of ecophysiological quantities obtained in a CO2 enrichment experiment on soybean plants, were used to parameterize and validate the model. The results indicated that the model simulated the experiments with reasonable accuracy. The R2 values between simulations and observations are 0.94, 0.95, and 0.86 for total biomass, green biomass, and nodule biomass, respectively. The simulations for various combinations of atmospheric CO2 concentration, precipitation, and temperature, with or without nitrogen fixation, showed that increasing atmospheric CO2 concentration, precipitation, and efficiency of nitrogen fixation all have positive effects on biomass accumulation. On the other hand, an increased temperature induced lower rates of biomass accumulation under semi-arid conditions. In general, factors with positive effects on plant growth tended to promote each other in the simulation range, except the relationship between CO2 concentration and climatic factors. Because of the enhanced water use efficiency with a higher CO2 concentration, more significant effects of CO2 concentration were associated with a worse (dryer and warmer in this study) climate.

  8. The effect of nutrients on carbon and nitrogen fixation by the UCYN-A–haptophyte symbiosis

    PubMed Central

    Krupke, Andreas; Mohr, Wiebke; LaRoche, Julie; Fuchs, Bernhard M; Amann, Rudolf I; Kuypers, Marcel MM

    2015-01-01

    Symbiotic relationships between phytoplankton and N2-fixing microorganisms play a crucial role in marine ecosystems. The abundant and widespread unicellular cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron (Fe) and Saharan dust additions on nitrogen (N2) fixation and primary production by the UCYN-A–haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements. N2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust, although this was not reflected in the nifH expression. CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust. Intriguingly, the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the transfer of N2-derived N to the haptophyte. Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes. However, it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association. PMID:25535939

  9. The effect of nutrients on carbon and nitrogen fixation by the UCYN-A-haptophyte symbiosis.

    PubMed

    Krupke, Andreas; Mohr, Wiebke; LaRoche, Julie; Fuchs, Bernhard M; Amann, Rudolf I; Kuypers, Marcel M M

    2015-07-01

    Symbiotic relationships between phytoplankton and N2-fixing microorganisms play a crucial role in marine ecosystems. The abundant and widespread unicellular cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron (Fe) and Saharan dust additions on nitrogen (N2) fixation and primary production by the UCYN-A-haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements. N2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust, although this was not reflected in the nifH expression. CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust. Intriguingly, the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N2 fixation and the transfer of N2-derived N to the haptophyte. Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes. However, it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association.

  10. Nitrogen fixation in distinct microbial niches within a chemoautotrophy-driven cave ecosystem

    PubMed Central

    Desai, Mahesh S; Assig, Karoline; Dattagupta, Sharmishtha

    2013-01-01

    Microbial sulfur and carbon cycles in ecosystems driven by chemoautotrophy—present at deep-sea hydrothermal vents, cold seeps and sulfidic caves—have been studied to some extent, yet little is known about nitrogen fixation in these systems. Using a comprehensive approach comprising of 15N2 isotope labeling, acetylene reduction assay and nitrogenase gene expression analyses, we investigated nitrogen fixation in the sulfide-rich, chemoautotrophy-based Frasassi cave ecosystem (Italy). Nitrogen fixation was examined in three different microbial niches within the cave waters: (1) symbiotic bacterial community of Niphargus amphipods, (2) Beggiatoa-dominated biofilms, which occur at the sulfide–oxygen interface, and (3) sulfidic sediment. We found evidence for nitrogen fixation in all the three niches, and the nitrogenase gene (homologs of nifH) expression data clearly show niche differentiation of diazotrophic Proteobacteria within the water streams. The nifH transcript originated from the symbiotic community of Niphargus amphipods might belong to the Thiothrix ectosymbionts. Two abundantly expressed nifH genes in the Beggiatoa-dominated biofilms are closely related to those from Beggiatoa- and Desulfovibrio-related bacteria. These two diazotrophs were consistently found in Beggiatoa-dominated biofilms collected at various time points, thus illustrating species-specific associations of the diazotrophs in biofilm formation, and micron-scale niche partitioning of sulfur-oxidizing and sulfate-reducing bacteria driven by steep redox gradients within the biofilm. Finally, putative heterotrophs (Geobacter, Azoarcus and Desulfovibrio related) were the active diazotrophs in the sulfidic sediment. Our study is the first to shed light on nitrogen fixation in permanently dark caves and suggests that diazotrophy may be widespread in chemosynthetic communities. PMID:23924780

  11. Seasonal dynamics of nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

    NASA Astrophysics Data System (ADS)

    Shiozaki, T.; Nagata, T.; Ijichi, M.; Furuya, K.

    2015-01-01

    Nitrogen fixation in temperate oceans is a potentially important, but poorly understood process that may influence the marine nitrogen budget. This study determined seasonal variations in nitrogen fixation and nifH gene diversity within the euphotic zone in the temperate coastal region of the northwestern North Pacific. Nitrogen fixation as high as 13.6 nmolN L-1 d-1 was measured from early summer to fall when the surface temperature exceeded 14.2 °C and the surface nitrate concentration was low (≤ 0.30 μM), although we also detected nitrogen fixation in subsurface layers (42-62 m) where nitrate concentrations were high (> 1 μM). During periods with high nitrogen fixation, the nifH sequences of UCYN-A were recovered, suggesting that these groups played a key role in nitrogen fixation. The nifH genes were also recovered in spring and winter when nitrogen fixation was undetectable. These genes consisted of many sequences affiliated with Cluster III diazotrophs (putative anaerobic bacteria), which hitherto have rarely been reported to be abundant in surface diazotroph communities in marine environments.

  12. Biological nitrogen fixation and future challenges of agriculture. The endophytic connection.

    PubMed

    Sánchez, F; Cárdenas, L; Quinto, C

    1999-01-01

    Feeding the growing global population, anticipated to be 8 billion by the year 2020, is one of the most important recent challenges of agriculture. The increase in cereal grain yield, to cope with this demand, directly implies a dramatic increase in the use of nitrogen-based fertilizers and agrochemicals. Some of these intensive agricultural practices have progressive detrimental effects on the environment. This review is focused on some novel insights gained into the understanding of associative and symbiotic interactions of plants with nitrogen-fixing organisms that makes Biological Nitrogen Fixation (BNF) a viable answer to this compelling dilemma.

  13. Understanding the Variability in Soybean Nitrogen Fixation across Agroecosystems

    USDA-ARS?s Scientific Manuscript database

    Conventional farming practices have uncoupled carbon (C) and nitrogen (N) cycles through the application of inorganic N fertilizers applied in plant available forms at levels that saturate the system. As a result, extensive N losses via leaching and denitrification are having significant environment...

  14. Nitrogen fixation in biological soil crusts from southeast Utah, USA

    USGS Publications Warehouse

    Belnap, J.

    2002-01-01

    Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (26??C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days (r2=0.93 for Collema crusts; r2=0.86 for dark crusts and r2=0.83 for light crusts) for temperatures between 1??C and 26??C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha-1 year-1. With 20% cover of the N-fixing soil lichen Collema, inputs are estimated at 13 kg ha-1 year-1. N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha-1 year-1. The rates in light crusts are expected to be highly variable, as

  15. Nitrogen Cycling in Seagrass Beds Dominated by Thalassia testudinum and Halodule wrightii: the Role of Nitrogen Fixation and Ammonium Oxidation in Regulating Ammonium Availability

    NASA Astrophysics Data System (ADS)

    Capps, R.; Caffrey, J. M.; Hester, C.

    2016-02-01

    Seagrass meadows provide key ecosystem services including nursery and foraging grounds, storm and erosion buffers, biodiversity enhancers and global carbon and nutrient cycling. Nitrogen concentrations are often very low in coastal waters and sediments, which may limit primary productivity. Biological nitrogen fixation is a microbial process that converts dinitrogen to ammonium, which is readily taken up by seagrasses. In the oxygenated rhizospheres, diazotrophs provide the plant with ammonium and use root exudates as an energy source. Nitrogen fixation rates and nutrient concentrations differ between seagrass species and substrate types. Thalassia testudinum has a higher biomass and is a climax species than Halodule wrightii, which is a pioneer species. Nitrogen fixation rates are relatively consistent in Thalassia testudinum dominated sediments. However, it is relatively variable in sediments occupied by Halodule wrightii. Nitrogen fixation rates are higher in bare substrate compared to areas with Thalassia testudinum, which may be due to T. testudinum's greater efficiency in nutrient retention because it is a climax species. We hypothesize that seasonal shifts in nitrogen fixation will coincide with seasonal shifts in seagrass biomass due to higher nutrient requirements during peak growth and lower requirements during senescence and dormancy. The ratio of porewater ammonium to phosphate suggests that seagrass growth may be nitrogen limited as does nitrogen demand, estimated from gross primary productivity. Significant rates of ammonium oxidation in both surface and rhizosphere sediments contribute to this imbalance. Thus, nitrogen fixation may be critical in supporting plant growth.

  16. Quantifying nitrogen-fixation in feather moss carpets of boreal forests.

    PubMed

    DeLuca, Thomas H; Zackrisson, Olle; Nilsson, Marie-Charlotte; Sellstedt, Anita

    2002-10-31

    Biological nitrogen (N) fixation is the primary source of N within natural ecosystems, yet the origin of boreal forest N has remained elusive. The boreal forests of Eurasia and North America lack any significant, widespread symbiotic N-fixing plants. With the exception of scattered stands of alder in early primary successional forests, N-fixation in boreal forests is considered to be extremely limited. Nitrogen-fixation in northern European boreal forests has been estimated at only 0.5 kg N ha(-1) yr(-1); however, organic N is accumulated in these ecosystems at a rate of 3 kg N ha(-1) yr(-1) (ref. 8). Our limited understanding of the origin of boreal N is unacceptable given the extent of the boreal forest region, but predictable given our imperfect knowledge of N-fixation. Herein we report on a N-fixing symbiosis between a cyanobacterium (Nostoc sp.) and the ubiquitous feather moss, Pleurozium schreberi (Bird) Mitt. that alone fixes between 1.5 and 2.0 kg N ha(-1) yr(-1) in mid- to late-successional forests of northern Scandinavia and Finland. Previous efforts have probably underestimated N-fixation potential in boreal forests.

  17. Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age.

    PubMed

    Sherwood, Owen A; Guilderson, Thomas P; Batista, Fabian C; Schiff, John T; McCarthy, Matthew D

    2014-01-02

    The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific (15)N/(14)N isotopic ratios (δ(15)N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, δ(15)N decreases between 1850 and the present. The total shift in δ(15)N of -2 per mil over this period is comparable to the total change in global mean sedimentary δ(15)N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

  18. Increasing subtropical North Pacific Ocean nitrogen fixation since the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Sherwood, Owen A.; Guilderson, Thomas P.; Batista, Fabian C.; Schiff, John T.; McCarthy, Matthew D.

    2014-01-01

    The North Pacific subtropical gyre (NPSG) plays a major part in the export of carbon and other nutrients to the deep ocean. Primary production in the NPSG has increased in recent decades despite a reduction in nutrient supply to surface waters. It is thought that this apparent paradox can be explained by a shift in plankton community structure from mostly eukaryotes to mostly nitrogen-fixing prokaryotes. It remains uncertain, however, whether the plankton community domain shift can be linked to cyclical climate variability or a long-term global warming trend. Here we analyse records of bulk and amino-acid-specific 15N/14N isotopic ratios (δ15N) preserved in the skeletons of long-lived deep-sea proteinaceous corals collected from the Hawaiian archipelago; these isotopic records serve as a proxy for the source of nitrogen-supported export production through time. We find that the recent increase in nitrogen fixation is the continuation of a much larger, centennial-scale trend. After a millennium of relatively minor fluctuation, δ15N decreases between 1850 and the present. The total shift in δ15N of -2 per mil over this period is comparable to the total change in global mean sedimentary δ15N across the Pleistocene-Holocene transition, but it is happening an order of magnitude faster. We use a steady-state model and find that the isotopic mass balance between nitrate and nitrogen fixation implies a 17 to 27 per cent increase in nitrogen fixation over this time period. A comparison with independent records suggests that the increase in nitrogen fixation might be linked to Northern Hemisphere climate change since the end of the Little Ice Age.

  19. Robust biological nitrogen fixation in a model grass-bacterial association.

    PubMed

    Pankievicz, Vânia C S; do Amaral, Fernanda P; Santos, Karina F D N; Agtuca, Beverly; Xu, Youwen; Schueller, Michael J; Arisi, Ana Carolina M; Steffens, Maria B R; de Souza, Emanuel M; Pedrosa, Fábio O; Stacey, Gary; Ferrieri, Richard A

    2015-03-01

    Nitrogen-fixing rhizobacteria can promote plant growth; however, it is controversial whether biological nitrogen fixation (BNF) from associative interaction contributes to growth promotion. The roots of Setaria viridis, a model C4 grass, were effectively colonized by bacterial inoculants resulting in a significant enhancement of growth. Nitrogen-13 tracer studies provided direct evidence for tracer uptake by the host plant and incorporation into protein. Indeed, plants showed robust growth under nitrogen-limiting conditions when inoculated with an ammonium-excreting strain of Azospirillum brasilense. (11)C-labeling experiments showed that patterns in central carbon metabolism and resource allocation exhibited by nitrogen-starved plants were largely reversed by bacterial inoculation, such that they resembled plants grown under nitrogen-sufficient conditions. Adoption of S. viridis as a model should promote research into the mechanisms of associative nitrogen fixation with the ultimate goal of greater adoption of BNF for sustainable crop production. © 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.

  20. Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern north atlantic.

    SciTech Connect

    Turk, K. A.; Rees, A. P.; Zehr, J. P.; Pereira, N.; Swift, P.; Shelley, R.; Lohan, M.; Woodward, E. M. S.; Gilbert, J.

    2011-01-01

    Expression of nifH in 28 surface water samples collected during fall 2007 from six stations in the vicinity of the Cape Verde Islands (north-east Atlantic) was examined using reverse transcription-polymerase chain reaction (RT-PCR)-based clone libraries and quantitative RT-PCR (RT-qPCR) analysis of seven diazotrophic phylotypes. Biological nitrogen fixation (BNF) rates and nutrient concentrations were determined for these stations, which were selected based on a range in surface chlorophyll concentrations to target a gradient of primary productivity. BNF rates greater than 6 nmolN I{sup -1} h{sup -1} were measured at two of the near-shore stations where high concentrations of Fe and PO{sub 4}{sup 3-} were also measured. Six hundred and five nifH transcripts were amplified by RT-PCR, of which 76% are described by six operational taxonomic units, including Trichodesmium and the uncultivated UCYN-A, and four non-cyanobacterial diazotrophs that clustered with uncultivated Proteobacteria. Although all five cyanobacterial phylotypes quantified in RT-qPCR assays were detected at different stations in this study, UCYN-A contributed most significantly to the pool of nifH transcripts in both coastal and oligotrophic waters. A comparison of results from RT-PCR clone libraries and RT-qPCR indicated that a {gamma}-proteobacterial phylotype was preferentially amplified in clone libraries, which underscores the need to use caution interpreting clone-library-based nifH studies, especially when considering the importance of uncultivated proteobacterial diazotrophs.

  1. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

    NASA Astrophysics Data System (ADS)

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L.; Loza, Virginia; Muñoz-Martín, M. Ángeles; Mateo, Pilar

    2016-08-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.

  2. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river.

    PubMed

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L; Loza, Virginia; Muñoz-Martín, M Ángeles; Mateo, Pilar

    2016-08-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats.

  3. Nitrogen fixation in a non-heterocystous cyanobacterial mat from a mountain river

    PubMed Central

    Berrendero, Esther; Valiente, Eduardo Fernández; Perona, Elvira; Gómez, Claudia L.; Loza, Virginia; Muñoz-Martín, M. Ángeles; Mateo, Pilar

    2016-01-01

    In situ nitrogen fixation was investigated in a cyanobacterial mat growing on the bed of rocks of the Muga River, Spain. The filamentous non-heterocystous cyanobacterium Schizothrix dominated the mat, showing nitrogenase activity in the light at similar rates to those found in nearby heterocystous Rivularia colonies. N2 fixation in the light was significantly increased by an inhibitor of PSII and oxygen evolution, DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea), and anaerobic conditions. However, no nitrogenase activity was found in the dark. Addition of fructose as a respiratory substrate induced nitrogenase activity in samples incubated under aerobic conditions in the dark but not in anaerobic conditions. Microelectrode oxygen profiles showed internal microaerobic microzones where nitrogen fixation might concentrate. Analyses of the 16S rRNA gene revealed only the presence of sequences belonging to filamentous non-heterocystous cyanobacteria. nifH gene diversity showed that the major phylotypes also belonged to this group. One of the three strains isolated from the Schizothrix mat was capable of fixing N2 and growing in the absence of combined N. This was consistent with the nifH gene analysis. These results suggest a relevant contribution of non-heterocystous cyanobacteria to nitrogen fixation in these mats. PMID:27476439

  4. The Role of Nitrogen Fixation in Cyanobacterial Bloom Toxicity in a Temperate, Eutrophic Lake

    PubMed Central

    Beversdorf, Lucas J.; Miller, Todd R.; McMahon, Katherine D.

    2013-01-01

    Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N2 fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N2 fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N2 fixation rates were observed. Then, following large early summer N2 fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N2 fixation rates and Aphanizomenon abundance increased before the lake mixed in

  5. Iron availability influences 15N-isotope fractionation during nitrogen fixation by aerobic chemoheterotroph Azotobacter vinelandii

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Kopf, S.; Lee, A. C.

    2016-12-01

    The N stable isotope composition (δ15N) of biomass provides a powerful tool for reconstructing present and past N cycling, but its interpretation hinges on a complete understanding of the isotopic signature of biological nitrogen fixation, which sets the δ15N of newly fixed N. All biological nitrogen fixation is catalyzed by the metalloenzyme nitrogenase in a complex reaction that reduces inert atmospheric N2 gas into bioavailable ammonium. Recent investigations into the metal cofactor variants of nitrogenase revealed that the canonical Mo-, and alternative V-, and Fe-only isoforms of nitrogenase impart different isotope fractionations during N2 fixation in vivo, challenging the traditional view that N2 fixation only imparts small, invariable isotope effects of 0-2‰. However, the mechanistic basis for the fractionation of N2 fixation remains largely unknown. To better understand mechanisms underlying fractionation, we varied Fe availability and measured in vivo fractionations for the aerobic chemoheterotroph Azotobacter vinelandii utilizing Mo- or V-nitrogenase under batch culture conditions. Under all iron conditions, N2 fixation based on Mo-nitrogenase yielded lower fractionations (heavier biomasss δ15N) compared to V-nitrogenase. For fractionations associated with a single metalloenzyme, higher Fe concentrations, which correlated with faster growth rates, yielded small but systematically larger fractionations ( 1 ‰ increase for Mo- and V- nitrogenases). To directly determine the effect of growth rate on fractionation, we grew Mo-nitrogenase expressing A. vinelandii in Fe-replete medium at different growth rates using chemostats and found that growth rate alone does not alter fractionation. The results indicate that Fe availability, in addition to the type of nitrogenase metalloenzyme, controls 15N fractionation during N2 fixation by A. vinelandii.

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

    NASA Astrophysics Data System (ADS)

    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

  7. Effect of Interactions Among Algae on Nitrogen Fixation by Blue-Green Algae (Cyanobacteria) in Flooded Soils

    PubMed Central

    Wilson, John T.; Greene, Sarah; Alexander, Martin

    1979-01-01

    Nitrogen fixation (C2H2 reduction) by algae in flooded soil was limited by interactions within the algal community. Nitrogen fixation by either indigenous algae or Tolypothrix tenuis was reduced severalfold by a dense suspension of the green alga Nephrocytium sp. Similarly, interactions between the nitrogen-fixing alga (cyanobacterium) Aulosira 68 and natural densities of indigenous algae limited nitrogen-fixing activity in one of two soils examined. This was demonstrated by developing a variant of Aulosira 68 that was resistant to the herbicide simetryne at concentrations that prevented development of indigenous algae. More nitrogen was fixed by the resistant variant in flooded soil containing herbicide than was fixed in herbicide-free soil by either the indigenous algae or indigenous algae plus the parent strain of Aulosira. Interference from indigenous algae may hamper the development of nitrogen-fixing algae introduced into rice fields in attempts to increase biological nitrogen fixation. PMID:16345463

  8. Nitrogen fixation in sediments along a depth transect through the Peruvian oxygen minimum zone

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Benthic nitrogen (N2) fixation and sulfate reduction (SR) were investigated in the Peruvian oxygen minimum zone (OMZ). Sediment samples, retrieved by a multiple corer were taken at six stations (70-1025 m) along a depth transect at 12° S, covering anoxic and hypoxic bottom water conditions. Benthic N2 fixation was detected at all sites, with high rates measured in OMZ mid-waters between the 70 and 253 m and lowest N2 fixation rates below 253 m down to 1025 m water depth. SR rates were decreasing with increasing water depth, with highest rates at the shallow site. Benthic N2 fixation depth profiles largely overlapped with SR depth profiles, suggesting that both processes are coupled. The potential of N2 fixation by SR bacteria was verified by the molecular analysis of nifH genes. Detected nifH sequences clustered with SR bacteria that have been demonstrated to fix N2 in other benthic environments. Depth-integrated rates of N2 fixation and SR showed no direct correlation along the 12° S transect, suggesting that the benthic diazotrophs in the Peruvian OMZ are being controlled by additional various environmental factors. The organic matter availability and the presence of sulfide appear to be major drivers for benthic diazotrophy. It was further found that N2 fixation was not inhibited by high ammonium concentrations. N2 fixation rates in OMZ sediments were similar to rates measured in other organic-rich sediments. Overall, this work improves our knowledge on N sources in marine sediments and contributes to a better understanding of N cycling in OMZ sediments.

  9. Tree species control rates of free-living nitrogen fixation in a tropical rain forest.

    PubMed

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

    2008-10-01

    Tropical rain forests represent some of the most diverse ecosystems on earth, yet mechanistic links between tree species identity and ecosystem function in these forests remains poorly understood. Here, using free-living nitrogen (N) fixation as a model, we explore the idea that interspecies variation in canopy nutrient concentrations may drive significant local-scale variation in biogeochemical processes. Biological N fixation is the largest "natural" source of newly available N to terrestrial ecosystems, and estimates suggest the highest such inputs occur in tropical ecosystems. While patterns of and controls over N fixation in these systems remain poorly known, the data we do have suggest that chemical differences among tree species canopies could affect free-living N fixation rates. In a diverse lowland rain forest in Costa Rica, we established a series of vertical, canopy-to-soil profiles for six common canopy tree species, and we measured free-living N fixation rates and multiple aspects of chemistry of live canopy leaves, senesced canopy leaves, bulk leaf litter, and soil for eight individuals of each tree species. Free-living N fixation rates varied significantly among tree species for all four components, and independent of species identity, rates of N fixation ranged by orders of magnitude along the vertical profile. Our data suggest that variations in phosphorus (P) concentration drove a significant fraction of the observed species-specific variation in free-living N fixation rates within each layer of the vertical profile. Furthermore, our data suggest significant links between canopy and forest floor nutrient concentrations; canopy P was correlated with bulk leaf litter P below individual tree crowns. Thus, canopy chemistry may affect a suite of ecosystem processes not only within the canopy itself, but at and beneath the forest floor as well.

  10. Nitrogen fixation by immobilized NIF derepressed Klebsiella pneumoniae cells

    SciTech Connect

    Venkatasubramanian, K.; Toda, Y.

    1980-01-01

    In vitro production of ammonia through biological means poses a number of challenges. The organisms should be able to accumulate considerable concentrations of ammonia in the medium. Secondly, nonphotosynthetic organisms must be supplied with high-energy substrates to carry out the fixation reaction. Thirdly, the organisms must be kept in a viable state to produce ammonia over long periods of time. In this article, preliminary results on the production of ammonia by a mutant strain of Klebsiella pneumoniae in continuous reactor systems are discussed. Continuous production of ammonia becomes feasible through the immobilization of the whole microbial cells and then through the use of the resulting catalyst system in a flow-through reactor. The rationale for immobilizing microbial cells and the advantages of such an approach over traditional fermentation processes are briefly described as they relate to the microbial production of ammonia. The microbial cells can be immobilized in such a way that their viability is still maintained in the immobilized state. This, in turn, obviates addition of cofactors, which is often an expensive step associated with immobilized multi-enzyme systems. Reconstituted bovine-hide collagen as the carrier matrix for fixing the cells was the carrier of choice for our work on immobilized Klebsiella cells. Polyacrylamide gels were examined as an alternate carrier matrix but results from this were found to be inferior to those collagen immobilized cell system.

  11. Insights into symbiotic nitrogen fixation in Medicago truncatula.

    PubMed

    Tesfaye, Mesfin; Samac, Deborah A; Vance, Carroll P

    2006-03-01

    In silico analysis of the Medicago truncatula gene index release 8.0 at The Institute for Genomic Research identified approximately 530 tentative consensus sequences (TC) clustered from 2,700 expressed sequence tags (EST) derived solely from Sinorhizobium meliloti-inoculated root and nodule tissues. A great majority (76%) of these TC were derived exclusively from nitrogen-fixing and senescent nodules. A cDNA filter array was constructed using approximately 58% of the in silico-identified TC as well as cDNAs representing selected carbon and nitrogen metabolic pathways. The purpose of the array was to analyze transcript abundance in M. truncatula roots and nodules following inoculation by a wild-type S. meliloti strain, a mutant strain that forms ineffective nodules, an uninoculated root control, and roots following nitrate or ammonium treatments. In all, 81 cDNAs were upregulated in both effective and ineffective nodules, and 78% of these cDNAs represent in silico-identified TC. One group of in silico-identified TC encodes genes with similarity to putative plant disease resistance (R) genes of the nucleotide binding site-leucine-rich repeat type. Expression of R genes was enhanced in effective nodules, and transcripts also were detected in ineffective nodules at 14 days postinoculation (dpi). Homologous R gene sequences also have been identified in the Medicago genome. However, their functional importance in nodules remains to be established. Genes for enzymes involved in organic acid synthesis along with genes involved in nitrogen metabolism were shown to be coexpressed in nitrate-fed roots and effective nodules of M. truncatula.

  12. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr

    NASA Astrophysics Data System (ADS)

    Stüeken, Eva E.; Buick, Roger; Guy, Bradley M.; Koehler, Matthew C.

    2015-04-01

    Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction, photochemical reactions, or lightning discharge could have converted atmospheric N2 into assimilable NH4+, HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4+, thus represented a major breakthrough in the radiation of life, but its timing is uncertain. Here we present nitrogen isotope ratios with a mean of 0.0 +/- 1.2‰ from marine and fluvial sedimentary rocks of prehnite-pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitrogenase as opposed to other variants that impart significant negative fractionations. Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event.

  13. Environmental Forcing of Nitrogen Fixation in the Eastern Tropical and Sub-Tropical North Atlantic Ocean

    PubMed Central

    Rijkenberg, Micha J. A.; Langlois, Rebecca J.; Mills, Matthew M.; Patey, Matthew D.; Hill, Polly G.; Nielsdóttir, Maria C.; Compton, Tanya J.; LaRoche, Julie; Achterberg, Eric P.

    2011-01-01

    During the winter of 2006 we measured nifH gene abundances, dinitrogen (N2) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 106 L−1 nifH gene copies, unicellular group A cyanobacteria with up to 105 L−1 nifH gene copies and gamma A proteobacteria with up to 104 L−1 nifH gene copies. N2 fixation rates were low and ranged between 0.032–1.28 nmol N L−1 d−1 with a mean of 0.30±0.29 nmol N L−1 d−1 (1σ, n = 65). CO2-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2±3.2 in surface waters. Nevertheless, N2 fixation rates contributed only 0.55±0.87% (range 0.03–5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N2 fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N2 fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the consequences of climate

  14. Environmental forcing of nitrogen fixation in the eastern tropical and sub-tropical North Atlantic Ocean.

    PubMed

    Rijkenberg, Micha J A; Langlois, Rebecca J; Mills, Matthew M; Patey, Matthew D; Hill, Polly G; Nielsdóttir, Maria C; Compton, Tanya J; Laroche, Julie; Achterberg, Eric P

    2011-01-01

    During the winter of 2006 we measured nifH gene abundances, dinitrogen (N(2)) fixation rates and carbon fixation rates in the eastern tropical and sub-tropical North Atlantic Ocean. The dominant diazotrophic phylotypes were filamentous cyanobacteria, which may include Trichodesmium and Katagnymene, with up to 10(6) L(-1)nifH gene copies, unicellular group A cyanobacteria with up to 10(5) L(-1)nifH gene copies and gamma A proteobacteria with up to 10(4) L(-1)nifH gene copies. N(2) fixation rates were low and ranged between 0.032-1.28 nmol N L(-1) d(-1) with a mean of 0.30 ± 0.29 nmol N L(-1) d(-1) (1σ, n = 65). CO(2)-fixation rates, representing primary production, appeared to be nitrogen limited as suggested by low dissolved inorganic nitrogen to phosphate ratios (DIN:DIP) of about 2 ± 3.2 in surface waters. Nevertheless, N(2) fixation rates contributed only 0.55 ± 0.87% (range 0.03-5.24%) of the N required for primary production. Boosted regression trees analysis (BRT) showed that the distribution of the gamma A proteobacteria and filamentous cyanobacteria nifH genes was mainly predicted by the distribution of Prochlorococcus, Synechococcus, picoeukaryotes and heterotrophic bacteria. In addition, BRT indicated that multiple a-biotic environmental variables including nutrients DIN, dissolved organic nitrogen (DON) and DIP, trace metals like dissolved aluminum (DAl), as a proxy of dust inputs, dissolved iron (DFe) and Fe-binding ligands as well as oxygen and temperature influenced N(2) fixation rates and the distribution of the dominant diazotrophic phylotypes. Our results suggest that lower predicted oxygen concentrations and higher temperatures due to climate warming may increase N(2) fixation rates. However, the balance between a decreased supply of DIP and DFe from deep waters as a result of more pronounced stratification and an enhanced supply of these nutrients with a predicted increase in deposition of Saharan dust may ultimately determine the

  15. Climatic and Grazing Controls on Biological Soil Crust Nitrogen Fixation in Semi-arid Ecosystems

    NASA Astrophysics Data System (ADS)

    Schwabedissen, S. G.; Reed, S.; Lohse, K. A.; Magnuson, T. S.

    2014-12-01

    Nitrogen, next to water, is believed to be the main limiting resource in arid and semi-arid ecosystems. Biological soil crusts (biocrusts) -a surface community of mosses, lichens and cyanobacteria-have been found to be the main influx of "new" nitrogen (N) into many dryland ecosystems. Controls on biocrust N fixation rates include climate (temperature and moisture), phosphorus availability, and disturbance factors such as trampling, yet a systematic examination of climatic and disturbance controls on biocrusts communities is lacking. Biocrust samples were collected along an elevation gradient in the Reynolds Creek Experimental Watershed near Murphy, Idaho. Four sites were selected from a sagebrush steppe ecosystem with precipitation ranging from ≤250mm/yr to ≥1100mm/yr. Each site included 5 grazed plots and one historic exclosure plot that has been free from grazing for more than 40 years. Five samples each were collected from under plants and from interplant spaces from the grazed plots and exclosures and analyzed for potential N fixation using an acetylene reduction assay. We hypothesized that N fixation rates would be the highest in the exclosures of the two middle sites along the elevation gradient, due to the lack of disturbance and optimal temperature and moisture, respectively. As predicted, results showed higher rates of potential N fixation in exclosures than non-exclosures at a mid-elevation 8.4 ± 3.1 kg N/ha/yr in the exclosures compared to 1.8 ± 1.5 kg N/ha/yr indicating that grazing may reduce N fixation activity. Interestingly, rates were 2-5 times lower under plant canopies compared to interplant spaces at all but the highest elevation site. Findings from our study suggest that biocrust N fixation may be a dominant input of N into theses dryland systems and, in line with our hypotheses, that climate, location within the landscape, and disturbance may interact to regulate the rates of this fundamental ecosystem process.

  16. Bedrock nitrogen inputs support litter nitrogen fixation and temperate forest ecosystem fertility

    NASA Astrophysics Data System (ADS)

    Dynarski, K. A.; Mitchell, S. A.; Morford, S.; Houlton, B. Z.

    2015-12-01

    Nitrogen (N) is one of the most frequently limiting nutrients to terrestrial ecosystem productivity worldwide. As atmospheric carbon dioxide concentrations continue to rise, progressive N limitation is expected to constrain the ability of terrestrial ecosystems to store additional C, making an understanding of N inputs to terrestrial ecosystems increasingly important. In temperate forests, rock reservoirs and biological N fixation (BNF) represent two significant, but poorly characterized, inputs of bioavailable N. Recent research has demonstrated that bedrock can provide a substantial amount of ecosystem-available N in moderate-to-high relief areas with N-rich sedimentary bedrock. In these same ecosystems, asymbiotic BNF performed by heterotrophic microbes in plant litter can provide an additional N input of up to ~2 kg N ha-1 yr-1. Here, we tested the hypothesis that rock N inputs support increased litter BNF via enhanced ecosystem N fertility. We measured rates of BNF along with rock, soil, foliage, and litter chemistry across sites varying substantially in rock N concentrations (from 32 to 800 ppm N). The sites are dominated by Douglas fir and share similar climates and landscape positions (eroding slopes), yet display marked increases in foliar and soil N content as a function of rock N concentrations (foliar: R2=0.18, p<0.001, soil: R2=0.50, p=0.001). We found a significant positive correlation between rock N content and litter BNF rates (R2=0.11, p=0.0035), with rates of BNF at sites with greater than 400 ppm N in bedrock more than double rates of BNF at sites with lower than 400 ppm N in bedrock (p<0.001). These patterns could not be explained by increases in other rock-derived nutrients such as phosphorus or molybdenum, as neither of these known BNF controls increased over the rock N gradient. We found declining foliar lignin:N ratios with increased rock N, suggesting that rock N inputs can increase litter quality, supporting greater microbial activity

  17. Is there a link between free-living nitrogen fixation rates and nitrogen mineralization rates?

    NASA Astrophysics Data System (ADS)

    Smercina, D.; Tiemann, L. K.; Friesen, M.; Evans, S. E.; West, W.

    2016-12-01

    Plant accessible nitrogen (N) is controlled by the rates of N fixation (N-fix) and N mineralization (N-min), yet the relationship between these two processes is relatively unexplored. In particular, we know relatively little about the rates of free-living N-fix, thought to be supported mainly by plant root exudates. Furthermore, there is no consensus on the link between N-fix and N-min rates in terrestrial soil systems. To address this knowledge gap, we are using a three-pronged approach, including a meta-analysis, a greenhouse study and field experiments. Following an extensive literature search, we found 12 papers that simultaneously reported N-fix and N-min rates. Surprisingly, these data indicated a positive relationship between N-fix and N-min rates; however, the scarcity of data limits our ability to draw any strong conclusions. We have explored the relationship between N-fix and N-min in a controlled greenhouse experiment using switchgrass (Panicum virgatum) because recent evidence suggests switchgrass may support free-living N-fix when N limited. Indeed, in our study, switchgrass and soils exposed to N limiting conditions experienced no adverse effects, namely no differences in plant growth or tissue chemistry (C:N), or soil enzyme activities compared to non-N limiting conditions. Soils used in this study are from marginal lands, low in soil organic matter and N, so it is likely N deficits are compensated for via N-fix. Analysis of 15N2 -fix and gross N-min rates, determined via 15N pool dilution, will elucidate this source of N. Finally, our field experiment encompasses six marginal land sites across MI and WI, part of the Great Lakes Bioenergy Research Center. In 2016, we measured N-fix and N-min rates in switchgrass monoculture plots at all six sites once, at the peak of growing season, and bi-weekly, from April to September, at two MI field sites. Data collected to date from two MI sites show no difference in N-min rates in N fertilized versus

  18. Variations in the rhythms of respiration and nitrogen fixation in members of the unicellular diazotrophic cyanobacterial genus Cyanothece.

    PubMed

    Bandyopadhyay, Anindita; Elvitigala, Thanura; Liberton, Michelle; Pakrasi, Himadri B

    2013-03-01

    In order to accommodate the physiologically incompatible processes of photosynthesis and nitrogen fixation within the same cell, unicellular nitrogen-fixing cyanobacteria have to maintain a dynamic metabolic profile in the light as well as the dark phase of a diel cycle. The transition from the photosynthetic to the nitrogen-fixing phase is marked by the onset of various biochemical and regulatory responses, which prime the intracellular environment for nitrogenase activity. Cellular respiration plays an important role during this transition, quenching the oxygen generated by photosynthesis and by providing energy necessary for the process. Although the underlying principles of nitrogen fixation predict unicellular nitrogen-fixing cyanobacteria to function in a certain way, significant variations are observed in the diazotrophic behavior of these microbes. In an effort to elucidate the underlying differences and similarities that govern the nitrogen-fixing ability of unicellular diazotrophic cyanobacteria, we analyzed six members of the genus Cyanothece. Cyanothece sp. ATCC 51142, a member of this genus, has been shown to perform efficient aerobic nitrogen fixation and hydrogen production. Our study revealed significant differences in the patterns of respiration and nitrogen fixation among the Cyanothece spp. strains that were grown under identical culture conditions, suggesting that these processes are not solely controlled by cues from the diurnal cycle but that strain-specific intracellular metabolic signals play a major role. Despite these inherent differences, the ability to perform high rates of aerobic nitrogen fixation and hydrogen production appears to be a characteristic of this genus.

  19. Reiteration of genes involved in symbiotic nitrogen fixation by fast-growing Rhizobium japonicum.

    PubMed Central

    Prakash, R K; Atherly, A G

    1984-01-01

    By using cloned Rhizobium meliloti nodulation (nod) genes and nitrogen fixation (nif) genes, we found that the genes for both nodulation and nitrogen fixation were on a plasmid present in fast-growing Rhizobium japonicum strains. Two EcoRI restriction fragments from a plasmid of fast-growing R. japonicum hybridized with nif structural genes of R. meliloti, and three EcoRI restriction fragments hybridized with the nod clone of R. meliloti. Cross-hybridization between the hybridizing fragments revealed a reiteration of nod and nif DNA sequences in fast-growing R. japonicum. Both nif structural genes D and H were present on 4.2- and 4.9-kilobase EcoRI fragments, whereas nifK was present only on the 4.2-kilobase EcoR2 fragment. These results suggest that the nif gene organizations in fast-growing and in slow-growing R. japonicum strains are different. Images PMID:6094491

  20. High potential of nitrogen fixation in pristine, ombrotrophic bogs in Southern Patagonia

    NASA Astrophysics Data System (ADS)

    Knorr, Klaus-Holger; Horn, Marcus A.; Bahamonde Aguilar, Nelson A.; Borken, Werner

    2015-04-01

    Nitrogen (N) input in pristine peatlands occurs via natural input of inorganic N through atmospheric deposition or biological dinitrogen (N2) fixation. However, N2 fixation is to date mostly attributed to bacteria and algae associated to Sphagnum and its contribution to plant productivity and peat buildup has been often underestimated in previous studies. Based on net N storage, exceptionally low N deposition, and high abundance of vascular plants at pristine peatlands in Southern Patagonia, we hypothesized that there must be a high potential of non-symbiotic N2 fixation not limited to the occurrence of Sphagnum. To this end, we chose two ombrotrophic bogs with spots that are dominated either by Sphagnum or by vascular, cushion-forming plants and sampled peat from different depths for incubation with 15N2 to determine N2 fixation potentials. Moreover, we analyzed 15N2 fixation by a nodule-forming, endemic conifer inhabiting the peatlands. Results from 15N2 uptake were compared to the conventional approach to study N2 fixation by the acetylene reduction assay (ARA). Using 15N2 as a tracer, high non-symbiotic N2 fixation rates of 0.3-1.4 μmol N g-1 d-1 were found down to 50 cm under micro-oxic conditions (2 vol.%) in samples from both plots either covered by Sphagnum magellanicum or by vascular cushion plants. Peat N concentrations suggested a higher potential of non-symbiotic N2 fixation under cushion plants, likely because of the availability of easily decomposable organic compounds as substrates and oxic conditions in the rhizosphere. In the Sphagnum plots, high N2 fixation below 10 cm depth would rather reflect a potential fixation that may switch on during periods of low water levels when oxygen penetrates deeper into the peat. 15N natural abundance of live Sphagnum from 0-10 cm pointed to N uptake solely from atmospheric deposition and non-symbiotic N2 fixation. 15N signatures of peat from the cushion plant plots indicated additional N supply from N

  1. In Situ Denitrification and Biological Nitrogen Fixation Under Enhanced Atmospheric Reactive Nitrogen Deposition in UK Peatlands

    NASA Astrophysics Data System (ADS)

    Ullah, Sami; Saiz Val, Ernesto; Sgouridis, Fotis; Peichl, Matthias; Nilsson, Mats

    2017-04-01

    Dinitrogen (N2) and nitrous oxide (N2O) losses due to denitrification and biological N2 fixation (BNF) are the most uncertain components of the nitrogen (N) cycle in peatlands under enhanced atmospheric reactive nitrogen (Nr) deposition. This uncertainty hampers our ability to assess the contribution of denitrification to the removal of biologically fixed and/or atmospherically deposited Nr in peatlands. This uncertainty emanates from the difficulty in measuring in situ soil N2 and N2O production and consumption in peatlands. In situ denitrification and its contribution to total N2O flux was measured monthly between April 2013 and October 2014 in peatlands in two UK catchments. An adapted 15N-Gas Flux method1 with low level addition of 15N tracer (0.03 ± 0.005 kg 15N ha-1) was used to measure denitrification and its contribution to net N2O production (DN2O/TN2O). BNF was measured in situ through incubation of selected sphagnum species under 15N2 gas tracer. Denitrification2 varied temporally and averaged 8 kg N-N2 ha-1 y-1. The contribution of denitrification was about 48% to total N2O flux3 of 0.05 kg N ha-1 y-1. Soil moisture, temperature, ecosystem respiration, pH and mineral N content mainly regulated the flux of N2 and N2O. Preliminary results showed suppression of BNF, which was 1.8 to 7 times lower in peatland mosses exposed to ˜15 to 20 kg N ha-1 y-1 Nr deposition in the UK than in peatland mosses in northern Sweden with background Nr deposition. Overall, the contribution of denitrification to Nr removal in the selected peatlands was ˜50% of the annual Nr deposition rates, making these ecosystems vulnerable to chronic N saturation. These results point to a need for a more comprehensive annual BNF measurement to more accurately account for total Nr input into peatlands and its atmospheric loss due to denitrification. References Sgouridis F, Stott A & Ullah S, 2016. Application of the 15N-Gas Flux method for measuring in situ N2 and N2O fluxes due to

  2. Growth, nitrogen fixation and mineral acquisition of Alnus sieboldiana after inoculation of Frankia together with Gigaspora margarita and Pseudomonas putida.

    Treesearch

    Takashi Yamanaka; Akio Akama; Ching-Yan Li; Hiroaki. Okabe

    2005-01-01

    The role of tetrapartite associations among Frankia, Gigaspora margarita (an arbuscular mycorrhizal fungus), Pseudomonas putida (rhizobacterium), and Alnus sieboldiana in growth, nitrogen fixation, and mineral acquisition of A. sieboldiana was investigated....

  3. The Effects of Salinity and Sodicity upon Nodulation and Nitrogen Fixation in Chickpea (Cicer arietinum)

    PubMed Central

    RAO, D. L. N.; GILLER, K. E.; YEO, A. R.; FLOWERS, T. J.

    2002-01-01

    Production of grain legumes is severely reduced in salt‐affected soils because their ability to form and maintain nitrogen‐fixing nodules is impaired by both salinity and sodicity (alkalinity). Genotypes of chickpea, Cicer arietinum, with high nodulation capacity under stress were identified by field screening in a sodic soil in India and subsequently evaluated quantitatively for nitrogen fixation in a glasshouse study in a saline but neutral soil in the UK. In the field, pH 8·9 was the critical upper limit for most genotypes studied but genotypes with high nodulation outperformed all others at pH 9·0–9·2. The threshold limit of soil salinity for shoot growth was at ECe 3 dS m–1, except for the high‐nodulation selection for which it was ECe 6. Nodulation was reduced in all genotypes at salinities above 3 dS m–1 but to a lesser extent in the high‐nodulation selection, which proved inherently superior under both non‐saline and stress conditions. Nitrogen fixation was also much more tolerant of salinity in this selection than in the other genotypes studied. The results show that chickpea genotypes tolerant of salt‐affected soil have better nodulation and support higher rates of symbiotic nitrogen fixation than sensitive genotypes. PMID:12099530

  4. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide.

    PubMed

    Hutchins, David A; Walworth, Nathan G; Webb, Eric A; Saito, Mak A; Moran, Dawn; McIlvin, Matthew R; Gale, Jasmine; Fu, Fei-Xue

    2015-09-01

    Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.

  5. Hydrogenated Bismuth Molybdate Nanoframe for Efficient Sunlight-Driven Nitrogen Fixation from Air.

    PubMed

    Hao, Yuchen; Dong, Xiaoli; Zhai, Shangru; Ma, Hongchao; Wang, Xiuying; Zhang, Xiufang

    2016-12-23

    Sunlight-driven dinitrogen fixation can lead to a novel concept for the production of ammonia under mild conditions. However, the efficient artificial photosynthesis of ammonia from ordinary air (instead of high pure N2 ) has never been implemented. Here, we report for the first time the intrinsic catalytic activity of Bi2 MoO6 catalyst for direct ammonia synthesis under light irradiation. The edge-exposed coordinatively unsaturated Mo atoms in an Mo-O coordination polyhedron can act as activation centers to achieve the chemisorption, activation, and photoreduction of dinitrogen efficiently. Using that insight as a starting point, through rational structure and defect engineering, the optimized Bi2 MoO6 sunlight-driven nitrogen fixation system, which simultaneously possesses robust nitrogen activation ability, excellent light-harvesting performance, and efficient charge transmission was successfully constructed. As a surprising achievement, this photocatalytic system demonstrated for the first time ultra-efficient (1.3 mmol g(-1)  h(-1) ) and stable sunlight-driven nitrogen fixation from air in the absence of any organic scavengers.

  6. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide

    NASA Astrophysics Data System (ADS)

    Hutchins, David A.; Walworth, Nathan G.; Webb, Eric A.; Saito, Mak A.; Moran, Dawn; McIlvin, Matthew R.; Gale, Jasmine; Fu, Fei-Xue

    2015-09-01

    Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean.

  7. Irreversibly increased nitrogen fixation in Trichodesmium experimentally adapted to elevated carbon dioxide

    PubMed Central

    Hutchins, David A.; Walworth, Nathan G.; Webb, Eric A.; Saito, Mak A.; Moran, Dawn; McIlvin, Matthew R.; Gale, Jasmine; Fu, Fei-Xue

    2015-01-01

    Nitrogen fixation rates of the globally distributed, biogeochemically important marine cyanobacterium Trichodesmium increase under high carbon dioxide (CO2) levels in short-term studies due to physiological plasticity. However, its long-term adaptive responses to ongoing anthropogenic CO2 increases are unknown. Here we show that experimental evolution under extended selection at projected future elevated CO2 levels results in irreversible, large increases in nitrogen fixation and growth rates, even after being moved back to lower present day CO2 levels for hundreds of generations. This represents an unprecedented microbial evolutionary response, as reproductive fitness increases acquired in the selection environment are maintained after returning to the ancestral environment. Constitutive rate increases are accompanied by irreversible shifts in diel nitrogen fixation patterns, and increased activity of a potentially regulatory DNA methyltransferase enzyme. High CO2-selected cell lines also exhibit increased phosphorus-limited growth rates, suggesting a potential advantage for this keystone organism in a more nutrient-limited, acidified future ocean. PMID:26327191

  8. Nodule and Leaf Nitrate Reductases and Nitrogen Fixation in Medicago sativa L. under Water Stress

    PubMed Central

    Aparicio-Tejo, P.; Sánchez-Díaz, Manuel

    1982-01-01

    The effect of water stress on patterns of nitrate reductase activity in the leaves and nodules and on nitrogen fixation were investigated in Medicago sativa L. plants watered 1 week before drought with or without NO3−. Nitrogen fixation was decreased by water stress and also inhibited strongly by the presence of NO3−. During drought, leaf nitrate reductase activity (NRA) decreased significantly particularly in plants watered with NO3−, while with rewatering, leaf NRA recovery was quite important especially in the NO3−-watered plants. As water stress progressed, the nodular NRA increased both in plants watered with NO3− and in those without NO3− contrary to the behavior of the leaves. Beyond −15.105 pascal, nodular NRA began to decrease in plants watered with NO3−. This phenomenon was not observed in nodules of plants given water only. Upon rewatering, it was observed that in plants watered with NO3− the nodular NRA increased again, while in plants watered but not given NO3−, such activity began to decrease. Nitrogen fixation increased only in plants without NO3−. PMID:16662233

  9. The significance of nitrogen fixation to new production during early summer in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Ohlendieck, U.; Gundersen, K.; Meyerhöfer, M.; Fritsche, P.; Nachtigall, K.; Bergmann, B.

    2006-08-01

    Rates of dinitrogen (N2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June-July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m-2 (1998) and 33 mmol N m-2 (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12-26% more new N than other annual estimates (mid July-mid October) from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasize the need for multiple stations and seasonal sampling strategies in biochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28-150% of N needed to meet the rate of C incorporation by primary production. Since the molar C:N rate incorporation ratio (C:NRATE) in filamentous cyanobacterial cells was almost twice as high as the molar C:N mass ratio (C:NMASS) in both years, we suggest that the diazotrophs incorporated excess C on a short term basis (for carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4-24) in 1998 and 18% (range 2-45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be attributed to regenerated incorporation of dissolved organic N (DON) and ammonium generated from larger diazotroph cyanobacteria. Therefore, N excretion from filamentous cyanobacteria

  10. Global terrestrial carbon and nitrogen cycling insensitive to estimates of biological N fixation

    NASA Astrophysics Data System (ADS)

    Steinkamp, J.; Weber, B.; Werner, C.; Hickler, T.

    2015-12-01

    Dinitrogen (N2) is the most abundant molecule in the atmosphere and incorporated in other molecules an essential nutrient for life on earth. However, only few natural processes can initiate a reaction of N2. These natural processes are fire, lightning and biological nitrogen fixation (BNF) with BNF being the largest source. In the course of the last century humans have outperformed the natural processes of nitrogen fixation by the production of fertilizer. Industrial and other human emission of reactive nitrogen, as well as fire and lightning lead to a deposition of 63 Tg (N) per year. This is twice the amount of BNF estimated by the default setup of the dynamic global vegetation model LPJ-GUESS (30 Tg), which is a conservative approach. We use different methods and parameterizations for BNF in LPJ-GUESS: 1.) varying total annual amount; 2.) annual evenly distributed and daily calculated fixation rates; 3.) an improved dataset of BNF by cryptogamic covers (free-living N-fixers). With this setup BNF is ranging from 30 Tg to 60 Tg. We assess the impact of BNF on carbon storage and grand primary production (GPP) of the natural vegetation. These results are compared to and evaluated against available independent datasets. We do not see major differences in the productivity and carbon stocks with these BNF estimates, suggesting that natural vegetation is insensitive to BNF on a global scale and the vegetation can compensate for the different nitrogen availabilities. Current deposition of nitrogen compounds and internal cycling through mineralization and uptake is sufficient for natural vegetation productivity. However, due to the coarse model grid and spatial heterogeneity in the real world this conclusion does not exclude the existence of habitats constrained by BNF.

  11. Occurrence, structure, and nitrogen-fixation of root nodules of actinorhizal Arizona alder

    Treesearch

    J. O. Dawson; Gerald J. Gottfried; D. Hahn

    2005-01-01

    Actinorhizal plants are nodulated by the symbiotic, nitrogen-fixing actinomycete Frankia. The genus Alnus in the family Betulaceae is one of the 24 genera in 8 families of angiospermous plants that are actinorhizal. Arizona alder (Alnus oblongifolia Torr.) occurs in isolated populations associated with the watersheds of Madrean Sky Islands in the...

  12. A quantitative analysis of the direct and indirect costs of nitrogen fixation: a model based on Azotobacter vinelandii.

    PubMed

    Inomura, Keisuke; Bragg, Jason; Follows, Michael J

    2017-01-01

    Nitrogen fixation is advantageous in microbial competition when bioavailable nitrogen is scarce, but has substantial costs for growth rate and growth efficiency. To quantify these costs, we have developed a model of a nitrogen-fixing bacterium that constrains mass, electron and energy flow at the scale of the individual. When tested and calibrated with laboratory data for the soil bacterium Azotobacter vinelandii, the model reveals that the direct energetic cost of nitrogen fixation is small relative to the cost of managing intracellular oxygen. It quantifies the costs and benefits of several potential oxygen protection mechanisms present in nature including enhanced respiration (respiratory protection) as well as the production of extracellular polymers as a barrier to O2 diffusion, and increasing cell size. The latter mechanisms lead to higher growth efficiencies relative to respiratory protection alone. This simple, yet mechanistic framework provides a quantitative model of nitrogen fixation, which can be applied in ecological simulations.

  13. A quantitative analysis of the direct and indirect costs of nitrogen fixation: a model based on Azotobacter vinelandii

    PubMed Central

    Inomura, Keisuke; Bragg, Jason; Follows, Michael J

    2017-01-01

    Nitrogen fixation is advantageous in microbial competition when bioavailable nitrogen is scarce, but has substantial costs for growth rate and growth efficiency. To quantify these costs, we have developed a model of a nitrogen-fixing bacterium that constrains mass, electron and energy flow at the scale of the individual. When tested and calibrated with laboratory data for the soil bacterium Azotobacter vinelandii, the model reveals that the direct energetic cost of nitrogen fixation is small relative to the cost of managing intracellular oxygen. It quantifies the costs and benefits of several potential oxygen protection mechanisms present in nature including enhanced respiration (respiratory protection) as well as the production of extracellular polymers as a barrier to O2 diffusion, and increasing cell size. The latter mechanisms lead to higher growth efficiencies relative to respiratory protection alone. This simple, yet mechanistic framework provides a quantitative model of nitrogen fixation, which can be applied in ecological simulations. PMID:27740611

  14. N-nitrosamines formation from secondary amines by nitrogen fixation on the surface of activated carbon.

    PubMed

    Padhye, Lokesh P; Hertzberg, Benjamin; Yushin, Gleb; Huang, Ching-Hua

    2011-10-01

    Our previous study demonstrated that many commercial activated carbon (AC) particles may catalyze transformation of secondary amines to yield trace levels of N-nitrosamines under ambient aerobic conditions. Because of the widespread usage of AC materials in numerous analytical and environmental applications, it is imperative to understand the reaction mechanism responsible for formation of nitrosamine on the surface of ACs to minimize their occurrence in water treatment systems and during analytical methods employing ACs. The study results show that the AC-catalyzed nitrosamine formation requires both atmospheric oxygen and nitrogen. AC's surface reactive sites react with molecular oxygen to form reactive oxygen species (ROS), which facilitate fixation of molecular nitrogen on the carbon surfaces to generate reactive nitrogen species (RNS) likely nitrous oxide and hydroxylamine that can react with adsorbed amines to form nitrosamines. AC's properties play a crucial role as more nitrosamine formation is associated with carbon surfaces with higher surface area, more surface defects, reduced surface properties, higher O(2) uptake capacity, and higher carbonyl group content. This study is a first of its kind on the nitrosamine formation mechanism involving nitrogen fixation on AC surfaces, and the information will be useful for minimization of nitrosamines in AC-based processes.

  15. Glutamine synthetase stabilizes the binding of GlnR to nitrogen fixation gene operators.

    PubMed

    Fernandes, Gabriela de C; Hauf, Ksenia; Sant'Anna, Fernando H; Forchhammer, Karl; Passaglia, Luciane M P

    2017-03-01

    Biological nitrogen fixation (BNF) is a high energy demanding process carried out by diazotrophic microorganisms that supply combined nitrogen to the biosphere. The genes related to BNF are strictly regulated, but these mechanisms are poorly understood in gram-positive bacteria. The transcription factor GlnR was proposed to regulate nitrogen fixation-related genes based on Paenibacillus comparative genomics. In order to validate this proposal, we investigated BNF regulatory sequences in Paenibacillus riograndensis SBR5(T) genome. We identified GlnR-binding sites flanking σ(A) -binding sites upstream from BNF-related genes. GlnR binding to these sites was demonstrated by surface plasmon resonance spectroscopy. GlnR-DNA affinity is greatly enhanced when GlnR is in complex with feedback-inhibited (glutamine-occupied) glutamine synthetase (GS). GlnR-GS complex formation is also modulated by ATP and AMP. Thereby, gene repression exerted by the GlnR-GS complex is coupled with nitrogen (glutamine levels) and energetic status (ATP and AMP). Finally, we propose a DNA-looping model based on multiple operator sites that represents a strong and strict regulation for these genes. © 2017 Federation of European Biochemical Societies.

  16. [Recent advances in research and application of associated nitrogen-fixation with graminaceous plants].

    PubMed

    Zhang, Limei; Fang, Ping; Zhu, Riqing

    2004-09-01

    The category, characteristic of diazotrophs isolated from inside and/or rhizosphere of graminaceous plants in recent year and the mechanism of the promoting effects on their host plant were reviewed in this paper. The current status of application of associative nitrogen-fixation inoculants and the problems in inoculation were discussed. It was indicated that the main factors influencing the effects of inoculants include the competition of indigenous micro-organism with inoculants for nutritions and energy, difference of host plant genotypes in associative relationship, and variance of environmental conditions such as the concentration of ammonium in soil solution and the oxygen partial pressure in soil air. The trends of future research in this field were prospected, for example, to isolate and identify the high nitrogen fixing efficiency strains with wider environmental adaptability, to create associative nitrogen fixing bacteria strain which is able to bear or endure higher concentration of ammonium by gene engineering technique, to induce graminaceous plant forming root nodule for nitrogen fixation and to exert the predominance of endophytic diazotrophs.

  17. Ca2+ Requirement for Aerobic Nitrogen Fixation by Heterocystous Blue-Green Algae 1

    PubMed Central

    Rodríguez, Herminia; Rivas, Joaquín; Guerrero, Miguel G.; Losada, Manuel

    1990-01-01

    The requirement of Ca2+ for growth and nitrogen fixation has been investigated in two strains of heterocystous blue-green algae (Anabaena sp. and Anabaena ATCC 33047). With combined nitrogen (nitrate or ammonium) or with N2 under microaerobic conditions, Ca2+ was not required for growth, at least in concentrations greater than traces. In contrast, Ca2+ was required as a macronutrient for growth and nitrogen fixation with air as the nitrogen source. Addition of Ca2+ to an aerobic culture without Ca2+ promoted, after a lag of several hours, development of nitrogenase activity and cell growth. Provision of air to a microaerobic culture in the absence of Ca2+ promoted a drastic drop in nitrogenase activity, which rapidly recovered its initial level upon restoration of microaerobic conditions. Development of nitrogenase activity in response to either Ca2+ or low oxygen tension was dependent on de novo protein synthesis. The role of Ca2+ seems to be related to protection of nitrogenase from inactivation, by conferring heterocysts resistance to oxygen. PMID:16667401

  18. Understanding the Red Sea nutrient cycle - a first look into nitrogen fixation in the Red Sea

    NASA Astrophysics Data System (ADS)

    Mohamed, Roslinda; Arrieta, Jesus; Alam, Intikhab; Duarte, Carlos

    2016-04-01

    The Red Sea is an elongated and semi-enclosed system bordered by Africa and Saudi Arabia. Positioned in an arid, tropical zone, the system receives high solar irradiance and heat flux, extensive evaporation, low rainfall and therefore high salinity. These harsh environmental conditions has set the Red Sea to be one of the fastest warming and saltiest ecosystem in the world. Although nutrients are known to be at very low concentrations, the ultimately limiting nutrient in the system is still undefined. Therefore, like most other oligotrophic systems, we regard the Red Sea as being nitrogen-limited and we foresee nitrogen fixation as the most probable bottleneck in the Red Sea nitrogen budget. On the basis of metagenomes from pelagic microbial communities along the Red Sea, we looked into the distribution of nitrogenase, an enzyme involved in nitrogen fixation, in this system and provide a first insight into the microbial community that is involved in the process. The implications of this study will not only help improve our understanding of the Red Sea nutrient regime, but may also hint on future ocean responses to rising climates.

  19. Effect of composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea.

    PubMed

    Araújo, A S F; Monteiro, R T R; Carvalho, E M S

    2007-03-01

    The effect of composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea was evaluated in a greenhouse experiment. The compost was incorporated into soil at 0, 9.5, 19 and 38 t ha(-1) (bases upon the N requirement of the crops, i.e., 0, 50, 100 and 200 kg available N ha(-1)). Growth, nodulation and shoot accumulation of nitrogen were evaluated 36 and 63 days after plant emergence. Nodule glutamine synthetase (GS) activity and leghemoglobin content were evaluated 63 days after emergence. Composted textile sludge did not show negative effects on nodule number and weight, nodule GS activity and leghemoglobin content. Nitrogen accumulation in shoot dry matter in soybean and cowpea was higher than other treatments with application of 19 t ha(-1) of compost. Composting can be an alternate technology for the management of solid textile mill sludge. This study verifies that the composted textile sludge was not harmful to growth, nodulation and nitrogen fixation of soybean and cowpea.

  20. Genome evolution and nitrogen fixation in bacterial ectosymbionts of a protist inhabiting wood-feeding cockroaches

    SciTech Connect

    Tai, Vera; Carpenter, Kevin J.; Weber, Peter K.; Nalepa, Christine A.; Perlman, Steve J.; Keeling, Patrick J.

    2016-05-27

    By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protistBarbulanymphafrom the hindguts of the wood-eating cockroachCryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesis of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis ofC. punctulatushindgut symbionts exposedin vivoto15N2 supports the hypothesis thatBarbulanymphaectosymbionts are capable of nitrogen fixation. This genomic andin vivofunctional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. Here in this study, we investigated the

  1. Genome evolution and nitrogen fixation in bacterial ectosymbionts of a protist inhabiting wood-feeding cockroaches

    DOE PAGES

    Tai, Vera; Carpenter, Kevin J.; Weber, Peter K.; ...

    2016-05-27

    By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protistBarbulanymphafrom the hindguts of the wood-eating cockroachCryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesismore » of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis ofC. punctulatushindgut symbionts exposedin vivoto15N2 supports the hypothesis thatBarbulanymphaectosymbionts are capable of nitrogen fixation. This genomic andin vivofunctional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. Here in this study, we investigated the evolution and nitrogen fixation capabilities of ectosymbionts attached to the protist Barbulanympha from the hindgut of the wood-eating cockroach Cryptocercus punctulatus. In addressing genome evolution of protist ectosymbionts, our data suggest that the ecological pressures influencing the evolution of extracellular symbionts clearly differ from intracellular symbionts and organelles. Using NanoSIMS analysis

  2. Genome Evolution and Nitrogen Fixation in Bacterial Ectosymbionts of a Protist Inhabiting Wood-Feeding Cockroaches

    PubMed Central

    Carpenter, Kevin J.; Weber, Peter K.; Nalepa, Christine A.; Perlman, Steve J.; Keeling, Patrick J.

    2016-01-01

    ABSTRACT By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protist Barbulanympha from the hindguts of the wood-eating cockroach Cryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesis of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis of C. punctulatus hindgut symbionts exposed in vivo to 15N2 supports the hypothesis that Barbulanympha ectosymbionts are capable of nitrogen fixation. This genomic and in vivo functional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. IMPORTANCE The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. In this study, we investigated the evolution and nitrogen fixation capabilities of ectosymbionts attached to the protist Barbulanympha from the hindgut of the wood-eating cockroach Cryptocercus punctulatus. In addressing genome evolution of protist ectosymbionts, our data suggest that the ecological pressures influencing the evolution of extracellular symbionts clearly differ from intracellular symbionts and organelles. Using

  3. Genome evolution and nitrogen fixation in bacterial ectosymbionts of a protist inhabiting wood-feeding cockroaches

    SciTech Connect

    Tai, Vera; Carpenter, Kevin J.; Weber, Peter K.; Nalepa, Christine A.; Perlman, Steve J.; Keeling, Patrick J.

    2016-05-27

    By combining genomics and isotope imaging analysis using high-resolution secondary ion mass spectrometry (NanoSIMS), we examined the function and evolution of Bacteroidales ectosymbionts of the protistBarbulanymphafrom the hindguts of the wood-eating cockroachCryptocercus punctulatus. In particular, we investigated the structure of ectosymbiont genomes, which, in contrast to those of endosymbionts, has been little studied to date, and tested the hypothesis that these ectosymbionts fix nitrogen. Unlike with most obligate endosymbionts, genome reduction has not played a major role in the evolution of the Barbulanympha ectosymbionts. Instead, interaction with the external environment has remained important for this symbiont as genes for synthesis of transporters, outer membrane proteins, lipopolysaccharides, and lipoproteins have been retained. The ectosymbiont genome carried two complete operons for nitrogen fixation, a urea transporter, and a urease, indicating the availability of nitrogen as a driving force behind the symbiosis. NanoSIMS analysis ofC. punctulatushindgut symbionts exposedin vivoto15N2 supports the hypothesis thatBarbulanymphaectosymbionts are capable of nitrogen fixation. This genomic andin vivofunctional investigation of protist ectosymbionts highlights the diversity of evolutionary forces and trajectories that shape symbiotic interactions. The ecological and evolutionary importance of symbioses is increasingly clear, but the overall diversity of symbiotic interactions remains poorly explored. Here in this study, we investigated the

  4. Direct Raman Spectroscopic Measurements of Biological Nitrogen Fixation under Natural Conditions: An Analytical Approach for Studying Nitrogenase Activity.

    PubMed

    Jochum, Tobias; Fastnacht, Agnes; Trumbore, Susan E; Popp, Jürgen; Frosch, Torsten

    2017-01-17

    Biological N2 fixation is a major input of bioavailable nitrogen, which represents the most frequent factor limiting the agricultural production throughout the world. Especially, the symbiotic association between legumes and Rhizobium bacteria can provide substantial amounts of nitrogen (N) and reduce the need for industrial fertilizers. Despite its importance in the global N cycle, rates of biological nitrogen fixation have proven difficult to quantify. In this work, we propose and demonstrate a simple analytical approach to measure biological N2 fixation rates directly without a proxy or isotopic labeling. We determined a mean N2 fixation rate of 78 ± 5 μmol N2 (g dry weight nodule)(-1) h(-1) of a Medicago sativa-Rhizobium consortium by continuously analyzing the amount of atmospheric N2 in static environmental chambers with Raman gas spectroscopy. By simultaneously analyzing the CO2 uptake and photosynthetic plant activity, we think that a minimum CO2 mixing ratio might be needed for natural N2 fixation and only used the time interval above this minimum CO2 mixing ratio for N2 fixation rate calculations. The proposed approach relies only on noninvasive measurements of the gas phase and, given its simplicity, indicates the potential to estimate biological nitrogen fixation of legume symbioses not only in laboratory experiments. The same methods can presumably also be used to detect N2 fluxes by denitrification from ecosystems to the atmosphere.

  5. Nitrogen and Phosphorus Addition Affects Biological N2 Fixation and Sphagnum Moss in an Ombrotrophic Bog

    NASA Astrophysics Data System (ADS)

    Zivkovic, T.; Ardichvili, A.; Moore, T. R.

    2016-12-01

    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. Where atmospheric N deposition is low (< 0.2 g m-2 y-1), ombrotrophic bogs rely on N2 fixation as the primary source of N that sustains primary production. The industrial revolution and anthropogenic impacts in the last 200 years have resulted in larger atmospheric N deposition as ammonium (NH4) and nitrate (NO3). One effect of increased N deposition in Sphagnum is a switch from N to phosphorus (P) limitation suggested by the increase in tissue N:P>16. It is unclear how Sphagnum hosted diazotrophic activity may be affected by N deposition and thus changes in N:P ratio. 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-1 as NH4Cl and NaNO3), and phosphorus (5 g P m-2 y-1 as KH2PO4) on Sphagnum nutrient status (N, P and N:P), net primary productivity (NPP) and Sphagnum-associated N2 fixation at Mer Bleue, a temperate ombrotrophic bog. Our study shows 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. N2 fixation 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. Although elevated N deposition substantially decreases N2 fixation, the N:P ratio in Sphagnum may be a good predictor, likely

  6. Molecular Ecological and Stable Isotopic Studies of Nitrogen Fixation in Modern Microbial Mats

    NASA Technical Reports Server (NTRS)

    Bebout, B. M.; Crumbliss, L. L.; DesMarais, D. J.; Hogan, M. E.; Omoregie, E.; Turk, K. A.; Zehr, J. P.

    2003-01-01

    Nitrogen is usually the element limiting biological productivity in the marine environment. Microbial mats, laminated microbial communities analogous to some of the oldest forms of life on Earth, are often the sites of high rates of N fixation (the energetically expensive conversion of atmospheric dinitrogen into a biologically useful form). The N fixing enzyme nitrogenase is generally considered to be of ancient origin, and is widely distributed throughout the Bacterial and Archaeal domains of life, indicating an important role for this process over evolutionary time. The stable isotopic signature of N fixation is purportedly recognizable in organic matter (ancient kerogens as well as present-day microbial mats) as a delta (15)N(sub organic) near zero. We studied two microbial mats exhibiting different rates of N fixation in order to better understand the impact of N fixation on the delta (15)N (sub organic) of the mats, as well as what organisms are important in this process. Mats dominated by the cyanobacterium Microcoleus chthonoplastes grow in permanently submerged hypersaline salterns, and exhibit low rates of N fixation, whereas mats dominated by the cyanobacterium Lyngbya spp grow in an intertidal area, and exhibit rates of N fixation an order of magnitude higher. To examine successional stages in mat growth, both developing and established mats at each location were sampled. PCR and RT-PCR based approaches were used to identify, respectively, the organisms containing nifH (one of the genes that encode nitrogenase) as well as those expressing nifH in these mats. Both mats exhibited a distinct diel cycle of N fixation, with highest rates occurring at night. The delta (15)N(sub organic) of the subtidal Microcoleus mats is near zero whereas the delta (15)N(sub organic) is slightly more positive (+ 2-3%), in the intertidal Lyngbya mats, an interesting difference in view of the fact that overall rates of activity in the intertidal mats are much higher that those

  7. The importance of nodule CO2 fixation for the efficiency of symbiotic nitrogen fixation in pea at vegetative growth and during pod formation.

    PubMed

    Fischinger, Stephanie Anastasia; Schulze, Joachim

    2010-05-01

    Nodule CO2 fixation is of pivotal importance for N2 fixation. The process provides malate for bacteroids and oxaloacetate for nitrogen assimilation. The hypothesis of the present paper was that grain legume nodules would adapt to higher plant N demand and more restricted carbon availability at pod formation through increased nodule CO2 fixation and a more efficient N2 fixation. Growth, N2 fixation, and nodule composition during vegetative growth and at pod formation were studied in pea plants (Pisum sativum L.). In parallel experiments, 15N2 and 13CO2 uptake, as well as nodule hydrogen and CO2 release, was measured. Plants at pod formation showed higher growth rates and N2 fixation per plant when compared with vegetative growth. The specific activity of active nodules was about 25% higher at pod formation. The higher nodule activity was accompanied by higher amino acid concentration in nodules and xylem sap with a higher share of asparagine. Nodule 13CO2 fixation was increased at pod formation, both per plant and per 15N2 fixed unit. However, malate concentration in nodules was only 40% of that during vegetative growth and succinate was no longer detectable. The data indicate that increased N2 fixation at pod formation is connected with strongly increased nodule CO2 fixation. While the sugar concentration in nodules at pod formation was not altered, the concentration of organic acids, namely malate and succinate, was significantly lower. It is concluded that strategies to improve the capability of nodules to fix CO2 and form organic acids might prolong intensive N2 fixation into the later stages of pod formation and pod filling in grain legumes.

  8. The importance of nodule CO2 fixation for the efficiency of symbiotic nitrogen fixation in pea at vegetative growth and during pod formation

    PubMed Central

    Fischinger, Stephanie Anastasia; Schulze, Joachim

    2010-01-01

    Nodule CO2 fixation is of pivotal importance for N2 fixation. The process provides malate for bacteroids and oxaloacetate for nitrogen assimilation. The hypothesis of the present paper was that grain legume nodules would adapt to higher plant N demand and more restricted carbon availability at pod formation through increased nodule CO2 fixation and a more efficient N2 fixation. Growth, N2 fixation, and nodule composition during vegetative growth and at pod formation were studied in pea plants (Pisum sativum L.). In parallel experiments, 15N2 and 13CO2 uptake, as well as nodule hydrogen and CO2 release, was measured. Plants at pod formation showed higher growth rates and N2 fixation per plant when compared with vegetative growth. The specific activity of active nodules was about 25% higher at pod formation. The higher nodule activity was accompanied by higher amino acid concentration in nodules and xylem sap with a higher share of asparagine. Nodule 13CO2 fixation was increased at pod formation, both per plant and per 15N2 fixed unit. However, malate concentration in nodules was only 40% of that during vegetative growth and succinate was no longer detectable. The data indicate that increased N2 fixation at pod formation is connected with strongly increased nodule CO2 fixation. While the sugar concentration in nodules at pod formation was not altered, the concentration of organic acids, namely malate and succinate, was significantly lower. It is concluded that strategies to improve the capability of nodules to fix CO2 and form organic acids might prolong intensive N2 fixation into the later stages of pod formation and pod filling in grain legumes. PMID:20363863

  9. BMAA inhibits nitrogen fixation in the cyanobacterium Nostoc sp. PCC 7120.

    PubMed

    Berntzon, Lotta; Erasmie, Sven; Celepli, Narin; Eriksson, Johan; Rasmussen, Ulla; Bergman, Birgitta

    2013-08-21

    Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms.

  10. BMAA Inhibits Nitrogen Fixation in the Cyanobacterium Nostoc sp. PCC 7120

    PubMed Central

    Berntzon, Lotta; Erasmie, Sven; Celepli, Narin; Eriksson, Johan; Rasmussen, Ulla; Bergman, Birgitta

    2013-01-01

    Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms. PMID:23966039

  11. Effect of dissolved oxygen on nitrogen fixation by A. vinelandii. II. Ionically adsorbed cells.

    PubMed

    Diluccio, R C; Kirwan, D J

    1984-01-01

    Continuous culture studies of Azotobacter vinelandii cells immobilized by ionic adsorption to Cellex E anion exchange resin were conducted under oxygen-limited conditions for comparison to free-cell cultures. Immobilization had little effect upon the specific respiration and sucrose consumption rates as compared to free cells. However, maxima in specific nitrogen fixation rate and nitrogenase activity as a function of dissolved oxygen occurred at a C(O(2) ) value of approximately 0.005 mM as opposed to 0.02 mM for free cells. Further, in contrast to free-cell culture, most of the fixed nitrogen appeared in the medium rather than within intact cells. There were strong indications that reproduction of bound cells often resulted in cell lysis accounting for the fixed nitrogen content in solution.

  12. New evidence for nitrogen fixation within the Italian white truffle Tuber magnatum.

    PubMed

    Barbieri, Elena; Ceccaroli, Paola; Saltarelli, Roberta; Guidi, Chiara; Potenza, Lucia; Basaglia, Marina; Fontana, Federico; Baldan, Enrico; Casella, Sergio; Ryahi, Ouafae; Zambonelli, Alessandra; Stocchi, Vilberto

    2010-01-01

    Diversity of nitrogen-fixing bacteria and the nitrogen-fixation activity was investigated in Tuber magnatum, the most well-known prized species of Italian white truffle. Degenerate PCR primers were applied to amplify the nitrogenase gene nifH from T. magnatum ascomata at different stages of maturation. Putative amino acid sequences revealed mainly the presence of Alphaproteobacteria belonging to Bradyrhizobium spp. and expression of nifH genes from Bradyrhizobia was detected. The nitrogenase activity evaluated by acetylene reduction assay was 0.5-7.5μmolC(2)H(4)h(-1)g(-1), comparable with early nodules of legumes associated with specific nitrogen-fixing bacteria. This is the first demonstration of nitrogenase expression gene and activity within truffle.

  13. Co-occurrence of denitrification and nitrogen fixation in a meromictic lake, Lake Cadagno (Switzerland).

    PubMed

    Halm, Hannah; Musat, Niculina; Lam, Phyllis; Langlois, Rebecca; Musat, Florin; Peduzzi, Sandro; Lavik, Gaute; Schubert, Carsten J; Sinha, Bärbel; Singha, Bärbel; LaRoche, Julie; Kuypers, Marcel M M

    2009-08-01

    The nitrogen cycling of Lake Cadagno was investigated by using a combination of biogeochemical and molecular ecological techniques. In the upper oxic freshwater zone inorganic nitrogen concentrations were low (up to approximately 3.4 microM nitrate at the base of the oxic zone), while in the lower anoxic zone there were high concentrations of ammonium (up to 40 microM). Between these zones, a narrow zone was characterized by no measurable inorganic nitrogen, but high microbial biomass (up to 4 x 10(7) cells ml(-1)). Incubation experiments with (15)N-nitrite revealed nitrogen loss occurring in the chemocline through denitrification (approximately 3 nM N h(-1)). At the same depth, incubations experiments with (15)N(2)- and (13)C(DIC)-labelled bicarbonate, indicated substantial N(2) fixation (31.7-42.1 pM h(-1)) and inorganic carbon assimilation (40-85 nM h(-1)). Catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) and sequencing of 16S rRNA genes showed that the microbial community at the chemocline was dominated by the phototrophic green sulfur bacterium Chlorobium clathratiforme. Phylogenetic analyses of the nifH genes expressed as mRNA revealed a high diversity of N(2) fixers, with the highest expression levels right at the chemocline. The majority of N(2) fixers were related to Chlorobium tepidum/C. phaeobacteroides. By using Halogen In Situ Hybridization-Secondary Ion Mass Spectroscopy (HISH-SIMS), we could for the first time directly link Chlorobium to N(2) fixation in the environment. Moreover, our results show that N(2) fixation could partly compensate for the N loss and that both processes occur at the same locale at the same time as suggested for the ancient Ocean.

  14. Molybdenum and phosphorus limitation of moss-associated nitrogen fixation in boreal ecosystems.

    PubMed

    Rousk, Kathrin; Degboe, Jefferson; Michelsen, Anders; Bradley, Robert; Bellenger, Jean-Philippe

    2017-04-01

    Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a (15) N2 tracer technique to assess the ARA to N2 fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA : (15) N2 ratios increased with increasing Mo additions. These findings show that N2 fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.

  15. Quantifying the effect of fire disturbance on free-living nitrogen fixation in tropical ecosystems

    NASA Astrophysics Data System (ADS)

    De Oliveira Bomfim, B.; Silva, L. C. R.; Marimon-Junior, B. H.; Marimon, B.; Horwath, W. R.; Neves, L.

    2015-12-01

    Tropical forests and savannas are among the most important biomes on Earth, supporting more than half of all plant and animal species on the planet. Despite growing interest in biogeochemical processes that affect tropical forest dynamics, many, including biological nitrogen fixation (BNF), are still poorly understood. Free-living N-fixers are thought to play a key role in tropical ecosystems, alleviating N and P limitation, supporting above and below ground biomass production, as well as carbon storage in plants and soil, but this influence has yet to be quantified. Of particular interest, the spatial distribution and identity of free-living BNF under disturbance regimes that commonly lead to the conversion of forests to savannas is currently unknown. To address this critical gap in knowledge, we measured free-living BNF quantifying rates of N fixation under contrasting fire regimes in the Amazon-Cerrado transition of central Brazil. Samples were collected in 4 ha of floodable forests affected by fire and 1 ha of unburned (seasonally flooded) forest located at the Araguaia State Park, Mato Grosso State, Brazil. Free-living N-fixation rates were measured by both 15N2 (98 atom% 15N) and acethylene reduction assay (ARA). Samples were incubated in the field and left in the dark at room temperature for 12 hours. In the next few weeks we will quantify N fixation rates that will be presented in the upcoming AGU meeting.

  16. Nitrogen fixation and metabolism by groundwater-dependent perennial plants in a hyperarid desert.

    PubMed

    Arndt, Stefan K; Kahmen, Ansgar; Arampatsis, Christina; Popp, Marianne; Adams, Mark

    2004-11-01

    The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 micromol NO2- g(-1) FW h(-1)). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 microM NO3-. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the 15N natural abundance method and was a significant component of the N-requirement of the legume Alhagi, the average contribution of biologically fixed nitrogen in Alhagi was 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through

  17. Anoxygenic Photosynthesis and Nitrogen Fixation by a Microbial Mat Community in a Bahamian Hypersaline Lagoon

    PubMed Central

    Pinckney, J. L.; Paerl, H. W.

    1997-01-01

    Simultaneous measurements of photosynthesis (both oxygenic and anoxygenic) and N(inf2) fixation were conducted to discern the relationships between photosynthesis, N(inf2) fixation, and environmental factors potentially regulating these processes in microbial mats in a tropical hypersaline lagoon (Salt Pond, San Salvador Island, Bahamas). Major photoautotrophs included cyanobacteria, purple phototrophic bacteria, and diatoms. Chemosystematic photopigments were used as indicators of the relative abundance of mat phototrophs. Experimental manipulations consisted of light and dark incubations of intact mat samples exposed to the photosystem II inhibitor DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea], a dissolved organic carbon source (D-glucose), and normal seawater (37(permil)). Photosynthetic rates were measured by both O(inf2) and (sup14)C methods, and nitrogenase activity (NA) was estimated by the acetylene reduction assay. Moderate reductions in salinity (from 74 to 37(permil)) had no measurable effect on photosynthesis, O(inf2) consumption, or NA. CO(inf2) fixation in DCMU-amended samples was (symbl)25% of that in the control (nonamended) samples and demonstrated photosynthetic activity by anoxygenic phototrophs. NA in DCMU-amended samples, which was consistently higher (by a factor of 2 to 3) than the other (light and dark) treatments, was also attributed to purple phototrophic bacteria. The ecological implication is that N(inf2) fixation by anoxygenic phototrophs (purple phototrophic bacteria and possibly cyanobacteria) may be regulated by the activity of oxygenic phototrophs (cyanobacteria and diatoms). Consortial interactions that enhance the physiological plasticity of the mat community may be a key for optimizing production, N(inf2) fixation, and persistence in these extreme environments. PMID:16535506

  18. Foraminiferal isotope evidence of reduced nitrogen fixation in the ice age Atlantic Ocean.

    PubMed

    Ren, H; Sigman, D M; Meckler, A N; Plessen, B; Robinson, R S; Rosenthal, Y; Haug, G H

    2009-01-09

    Fixed nitrogen (N) is a limiting nutrient for algae in the low-latitude ocean, and its oceanic inventory may have been higher during ice ages, thus helping to lower atmospheric CO2 during those intervals. In organic matter within planktonic foraminifera shells in Caribbean Sea sediments, we found that the 15N/14N ratio from the last ice age is higher than that from the current interglacial, indicating a higher nitrate 15N/14N ratio in the Caribbean thermocline. This change and other species-specific differences are best explained by less N fixation in the Atlantic during the last ice age. The fixation decrease was most likely a response to a known ice age reduction in ocean N loss, and it would have worked to balance the ocean N budget and to curb ice age-interglacial change in the N inventory.

  19. Photosystem-II shutdown evolved with Nitrogen fixation in the unicellular diazotroph Crocosphaera watsonii.

    PubMed

    Rabouille, Sophie; Claquin, Pascal

    2016-02-01

    Protection of nitrogenase from oxygen in unicellular Cyanobacteria is obtained by temporal separation of photosynthesis and diazotrophy through transcriptional and translational regulations of nitrogenase. But diazotrophs can face environmental situations in which N2 fixation occurs significantly in the light, and we believe that another control operates to make it possible. The night-time shutdown of PSII activity is a peculiar behaviour that discriminates Crocosphaera watsonii WH8501 from any other phototroph, whether prokaryote or eukaryote. This phenomenon is not only due to the plastoquinone pool redox status, and suggests that the sentinel D1 protein, expressed in periods of nitrogen fixation, is inactive. Results demonstrate a tight constraint of oxygen evolution in C. watsonii as additional protection of nitrogenase activity and suggest a possible recycling of cellular components.

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

    PubMed

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

    2007-01-01

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

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

    PubMed

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

    2007-01-01

    •  Leguminous trees are very common in the tropical rainforests of Guyana. Here, species-specific differences in N2 fixation capability among nodulating legumes growing on different soils and a possible limitation of N2 fixation by a relatively high nitrogen (N) and low phosphorus (P) availability in the forest were investigated. •  Leaves of 17 nodulating species and 17 non-nodulating reference trees were sampled and their δ(15) N values measured. Estimates of N2 fixation rates were calculated using the (15) N natural abundance method. Pot experiments were conducted on the effect of N and P availability on N2 fixation using the (15) N-enriched isotope dilution method. •  Nine species showed estimates of > 33% leaf N derived from N2 fixation, while the others had low or undetectable N2 fixation rates. High N and low P availability reduced N2 fixation substantially. •  The results suggest that a high N and low P availability in the forest limit N2 fixation. At the forest ecosystem level, N2 fixation was estimated at c. 6% of total N uptake by the tree community. We conclude that symbiotic N2 fixation plays an important role in maintaining high amounts of soil available N in undisturbed forest.

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

    PubMed

    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.

  3. Influence of Co and B12 on the growth and nitrogen fixation of Trichodesmium

    PubMed Central

    Rodriguez, Irene B.; Ho, Tung-Yuan

    2015-01-01

    We investigated the influence of varying cobalt (Co) and B12 concentrations to growth and nitrogen fixation of Trichodesmium, a major diazotroph in the tropical and subtropical oligotrophic ocean. Here we show that sufficient inorganic Co, 20 pmol L-1, sustains the growth of Trichodesmium either with or without an additional B12 supply. We also found that in these culture conditions, nitrogen levels fixed by Trichodesmium were higher in treatments with insufficient B12 than in treatments with higher B12 availability. Under limited inorganic Co availability, ranging from 0.2 to 2 pmol L-1, Trichodesmium growth was significantly compromised in cultures without B12. In these low Co concentrations, addition of 400 pmol L-1 of B12 supported phytoplankton growth indicating that B12 supply augmented for the low Co concentrations. Our study demonstrates that Trichodesmium has an absolute Co requirement, which is not replaceable with Zn, and that B12 supply alleviates stress in cases where Co is limiting. These results show that the interlocking availabilities of Co and B12 may influence the growth and nitrogen fixation of Trichodesmium in the ocean. PMID:26150813

  4. Influence of Co and B 12 on the growth and nitrogen fixation of Trichodesmium.

    PubMed

    Rodriguez, Irene B; Ho, Tung-Yuan

    2015-01-01

    We investigated the influence of varying cobalt (Co) and B12 concentrations to growth and nitrogen fixation of Trichodesmium, a major diazotroph in the tropical and subtropical oligotrophic ocean. Here we show that sufficient inorganic Co, 20 pmol L(-1), sustains the growth of Trichodesmium either with or without an additional B12 supply. We also found that in these culture conditions, nitrogen levels fixed by Trichodesmium were higher in treatments with insufficient B12 than in treatments with higher B12 availability. Under limited inorganic Co availability, ranging from 0.2 to 2 pmol L(-1), Trichodesmium growth was significantly compromised in cultures without B12. In these low Co concentrations, addition of 400 pmol L(-1) of B12 supported phytoplankton growth indicating that B12 supply augmented for the low Co concentrations. Our study demonstrates that Trichodesmium has an absolute Co requirement, which is not replaceable with Zn, and that B12 supply alleviates stress in cases where Co is limiting. These results show that the interlocking availabilities of Co and B12 may influence the growth and nitrogen fixation of Trichodesmium in the ocean.

  5. Identification and characterization of a novel Bradyrhizobium japonicum gene involved in host-specific nitrogen fixation.

    PubMed Central

    Chun, J Y; Sexton, G L; Roth, L E; Stacey, G

    1994-01-01

    To understand the genetic mechanism of host specificity in the interaction between rhizobia and their hosts, it is important to identify genes that influence both early and late steps in symbiotic development. This paper focuses on the little-understood genetics of host-specific nitrogen fixation. A deletion mutant of Bradyrhizobium japonicum, strain NAD163, was found to induce effective, nitrogen-fixing nodules on soybean and siratro plants but produced ineffective nodules on cowpea plants. Additional transposon and deletion mutants defined a small region that conferred this phenotype, and this region was sequenced to identify two putative open reading frames (ORFs). Data indicate that only one of these ORFs is detectable in bacteroids. This ORF was termed hsfA, with a predicted protein product of 11 kDa. The transcriptional start site of hsfA was determined and found to coincide with a predicted RpoN-dependent promoter. Microscopic studies of nodules induced by the wild type and hsfA mutants on cowpea and soybean plants indicate that the cowpea mutant nodules are slow to develop. The data indicate that hsfA appears to play a crucial role in bacteroid development on cowpea but does not appear to be essential for nitrogen fixation on the other hosts tested. Images PMID:7961425

  6. Increase in alfalfa nodulation, nitrogen fixation, and plant growth by specific DNA amplification in Sinorhizobium meliloti.

    PubMed

    Castillo, M; Flores, M; Mavingui, P; Martínez-Romero, E; Palacios, R; Hernández, G

    1999-06-01

    To improve symbiotic nitrogen fixation on alfalfa plants, Sinorhizobium meliloti strains containing different average copy numbers of a symbiotic DNA region were constructed by specific DNA amplification (SDA). A DNA fragment containing a regulatory gene (nodD1), the common nodulation genes (nodABC), and an operon essential for nitrogen fixation (nifN) from the nod regulon region of the symbiotic plasmid pSyma of S. meliloti was cloned into a plasmid unable to replicate in this organism. The plasmid then was integrated into the homologous DNA region of S. meliloti strains 41 and 1021, which resulted in a duplication of the symbiotic region. Sinorhizobium derivatives carrying further amplification were selected by growing the bacteria in increased concentrations of an antibiotic marker present in the integrated vector. Derivatives of strain 41 containing averages of 3 and 6 copies and a derivative of strain 1021 containing an average of 2.5 copies of the symbiotic region were obtained. In addition, the same region was introduced into both strains as a multicopy plasmid, yielding derivatives with an average of seven copies per cell. Nodulation, nitrogenase activity, plant nitrogen content, and plant growth were analyzed in alfalfa plants inoculated with the different strains. The copy number of the symbiotic region was critical in determining the plant phenotype. In the case of the strains with a moderate increase in copy number, symbiotic properties were improved significantly. The inoculation of alfalfa with these strains resulted in an enhancement of plant growth.

  7. Biological nitrogen fixation by alternative nitrogenases in boreal cyanolichens: importance of molybdenum availability and implications for current biological nitrogen fixation estimates.

    PubMed

    Darnajoux, Romain; Zhang, Xinning; McRose, Darcy L; Miadlikowska, Jolanta; Lutzoni, François; Kraepiel, Anne M L; Bellenger, Jean-Philippe

    2017-01-01

    Cryptogamic species and their associated cyanobacteria have attracted the attention of biogeochemists because of their critical roles in the nitrogen cycle through symbiotic and asymbiotic biological fixation of nitrogen (BNF). BNF is mediated by the nitrogenase enzyme, which, in its most common form, requires molybdenum at its active site. Molybdenum has been reported as a limiting nutrient for BNF in many ecosystems, including tropical and temperate forests. Recent studies have suggested that alternative nitrogenases, which use vanadium or iron in place of molybdenum at their active site, might play a more prominent role in natural ecosystems than previously recognized. Here, we studied the occurrence of vanadium, the role of molybdenum availability on vanadium acquisition and the contribution of alternative nitrogenases to BNF in the ubiquitous cyanolichen Peltigera aphthosa s.l. We confirmed the use of the alternative vanadium-based nitrogenase in the Nostoc cyanobiont of these lichens and its substantial contribution to BNF in this organism. We also showed that the acquisition of vanadium is strongly regulated by the abundance of molybdenum. These findings show that alternative nitrogenase can no longer be neglected in natural ecosystems, particularly in molybdenum-limited habitats.

  8. Nitrogen fixation in moss-cyanobacteria associations in boreal forest ecosystems

    NASA Astrophysics Data System (ADS)

    Rousk, Kathrin

    2014-05-01

    Nitrogen (N) limits the productivity in boreal forests. A major source of 'new' N for these forests is the fixation of atmospheric N2 preformed by cyanobacteria living in association with mosses and lichens. Mosses are a dominant feature in boreal forests, accounting for 60-90% of the groundcover in pristine boreal forests and have been found to be colonized by several N2-fixing cyanobacteria. Given the ubiquitous nature of mosses in these forests, their association with N2-fixing cyanobacteria could characterize the N cycle in these ecosystems. For instance, the feather moss Pleurozium schreberi with its associated cyanobacteria fixes 1-2 kg N ha-1 yr-1, which equals the amount that enters northern boreal forests via atmospheric N deposition. Nitrogen fixation in moss-cyanobacteria associations is affected by numerous abiotic factors that could modulate the N input to the system via the moss-cyanobacteria pathway. For instance, high N availability and dry conditions inhibit N2 fixation in moss-cyanobacteria associations while phosphorus availability and moist conditions promote N2 fixation. Further, N2fixation in moss-cyanobacteria associations is resilient, and can recover from increased N inputs (12 - 15 kg N ha-1 yr-1) as well as from drought stress (moss < 9% field moisture) upon removal of these stressors. Nevertheless, the question as to how important the N2 fixing capability of moss-cyanobacteria associations is as a source of 'new' N for the N cycle in boreal forests remains. For instance, mosses can retain acquired N over long periods of time (> 1 year) and the transfer of N from moss to soil in the short-term has so far only been shown to occur after disturbances (e.g. drying rewetting events, fires). I will present results from laboratory as well as field experiments aimed to elucidate the role moss-cyanobacteria associations play for the N cycle in boreal forests and how abiotic factors control the fixation of atmospheric N2.

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

    NASA Astrophysics Data System (ADS)

    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

  10. Nitrogen fixation in the eastern Atlantic reaches similar levels in the Southern and Northern Hemisphere

    NASA Astrophysics Data System (ADS)

    Fonseca-Batista, Debany; Dehairs, Frank; Riou, Virginie; Fripiat, François; Elskens, Marc; Deman, Florian; Brion, Natacha; Quéroué, Fabien; Bode, Maya; Auel, Holger

    2017-01-01

    Euphotic layer dinitrogen (N2) fixation and primary production (PP) were measured in the eastern Atlantic Ocean (38°N-21°S) using 15N2 and 13C bicarbonate tracer incubations. This region is influenced by Saharan dust deposition and waters with low nitrogen to phosphorus (N/P) ratios originating from the Subantarctic and the Benguela upwelling system. Depth-integrated rates of N2 fixation in the north (0°N-38°N) ranged from 59 to 370 µmol N m-2 d-1, with the maximal value at 19°N under the influence of the northwest African upwelling. Diazotrophic activity in the south (0°S-21°S), though slightly lower, was surprisingly close to observations in the north, with values ranging from 47 to 119 µmol N m-2 d-1. Our North Atlantic N2 fixation rates correlate well with dust deposition, while those in the South Atlantic correlate strongly with excess phosphate relative to nitrate. There, the necessary iron is assumed to be supplied from the Benguela upwelling system. When converting N2 fixation to carbon uptake using a Redfield ratio (6.6), we find that N2 fixation may support up to 9% of PP in the subtropical North Atlantic (20°N-38°N), 5% in the tropical North Atlantic (0°N-20°N), and 1% of PP in the South Atlantic (0°S-21°S). Combining our data with published data sets, we estimate an annual N input of 27.6 ± 10 Tg N yr-1 over the open Atlantic Ocean, 11% of which enters the region between 20°N and 50°N, 71% between 20°N and 10°S, and 18% between 10°N and 45°S.

  11. Nitrogen Fixation by Gliding Arc Plasma: Better Insight by Chemical Kinetics Modelling.

    PubMed

    Wang, Weizong; Patil, Bhaskar; Heijkers, Stjin; Hessel, Volker; Bogaerts, Annemie

    2017-03-08

    The conversion of atmospheric nitrogen into valuable compounds, that is, so-called nitrogen fixation, is gaining increased interest, owing to the essential role in the nitrogen cycle of the biosphere. Plasma technology, and more specifically gliding arc plasma, has great potential in this area, but little is known about the underlying mechanisms. Therefore, we developed a detailed chemical kinetics model for a pulsed-power gliding-arc reactor operating at atmospheric pressure for nitrogen oxide synthesis. Experiments are performed to validate the model and reasonable agreement is reached between the calculated and measured NO and NO2 yields and the corresponding energy efficiency for NOx formation for different N2 /O2 ratios, indicating that the model can provide a realistic picture of the plasma chemistry. Therefore, we can use the model to investigate the reaction pathways for the formation and loss of NOx . The results indicate that vibrational excitation of N2 in the gliding arc contributes significantly to activating the N2 molecules, and leads to an energy efficient way of NOx production, compared to the thermal process. Based on the underlying chemistry, the model allows us to propose solutions on how to further improve the NOx formation by gliding arc technology. Although the energy efficiency of the gliding-arc-based nitrogen fixation process at the present stage is not comparable to the world-scale Haber-Bosch process, we believe our study helps us to come up with more realistic scenarios of entering a cutting-edge innovation in new business cases for the decentralised production of fertilisers for agriculture, in which low-temperature plasma technology might play an important role.

  12. Introduction of the Escherichia coli gdhA gene into Rhizobium phaseoli: effect on nitrogen fixation.

    PubMed Central

    Bravo, A; Becerril, B; Mora, J

    1988-01-01

    Rhizobium phaseoli lacks glutamate dehydrogenase (GDH) and assimilates ammonium by the glutamine synthetase-glutamate synthase pathway. A strain of R. phaseoli harboring the Escherichia coli GDH structural gene (gdhA) was constructed. GDH activity was expressed in R. phaseoli in the free-living state and in symbiosis. Nodules with bacteroids that expressed GDH activity had severe impairment of nitrogen fixation. Also, R. phaseoli cells that lost GDH activity and assimilated ammonium by the glutamine synthetase-glutamate synthase pathway preferentially nodulated Phaseolus vulgaris. PMID:2892830

  13. Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals.

    PubMed

    Middelburg, Jack J; Mueller, Christina E; Veuger, Bart; Larsson, Ann I; Form, Armin; van Oevelen, Dick

    2015-12-08

    Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world's deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean.

  14. Discovery of symbiotic nitrogen fixation and chemoautotrophy in cold-water corals

    PubMed Central

    Middelburg, Jack J.; Mueller, Christina E.; Veuger, Bart; Larsson, Ann I.; Form, Armin; Oevelen, Dick van

    2015-01-01

    Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world’s deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean. PMID:26644069

  15. Major cereal crops benefit from biological nitrogen fixation when inoculated with the nitrogen-fixing bacterium Pseudomonas protegens Pf-5 X940.

    PubMed

    Fox, Ana Romina; Soto, Gabriela; Valverde, Claudio; Russo, Daniela; Lagares, Antonio; Zorreguieta, Ángeles; Alleva, Karina; Pascuan, Cecilia; Frare, Romina; Mercado-Blanco, Jesús; Dixon, Ray; Ayub, Nicolás Daniel

    2016-10-01

    A main goal of biological nitrogen fixation research has been to expand the nitrogen-fixing ability to major cereal crops. In this work, we demonstrate the use of the efficient nitrogen-fixing rhizobacterium Pseudomonas protegens Pf-5 X940 as a chassis to engineer the transfer of nitrogen fixed by BNF to maize and wheat under non-gnotobiotic conditions. Inoculation of maize and wheat with Pf-5 X940 largely improved nitrogen content and biomass accumulation in both vegetative and reproductive tissues, and this beneficial effect was positively associated with high nitrogen fixation rates in roots. (15) N isotope dilution analysis showed that maize and wheat plants obtained substantial amounts of fixed nitrogen from the atmosphere. Pf-5 X940-GFP-tagged cells were always reisolated from the maize and wheat root surface but never from the inner root tissues. Confocal laser scanning microscopy confirmed root surface colonization of Pf-5 X940-GFP in wheat plants, and microcolonies were mostly visualized at the junctions between epidermal root cells. Genetic analysis using biofilm formation-related Pseudomonas mutants confirmed the relevance of bacterial root adhesion in the increase in nitrogen content, biomass accumulation and nitrogen fixation rates in wheat roots. To our knowledge, this is the first report of robust BNF in major cereal crops. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

  16. Nitrogen fixation by Klebsiella pneumoniae is inhibited by certain multicopy hybrid nif plasmids.

    PubMed Central

    Riedel, G E; Brown, S E; Ausubel, F M

    1983-01-01

    In our studies of nif gene regulation, we have observed that certain hybrid nif plasmids drastically inhibit the expression of the chromosomal nif genes of Klebsiella pneumonia. Wild-type (Nif+) K. pneumoniae strains that acquire certain hybrid nif plasmids also acquire the Nif- phenotype; these strains lose 90 to 99% of all detectable nitrogen fixation activity and grow poorly (or not at all) on solid media with N2 as the sole nitrogen source. We describe experiments which defined this inhibition of the Nif+ phenotype by hybrid nif plasmids and identify and characterize four nif DNA regions associated with this inhibition. We show that plasmids carrying these nif regions could recombine with, but not complement, nif chromosomal mutations. Our results suggest that inhibition of the Nif+ phenotype will provide a useful bioassay for some of the factors that mediate nif gene expression. PMID:6336738

  17. Efficient Solar-Driven Nitrogen Fixation over Carbon-Tungstic-Acid Hybrids.

    PubMed

    Li, Xiaoman; Wang, Wenzhong; Jiang, Dong; Sun, Songmei; Zhang, Ling; Sun, Xiang

    2016-09-19

    Ammonia synthesis under mild conditions is of supreme interest. Photocatalytic nitrogen fixation with water at room temperature and atmospheric pressure is an intriguing strategy. However, the efficiency of this method has been far from satisfied for industrialization, mainly due to the sluggish cleavage of the N≡N bond. Herein, we report a carbon-tungstic-acid (WO3 ⋅H2 O) hybrid for the co-optimization of N2 activation as well as subsequent photoinduced protonation. Efficient ammonia evolution reached 205 μmol g(-1)  h(-1) over this hybrid under simulated sunlight. Nitrogen temperature-programmed desorption revealed the decisive role of carbon in N2 adsorption. Photoactive WO3 ⋅H2 O guaranteed the supply of electrons and protons for subsequent protonation. The universality of carbon modification for enhancing the N2 reduction was further verified over various photocatalysts, shedding light on future materials design for ideal solar energy utilization.

  18. The significance of nitrogen fixation to new production during early summer in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Ohlendieck, U.; Gundersen, K.; Meyerhöfer, M.; Fritsche, P.; Nachtigall, K.; Bergmann, B.

    2007-01-01

    Rates of dinitrogen (N2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June-July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N2 fixation contributed 15 mmol N m-2 (1998) and 33 mmol N m-2 (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12-26% more new N than other annual estimates (mid July-mid October) from the same region. The between-station variability observed in both total N2 fixation and primary productivity greatly emphasizes the need for multiple stations and seasonal sampling strategies in biogeochemical studies of the Baltic Sea. The majority of new N from N2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells >20 µm were able to supply a major part of their N requirements for growth by N2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28-150% of N needed to meet the rate of C incorporation by primary production. The molar C:N rate incorporation ratio (C:NRATE) in filamentous cyanobacterial cells was variable (range 7-28) and the average almost twice as high as the Redfield ratio (6.6) in both years. Since the molar C:N mass ratio (C:NMASS) in filamentous cyanobacterial cells was generally lower than C:NRATE at a number of stations, we suggest that the diazotrophs incorporated excess C on a short term basis (carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N2 fixation contributed only a minor fraction of 13% (range 4-24) in 1998 and 18% (range 2-45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N2 fixation was found in cells <5 µm. Since cells <5 µm did not show any detectable rates of N2 fixation, the 15N-enrichment could be attributed to regenerated

  19. Genomics of variation in nitrogen fixation activity in a population of the thermophilic cyanobacterium Mastigocladus laminosus.

    PubMed

    Hutchins, Patrick R; Miller, Scott R

    2017-01-01

    Variation in phenotypic traits that contribute to fitness influences a population's evolutionary response and its impact on ecosystem function following environmental change, yet its amount and nature are rarely known. Here, we investigated variation in nitrogen (N) fixation activity and its genetic basis for a random sample of laboratory strains of the cyanobacterium Mastigocladus laminosus from a N-limited, geothermally influenced stream in Yellowstone National Park. In a linear mixed-effects model, temperature and genetic differences among strains were the most important factors explaining variation in activity. Genome-wide analyses of genetic divergence between groups of strains that varied in N fixation activity revealed that few loci were strongly associated with these phenotypic differences. Notably, a single nonsynonymous polymorphism in the sulfate assimilation gene apsK explained >25% of the variation in activity at high temperature. We further identified a role for allelic variation of multiple terminal cytochrome oxidases for different aspects of N fixation. In addition, genomes of strains that fixed the most N overall contained a nonsense mutation in a histidine kinase gene that is expected to disrupt normal protein function and may result in transcriptional rewiring. This study illustrates how taking complementary approaches to link phenotype and genotype can inform our understanding of microbial population diversity.

  20. Condensed tannin accumulation and nitrogen fixation potential of Onobrychis viciifolia Scop. grown in a Mediterranean environment.

    PubMed

    Re, Giovanni A; Piluzza, Giovanna; Sulas, Leonardo; Franca, Antonello; Porqueddu, Claudio; Sanna, Federico; Bullitta, Simonetta

    2014-03-15

    Sainfoin (Onobrychis viciifolia Scop.) is a forage legume found in temperate areas but is less widespread in Mediterranean environments. Compared with other perennial legumes, it has the advantage of containing condensed tannins (CT) that can be important for their implications on ruminant nutrition and health. Data on nitrogen (N) fixation by sainfoin in the literature originate from very different environments and only a few field data are available, so it is important to improve knowledge on the N fixation potential of this species, particularly under a Mediterranean climate. Here the accumulation pattern of polyphenolic compounds (total, non-tannic polyphenols and CT) and the N fixation potential of sainfoin were studied in order to contribute to its valorisation for sustainable farming management in Mediterranean environments. CT concentrations were always in the range considered beneficial for animals, not exceeding 50 g delphinidin equivalent kg⁻¹ dry matter (DM). The regression of aerial fixed N on aerial DM showed a relationship of 22 kg fixed N t⁻¹ aerial DM in a Mediterranean environment. A wider exploitation of sainfoin is suggested for production under rain-fed conditions, thus enlarging the limited set of available perennial legumes suitable for Mediterranean environments. © 2013 Society of Chemical Industry.

  1. Pronounced fixation, strong population differentiation and complex population history in the Canary Islands blue tit subspecies complex.

    PubMed

    Hansson, Bengt; Ljungqvist, Marcus; Illera, Juan-Carlos; Kvist, Laura

    2014-01-01

    Evolutionary molecular studies of island radiations may lead to insights in the role of vicariance, founder events, population size and drift in the processes of population differentiation. We evaluate the degree of population genetic differentiation and fixation of the Canary Islands blue tit subspecies complex using microsatellite markers and aim to get insights in the population history using coalescence based methods. The Canary Island populations were strongly genetically differentiated and had reduced diversity with pronounced fixation including many private alleles. In population structure models, the relationship between the central island populations (La Gomera, Tenerife and Gran Canaria) and El Hierro was difficult to disentangle whereas the two European populations showed consistent clustering, the two eastern islands (Fuerteventura and Lanzarote) and Morocco weak clustering, and La Palma a consistent unique lineage. Coalescence based models suggested that the European mainland forms an outgroup to the Afrocanarian population, a split between the western island group (La Palma and El Hierro) and the central island group, and recent splits between the three central islands, and between the two eastern islands and Morocco, respectively. It is clear that strong genetic drift and low level of concurrent gene flow among populations have shaped complex allelic patterns of fixation and skewed frequencies over the archipelago. However, understanding the population history remains challenging; in particular, the pattern of extreme divergence with low genetic diversity and yet unique genetic material in the Canary Island system requires an explanation. A potential scenario is population contractions of a historically large and genetically variable Afrocanarian population, with vicariance and drift following in the wake. The suggestion from sequence-based analyses of a Pleistocene extinction of a substantial part of North Africa and a Pleistocene/Holocene eastward

  2. Microgravity Effects on the Early Events of Biological Nitrogen Fixation in Medicago Truncatula: Results from the SyNRGE Experiment

    NASA Technical Reports Server (NTRS)

    Stutte, Gary W.; Roberts, Michael

    2012-01-01

    SyNRGE (Symbiotic Nodulation in a Reduced Gravity Environment) was a sortie mission on STS-135 in the Biological Research in Canisters (BRIC) hardware to study the effect of microgravity on a plant-microbe symbiosis resulting in biological nitrogen fixation. Medicago truncatula, a model species for th legume family, was inoculated with its bacterial symbiont, Sinorhizobium meliloti, to observe early biomolecular events associated with infection and nodulation in Petri Dish Fixation Units (PDFU's).

  3. Nitrogen fixation in the activated sludge treatment of thermomechanical pulping wastewater: effect of dissolved oxygen.

    PubMed

    Slade, A H; Anderson, S M; Evans, B G

    2003-01-01

    N-ViroTech, a novel technology which selects for nitrogen-fixing bacteria as the bacteria primarily responsible for carbon removal, has been developed to treat nutrient limited wastewaters to a high quality without the addition of nitrogen, and only minimal addition of phosphorus. Selection of the operating dissolved oxygen level to maximise nitrogen fixation forms a key component of the technology. Pilot scale activated sludge treatment of a thermomechanical pulping wastewater was carried out in nitrogen-fixing mode over a 15 month period. The effect of dissolved oxygen was studied at three levels: 14% (Phase 1), 5% (Phase 2) and 30% (Phase 3). The plant was operated at an organic loading of 0.7-1.1 kg BOD5/m3/d, a solids retention time of approximately 10 d, a hydraulic retention time of 1.4 d and a F:M ratio of 0.17-0.23 mg BOD5/mg VSS/d. Treatment performance was very stable over the three dissolved oxygen operating levels. The plant achieved 94-96% BOD removal, 82-87% total COD removal, 79-87% soluble COD removal, and >99% total extractives removal. The lowest organic carbon removals were observed during operation at 30% DO but were more likely to be due to phosphorus limitation than operation at high dissolved oxygen, as there was a significant decrease in phosphorus entering the plant during Phase 3. Discharge of dissolved nitrogen, ammonium and oxidised nitrogen were consistently low (1.1-1.6 mg/L DKN, 0.1-0.2 mg/L NH4+-N and 0.0 mg/L oxidised nitrogen). Discharge of dissolved phosphorus was 2.8 mg/L, 0.1 mg/L and 0.6 mg/L DRP in Phases 1, 2 and 3 respectively. It was postulated that a population of polyphosphate accumulating bacteria developed during Phase 1. Operation at low dissolved oxygen during Phase 2 appeared to promote biological phosphorus uptake which may have been affected by raising the dissolved oxygen to 30% in Phase 3. Total nitrogen and phosphorus discharge was dependent on efficient secondary clarification, and improved over the course of

  4. Modeling the distribution of Trichodesmium and nitrogen fixation in the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

    In this paper we use a coupled, 3-dimensional, biological-physical model, which includes an explicit, dynamic representation of Trichodesmium, to predict the distribution of Trichodesmium and rates of N2-fixation in the tropical and subtropical Atlantic Ocean. It is shown that the model reproduces the approximate observed meridional distribution of Trichodesmium in the Atlantic and elevated concentrations in specific coastal and open ocean regions where this organism is known to occur. The model also appears to reproduce the observed seasonality of Trichodesmium populations at higher latitudes (highest concentrations in summer and fall), but this seasonal cycle may be too pronounced at low latitudes. High and persistent Trichodesmium concentrations and rates of N2-fixation are generated by the model in the Gulf of Guinea off of Africa. This unexpected finding appears to be confirmed by historical measurements. In general, increased Trichodesmium concentrations develop in regions where the mixed layer is relatively thin (resulting in high mean light levels) and dissolved inorganic nitrogen (DIN) concentrations and phytoplankton biomass are low for extended periods of time. The model-predicted Trichodesmium distributions are therefore very sensitive to the fidelity of the physical model's representation of mixed layer depth variability, and upwelling intensity, and the biological model's estimated DIN and phytoplankton concentrations. The model generates a three-step successional sequence where (1) high DIN concentrations due to upwelling and/or mixing stimulate phytoplankton growth, followed by (2) Trichodesmium growth after DIN depletion and phytoplankton decline, followed by (3) enhanced phytoplankton growth due to new nitrogen inputs from N2-fixation. This sequence develops in response to seasonal variations in mixing in the southwestern North Atlantic and in response to upwelling along the coast of Africa and the equator. We interpret this sequence as

  5. Using Synthetic Biology to Distinguish and Overcome Regulatory and Functional Barriers Related to Nitrogen Fixation

    PubMed Central

    Wang, Xia; Yang, Jian-Guo; Chen, Li; Wang, Ji-Long; Cheng, Qi; Dixon, Ray; Wang, Yi-Ping

    2013-01-01

    Biological nitrogen fixation is a complex process requiring multiple genes working in concert. To date, the Klebsiella pneumoniae nif gene cluster, divided into seven operons, is one of the most studied systems. Its nitrogen fixation capacity is subject to complex cascade regulation and physiological limitations. In this report, the entire K. pneumoniae nif gene cluster was reassembled as operon-based BioBrick parts in Escherichia coli. It provided ∼100% activity of native K. pneumoniae system. Based on the expression levels of these BioBrick parts, a T7 RNA polymerase–LacI expression system was used to replace the σ54-dependent promoters located upstream of nif operons. Expression patterns of nif operons were critical for the maximum activity of the recombinant system. By mimicking these expression levels with variable-strength T7-dependent promoters, ∼42% of the nitrogenase activity of the σ54-dependent nif system was achieved in E. coli. When the newly constructed T7-dependent nif system was challenged with different genetic and physiological conditions, it bypassed the original complex regulatory circuits, with minor physiological limitations. Therefore, we have successfully replaced the nif regulatory elements with a simple expression system that may provide the first step for further research of introducing nif genes into eukaryotic organelles, which has considerable potentials in agro-biotechnology. PMID:23935879

  6. Distribution and evolution of nitrogen fixation genes in the phylum Bacteroidetes.

    PubMed

    Inoue, Jun-ichi; Oshima, Kenshiro; Suda, Wataru; Sakamoto, Mitsuo; Iino, Takao; Noda, Satoko; Hongoh, Yuichi; Hattori, Masahira; Ohkuma, Moriya

    2015-01-01

    Diazotrophs had not previously been identified among bacterial species in the phylum Bacteroidetes until the rapid expansion of bacterial genome sequences, which revealed the presence of nitrogen fixation (nif) genes in this phylum. We herein determined the draft genome sequences of Bacteroides graminisolvens JCM 15093(T) and Geofilum rubicundum JCM 15548(T). In addition to these and previously reported 'Candidatus Azobacteroides pseudotrichonymphae' and Paludibacter propionicigenes, an extensive survey of the genome sequences of diverse Bacteroidetes members revealed the presence of a set of nif genes (nifHDKENB) in strains of Dysgonomonas gadei, Dysgonomonas capnocytophagoides, Saccharicrinis fermentans, and Alkaliflexus imshenetskii. These eight species belonged to and were distributed sporadically within the order Bacteroidales. Acetylene reduction activity was detected in the five species examined, strongly suggesting their diazotrophic nature. Phylogenetic analyses showed monophyletic clustering of the six Nif protein sequences in the eight Bacteroidales species, implying that nitrogen fixation is ancestral to Bacteroidales and has been retained in these species, but lost in many other lineages. The identification of nif genes in Bacteroidales facilitates the prediction of the organismal origins of related sequences directly obtained from various environments.

  7. Distribution and Evolution of Nitrogen Fixation Genes in the Phylum Bacteroidetes

    PubMed Central

    Inoue, Jun-ichi; Oshima, Kenshiro; Suda, Wataru; Sakamoto, Mitsuo; Iino, Takao; Noda, Satoko; Hongoh, Yuichi; Hattori, Masahira; Ohkuma, Moriya

    2015-01-01

    Diazotrophs had not previously been identified among bacterial species in the phylum Bacteroidetes until the rapid expansion of bacterial genome sequences, which revealed the presence of nitrogen fixation (nif) genes in this phylum. We herein determined the draft genome sequences of Bacteroides graminisolvens JCM 15093T and Geofilum rubicundum JCM 15548T. In addition to these and previously reported ‘Candidatus Azobacteroides pseudotrichonymphae’ and Paludibacter propionicigenes, an extensive survey of the genome sequences of diverse Bacteroidetes members revealed the presence of a set of nif genes (nifHDKENB) in strains of Dysgonomonas gadei, Dysgonomonas capnocytophagoides, Saccharicrinis fermentans, and Alkaliflexus imshenetskii. These eight species belonged to and were distributed sporadically within the order Bacteroidales. Acetylene reduction activity was detected in the five species examined, strongly suggesting their diazotrophic nature. Phylogenetic analyses showed monophyletic clustering of the six Nif protein sequences in the eight Bacteroidales species, implying that nitrogen fixation is ancestral to Bacteroidales and has been retained in these species, but lost in many other lineages. The identification of nif genes in Bacteroidales facilitates the prediction of the organismal origins of related sequences directly obtained from various environments. PMID:25736980

  8. Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria

    PubMed Central

    Garcia, Nathan S; Fu, Feixue; Sedwick, Peter N; Hutchins, David A

    2015-01-01

    Marine dinitrogen (N2)-fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide (CO2) and fertilize oligotrophic ocean waters with new nitrogen. Iron (Fe) and phosphorus (P) are the two most important limiting nutrients for marine biological N2 fixation, and their availabilities vary between major ocean basins and regions. A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria, unicellular Crocosphaera and filamentous Trichodesmium, to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce. We show that under P-deficient conditions, cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete. In addition, growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations. In Crocosphaera, this effect is accompanied by a reduction in cell sizes and elemental quotas. Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P, low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers. The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past, present and future oceans could have large consequences for global carbon and nitrogen cycles. PMID:24972068

  9. Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria.

    PubMed

    Garcia, Nathan S; Fu, Feixue; Sedwick, Peter N; Hutchins, David A

    2015-01-01

    Marine dinitrogen (N2)-fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide (CO2) and fertilize oligotrophic ocean waters with new nitrogen. Iron (Fe) and phosphorus (P) are the two most important limiting nutrients for marine biological N2 fixation, and their availabilities vary between major ocean basins and regions. A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria, unicellular Crocosphaera and filamentous Trichodesmium, to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce. We show that under P-deficient conditions, cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete. In addition, growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations. In Crocosphaera, this effect is accompanied by a reduction in cell sizes and elemental quotas. Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P, low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers. The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past, present and future oceans could have large consequences for global carbon and nitrogen cycles.

  10. Environmental and Genotypic Effects on the Respiration Associated with Symbiotic Nitrogen Fixation in Peas 1

    PubMed Central

    Mahon, John D.

    1979-01-01

    Estimated values for the respiration associated with symbiotic nitrogen fixation in Pisum sativum L. were independent of irradiance, temperature, plant age, and CO2 concentration, despite large variation in the total rates of C2H2 reduction and root + nodule respiration. Similar values were also found in Phaseolus vulgaris L., Vicia faba L. and Glycine max (L.) Merr. Among all combinations of four Pisum cultivars with four Rhizobium leguminosarum inoculants only the plant genotype significantly affected the fixation-linked respiration, although both plant and bacterial types significantly influenced the total rate of C2H2 reduction. On the basis of measured rates of H2 evolution and C2H2 reduction, or total nitrogen gain in the same system, the least respiration per unit of ammonia produced symbiotically was estimated as 4.8 to 6.9 moles CO2 (mole NH3)−1 in Laxton's Progress and the greatest as 9.3 to 13.3 moles CO2 (mole NH3)−1 in an Indian cultivar, as compared to a theoretical minimum respiration requirement of 4.7 moles CO2 (mole NH3)−1 in peas. PMID:16660833

  11. Nitrogen fixation amplifies the ocean biogeochemical response to decadal timescale variations in mineral dust deposition

    NASA Astrophysics Data System (ADS)

    Moore, J. Keith; Doney, Scott C.; Lindsay, Keith; Mahowald, Natalie; Michaels, Anthony F.

    2006-11-01

    A global ocean biogeochemical model is used to quantify the sensitivity of marine biogeochemistry and air-sea CO2 exchange to variations in dust deposition over decadal timescales. Estimates of dust deposition generated under four climate states provide a large range in total deposition with spatially realistic patterns; transient ocean model experiments are conducted by applying a step-function change in deposition from a current climate control. Relative to current conditions, higher dust deposition increases diatom and export production, nitrogen fixation and oceanic net CO2 uptake from the atmosphere, while reduced dust deposition has the opposite effects. Over timescales less than a decade, dust modulation of marine productivity and export is dominated by direct effects in high-nutrient, low-chlorophyll regions, where iron is the primary limiting nutrient. On longer timescales, an indirect nitrogen fixation pathway has increased importance, significantly amplifying the ocean biogeochemical response. Because dust iron input decouples carbon cycling from subsurface macronutrient supply, the ratio of the change in net ocean CO2 uptake to change in export flux is large, 0.45-0.6. Decreasing dust deposition and reduced oceanic CO2 uptake over the next century could provide a positive feedback to global warming, distinct from feedbacks associated with changes in stratification and circulation.

  12. Aerosol Deposition of Molybdenum: A Control on Nitrogen-Fixation and Tropical Forest Function

    NASA Astrophysics Data System (ADS)

    Wong, M.; Howarth, R. W.; Marino, R. M.; Mahowald, N. M.; Williams, E. R.

    2015-12-01

    Nitrogen fixation, the primary source of new nitrogen (N) to tropical forests, is exclusively catalyzed by the nitrogenase enzyme, which almost always requires molybdenum (Mo). Increasing evidence in recent years suggests that Mo availability may be low in highly weathered soils and can constrain N-fixation rates. Mo is generally either present in a highly soluble form (MoO42-) that is susceptible to leaching or tightly bound in minerals unavailable for biological uptake. To address how Mo is retained in highly weathered tropical systems to support N-fixation, atmospheric transport through dust and sea-salt aerosol spray were examined. Using a global atmospheric transport model computed from modeled meteorological fields, extrapolated dust and sea-salt aerosol Mo sources were used to calculate global distribution of Mo deposition. Dust deposition occurs across the entirety of some tropical forests, particularly the world's largest tropical forest in the Amazon Basin. The model indicates that the Amazon Basin receives substantial inputs of dust, especially the entire northern Amazon Basin, while the southern half receives less. Most of the dust reaching the Amazon originates from the Sahara Desert, and about half of this dust originates from one part of the Sahara, the Bodélé Depression. Mo in dust from the Bodélé Depression was measured with an average concentration of 1.14 ± 0.05 μg/g, similar to the crustal abundance. The model predicts Mo inputs from sea-salt aerosols in coastal regions up to 0.002 mg m-2yr-1. Significant sea-salt deposition occurs up to 300 km inland. Mo from fossil fuel combustion and biomass burning were also evaluated to determine the potential influence of anthropogenic emissions on releasing Mo into the environment.

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

    PubMed

    Sulieman, Saad; Tran, Lam-Son Phan

    2013-09-01

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

  14. Biological nitrogen fixation in acidic high-temperature geothermal springs in Yellowstone National Park, Wyoming.

    PubMed

    Hamilton, Trinity L; Lange, Rachel K; Boyd, Eric S; Peters, John W

    2011-08-01

    The near ubiquitous distribution of nifH genes in sediments sampled from 14 high-temperature (48.0-89.0°C) and acidic (pH 1.90-5.02) geothermal springs in Yellowstone National Park suggested a role for the biological reduction of dinitrogen (N(2)) to ammonia (NH(3)) (e.g. nitrogen fixation or diazotrophy) in these environments. nifH genes from these environments formed three unique phylotypes that were distantly related to acidiphilic, mesophilic diazotrophs. Acetylene reduction assays and (15) N(2) tracer studies in microcosms containing sediments sampled from acidic and high-temperature environments where nifH genes were detected confirmed the potential for biological N(2) reduction in these environments. Rates of acetylene reduction by sediment-associated populations were positively correlated with the concentration of NH(4)(+), suggesting a potential relationship between NH(4)(+) consumption and N(2) fixation activity. Amendment of microcosms with NH(4)(+) resulted in increased lag times in acetylene reduction assays. Manipulation of incubation temperature and pH in acetylene reduction assays indicated that diazotrophic populations are specifically adapted to local conditions. Incubation of sediments in the presence of a N(2) headspace yielded a highly enriched culture containing a single nifH phylotype. This phylotype was detected in all 14 geothermal spring sediments examined and its abundance ranged from ≈ 780 to ≈ 6800 copies (g dry weight sediment)(-1), suggesting that this organism may contribute N to the ecosystems. Collectively, these results for the first time demonstrate thermoacidiphilic N(2) fixation in the natural environment and extend the upper temperature for biological N(2) fixation in terrestrial systems.

  15. Hydrogen oxidation and nitrogen fixation in rhizobia, with special attention focused on strain ORS 571.

    PubMed

    de Vries, W; Stam, H; Stouthamer, A H

    1984-01-01

    In this survey we describe the influence of hydrogen oxidation on the physiology of Rhizobium ORS 571. The presence of hydrogen is required for the synthesis of hydrogenase. Carbon substrates do not repress the synthesis of hydrogenase. The respiratory system contains cytrochromes of the b- and c-type. Cytochrome alpha 600 is present after growth at high oxygen tensions. The nature of the terminal oxidases functioning at low oxygen tensions has not been established yet----H+/O values with endogenous substrates are between 6 and 7. The results show the presence of two phosphorylation sites: site 1 (ATP/2e = 1.0) and site 2(ATP/2e = 1.33). By measuring molar growth yields it has been demonstrated that carbon-limited, nitrogen-fixing cultures obtain additional ATP from hydrogen oxidation, and that site 2 of oxidative phosphorylation is passed during hydrogen oxidation. A method is described to calculate ATP/N2 values (the total amount of ATP used by nitrogenase during the fixation of 1 mol N2) and H2/N2 ratios (mol hydrogen formed per mol N2 fixed) in aerobic organisms. For Rhizobium ORS 571 the ATP/N2 value is about 40 and the H2/N2 ratio is between 5 and 7.5. Cells obtained from oxygen-limited nitrogen-fixing cultures contain 30-40% poly-beta-hydroxybutyrate, which explains the high molar growth yields found. Hydrogen has not been detected in the effluent gas of these cultures, which may point to reoxidation of the hydrogen formed at nitrogen fixation. Calculations show that the effect of hydrogen reoxidation on the efficiency of nitrogen fixation (g N fixed X mol-1 substrate converted) is not very large and that the actual H2/N2 ratio is of much more importance. After addition of hydrogen to succinate-limited, ammonia-assimilating cultures, an initial increase of the Ysuccinate value (g dry wt X mol-1 succinate) is followed by a gradual decrease. This is accompanied by a large decrease of the YO2 value, and an increased permeability of the cytoplasmic membrane to

  16. nifH Sequences and Nitrogen Fixation in Type I and Type II Methanotrophs

    PubMed Central

    Auman, Ann J.; Speake, Catherine C.; Lidstrom, Mary E.

    2001-01-01

    Some methane-oxidizing bacteria (methanotrophs) are known to be capable of expressing nitrogenase and utilizing N2 as a nitrogen source. However, no sequences are available for nif genes in these strains, and the known nitrogen-fixing methanotrophs are confined mainly to a few genera. The purpose of this work was to assess the nitrogen-fixing capabilities of a variety of methanotroph strains. nifH gene fragments from four type I methanotrophs and seven type II methanotrophs were PCR amplified and sequenced. Nitrogenase activity was confirmed in selected type I and type II strains by acetylene reduction. Activities ranged from 0.4 to 3.3 nmol/min/mg of protein. Sequence analysis shows that the nifH sequences from the type I and type II strains cluster with nifH sequences from other gamma proteobacteria and alpha proteobacteria, respectively. The translated nifH sequences from three Methylomonas strains show high identity (95 to 99%) to several published translated environmental nifH sequences PCR amplified from rice roots and a freshwater lake. The translated nifH sequences from the type II strains show high identity (94 to 99%) to published translated nifH sequences from a variety of environments, including rice roots, a freshwater lake, an oligotrophic ocean, and forest soil. These results provide evidence for nitrogen fixation in a broad range of methanotrophs and suggest that nitrogen-fixing methanotrophs may be widespread and important in the nitrogen cycling of many environments. PMID:11525998

  17. Genetic Variability in Nodulation and Root Growth Affects Nitrogen Fixation and Accumulation in Pea

    PubMed Central

    Bourion, Virginie; Laguerre, Gisele; Depret, Geraldine; Voisin, Anne-Sophie; Salon, Christophe; Duc, Gerard

    2007-01-01

    Background and Aims Legume nitrogen is derived from two different sources, symbiotically fixed atmospheric N2 and soil N. The effect of genetic variability of root and nodule establishment on N acquisition and seed protein yield was investigated under field conditions in pea (Pisum sativum). In addition, these parameters were related to the variability in preference for rhizobial genotypes. Methods Five different spring pea lines (two hypernodulating mutants and three cultivars), previously identified in artificial conditions as contrasted for both root and nodule development, were characterized under field conditions. Root and nodule establishment was examined from the four-leaf stage up to the beginning of seed filling and was related to the patterns of shoot dry matter and nitrogen accumulation. The genetic structure of rhizobial populations associated with the pea lines was obtained by analysis of nodule samples. The fraction of nitrogen derived from symbiotic fixation was estimated at the beginning of seed filling and at physiological maturity, when seed protein content and yield were determined. Key Results The hypernodulating mutants established nodules earlier and maintained them longer than was the case for the three cultivars, whereas their root development and nitrogen accumulation were lower. The seed protein yield was higher in ‘Athos’ and ‘Austin’, the two cultivars with increased root development, consistent with their higher N absorption during seed filling. Conclusion The hypernodulating mutants did not accumulate more nitrogen, probably due to the C cost for nodulation being higher than for root development. Enhancing exogenous nitrogen supply at the end of the growth cycle, by increasing the potential for root N uptake from soil, seems a good option for improving pea seed filling. PMID:17670753

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

    NASA Astrophysics Data System (ADS)

    Siczek, A.; Lipiec, J.

    2009-04-01

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

  19. Bd oxidase homologue of photosynthetic purple sulfur bacterium Allochromatium vinosum is co-transcribed with a nitrogen fixation related gene.

    PubMed

    Dincturk, H Benan; Demir, Volkan; Aykanat, Tutku

    2011-02-01

    Purple sulfur bacteria, which are known to be the most ancient among anoxygenic phototrophs, play an important role in the global sulfur cycle. Allochromatium vinosum oxidizes reduced sulfur compounds such as hydrogen sulfide, elemental sulfur and thiosulfide. At low oxygen concentrations, A. vinosum can grow chemotrophically using oxygen as the terminal electron acceptor. Being also a nitrogen fixer, A. vinosum is faced with the paradox of co-existence of aerobic metabolism and nitrogen fixation. Due to growth difficulties, only a few studies have dealt with the aerobic metabolism of the organism and, until now, there has been no information about the genes involved in the respiratory metabolism of purple sulfur bacteria. In this article we show the first terminal oxidase gene for A. vinosum. The presence of a Bd type of quinol oxidase is necessary to protect nitrogenases against the inhibitory effects of oxygen. In this case, a nitrogen fixation related gene is part of the cyd operon and this gene is co-transcribed with cydAB genes. Bd oxidase of A. vinosum may be the earliest form of oxidase where the function of the enzyme is to scavenge the contaminant oxygen during nitrogen fixation. This may be an important clue about the early evolution of oxygenic photosynthesis, perhaps as a protective mechanism for nitrogen fixation.

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

    PubMed Central

    Kamfwa, Kelvin; Zhao, Dongyan; Kelly, James D.

    2017-01-01

    Common bean (Phaseolus vulgaris L.) fixes atmospheric nitrogen (N2) through symbiotic nitrogen fixation (SNF) at levels lower than other grain legume crops. An understanding of the genes and molecular mechanisms underlying SNF will enable more effective strategies for the genetic improvement of SNF traits in common bean. In this study, transcriptome profiling was used to identify genes and molecular mechanisms underlying SNF differences between two common bean recombinant inbred lines that differed in their N-fixing abilities. Differential gene expression and functional enrichment analyses were performed on leaves, nodules and roots of the two lines when grown under N-fixing and non-fixing conditions. Receptor kinases, transmembrane transporters, and transcription factors were among the differentially expressed genes identified under N-fixing conditions, but not under non-fixing conditions. Genes up-regulated in the stronger nitrogen fixer, SA36, included those involved in molecular functions such as purine nucleoside binding, oxidoreductase and transmembrane receptor activities in nodules, and transport activity in roots. Transcription factors identified in this study are candidates for future work aimed at understanding the functional role of these genes in SNF. Information generated in this study will support the development of gene-based markers to accelerate genetic improvement of SNF in common bean. PMID:28192540

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

    PubMed

    Kamfwa, Kelvin; Zhao, Dongyan; Kelly, James D; Cichy, Karen A

    2017-01-01

    Common bean (Phaseolus vulgaris L.) fixes atmospheric nitrogen (N2) through symbiotic nitrogen fixation (SNF) at levels lower than other grain legume crops. An understanding of the genes and molecular mechanisms underlying SNF will enable more effective strategies for the genetic improvement of SNF traits in common bean. In this study, transcriptome profiling was used to identify genes and molecular mechanisms underlying SNF differences between two common bean recombinant inbred lines that differed in their N-fixing abilities. Differential gene expression and functional enrichment analyses were performed on leaves, nodules and roots of the two lines when grown under N-fixing and non-fixing conditions. Receptor kinases, transmembrane transporters, and transcription factors were among the differentially expressed genes identified under N-fixing conditions, but not under non-fixing conditions. Genes up-regulated in the stronger nitrogen fixer, SA36, included those involved in molecular functions such as purine nucleoside binding, oxidoreductase and transmembrane receptor activities in nodules, and transport activity in roots. Transcription factors identified in this study are candidates for future work aimed at understanding the functional role of these genes in SNF. Information generated in this study will support the development of gene-based markers to accelerate genetic improvement of SNF in common bean.

  2. The integral membrane protein SEN1 is required for symbiotic nitrogen fixation in Lotus japonicus nodules.

    PubMed

    Hakoyama, Tsuneo; Niimi, Kaori; Yamamoto, Takeshi; Isobe, Sawa; Sato, Shusei; Nakamura, Yasukazu; Tabata, Satoshi; Kumagai, Hirotaka; Umehara, Yosuke; Brossuleit, Katja; Petersen, Thomas R; Sandal, Niels; Stougaard, Jens; Udvardi, Michael K; Tamaoki, Masanori; Kawaguchi, Masayoshi; Kouchi, Hiroshi; Suganuma, Norio

    2012-01-01

    Legume plants establish a symbiotic association with bacteria called rhizobia, resulting in the formation of nitrogen-fixing root nodules. A Lotus japonicus symbiotic mutant, sen1, forms nodules that are infected by rhizobia but that do not fix nitrogen. Here, we report molecular identification of the causal gene, SEN1, by map-based cloning. The SEN1 gene encodes an integral membrane protein homologous to Glycine max nodulin-21, and also to CCC1, a vacuolar iron/manganese transporter of Saccharomyces cerevisiae, and VIT1, a vacuolar iron transporter of Arabidopsis thaliana. Expression of the SEN1 gene was detected exclusively in nodule-infected cells and increased during nodule development. Nif gene expression as well as the presence of nitrogenase proteins was detected in rhizobia from sen1 nodules, although the levels of expression were low compared with those from wild-type nodules. Microscopic observations revealed that symbiosome and/or bacteroid differentiation are impaired in the sen1 nodules even at a very early stage of nodule development. Phylogenetic analysis indicated that SEN1 belongs to a protein clade specific to legumes. These results indicate that SEN1 is essential for nitrogen fixation activity and symbiosome/bacteroid differentiation in legume nodules.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  4. Seasonally dependent iron limitation of nitrogen fixation in tropical forests of karst landscapes

    NASA Astrophysics Data System (ADS)

    Winbourne, J. B.; Brewer, S.; Houlton, B. Z.

    2015-12-01

    Limestone tropical forests in karst topography are one of the most poorly studied ecosystems on Earth, and has been substantially cleared by human activities throughout much of Central America. This ecosystem is noted for its high level of plant productivity, biomass, endemism and biological diversity compared to nearby neighboring tropical forests on volcanic rock substrates (Brewer et al. 2002). A question remains as to how limestone tropical forests are able to maintain the high nutrient demands of plant photosynthesis and tree biomass growth. Here, we demonstrate that rates of nitrogen (N) fixation are higher in limestone versus volcanic soil substrates, with direct evidence for the emergence of seasonally dependent iron limitation of N fixation in limestone tropical forest. N fixation rates showed a three-fold increase in response to iron additions, especially during the wet season when N demands of the forest trees are highest. In contrast, adjacent forests growing on the more classical acidic volcanic soils showed no response to iron or other nutrient additions. Biologically available pools of iron were exceedingly low in the limestone forest site, consistent with the complexation of iron under high pH conditions. Biological acquisition of iron, as measured by the concentration of iron chelating compounds (i.e. siderophores), provided additional evidence for iron limitation of microbial processes in limestone tropical forests, where concentrations were six times higher than those at the volcanic site. Our results suggest that the functioning of limestone tropical forest is strongly regulated by interactions between iron, soil pH, and N cycling.

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

    NASA Astrophysics Data System (ADS)

    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.

  6. Ocean acidification impacts on nitrogen fixation in the coastal western Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Rees, Andrew P.; Turk-Kubo, Kendra A.; Al-Moosawi, Lisa; Alliouane, Samir; Gazeau, Frédéric; Hogan, Mary E.; Zehr, Jonathan P.

    2017-02-01

    The effects of ocean acidification on nitrogen (N2) fixation rates and on the community composition of N2-fixing microbes (diazotrophs) were examined in coastal waters of the North-Western Mediterranean Sea. Nine experimental mesocosm enclosures of ∼50 m3 each were deployed for 20 days during June-July 2012 in the Bay of Calvi, Corsica, France. Three control mesocosms were maintained under ambient conditions of carbonate chemistry. The remainder were manipulated with CO2 saturated seawater to attain target amendments of pCO2 of 550, 650, 750, 850, 1000 and 1250 μatm. Rates of N2 fixation were elevated up to 10 times relative to control rates (2.00 ± 1.21 nmol L-1d-1) when pCO2 concentrations were >1000 μatm and pHT (total scale) < 7.74. Diazotrophic phylotypes commonly found in oligotrophic marine waters, including the Mediterranean, were not present at the onset of the experiment and therefore, the diazotroph community composition was characterised by amplifying partial nifH genes from the mesocosms. The diazotroph community was comprised primarily of cluster III nifH sequences (which include possible anaerobes), and proteobacterial (α and γ) sequences, in addition to small numbers of filamentous (or pseudo-filamentous) cyanobacterial phylotypes. The implication from this study is that there is some potential for elevated N2 fixation rates in the coastal western Mediterranean before the end of this century as a result of increasing ocean acidification. Observations made of variability in the diazotroph community composition could not be correlated with changes in carbon chemistry, which highlights the complexity of the relationship between ocean acidification and these keystone organisms.

  7. Nitrogen fixation rates at BATS and along the North Atlantic subtropical front

    NASA Astrophysics Data System (ADS)

    Charoenpong, C.; Larkum, J.; Lee, E. M.; Moisander, P.; Altabet, M. A.

    2012-12-01

    Nitrogen fixation is one of the major inputs of new N into the oligotrophic gyre of North Atlantic. In the Bermuda Atlantic Time-series Study (BATS), Trichodesmium spp. and diatom symbiont Richelia have been regarded as a major contributor to the newly fixed N. However, studies using nitrogenase gene (nifH) sequences have indicated a more diverse diazotroph assemblages including unicellular cyanobacteria in this oligotrophic system. Here, we report N2 fixation rates from diazotrophs of the size fraction that includes unicellular cyanobacteria and other bacteria. Samples were taken from BATS and several stations along the meridional transect from BATS southward to the area of the subtropical front (~27oN). Whole water samples were enriched with 15N-labelled N2, and incubated for 12-24 hours in simulated in situ conditions. Post-incubation filtration by using 20 micron size fractionation excluded Trichodesmium and potential diatom symbionts and constrained our rates to smaller non-filamentous N2-fixers. Sampling was conducted on two cruises during July and August 2012. 13C incorporation rates are also presented to show the photosynthetic activity. In addition, the 15N-enrichment of dissolved organic N (DON) was investigated in order to demonstrate the contribution of the diazotrophy to the regenerated nutrient and the potential link to the heterotrophic bacterial production.

  8. Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems

    USGS Publications Warehouse

    Vitousek, Peter M.; Menge, Duncan N.L.; Reed, Sasha C.; Cleveland, Cory C.

    2013-01-01

    New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)—greatly expanding our appreciation of the diversity and ubiquity of N fixers—but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with 15N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40–100) Tg N fixed yr−1; adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr−1. This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed.

  9. Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems

    PubMed Central

    Vitousek, Peter M.; Menge, Duncan N. L.; Reed, Sasha C.; Cleveland, Cory C.

    2013-01-01

    New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)—greatly expanding our appreciation of the diversity and ubiquity of N fixers—but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with 15N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40–100) Tg N fixed yr−1; adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr−1. This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed. PMID:23713117

  10. Evidence for foliar endophytic nitrogen fixation in a widely distributed subalpine conifer.

    PubMed

    Moyes, Andrew B; Kueppers, Lara M; Pett-Ridge, Jennifer; Carper, Dana L; Vandehey, Nick; O'Neil, James; Frank, A Carolin

    2016-04-01

    Coniferous forest nitrogen (N) budgets indicate unknown sources of N. A consistent association between limber pine (Pinus flexilis) and potential N2 -fixing acetic acid bacteria (AAB) indicates that native foliar endophytes may supply subalpine forests with N. To assess whether the P. flexilis-AAB association is consistent across years, we re-sampled P. flexilis twigs at Niwot Ridge, CO and characterized needle endophyte communities via 16S rRNA Illumina sequencing. To investigate whether endophytes have access to foliar N2 , we incubated twigs with (13) N2 -enriched air and imaged radioisotope distribution in needles, the first experiment of its kind using (13) N. We used the acetylene reduction assay to test for nitrogenase activity within P. flexilis twigs four times from June to September. We found evidence for N2 fixation in P. flexilis foliage. N2 diffused readily into needles and nitrogenase activity was positive across sampling dates. We estimate that this association could provide 6.8-13.6 μg N m(-2)  d(-1) to P. flexilis stands. AAB dominated the P. flexilis needle endophyte community. We propose that foliar endophytes represent a low-cost, evolutionarily stable N2 -fixing strategy for long-lived conifers. This novel source of biological N2 fixation has fundamental implications for understanding forest N budgets.

  11. Partner choice in nitrogen-fixation mutualisms of legumes and rhizobia.

    PubMed

    Simms, Ellen L; Taylor, D Lee

    2002-04-01

    Mutualistic interactions are widespread and obligatory for many organisms, yet their evolutionary persistence in the face of cheating is theoretically puzzling. Nutrient-acquisition symbioses between plants and soil microbes are critically important to plant evolution and ecosystem function, yet we know almost nothing about the evolutionary dynamics and mechanisms of persistence of these ancient mutualisms. Partner-choice and partner-fidelity are mechanisms for dealing with cheaters, and can theoretically allow mutualisms to persist despite cheaters.Many models of cooperative behavior assume pairwise interactions, while most plant-microbe nutrient-acquisition symbioses involve a single plant interacting with numerous microbes. Market models, in contrast, are well suited to mutualisms in which single plants attempt to conduct mutually beneficial resource exchange with multiple individuals. Market models assume that one partner chooses to trade with a subset of individuals selected from a market of potential partners. Hence, determining whether partner-choice occurs in plant-microbe mutualisms is critical to understanding the evolutionary persistence and dynamics of these symbioses. The nitrogen-fixation/carbon-fixation mutualism between leguminous plants and rhizobial bacteria is widespread, ancient, and important for ecosystem function and human nutrition. It also involves single plants interacting simultaneously with several to many bacterial partners, including ineffective ("cheating") strains. We review the existing literature and find that this mutualism displays several elements of partner-choice, and may match the requirements of the market paradigm. We conclude by identifying profitable questions for future research.

  12. Effects of salt stress and rhizobial inoculation on growth and nitrogen fixation of three peanut cultivars.

    PubMed

    El-Akhal, M R; Rincón, A; Coba de la Peña, T; Lucas, M M; El Mourabit, N; Barrijal, S; Pueyo, J J

    2013-03-01

    Increasing soil salinity represents a major constraint for agriculture in arid and semi-arid lands, where mineral nitrogen (N) deficiency is also a frequent characteristic of soils. Biological N fixation by legumes may constitute a sustainable alternative to chemical fertilisation in salinity-affected areas, provided that adapted cultivars and inoculants are available. Here, the performance of three peanut cultivars nodulated with two different rhizobial strains that differ in their salt tolerance was evaluated under moderately saline water irrigation and compared with that of N-fertilised plants. Shoot weight was used as an indicator of yield. Under non-saline conditions, higher yields were obtained using N fertilisation rather than inoculation for all the varieties tested. However, under salt stress, the yield of inoculated plants became comparable to that of N-fertilised plants, with minor differences depending on the peanut cultivar and rhizobial strain. Our results indicate that N fixation might represent an economical, competitive and environmentally friendly choice with respect to mineral N fertilisation for peanut cultivation under moderate saline conditions.

  13. Stable chromosomal integration of the entire nitrogen fixation gene cluster from Klebsiella pneumoniae in yeast.

    PubMed Central

    Zamir, A; Maina, C V; Fink, G R; Szalay, A A

    1981-01-01

    A bacterial plasmid containing the entire nitrogen fixation (nif) gene cluster (consisting of at least 15 genes) from Klebsiella pneumoniae was used in conjunction with an Escherichia coli-yeast shuttle plasmid containing the yeast his4 gene cluster to cotransform a his4- recipient strain of Saccharomyces cerevisiae. Of 87 histidine-independent clones screened, 2 contained nif DNA. Restriction and hybridization analyses showed that two copies of the nif plasmid (46 kilobases each) are integrated in tandem in the recipient chromosome by recombination between homologous regions in the transforming plasmids. Chromosomal integration was also verified by tetrad analysis, showing that the nif DNA behaved in meiosis like a Mendelian element. During mitotic growth, one of the two copies of the nif region is frequently lost. The remaining copy of nif is stable, even after 40 generations in nonselective medium. Images PMID:6267596

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

    USGS Publications Warehouse

    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.

  15. Biological nitrogen fixation in sugar cane: A key to energetically viable biofuel production

    SciTech Connect

    Boddey, R.M.

    1995-05-01

    The advantages of producing biofuels to replace fossil energy sources are derived from the fact that the energy accumulated in the biomass in captured directly from photosynthesis and is thus renewable, and that the cycle of carbon dioxide fixation by the crop, followed by burning of the fuel makes no overall contribution to atmospheric CO{sub 2} or, consequently, to global warming. However, these advantages are negated if large quantities of fossil fuels need to be used to grow or process the biofuel crop. In this regard, the Brazilian bioethanol program, based on the fermentation/distillation of sugar cane juice, is particularly favorable, not only because the crop is principally hand harvested, but also because of the low nitrogen fertilizer use on sugar cane in Brazil. Recent {sup 15}N and N balance studies have shown that in some Brazilian cane varieties, high yields are possible without N fertilization because the plants are able to obtain large contributions of nitrogen from plant-associated biological N{sub 2} fixation (BNF). The N{sub 2}-fixing acid-tolerant bacterium Acetobacter diazotrophicus was first found to occur within roots, stems, and leaves of sugar cane. Subsequently, two species of Herbaspirillum also have been found to occur within the interior of all sugar cane tissues. The discovery of these, and other N{sub 2}-fixing bacteria that survive poorly in soil but thrive within plant tissue (endophytic bacteria), may account for the high BNF contributions observed in sugar cane. Further study of this system should allow the gradual elimination of N fertilizer use on sugar cane, at least in Brazil, and opens up the possibility of the extension of this efficient N{sub 2}-fixing system to cereal and other crops with consequent immense potential benefits to tropical agriculture. 44 refs., 9 figs., 4 tabs.

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

    PubMed

    Yelenik, Stephanie; Perakis, Steven; Hibbs, David

    2013-03-01

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

  17. Approaches for enhancement of N₂ fixation efficiency of chickpea (Cicer arietinum L.) under limiting nitrogen conditions.

    PubMed

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

    2014-04-01

    Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N₂ inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar 'Bivanij' as well as studied the mechanism underlying the improvement of N₂ fixation efficiency. Our data revealed that C-15 strain manifested the most efficient N₂ fixation in comparison with Ch-191 or CP-36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C-15 nodules. Nodule specific activity was significantly higher in C-15 combination, partially as a result of higher electron allocation to N₂ versus H⁺. Interestingly, a striking difference in nodule carbon and nitrogen composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch-191 or CP-36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C-15 strain. As a result, the best symbiotic efficiency observed with C-15-induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C-15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and nitrogen metabolism. © 2013 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd.

  18. Global changes in the transcript and metabolic profiles during symbiotic nitrogen fixation in phosphorus-stressed common bean plants

    USDA-ARS?s Scientific Manuscript database

    Phosphorus (P) deficiency is widespread in regions where the common bean (Phaseolus vulgaris L.), the most important legume for human consumption, is produced and is perhaps the factor that most limits nitrogen (N) fixation. Global gene expression and metabolome approaches were used to investigate t...

  19. Transcriptional Analysis of an Ammonium-Excreting strain of Azotobacter vinelandii Deregulated for Nitrogen Fixation.

    PubMed

    Barney, Brett M; Plunkett, Mary H; Natarajan, Velmurugan; Mus, Florence; Knutson, Carolann M; Peters, John W

    2017-08-11

    Biological nitrogen fixation is accomplished by a diverse group of organisms known as diazotrophs, and requires the function of the complex metalloenzyme nitrogenase. Nitrogenase and many of the accessory proteins required for proper cofactor biosynthesis and incorporation into the enzyme have been characterized, but a complete picture of the reaction mechanism and key cellular changes that accompany biological nitrogen fixation remain to be fully elucidated. Studies have revealed that specific disruptions to the anti-activator encoding gene nifL result in the deregulation of the nif transcriptional activator NifA in the nitrogen-fixing bacterium Azotobacter vinelandii, triggering the production of extracellular ammonium levels approaching 30 mM during the stationary phase of growth. In this work, we have characterized the global patterns of gene expression of this high-ammonium releasing phenotype. The findings reported here indicated that cultures of this high-ammonium accumulating strain may be experiencing metal limitation when grown using standard Burk's medium, which could be amended by increasing molybdenum levels to further increase ammonium yield. In addition, elevated levels of nitrogenase gene transcription are not accompanied by a corresponding dramatic increase in hydrogenase gene transcription, or hydrogen uptake rates. Of the three potential electron donor systems for nitrogenase, only the rnf1 gene cluster showed a transcriptional correlation to the increased yield of ammonium. Our results also highlight several additional genes which may play a role in supporting elevated ammonium production in this aerobic nitrogen-fixing model bacterium.Importance: The transcriptional differences found during stationary-phase ammonium accumulation show a strong contrast between the deregulated (nifL disrupted) and wild-type strain, and to what was previously reported for the wild-type strain during exponential phase growth conditions. These results demonstrate

  20. Identification of nitrogenous organic species in Titan aerosols analogs: Nitrogen fixation routes in early atmospheres

    NASA Astrophysics Data System (ADS)

    He, Chao; Smith, Mark A.

    2013-09-01

    Titan, an icy world surrounded by auburn organic haze, is considered as one of the best targets for studying abiotic planetary organic chemistry. In spite of a great many efforts being made, the chemistry in Titan’s atmosphere and its resulting chemical structures are still not fully understood. In our previous work, we have investigated the structure of Titan aerosols analogs (tholin) by NMR and identified hexamethylenetetramine as a dominant small molecule in Titan tholin. Here we report a more complete and definitive structural investigation of the small molecule inventory in Titan tholin. We identified several nitrogenous organic molecules including cyanamide, guanidine, 2-cyanoguanidine, melamine, N‧-cyanoformamidine and 1,2,4-triazole in Titan tholin by using NMR and GC-MS and standard sample comparison. The structural characteristics of these molecules suggest a possible formation pathway from the reaction of HCN and NH3, both of which are known to exist in appreciable density in the atmosphere and were tentatively detected by the Huygens probe.

  1. Trends in nitrogen isotope ratios of juvenile winter flounder reflect changing nitrogen inputs to Rhode Island, USA estuarine systems

    EPA Science Inventory

    Nitrogen isotope ratios (d 15N) in juvenile winter flounder, Pseudopleuronectes americanus, were used to examine changes in nitrogen inputs to several Rhode Island, USA estuarine systems. Fish were collected over two three-year periods with a ten-year interval between sampling pe...

  2. A Minimal Nitrogen Fixation Gene Cluster from Paenibacillus sp. WLY78 Enables Expression of Active Nitrogenase in Escherichia coli

    PubMed Central

    Zhao, Dehua; Liu, Xiaomeng; Zhang, Bo; Xie, Jianbo; Hong, Yuanyuan; Li, Pengfei; Chen, Sanfeng; Dixon, Ray; Li, Jilun

    2013-01-01

    Most biological nitrogen fixation is catalyzed by molybdenum-dependent nitrogenase, an enzyme complex comprising two component proteins that contains three different metalloclusters. Diazotrophs contain a common core of nitrogen fixation nif genes that encode the structural subunits of the enzyme and components required to synthesize the metalloclusters. However, the complement of nif genes required to enable diazotrophic growth varies significantly amongst nitrogen fixing bacteria and archaea. In this study, we identified a minimal nif gene cluster consisting of nine nif genes in the genome of Paenibacillus sp. WLY78, a gram-positive, facultative anaerobe isolated from the rhizosphere of bamboo. We demonstrate that the nif genes in this organism are organized as an operon comprising nifB, nifH, nifD, nifK, nifE, nifN, nifX, hesA and nifV and that the nif cluster is under the control of a σ70 (σA)-dependent promoter located upstream of nifB. To investigate genetic requirements for diazotrophy, we transferred the Paenibacillus nif cluster to Escherichia coli. The minimal nif gene cluster enables synthesis of catalytically active nitrogenase in this host, when expressed either from the native nifB promoter or from the T7 promoter. Deletion analysis indicates that in addition to the core nif genes, hesA plays an important role in nitrogen fixation and is responsive to the availability of molybdenum. Whereas nif transcription in Paenibacillus is regulated in response to nitrogen availability and by the external oxygen concentration, transcription from the nifB promoter is constitutive in E. coli, indicating that negative regulation of nif transcription is bypassed in the heterologous host. This study demonstrates the potential for engineering nitrogen fixation in a non-nitrogen fixing organism with a minimum set of nine nif genes. PMID:24146630

  3. Projections of Biofuel Growth Patterns Reveal the Potential Importance of Nitrogen Fixation for Miscanthus Productivity

    NASA Astrophysics Data System (ADS)

    Davis, S. C.; Parton, W. J.; Dohleman, F. G.; Gottel, N. R.; Smith, C. M.; Kent, A. D.; Delucia, E. H.

    2008-12-01

    Demand for liquid biofuels is increasing because of the disparity between fuel demand and supply. Relative to grain crops, the more intensive harvest required for second generation liquid biofuel production leads to the removal of significantly more carbon and nitrogen from the soil. These elements are conventionally litter products of crops that are returned to the soil and can accumulate over time. This loss of organic matter represents a management challenge because the energy cost associated with fertilizers or external sources of organic matter reduce the net energy value of the biofuel crops. Plants that have exceptional strategies for exploiting nutrients may be the most viable options for sustainable biofuel yields because of low management and energy cost. Miscanthus x giganteus has high N retranslocation rates, maintains high photosynthetic rates over a large temperature range, exploits a longer-than-average growing season, and yields at least twice the biomass of other candidate biofuel grass crops (i.e. switchgrass). We employed the DAYCENT model to project potential productivity of Miscanthus, corn, switchgrass, and mixed prairie communities based on our current knowledge of these species. Ecosystem process descriptions that have been validated for many crop species did not accurately predict Miscanthus yields and lead to new hypotheses about unknown N cycling mechanisms for this species. We tested the hypothesis that Miscanthus hosts N-fixing bacteria in several ways. First, we used enrichment culture and molecular methods to detect N-fixing bacteria in Miscanthus. Then, we demonstrated the plant-growth promoting effect of diazotrophs isolated from Miscanthus rhizomes on a model grass. And finally, we applied 15N2 to the soil and rooting zone of field grown Miscanthus plants to determine if atmospheric N2 was incorporated into plant tissue, a process that requires N-fixation. These experiments are the first tests of N-fixation in Miscanthus x

  4. Relative efficacy of different distillery effluents on growth, nitrogen fixation and yield of groundnut.

    PubMed

    Ramana, S; Biswas, A K; Singh, A B; Yadava, R B R

    2002-01-01

    A field experiment with groundnut as test crop was conducted to evaluate the manurial potential of three distillery effluents: raw spent wash (RSW), biomethanated spent wash (BSW) and lagoon sludge (LS) vis-à-vis recommended fertilizers (NPK + farm yard manure (FYM)) and a control (no fertilizer or distillery effluent). It was found that all the three distillery effluents increased total chlorophyll content, crop growth rate (CGR), total dry matter, nutrient uptake (N, P and K) and finally seed yield compared to the control but inhibited nodulation and decreased nitrogen fixation. Among the three distillery effluents, BSW produced the highest seed yield (619 kg ha(-1)) twice that of control (3.10 kg ha(-1)), followed by RSW (557 kg ha(-1)) and LS (472 kg ha(-1)). However, the distillery effluents did not influence protein and oil contents. It was concluded that these distillery effluents because of their high manurial potential could supply nutrients, particularly potassium, nitrogen and sulphur, to the crops and thus reduce the fertilizer requirement of crops. Nevertheless, the crop performance and yield with three distillery effluents were overall less than that produced by recommended NPK + FYM probably on account of failure of the effluents to supply balanced nutrition to the plants for achieving their potential growth capacity.

  5. The Microbiome of Eucalyptus Roots under Different Management Conditions and Its Potential for Biological Nitrogen Fixation.

    PubMed

    Fonseca, Eduardo da Siva; Peixoto, Raquel Silva; Rosado, Alexandre Soares; Balieiro, Fabiano de Carvalho; Tiedje, James M; Rachid, Caio Tavora Coelho da Costa

    2017-06-21

    Eucalyptus plantations offer a cost-effective and renewable source of raw material. There is substantial interest in improving forestry production, especially through sustainable strategies such as the use of plant growth-promoting bacteria. However, little is known about Eucalyptus microbiology. In this study, the endophytic bacterial community was assessed in Eucalyptus urograndis roots using culture-dependent and culture-independent techniques with plants grown under different conditions. Three phyla accounted for approximately 95% of the community, with Actinobacteria corresponding to approximately 59%. This contrasts with previous studies in which Actinobacteria accounted for only 5 to 10%. Our data also revealed a high diversity of bacteria, with 359 different genera but a high level of dominance. Six genera, Mycobacterium, Bradyrhizobium, Streptomyces, Bacillus, Actinospica, and Burkholderia, accounted for more than 50% of the classified sequences. We observed a significant influence of the treatments on some genera, causing changes in the bacterial community structure. The obtained data also suggest that Eucalyptus may benefit from biological nitrogen fixation, with many abundant genera being closely related to nitrogen-fixing bacteria. Using N-depleted media, we also cultured 95 bacterial isolates, of which 24 tested positive for the nifH gene and were able to maintain growth without any N source in the medium.

  6. Effects of model structural uncertainty on carbon cycle projections: biological nitrogen fixation as a case study

    NASA Astrophysics Data System (ADS)

    Wieder, William R.; Cleveland, Cory C.; Lawrence, David M.; Bonan, Gordon B.

    2015-04-01

    Uncertainties in terrestrial carbon (C) cycle projections increase uncertainty of potential climate feedbacks. Efforts to improve model performance often include increased representation of biogeochemical processes, such as coupled carbon-nitrogen (N) cycles. In doing so, models are becoming more complex, generating structural uncertainties in model form that reflect incomplete knowledge of how to represent underlying processes. Here, we explore structural uncertainties associated with biological nitrogen fixation (BNF) and quantify their effects on C cycle projections. We find that alternative plausible structures to represent BNF result in nearly equivalent terrestrial C fluxes and pools through the twentieth century, but the strength of the terrestrial C sink varies by nearly a third (50 Pg C) by the end of the twenty-first century under a business-as-usual climate change scenario representative concentration pathway 8.5. These results indicate that actual uncertainty in future C cycle projections may be larger than previously estimated, and this uncertainty will limit C cycle projections until model structures can be evaluated and refined.

  7. Iron controls over di-nitrogen fixation in karst tropical forest.

    PubMed

    Winbourne, Joy B; Brewer, Steven W; Houlton, Benjamin Z

    2017-03-01

    Limestone tropical forests represent a meaningful fraction of the land area in Central America (25%) and Southeast Asia (40%). These ecosystems are marked by high biological diversity, CO2 uptake capacity, and high pH soils, the latter making them fundamentally different from the majority of lowland tropical forest areas in the Amazon and Congo basins. Here, we examine the role of bedrock geology in determining biological nitrogen fixation (BNF) rates in volcanic (low pH) vs. limestone (high pH) tropical forests located in the Maya Mountains of Belize. We experimentally test how BNF in the leaf-litter responds to nitrogen, phosphorus, molybdenum, and iron additions across different parent materials. We find evidence for iron limitation of BNF rates in limestone forests during the wet but not dry season (response ratio 3.2 ± 0.2; P = 0.03). In contrast, BNF in low pH volcanic forest soil was stimulated by the trace-metal molybdenum during the dry season. The parent-material induced patterns of limitation track changes in siderophore activity and iron bioavailability among parent materials. These findings point to a new role for iron in regulating BNF in karst tropical soils, consistent with observations for other high pH systems such as the open ocean and calcareous agricultural ecosystems. © 2016 by the Ecological Society of America.

  8. Endophytic Colonization and In Planta Nitrogen Fixation by a Herbaspirillum sp. Isolated from Wild Rice Species

    PubMed Central

    Elbeltagy, Adel; Nishioka, Kiyo; Sato, Tadashi; Suzuki, Hisa; Ye, Bin; Hamada, Toru; Isawa, Tsuyoshi; Mitsui, Hisayuki; Minamisawa, Kiwamu

    2001-01-01

    Nitrogen-fixing bacteria were isolated from the stems of wild and cultivated rice on a modified Rennie medium. Based on 16S ribosomal DNA (rDNA) sequences, the diazotrophic isolates were phylogenetically close to four genera: Herbaspirillum, Ideonella, Enterobacter, and Azospirillum. Phenotypic properties and signature sequences of 16S rDNA indicated that three isolates (B65, B501, and B512) belong to the Herbaspirillum genus. To examine whether Herbaspirillum sp. strain B501 isolated from wild rice, Oryza officinalis, endophytically colonizes rice plants, the gfp gene encoding green fluorescent protein (GFP) was introduced into the bacteria. Observations by fluorescence stereomicroscopy showed that the GFP-tagged bacteria colonized shoots and seeds of aseptically grown seedlings of the original wild rice after inoculation of the seeds. Conversely, for cultivated rice Oryza sativa, no GFP fluorescence was observed for shoots and only weak signals were observed for seeds. Observations by fluorescence and electron microscopy revealed that Herbaspirillum sp. strain B501 colonized mainly intercellular spaces in the leaves of wild rice. Colony counts of surface-sterilized rice seedlings inoculated with the GFP-tagged bacteria indicated significantly more bacterial populations inside the original wild rice than in cultivated rice varieties. Moreover, after bacterial inoculation, in planta nitrogen fixation in young seedlings of wild rice, O. officinalis, was detected by the acetylene reduction and 15N2 gas incorporation assays. Therefore, we conclude that Herbaspirillum sp. strain B501 is a diazotrophic endophyte compatible with wild rice, particularly O. officinalis. PMID:11679357

  9. Azide resistance in Rhizobium ciceri linked with superior symbiotic nitrogen fixation.

    PubMed

    Bhaskar, V Vijay

    2004-12-01

    Isolated azide resistant (AzR) native R. ciceri strain 18-7 was resistant to sodium azide at 10 microg/ml. To find if nif-reiteration is responsible for azide resistance and linked to superior symbiotic nitrogen fixation, transposon (Tn5) induced azide sensitive mutants were generated. Using 4 kb nif-reiterated Sinorhizobium meliloti DNA, a clone C4 that complemented azide sensitivity was isolated by DNA hybridization from genomic library of chickpea Rhizobium strain Rcd301. EcoRI restriction mapping revealed the presence of 7 recognition sites with a total insert size of 19.17 kb. Restriction analysis of C4 clone and nif-reiterated DNA (pRK 290.7) with EcoRI and XhoI revealed similar banding pattern. Wild type strain 18-7, mutant M126 and complemented mutant M126(C4) were characterized for symbiotic properties (viz., acetylene reduction assay, total nitrogen content, nodule number and fresh and dry weight of the infected plants) and explanta nitrogenase activity. Our results suggested that azide resistance, nif-reiteration, and superior symbiotic effectiveness were interlinked with no correlation between ex-planta nitrogenase activity and azide resistance in R. ciceri.

  10. Biological nitrogen fixation and biomass accumulation within poplar clones as a result of inoculations with diazotrophic endophyte consortia.

    PubMed

    Knoth, Jenny L; Kim, Soo-Hyung; Ettl, Gregory J; Doty, Sharon L

    2014-01-01

    Sustainable production of biomass for bioenergy relies on low-input crop production. Inoculation of bioenergy crops with plant growth-promoting endophytes has the potential to reduce fertilizer inputs through the enhancement of biological nitrogen fixation (BNF). Endophytes isolated from native poplar growing in nutrient-poor conditions were selected for a series of glasshouse and field trials designed to test the overall hypothesis that naturally occurring diazotrophic endophytes impart growth promotion of the host plants. Endophyte inoculations contributed to increased biomass over uninoculated control plants. This growth promotion was more pronounced with multi-strain consortia than with single-strain inocula. Biological nitrogen fixation was estimated through (15)N isotope dilution to be 65% nitrogen derived from air (Ndfa). Phenotypic plasticity in biomass allocation and branch production observed as a result of endophyte inoculations may be useful in bioenergy crop breeding and engineering programs.

  11. [Nitrogen fixation potential of biological soil crusts in Heidaigou open coal mine, Inner Mongolia, China].

    PubMed

    Zhang, Peng; Huang, Lei; Hu, Yi-gang; Zhao, Yang; Wu, Yong-chen

    2016-02-01

    Nitrogen limitation is common in terrestrial ecosystems, and it is particularly severe in damaged ecosystems in arid regions. Biological soil crusts (BSCs) , as a crucial component of recovered vegetation, play a vital role in nitrogen fixation during the ecological restoration processes of damaged ecosystems in arid and semi-arid regions. In this study, two dominant types of BSCs (i.e., cyanobacterial-algal crusts and moss crusts) that are widely distributed in the re-vegetated area of Heidaigou open pit coal mine were investigated. Samples were collected in the field and their nitrogenase activities (NA) were measured in the laboratory. The responses of NA to different hydro-thermal factors and the relationships between NA and herbs in addition to crust coverage were analyzed. The results indicated that BSCs under reconstructed vegetation at different succession stages, abandoned land and natural vegetation showed values of NA ranging from 9 to 150 µmol C2H4 . m-2 . h-1, and the NA value of algae crust (77 µmol C2H4 . m-2 . h-1) was markedly higher than that of moss crust (17 µmol C2H4 . m-2 . h-1). In the re-vegetated area, cyanobacterial-algal crust and moss crust under shrub-herb had higher NA values than those of crusts under arbor-shrnb and arbor-shrub-herb. The relationship between NA of the two BSCs and soil relative water content (10% - 100%) as well as culture temperature (5-45 °C) were of quadratic function. With elevated water content and cultural temperature, the NA values increased at the initial stage and then decreased, and reached the maximum value at 25 °C of cultural temperature and 60% or 80% of relative water content. The NA of cyanobacterial-algal crust had a significant quadratic function with herb coverage, as NA declined when herb coverage was higher than 20%. A significant negative correlation was observed between the NA of moss crusts and herb coverage. The NA values of the two types of BSCs had a significant positive correlation

  12. Nitrogen fixation in different biogeochemical niches along a 120 000-year chronosequence in New Zealand.

    PubMed

    Menge, Duncan N L; Hedin, Lars O

    2009-08-01

    Biological nitrogen fixation (BNF) is the major nitrogen (N) input in many terrestrial ecosystems, yet we know little about the mechanisms and feedbacks that control this process in natural ecosystems. We here examine BNF in four taxonomically and ecologically different groups over the course of forest ecosystem development. At nine sites along the Franz Josef soil chronosequence (South Westland, New Zealand) that range in age from 7 to 120000 yr old, we quantified BNF from the symbiotic plant Coriaria arborea, cyanolichens (primarily Pseudocyphellaria spp.), bryophytes (many species), and heterotrophic bacteria in leaf litter. We specifically examined whether these groups could act as "nitrostats" at the ecosystem level, turning BNF on when N is scarce (early in primary succession) and off when N is plentiful (later in succession and retrogression). Coriaria was abundant and actively fixing (approximately 11 kg N x ha(-1) x yr(-1)) in the youngest and most N-poor site (7 yr old), consistent with nitrostat dynamics. Coriaria maintained high BNF rates independent of soil N availability, however, until it was excluded from the community after a single generation. We infer that Coriaria is an obligate N fixer and that the nitrostat feedback is mechanistically governed by species replacement at the community level, rather than down-regulation of BNF at the physiological scale. Biological nitrogen fixation inputs from lichens (means of 0-2 kg N x ha(-1) x yr(-1)), bryophytes (0.7-10 kg N x ha(-1) x yr(-1)), and litter (1-2 kg N x ha(-1) x yr(-1)) were driven primarily by changes in density, which peaked at intermediate-aged sites (and increased with soil N availability) for both lichens and bryophytes, and grew monotonically with soil age (but did not change with soil N) for litter. This non-nitrostatic link between soil N availability and lichen/bryophyte BNF likely stems from increased tree biomass in more fertile sites, which increases epiphytic moisture conditions

  13. Nitrogen fixation activity in biological soil crusts dominated by cyanobacteria in the Subpolar Urals (European North-East Russia).

    PubMed

    Patova, Elena; Sivkov, Michail; Patova, Anna

    2016-09-01

    The nitrogen fixation by biological soil crusts with a dominance of cyanobacteria was studied using the acetylene reduction assay in the territory of the Subpolar Urals (65°11' N, 60°18' E), Russia. The field measurements of nitrogen fixation activity were conducted in situ for two different types of soil crusts dominated by Stigonema (V1 type) and Nostoc with Scytonema (V2 type). The nitrogen fixation process had similar dynamics in both crusts but nitrogen fixation rates were different. The crusts of the V2 type showed a significantly higher acetylene reduction activity, with ethylene production rate of 1.76 ± 0.49 g C2H4 m(-2) h(-1) at 15°C, compared with V1-type soil crusts, with a rate of 0.53 ± 0.21 mg C2H4 m(-2) h(-1) at 15°C. The daily value of acetylene reduction activity in V2-type soil crusts was 32.7 ± 6.2 mg C2H4 m(-2) d(-1) and in V1-type crusts, 12.3 ± 1.8 mg C2H4 m(-2) d(-1) After recalculation for N, the daily values of nitrogen fixation were in the range 3.3-22.3 mg N m(-2) d(-1), which is a few times higher than the values of N input from the precipitation to the soil in the studied regions. The dependence of nitrogen-fixation activity on temperature and light intensity of biological soil crusts was investigated. On the basis of temperature models obtained from the dependence, the nitrogen balance was calculated for the growing season (approximately 120 days). The crusts dominated by Stigonema species were fixing 0.3 g N m(-2) (ethylene production rate, 1.10 g C2H4 m(-2)) and crusts dominated by Nostoc and Scytonema were fixing 1.3 g N m(-2) (4.10 g C2H4 m(-2)).

  14. Evolutionary Dynamics of Nitrogen Fixation in the Legume–Rhizobia Symbiosis

    PubMed Central

    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

  15. Evolutionary dynamics of nitrogen fixation in the legume-rhizobia symbiosis.

    PubMed

    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

  16. Oxygen-poor microzones as potential sites of microbial n(2) fixation in nitrogen-depleted aerobic marine waters.

    PubMed

    Paerl, H W; Prufert, L E

    1987-05-01

    The nitrogen-deficient coastal waters of North Carolina contain suspended bacteria potentially able to fix N(2). Bioassays aimed at identifying environmental factors controlling the development and proliferation of N(2) fixation showed that dissolved organic carbon (as simple sugars and sugar alcohols) and particulate organic carbon (derived from Spartina alterniflora) additions elicited and enhanced N(2) fixation (nitrogenase activity) in these waters. Nitrogenase activity occurred in samples containing flocculent, mucilage-covered bacterial aggregates. Cyanobacterium-bacterium aggregates also revealed N(2) fixation. In all cases bacterial N(2) 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 O(2). Microelectrode O(2) profiles revealed that aggregates had lower internal O(2) 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 O(2) was excluded. Triphenyltetrazolium chloride reduction also strongly inhibited nitrogenase activity. These findings suggest that N(2) 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 N(2) fixation responses of these waters.

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

    PubMed Central

    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

  18. Compartmentalized microbial composition, oxygen gradients and nitrogen fixation in the gut of Odontotaenius disjunctus

    PubMed Central

    Ceja-Navarro, Javier A; Nguyen, Nhu H; Karaoz, Ulas; Gross, Stephanie R; Herman, Donald J; Andersen, Gary L; Bruns, Thomas D; Pett-Ridge, Jennifer; Blackwell, Meredith; Brodie, Eoin L

    2014-01-01

    Coarse woody debris is an important biomass pool in forest ecosystems that numerous groups of insects have evolved to take advantage of. These insects are ecologically important and represent useful natural analogs for biomass to biofuel conversion. Using a range of molecular approaches combined with microelectrode measurements of oxygen, we have characterized the gut microbiome and physiology of Odontotaenius disjunctus, a wood-feeding beetle native to the eastern United States. We hypothesized that morphological and physiological differences among gut regions would correspond to distinct microbial populations and activities. In fact, significantly different communities were found in the foregut (FG), midgut (MG)/posterior hindgut (PHG) and anterior hindgut (AHG), with Actinobacteria and Rhizobiales being more abundant toward the FG and PHG. Conversely, fermentative bacteria such as Bacteroidetes and Clostridia were more abundant in the AHG, and also the sole region where methanogenic Archaea were detected. Although each gut region possessed an anaerobic core, micron-scale profiling identified radial gradients in oxygen concentration in all regions. Nitrogen fixation was confirmed by 15N2 incorporation, and nitrogenase gene (nifH) expression was greatest in the AHG. Phylogenetic analysis of nifH identified the most abundant transcript as related to Ni–Fe nitrogenase of a Bacteroidetes species, Paludibacter propionicigenes. Overall, we demonstrate not only a compartmentalized microbiome in this beetle digestive tract but also sharp oxygen gradients that may permit aerobic and anaerobic metabolism to occur within the same regions in close proximity. We provide evidence for the microbial fixation of N2 that is important for this beetle to subsist on woody biomass. PMID:23985746

  19. Comparative assessment of nitrogen fixation methodologies, conducted in the oligotrophic North Pacific Ocean.

    PubMed

    Wilson, Samuel T; Böttjer, Daniela; Church, Matthew J; Karl, David M

    2012-09-01

    Resolution of the nitrogen (N) cycle in the marine environment requires an accurate assessment of dinitrogen (N(2)) fixation. We present here an update on progress in conducting field measurements of acetylene reduction (AR) and (15)N(2) tracer assimilation in the oligotrophic North Pacific Subtropical Gyre (NPSG). The AR assay was conducted on discrete seawater samples using a headspace analysis system, followed by quantification of ethylene (C(2)H(4)) with a reducing compound photodetector. The rates of C(2)H(4) production were measurable for nonconcentrated seawater samples after an incubation period of 3 to 4 h. The (15)N(2) tracer measurements compared the addition of (15)N(2) as a gas bubble and dissolved as (15)N(2) enriched seawater. On all sampling occasions and at all depths, a 2- to 6-fold increase in the rate of (15)N(2) assimilation was measured when (15)N(2)-enriched seawater was added to the seawater sample compared to the addition of (15)N(2) as a gas bubble. In addition, we show that the (15)N(2)-enriched seawater can be prepared prior to its use with no detectable loss (<1.7%) of dissolved (15)N(2) during 4 weeks of storage, facilitating its use in the field. The ratio of C(2)H(4) production to (15)N(2) assimilation varied from 7 to 27 when measured simultaneously in surface seawater samples. Collectively, the modifications to the AR assay and the (15)N(2) assimilation technique present opportunities for more accurate and high frequency measurements (e.g., diel scale) of N(2) fixation, providing further insight into the contribution of different groups of diazotrophs to the input of N in the global oceans.

  20. Compartmentalized microbial composition, oxygen gradients and nitrogen fixation in the gut of Odontotaenius disjunctus.

    PubMed

    Ceja-Navarro, Javier A; Nguyen, Nhu H; Karaoz, Ulas; Gross, Stephanie R; Herman, Donald J; Andersen, Gary L; Bruns, Thomas D; Pett-Ridge, Jennifer; Blackwell, Meredith; Brodie, Eoin L

    2014-01-01

    Coarse woody debris is an important biomass pool in forest ecosystems that numerous groups of insects have evolved to take advantage of. These insects are ecologically important and represent useful natural analogs for biomass to biofuel conversion. Using a range of molecular approaches combined with microelectrode measurements of oxygen, we have characterized the gut microbiome and physiology of Odontotaenius disjunctus, a wood-feeding beetle native to the eastern United States. We hypothesized that morphological and physiological differences among gut regions would correspond to distinct microbial populations and activities. In fact, significantly different communities were found in the foregut (FG), midgut (MG)/posterior hindgut (PHG) and anterior hindgut (AHG), with Actinobacteria and Rhizobiales being more abundant toward the FG and PHG. Conversely, fermentative bacteria such as Bacteroidetes and Clostridia were more abundant in the AHG, and also the sole region where methanogenic Archaea were detected. Although each gut region possessed an anaerobic core, micron-scale profiling identified radial gradients in oxygen concentration in all regions. Nitrogen fixation was confirmed by (15)N2 incorporation, and nitrogenase gene (nifH) expression was greatest in the AHG. Phylogenetic analysis of nifH identified the most abundant transcript as related to Ni-Fe nitrogenase of a Bacteroidetes species, Paludibacter propionicigenes. Overall, we demonstrate not only a compartmentalized microbiome in this beetle digestive tract but also sharp oxygen gradients that may permit aerobic and anaerobic metabolism to occur within the same regions in close proximity. We provide evidence for the microbial fixation of N2 that is important for this beetle to subsist on woody biomass.

  1. Comparative Assessment of Nitrogen Fixation Methodologies, Conducted in the Oligotrophic North Pacific Ocean

    PubMed Central

    Böttjer, Daniela; Church, Matthew J.; Karl, David M.

    2012-01-01

    Resolution of the nitrogen (N) cycle in the marine environment requires an accurate assessment of dinitrogen (N2) fixation. We present here an update on progress in conducting field measurements of acetylene reduction (AR) and 15N2 tracer assimilation in the oligotrophic North Pacific Subtropical Gyre (NPSG). The AR assay was conducted on discrete seawater samples using a headspace analysis system, followed by quantification of ethylene (C2H4) with a reducing compound photodetector. The rates of C2H4 production were measurable for nonconcentrated seawater samples after an incubation period of 3 to 4 h. The 15N2 tracer measurements compared the addition of 15N2 as a gas bubble and dissolved as 15N2 enriched seawater. On all sampling occasions and at all depths, a 2- to 6-fold increase in the rate of 15N2 assimilation was measured when 15N2-enriched seawater was added to the seawater sample compared to the addition of 15N2 as a gas bubble. In addition, we show that the 15N2-enriched seawater can be prepared prior to its use with no detectable loss (<1.7%) of dissolved 15N2 during 4 weeks of storage, facilitating its use in the field. The ratio of C2H4 production to 15N2 assimilation varied from 7 to 27 when measured simultaneously in surface seawater samples. Collectively, the modifications to the AR assay and the 15N2 assimilation technique present opportunities for more accurate and high frequency measurements (e.g., diel scale) of N2 fixation, providing further insight into the contribution of different groups of diazotrophs to the input of N in the global oceans. PMID:22773638

  2. A novel endo-hydrogenase activity recycles hydrogen produced by nitrogen fixation.

    PubMed

    Ng, Gordon; Tom, Curtis G S; Park, Angela S; Zenad, Lounis; Ludwig, Robert A

    2009-01-01

    Nitrogen (N(2)) fixation also yields hydrogen (H(2)) at 1:1 stoichiometric amounts. In aerobic diazotrophic (able to grow on N(2) as sole N-source) bacteria, orthodox respiratory hupSL-encoded hydrogenase activity, associated with the cell membrane but facing the periplasm (exo-hydrogenase), has nevertheless been presumed responsible for recycling such endogenous hydrogen. As shown here, for Azorhizobium caulinodans diazotrophic cultures open to the atmosphere, exo-hydrogenase activity is of no consequence to hydrogen recycling. In a bioinformatic analysis, a novel seven-gene A. caulinodans hyq cluster encoding an integral-membrane, group-4, Ni,Fe-hydrogenase with homology to respiratory complex I (NADH: quinone dehydrogenase) was identified. By analogy, Hyq hydrogenase is also integral to the cell membrane, but its active site faces the cytoplasm (endo-hydrogenase). An A. caulinodans in-frame hyq operon deletion mutant, constructed by "crossover PCR", showed markedly decreased growth rates in diazotrophic cultures; normal growth was restored with added ammonium--as expected of an H(2)-recycling mutant phenotype. Using A. caulinodans hyq merodiploid strains expressing beta-glucuronidase as promoter-reporter, the hyq operon proved strongly and specifically induced in diazotrophic culture; as well, hyq operon induction required the NIFA transcriptional activator. Therefore, the hyq operon is constituent of the nif regulon. Representative of aerobic N(2)-fixing and H(2)-recycling alpha-proteobacteria, A. caulinodans possesses two respiratory Ni,Fe-hydrogenases: HupSL exo-hydrogenase activity drives exogenous H(2) respiration, and Hyq endo-hydrogenase activity recycles endogenous H(2), specifically that produced by N(2) fixation. To benefit human civilization, H(2) has generated considerable interest as potential renewable energy source as its makings are ubiquitous and its combustion yields no greenhouse gases. As such, the reversible, group-4 Ni,Fe-hydrogenases, such

  3. Spatial and Temporal Variation in Feather Moss Associated Nitrogen Fixation in Coniferous and Deciduous Dominated Alaskan Boreal Forests

    NASA Astrophysics Data System (ADS)

    Jean, M.; Mack, M. C.; Johnstone, J. F.

    2015-12-01

    Dominant canopy tree species have strong effects on the composition and function of understory species. In boreal forests, forest floor bryophytes and their associated microbes are a primary source of ecosystem nitrogen (N) inputs, and thus an important process regulating ecosystem productivity. Bryophyte composition and abundance varies with forest composition, yet how such changes can affect ecosystem processes such as N fixation is still poorly understood. Our goal is to investigate how cyanobacteria-based N fixation occurring in the two most common feather mosses in the Alaskan boreal forest (Pleurozium schreberi and Hylocomium splendens) varies among coniferous and deciduous forest types, over the growing season, and across a nutrient availability gradient. Twelve patches of H. splendens and P. schreberi were identified in three pairs (blocks) of adjacent stands of paper birch (Betula neoalaskana) and black spruce (Picea mariana) near Fairbanks, interior Alaska. Sampling occurred in one block in June, July, August, and September 2014, and in the three blocks once in August 2014. Moss leaf area, moisture and weight, as well as environmental variables such as air temperature and canopy cover were recorded. Fixation rates were consistently higher for P. schreberi than for H. splendens. Overall, N fixation rates were lower in birch than in spruce stands and peaked in August, or July for P. schreberi in birch stands. Moreover, fixation rates varied along the nutrient availability gradient, with fixation rates higher where nutrient availability was lower. This difference was especially clear in spruce stands. Our preliminary results suggest that moss species, canopy type, and environmental factors all influence N fixation rates in Alaskan boreal forests. Our results will enhance the knowledge of the processes that drive N fixation in boreal forests, which is important for predicting ecosystem consequences of changing forest composition.

  4. OxyR-regulated catalase activity is critical for oxidative stress resistance, nodulation and nitrogen fixation in Azorhizobium caulinodans.

    PubMed

    Zhao, Yue; Nickels, Logan M; Wang, Hui; Ling, Jun; Zhong, Zengtao; Zhu, Jun

    2016-07-01

    The legume-rhizobial interaction results in the formation of symbiotic nodules in which rhizobia fix nitrogen. During the process of symbiosis, reactive oxygen species (ROS) are generated. Thus, the response of rhizobia to ROS is important for successful nodulation and nitrogen fixation. In this study, we investigated how Azorhizobium caulinodans, a rhizobium that forms both root and stem nodules on its host plant, regulates ROS resistance. We found that in-frame deletions of a gene encoding the putative catalase-peroxidase katG or a gene encoding a LysR-family regulatory protein, oxyR, exhibited increased sensitivity to H2O2 We then showed that OxyR positively regulated katG expression in an H2O2-independent fashion. Furthermore, we found that deletion of katG or oxyR led to significant reduction in the number of stem nodules and decrease of nitrogen fixation capacities in symbiosis. Our results revealed that KatG and OxyR are not only critical for antioxidant defense in vitro, but also important for nodule formation and nitrogen fixation during interaction with plant hosts. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  5. Low contribution of N2 fixation to new production and excess nitrogen in the subtropical northeast Atlantic margin

    NASA Astrophysics Data System (ADS)

    Benavides, Mar; Arístegui, Javier; Agawin, Nona S. R.; Álvarez-Salgado, Xosé Antón; Álvarez, Marta; Troupin, Charles

    2013-11-01

    We used 15N-labeled substrates to measure dinitrogen (N2) fixation, nitrate (NO3-) and ammonium () uptake, regeneration and associated dissolved organic nitrogen (DON) release in a coastal upwelling system (Cape Ghir, ˜31°N) and an open ocean grid (bounded between 25°-42°N and 20°W) in the Canary Current region during the summer of 2009. New production (Pnew=NO3-uptake+N2 fixation+DON released from NO3uptake-NO3- regeneration) was higher in the upwelling than in the open ocean zone (0.126 and 0.014 µmol N L-1 h-1, respectively), while regenerated production (Preg=NH4+ uptake+DON released from NH4+uptake+NH4+ regeneration) was similar in both zones (0.157 and 0.133 µmol N L-1 h-1, respectively). The resulting f-ratio (Pnew/Pnew+Preg) for the open ocean and upwelling zones was 0.08 and 0.48, respectively. The availability of nitrogen in excess of that expected from Redfield stoichiometry is generally attributed to N2 fixation. A previous study indicated that our open ocean grid zone had an excess nitrogen production rate of 40±22×1010 mol N yr-1. We revisited this budget including new dissolved organic matter and NO3-fluxes through the Strait of Gibraltar and estimated a revised nitrogen excess rate of 22±19×1010 mol N yr-1. The average volumetric rate of N2 fixation for this zone was only 1.3×10-3 nmol N L-1 d-1, indicating that its influence in Pnew and nitrogen excess production in this part of the Atlantic is negligible.

  6. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr.

    PubMed

    Stüeken, Eva E; Buick, Roger; Guy, Bradley M; Koehler, Matthew C

    2015-04-30

    Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction, photochemical reactions, or lightning discharge could have converted atmospheric N2 into assimilable NH4(+), HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4(+), thus represented a major breakthrough in the radiation of life, but its timing is uncertain. Here we present nitrogen isotope ratios with a mean of 0.0 ± 1.2‰ from marine and fluvial sedimentary rocks of prehnite-pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitrogenase as opposed to other variants that impart significant negative fractionations. Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event.

  7. Potential for Nitrogen Fixation and Nitrification in the Granite-Hosted Subsurface at Henderson Mine, CO

    PubMed Central

    Swanner, Elizabeth D.; Templeton, Alexis S.

    2011-01-01

    The existence of life in the deep terrestrial subsurface is established, yet few studies have investigated the origin of nitrogen that supports deep life. Previously, 16S rRNA gene surveys cataloged a diverse microbial community in subsurface fluids draining from boreholes 3000 feet deep at Henderson Mine, CO, USA (Sahl et al., 2008). The prior characterization of the fluid chemistry and microbial community forms the basis for the further investigation here of the source of NH4+. The reported fluid chemistry included N2, NH4+ (5–112 μM), NO2− (27–48 μM), and NO3− (17–72 μM). In this study, the correlation between low NH4+ concentrations in dominantly meteoric fluids and higher NH4+ in rock-reacted fluids is used to hypothesize that NH4+ is sourced from NH4+-bearing biotite. However, biotite samples from the host rocks and ore-body minerals were analyzed by Fourier transform infrared (FTIR) microscopy and none-contained NH4+. However, the nitrogenase-encoding gene nifH was successfully amplified from DNA of the fluid sample with high NH4+, suggesting that subsurface microbes have the capability to fix N2. If so, unregulated nitrogen fixation may account for the relatively high NH4+ concentrations in the fluids. Additionally, the amoA and nxrB genes for archaeal ammonium monooxygenase and nitrite oxidoreductase, respectively, were amplified from the high NH4+ fluid DNA, while bacterial amoA genes were not. Putative nitrifying organisms are closely related to ammonium-oxidizing Crenarchaeota and nitrite-oxidizing Nitrospira detected in other subsurface sites based upon 16S rRNA sequence analysis. Thermodynamic calculations underscore the importance of NH4+ as an energy source in a subsurface nitrification pathway. These results suggest that the subsurface microbial community at Henderson is adapted to the low nutrient and energy environment by their capability of fixing nitrogen, and that fixed nitrogen may support subsurface biomass via

  8. Temporal trends in nitrogen isotope ratios of winter flounder collected from Rhode Island coastal systems

    EPA Science Inventory

    Nitrogen isotope ratios (15N) were measured in muscle tissue of juvenile winter flounder, Pseudopleuronectes americanus, collected from several estuarine systems along the coast of Rhode Island, USA, including Narragansett Bay, Narrow River and three coastal lagoons. Fish collect...

  9. Temporal trends in nitrogen isotope ratios of winter flounder collected from Rhode Island coastal systems

    EPA Science Inventory

    Nitrogen isotope ratios (15N) were measured in muscle tissue of juvenile winter flounder, Pseudopleuronectes americanus, collected from several estuarine systems along the coast of Rhode Island, USA, including Narragansett Bay, Narrow River and three coastal lagoons. Fish collect...

  10. Nitrogen fixation in the Southern Ocean: a case of study of the Fe-fertilized Kerguelen region (KEOPS II cruise)

    NASA Astrophysics Data System (ADS)

    González, M. L.; Molina, V.; Florez-Leiva, L.; Oriol, L.; Cavagna, A. J.; Dehairs, F.; Farias, L.; Fernandez, C.

    2014-12-01

    N2 fixation rates were measured during the KEOPS2 cruise in the HNLC area of Southern Ocean and in naturally iron-fertilized waters (Kerguelen Island 49.25° S, 69.58° E) using the 15N isotopic technique. We detected N2 fixation within the mixed layer at all stations, from the surface to 140 m depth. The data shows high variability with rates ranging between 0.42 and 20.11 nmol N L-1 d-1. The highest rates were concentrated in the euphotic layer and maximum values were obtained north of polar front (station F-L), which coincide with a positive N* ([NO3]-16[PO4]), high chlorophyll concentration and dissolved iron. N2 fixation rates were also obtained in stations with moderate (A3-2; E-4W) and also low (R-2) iron levels as well as Chl a, suggesting that beside the microbial biomass, its composition/structure is a driving factor controlling N2 fixation activities. Molecular analysis showed a diazotrophic community dominated by heterotrophic bacterioplankton. Size fractioned experiments indicated that most of N2 fixating activities came from <5 μm community and it was on line with molecular analysis revealing a low diversity diazotrophic community dominated by heterotrophic bacterioplankton. This study shows for first time N2 fixation is occurring in the Southern Ocean, at rates exceeding previous reports for high latitudes. Our findings suggest an indirect role of dFe in the regulation of N2 fixation through the enhancement of regenerated primary production and the availability of phytoplankton-derived dissolved organic matter, which in turn may stimulate heterotrophic bacterioplankton.

  11. Resolution of Conflicting Signals at the Single-Cell Level in the Regulation of Cyanobacterial Photosynthesis and Nitrogen Fixation

    PubMed Central

    Mohr, Wiebke; Vagner, Tomas; Kuypers, Marcel M. M.; Ackermann, Martin; LaRoche, Julie

    2013-01-01

    Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes can overlap during transitions from dark to light. How do single cells avoid inactivation of nitrogenase during these periods? One possibility is that phenotypic heterogeneity in populations leads to segregation of the two processes. Here, we measured N2 fixation and photosynthesis of individual cells using nanometer-scale secondary ion mass spectrometry (nanoSIMS) to assess both processes in a culture of the unicellular, diazotrophic cyanobacterium Crocosphaera watsonii during a dark-light and a continuous light phase. We compared single-cell rates with bulk rates and gene expression profiles. During the regular dark and light phases, C. watsonii exhibited the temporal segregation of N2 fixation and photosynthesis commonly observed. However, N2 fixation and photosynthesis were concurrently measurable at the population level during the subjective dark phase in which cells were kept in the light rather than returned to the expected dark phase. At the single-cell level, though, cells discriminated against either one of the two processes. Cells that showed high levels of photosynthesis had low nitrogen fixing activities, and vice versa. These results suggest that, under ambiguous environmental signals, single cells discriminate against either photosynthesis or nitrogen fixation, and thereby might reduce costs associated with running incompatible processes in the same cell. PMID:23805199

  12. The efficiency of nitrogen fixation of the model legume Medicago truncatula (Jemalong A17) is low compared to Medicago sativa.

    PubMed

    Sulieman, Saad; Schulze, Joachim

    2010-06-15

    Medicago truncatula (Gaertn.) (barrel medic) serves as a model legume in plant biology. Numerous studies have addressed molecular aspects of the biology of M. truncatula, while comparatively little is known about the efficiency of N(2) fixation at the whole plant level. The objective of the present study was to compare the efficiency of N(2) fixation of M. truncatula to the genetically closely related Medicago sativa (L.) (alfalfa). The relative growth of both species relying exclusively on N(2) fixation versus nitrate nutrition, H(2) evolution, nitrogen assimilation, the concentration of amino acids and organic acids in nodules, and (15)N(2) uptake and distribution were studied. M. truncatula showed much lower efficiency of N(2) fixation. Nodule-specific activity was several-fold lower when compared to M. sativa, partially as a result of a lower electron allocation to N(2) versus H(+). M. truncatula or M. sativa plants grown solely on N(2) fixation as a nitrogen source reached about 30% or 80% of growth, respectively, when compared to plants supplied with sufficient nitrate. Moreover, M. truncatula had low %N in shoots and a lower allocation of (15)N to shoots during 1h (15)N(2) labeling period. Amino acid concentration was about 20% higher in M. sativa nodules, largely as a result of more asparagine, while the organic acid concentration was about double in M. sativa, coinciding with a six-fold higher concentration of malate. Total soluble protein in nodules was about three times lower in M. truncatula and the pattern of enzyme activity in that fraction was strongly different. Sucrose cleaving enzymes displayed higher activity in M. truncatula nodules, while the activity of phosphoenolpyruvate carboxylase (PEPC) was much lower. It is concluded that the low efficiency of the M. truncatula symbiotic system is related to a low capacity of organic acid formation and limited nitrogen export from nodules.

  13. Comparative sequence analysis of nitrogen fixation-related genes in six legumes

    PubMed Central

    Kim, Dong Hyun; Parupalli, Swathi; Azam, Sarwar; Lee, Suk-Ha; Varshney, Rajeev K.

    2013-01-01

    Legumes play an important role as food and forage crops in international agriculture especially in developing countries. Legumes have a unique biological process called nitrogen fixation (NF) by which they convert atmospheric nitrogen to ammonia. Although legume genomes have undergone polyploidization, duplication and divergence, NF-related genes, because of their essential functional role for legumes, might have remained conserved. To understand the relationship of divergence and evolutionary processes in legumes, this study analyzes orthologs and paralogs for selected 20 NF-related genes by using comparative genomic approaches in six legumes i.e., Medicago truncatula (Mt), Cicer arietinum, Lotus japonicus, Cajanus cajan (Cc), Phaseolus vulgaris (Pv), and Glycine max (Gm). Subsequently, sequence distances, numbers of synonymous substitutions per synonymous site (Ks) and non-synonymous substitutions per non-synonymous site (Ka) between orthologs and paralogs were calculated and compared across legumes. These analyses suggest the closest relationship between Gm and Cc and the highest distance between Mt and Pv in six legumes. Ks proportional plots clearly showed ancient genome duplication in all legumes, whole genome duplication event in Gm and also speciation pattern in different legumes. This study also reports some interesting observations e.g., no peak at Ks 0.4 in Gm-Gm, location of two independent genes next to each other in Mt and low Ks values for outparalogs for three genes as compared to other 12 genes. In summary, this study underlines the importance of NF-related genes and provides important insights in genome organization and evolutionary aspects of six legume species analyzed. PMID:23986765

  14. The reallocation of carbon in P deficient lupins affects biological nitrogen fixation.

    PubMed

    Kleinert, Aleysia; Venter, Mauritz; Kossmann, Jens; Valentine, Alexander

    2014-11-01

    It is not known how phosphate (P) deficiency affects the allocation of carbon (C) to biological nitrogen fixation (BNF) in legumes. The alteration of the respiratory and photosynthetic C costs of BNF was investigated under P deficiency. Although BNF can impose considerable sink stimulation on host respiratory and photosynthetic C, it is not known how the change in the C and energy allocation during P deficiency may affect BNF. Nodulated Lupinus luteus plants were grown in sand culture, using a modified Long Ashton nutrient solution containing no nitrogen (N) for ca. four weeks, after which one set was exposed to a P-deficient nutrient medium, while the other set continued growing on a P-sufficient nutrient medium. Phosphorus stress was measured at 20 days after onset of P-starvation. During P stress the decline in nodular P levels was associated with lower BNF and nodule growth. There was also a shift in the balance of photosynthetic and respiratory C toward a loss of C during P stress. Below-ground respiration declined under limiting P conditions. However, during this decline there was also a shift in the proportion of respiratory energy from maintenance toward growth respiration. Under P stress, there was an increased allocation of C toward root growth, thereby decreasing the amount of C available for maintenance respiration. It is therefore possible that the decline in BNF under P deficiency may be due to this change in resource allocation away from respiration associated with direct nutrient uptake, but rather toward a long term nutrient acquisition strategy of increased root growth.

  15. Interaction of root nodule size and oxygen pressure on the rate of nitrogen fixation by cowpea and peanut

    SciTech Connect

    Sen, D.; Weaver, R.W.

    1987-04-01

    Size and anatomical features of nodules influence the rate of O/sub 2/ diffusion into nodules. Availability of oxygen can be a limiting factor in nitrogen fixation. Larger nodules have thicker cortices and low surface to volume ratio leading to lower rates of gaseous diffusion. Increased oxygen pressure in the environment alters the rate of nitrogen fixation but the rate of change may depend on the nodule size. This was investigated by measuring /sup 15/N/sub 2/ incorporation into nodules. Root nodules from 38 day old cowpea and peanut plants were collected and sorted into size groups having diameters of >3 mm, 2-3 mm, and just below 2 mm. Samples of each size group were enclosed in tubes and exposed to various combination of oxygen (8-28%) and /sup 15/N/sub 2/. With higher O/sub 2/ pressure all nodules showed increased N/sub 2/ fixation but the largest nodules showed the maximum increase. Specific activity of larger nodules was higher for N/sub 2/ fixation. For the sizes of nodules examined the largest nodules did not reflect any of the disadvantages of the large size but the benefits of higher rates of O/sub 2/ entry was evident.

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

    PubMed

    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.

  17. Influence of Arbuscular Mycorrhizae on Biomass Production and Nitrogen Fixation of Berseem Clover Plants Subjected to Water Stress

    PubMed Central

    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. PMID:24595111

  18. Glycine 100 in the dinitrogenase reductase of Rhodospirillum rubrum is required for nitrogen fixation but not for ADP-ribosylation.

    PubMed Central

    Lehman, L J; Roberts, G P

    1991-01-01

    Dinitrogenase reductase (Rr2) is required for reduction of the molybdenum dinitrogenase in the nitrogen fixation reaction and is the target of posttranslational regulation in Rhodospirillum rubrum. This posttranslational regulation involves the ADP-ribosylation of Rr2. To study the structural requirements for these two functions of Rr2, i.e., activity and regulation, two site-directed mutations in nifH, the gene encoding Rr2, were constructed and analyzed. The mutations both affected a region of the protein known to be highly conserved in evolution and to be relevant to both of the above properties. These mutants were both Nif-, but one of the altered Rr2s was a substrate for ADP-ribosylation. This demonstrates that the ability of Rr2 to participate in nitrogen fixation can be separated from its ability to act as a substrate for ADP-ribosylation. Images PMID:1917849

  19. Nitrogen fixation in peanut nodules during dark periods and detopped conditions with special reference to lipid bodies

    SciTech Connect

    Siddique, A.M.; Bal, A.K. )

    1991-03-01

    The peanut plant (Arachis hypogaea L.), unlike other known legumes, can sustain nitrogen fixation when prolonged periods of darkness or detopping curtail the supply of photosynthate to the nodule. This ability to withstand photosynthate stress is attributed to the presence of lipid bodies in infected nodule cells. In both dark-treated and detopped plants, the lipid bodies show a gradual decrease in numbers, suggesting their utilization as a source of energy and carbon for nitrogen fixation. Lipolytic activity can be localized in the lipid bodies, and the existence of {beta}-oxidation pathway and glyoxylate cycle is shown by the release of {sup 14}CO{sub 2} from {sup 14}C lineoleoyl coenzyme A by the nodule homogenate.

  20. A purple acid phosphatase plays a role in nodule formation and nitrogen fixation in Astragalus sinicus.

    PubMed

    Wang, Jianyun; Si, Zaiyong; Li, Fang; Xiong, Xiaobo; Lei, Lei; Xie, Fuli; Chen, Dasong; Li, Yixing; Li, Youguo

    2015-08-01

    The AsPPD1 gene from Astragalus sinicus encodes a purple acid phosphatase. To address the functions of AsPPD1 in legume-rhizobium symbiosis, its expression patterns, enzyme activity, subcellular localization, and phenotypes associated with its over-expression and RNA interference (RNAi) were investigated. The expression of AsPPD1 was up-regulated in roots and nodules after inoculation with rhizobia. Phosphate starvation reduced the levels of AsPPD1 transcripts in roots while increased those levels in nodules. We confirmed the acid phosphatase and phosphodiesterase activities of recombinant AsPPD1 purified from Pichia pastoris, and demonstrated its ability to hydrolyze ADP and ATP in vitro. Subcellular localization showed that AsPPD1 located on the plasma membranes in hairy roots and on the symbiosomes membranes in root nodules. Over-expression of AsPPD1 in hairy roots inhibited nodulation, while its silencing resulted in nodules early senescence and significantly decreased nitrogenase activity. Furthermore, HPLC measurement showed that AsPPD1 overexpression affects the ADP levels in the infected roots and nodules, AsPPD1 silencing affects the ratio of ATP/ADP and the energy charge in nodules, and quantitative observation demonstrated the changes of AsPPD1 transcripts level affected nodule primordia formation. Taken together, it is speculated that AsPPD1 contributes to symbiotic ADP levels and energy charge control, and this is required for effective nodule organogenesis and nitrogen fixation.

  1. Primary productivity and nitrogen fixation by Trichodesmium spp. in the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Parab, Sushma G.; Matondkar, S. G. P.

    2012-12-01

    Trichodesmium was studied with the purpose of understanding its distribution, organic production and nitrogen fixation in the Arabian Sea. Out of the 143 stations sampled, a total of 93 stations showed the presence of Trichodesmium filaments. Two species of Trichodesmium namely, T. thiebautii and T. erythraeum were found. These were distributed on the basis of the physico-chemical conditions of the Arabian Sea. This was the first time that we managed to detect and record the presence of Trichodesmium thiebautii bloom in the Arabian Sea at depths as deep as 60-70 m. Total counts of Trichodesmium varied between 0 and 400737 filamentsL- 1. T. thiebautii developed in offshore waters during the fall intermonsoon, when the water temperature was around 28 °C and nitrate content was as low as 0.34 μM. After the northeast monsoon, Trichodesmium erythraeum developed in the offshore area and then spread to coastal waters. Both species of Trichodesmium together produced a total of 0.263 TgCyear- 1 and fixed a total of 0.2976 TgNyear- 1 in the Arabian Sea. The study revealed that Trichodesmium was a major contributor to the organic matter productivity of the Arabian Sea during the period from November to April. The seasonality of the blooms of Trichodesmium is discussed with the help of Ocean Color Monitoring (OCM) data and biogeochemical implication of these findings in the Arabian Sea.

  2. Crystallization of a flavodoxin involved in nitrogen fixation in Rhodobacter capsulatus

    SciTech Connect

    Pérez-Dorado, Inmaculada; Bortolotti, Ana; Cortez, Néstor; Hermoso, Juan A.

    2008-05-01

    The flavodoxin NifF from R. capsulatus, a candidate for nitrogenase reduction during nitrogen fixation, has been crystallized using the hanging-drop vapour-diffusion method. Preliminary X-ray data processing at 2.17 Å resolution allowed determination of the crystal system and unit-cell parameters. Flavodoxins are small electron-transfer proteins that contain one molecule of noncovalently bound flavin mononucleotide (FMN). The flavodoxin NifF from the photosynthetic bacterium Rhodobacter capsulatus is reduced by one electron from ferredoxin/flavodoxin:NADP(H) reductase and was postulated to be an electron donor to nitrogenase in vivo. NifF was cloned and overexpressed in Escherichia coli, purified and concentrated for crystallization using the hanging-drop vapour-diffusion method at 291 K. Crystals grew from a mixture of PEG 3350 and PEG 400 at pH 5.5 and belong to the tetragonal space group P4{sub 1}2{sub 1}2, with unit-cell parameters a = b = 66.49, c = 121.32 Å. X-ray data sets have been collected to 2.17 Å resolution.

  3. Nitrogen fixation in microbial mat and stromatolite communities from Cuatro Cienegas, Mexico.

    PubMed

    Falcón, L I; Cerritos, R; Eguiarte, L E; Souza, V

    2007-08-01

    Nitrogen fixation (nitrogenase activity, NA) of a microbial mat and a living stromatolite from Cuatro Cienegas, Mexico, was examined over spring, summer, and winter of 2004. The goal of the study was to characterize the diazotrophic community through molecular analysis of the nifH gene and using inhibitors of sulfate reduction and oxygenic and anoxygenic photosynthesis. We also evaluated the role of ultraviolet radiation on the diazotrophic activity of the microbial communities. Both microbial communities showed patterns of NA with maximum rates during the day that decreased significantly with 3-3,4-dichlorophenyl-1',1'-dimethylurea, suggesting the potential importance of heterocystous cyanobacteria. There is also evidence of NA by sulfur-reducing bacteria in both microbial communities suggested by the negative effect exerted by the addition of sodium molybdate. Elimination of infrared and ultraviolet radiation had no effect on NA. Both microbial communities had nifH sequences that related to group I, including cyanobacteria and purple sulfur and nonsulfur bacteria, as well as group II nitrogenases, including sulfur reducing and green sulfur bacteria.

  4. Local inhibition of nitrogen fixation and nodule metabolism in drought-stressed soybean

    PubMed Central

    Gil-Quintana, Erena; Larrainzar, Estíbaliz; Seminario, Amaia; Díaz-Leal, Juan Luis; Alamillo, Josefa M.; Pineda, Manuel; Arrese-Igor, Cesar; Wienkoop, Stefanie; González, Esther M.

    2013-01-01

    Drought stress is a major factor limiting symbiotic nitrogen fixation (NF) in soybean crop production. However, the regulatory mechanisms involved in this inhibition are still controversial. Soybean plants were symbiotically grown in a split-root system (SRS), which allowed for half of the root system to be irrigated at field capacity while the other half remained water deprived. NF declined in the water-deprived root system while nitrogenase activity was maintained at control values in the well-watered half. Concomitantly, amino acids and ureides accumulated in the water-deprived belowground organs regardless of transpiration rates. Ureide accumulation was found to be related to the decline in their degradation activities rather than increased biosynthesis. Finally, proteomic analysis suggests that plant carbon metabolism, protein synthesis, amino acid metabolism, and cell growth are among the processes most altered in soybean nodules under drought stress. Results presented here support the hypothesis of a local regulation of NF taking place in soybean and downplay the role of ureides in the inhibition of NF. PMID:23580751

  5. Short-term nitrate (nitrite) inhibition of nitrogen fixation in Azotobacter chroococcum

    SciTech Connect

    Cejudo, F.J.; Paneque, A.

    1986-01-01

    Nitrate-grown Azotobacter chroococcum ATCC 4412 cells lack the ability to fix N/sub 2/. Nitrogenase activity developed after the cells were suspended in a combined nitrogen-free medium and was paralleled by a concomitant decrease in nitrate assimilation capacity. In such treated cells exhibiting transitory nitrate assimilation and N/sub 2/-fixation capacity, nitrate or nitrite caused a short-term inhibitory effect on nitrogenase activity which ceased once the anion was exhausted from the medium. The glutamate analog L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase, prevented inhibition of nitrogenase activity by nitrate or nitrite without affecting the uptake of these anions, which were reduced and stoichiometrically released into the external medium as ammonium. Inhibition of nitrogenase by nitrate (nitrite) did not take place in A. chroococcum MCD1, which is unable to assimilate either. The authors conclude that the short-term inhibitory effect of nitrate (nitrite) on nitrogenase activity is due to some organic product(s) formed during the assimilation of the ammonium resulting from nitrate (nitrite) reduction.

  6. Biological nitrogen fixation in the oxygen-minimum region of the eastern tropical North Pacific ocean.

    PubMed

    Jayakumar, Amal; Chang, Bonnie X; Widner, Brittany; Bernhardt, Peter; Mulholland, Margaret R; Ward, Bess B

    2017-10-01

    Biological nitrogen fixation (BNF) was investigated above and within the oxygen-depleted waters of the oxygen-minimum zone of the Eastern Tropical North Pacific Ocean. BNF rates were estimated using an isotope tracer method that overcame the uncertainty of the conventional bubble method by directly measuring the tracer enrichment during the incubations. Highest rates of BNF (~4 nM day(-1)) occurred in coastal surface waters and lowest detectable rates (~0.2 nM day(-1)) were found in the anoxic region of offshore stations. BNF was not detectable in most samples from oxygen-depleted waters. The composition of the N2-fixing assemblage was investigated by sequencing of nifH genes. The diazotrophic assemblage in surface waters contained mainly Proteobacterial sequences (Cluster I nifH), while both Proteobacterial sequences and sequences with high identities to those of anaerobic microbes characterized as Clusters III and IV type nifH sequences were found in the anoxic waters. Our results indicate modest input of N through BNF in oxygen-depleted zones mainly due to the activity of proteobacterial diazotrophs.

  7. Isolation and Characterization of Frankia sp. Strain FaC1 Genes Involved in Nitrogen Fixation

    PubMed Central

    Ligon, James M.; Nakas, James P.

    1987-01-01

    Genomic DNA was isolated from Frankia sp. strain FaC1, an Alnus root nodule endophyte, and used to construct a genomic library in the cosmid vector pHC79. The genomic library was screened by in situ colony hybridization to identify clones of Frankia nitrogenase (nif) genes based on DNA sequence homology to structural nitrogenase genes from Klebsiella pneumoniae. Several Frankia nif clones were isolated, and hybridization with individual structural nitrogenase gene fragments (nifH, nifD, and nifK) from K. pneumoniae revealed that they all contain the nifD and nifK genes, but lack the nifH gene. Restriction endonuclease mapping of the nifD and nifK hybridizing region from one clone revealed that the nifD and nifK genes in Frankia sp. are contiguous, while the nifH gene is absent from a large region of DNA on either side of the nifDK gene cluster. Additional hybridizations with gene fragments derived from K. pneumoniae as probes and containing other genes involved in nitrogen fixation demonstrated that the Frankia nifE and nifN genes, which play a role in the biosynthesis of the iron-molybdenum cofactor, are located adjacent to the nifDK gene cluster. Images PMID:16347453

  8. Activity of purified NIFA, a transcriptional activator of nitrogen fixation genes.

    PubMed Central

    Lee, H S; Berger, D K; Kustu, S

    1993-01-01

    The NIFA protein activates transcription of nitrogen fixation (nif) operons by the sigma 54-holoenzyme form of RNA polymerase. We purified active NIFA from Klebsiella pneumoniae in the form of a maltose-binding protein (MBP)-NIFA fusion; proteolytic release of MBP yielded inactive and insoluble NIFA. MBP-NIFA activated transcription from the nifHDK promoter in a purified transcription system. Like the related transcriptional activator NTRC, MBP-NIFA catalyzed the ATP-dependent isomerization of closed complexes between sigma 54-holoenzyme and a promoter to open complexes. MBP-NIFA had a broader nucleotide specificity than NTRC, being able to utilize pyrimidine in addition to purine nucleoside triphosphates. Both MBP-NIFA and a purified C-terminal fragment of NIFA bound to the upstream activation sequence for the nifHDK promoter, as assessed by DNAse I footprinting. When assays were performed at 37 degrees C instead of the usual 30 degrees C, transcriptional activation, open complex formation, and DNA binding by MBP-NIFA were all abolished, consistent with the known heat lability of NIFA. However, the purified C-terminal fragment of NIFA still bound the upstream activation sequence at 37 degrees C, indicating that the function of the helix-turn-helix DNA-binding motif is not inherently heat-labile. Images Fig. 1 Fig. 2 Fig. 3 PMID:8460132

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

    PubMed

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

    2014-10-01

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

  10. Steric Switching from Photochemical to Thermal Reaction Pathways for Enhanced Efficiency in Metal-Mediated Nitrogen Fixation.

    PubMed

    Duman, Leila M; Farrell, Wesley S; Zavalij, Peter Y; Sita, Lawrence R

    2016-11-16

    Programmed manipulation of the subtle interplay of nonbonded steric interactions within a supporting ligand environment has been used for the conversion of a photochemically driven chemical cycle for group 6 metal-mediated nitrogen fixation into a thermally promoted process with increased energy efficiency and atom economy for key transformations involving N≡N bond cleavage and N-atom functionalization of coordinated N2.

  11. Agrobacterium rhizogenes transformed soybean roots differ in their nodulation and nitrogen fixation response to genistein and salt stress.

    PubMed

    Dolatabadian, Aria; Modarres Sanavy, Seyed Ali Mohammad; Ghanati, Faezeh; Gresshoff, Peter M

    2013-07-01

    We evaluated response differences of normal and transformed (so-called 'hairy') roots of soybean (Glycine max L. (Merr.), cv L17) to the Nod-factor inducing isoflavone genistein and salinity by quantifying growth, nodulation, nitrogen fixation and biochemical changes. Composite soybean plants were generated using Agrobacterium rhizogenes-mediated transformation of non-nodulating mutant nod139 (GmNFR5α minus) with complementing A. rhizogenes K599 carrying the wild-type GmNFR5α gene under control of the constitutive CaMV 35S promoter. We used genetic complementation for nodulation ability as only nodulated roots were scored. After hairy root emergence, primary roots were removed and composite plants were inoculated with Bradyrhizobium japonicum (strain CB1809) pre-induced with 10 μM genistein and watered with NaCl (0, 25, 50 and 100 mM). There were significant differences between hairy roots and natural roots in their responses to salt stress and genistein application. In addition, there were noticeable nodulation and nitrogen fixation differences. Composite plants had better growth, more root volume and chlorophyll as well as more nodules and higher nitrogenase activity (acetylene reduction) compared with natural roots. Decreased lipid peroxidation, proline accumulation and catalase/peroxidase activities were found in 'hairy' roots under salinity stress. Genistein significantly increased nodulation and nitrogen fixation and improved roots and shoot growth. Although genistein alleviated lipid peroxidation under salinity stress, it had no significant effect on the activity of antioxidant enzymes. In general, composite plants were more competitive in growth, nodulation and nitrogen fixation than normal non-transgenic even under salinity stress conditions.

  12. Carbon and nitrogen fixation differ between successional stages of biological soil crusts in the Colorado Plateau and Chihuahuan Desert

    USGS Publications Warehouse

    Housman, D.C.; Powers, H.H.; Collins, A.D.; Belnap, J.

    2006-01-01

    Biological soil crusts (cyanobacteria, mosses and lichens collectively) perform essential ecosystem services, including carbon (C) and nitrogen (N) fixation. Climate and land-use change are converting later successional soil crusts to early successional soil crusts with lower C and N fixation rates. To quantify the effect of such conversions on C and N dynamics in desert ecosystems we seasonally measured diurnal fixation rates in different biological soil crusts. We classified plots on the Colorado Plateau (Canyonlands) and Chihuahuan Desert (Jornada) as early (Microcoleus) or later successional (Nostoc/Scytonema or Placidium/Collema) and measured photosynthesis (Pn), nitrogenase activity (NA), and chlorophyll fluorescence (Fv/Fm) on metabolically active (moist) soil crusts. Later successional crusts typically had greater Pn, averaging 1.2-1.3-fold higher daily C fixation in Canyonlands and 2.4-2.8-fold higher in the Jornada. Later successional crusts also had greater NA, averaging 1.3-7.5-fold higher daily N fixation in Canyonlands and 1.3-25.0-fold higher in the Jornada. Mean daily Fv/Fm was also greater in later successional Canyonlands crusts during winter, and Jornada crusts during all seasons except summer. Together these findings indicate conversion of soil crusts back to early successional stages results in large reductions of C and N inputs into these ecosystems.

  13. Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System

    PubMed Central

    Bertics, Victoria J.; Sohm, Jill A.; Magnabosco, Cara

    2012-01-01

    Bioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N2) fixation. We investigated denitrification and N2 fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (Neotrypaea californiensis). Field studies were combined with detailed measurements of denitrification and N2 fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N2 fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N2 fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N2 fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N2 fixation. PMID:22447588

  14. Ureide assay for measuring nitrogen fixation by nodulated soybean calibrated by sup 15 N methods. [Glycine max

    SciTech Connect

    Herridge, D.F. ); Peoples, M.B. )

    1990-06-01

    We report experiments to quantify the relationships between the relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap, and hot water extracts of stems and petioles of nodulated soybean (Glycine max (L.) Merrill cv Bragg) and the proportion of plant N derived from nitrogen fixation. Additional experiments examined the effects of plant genotype and strain of rhizobia on these relationships. In each of the five experiments reported, plants of cv Bragg (experiment 1), cv Lincoln (experiments 3, 4, 5), or six cultivars/genotypes (experiment 2) were grown in a sand:vermiculite mixture in large pots in a naturally lit, temperature-controlled glasshouse during summer. Pots were inoculated at sowing with effective Bradyrhizobium japonicum CB 1809 (USDA 136) or with one of 21 different strains of rhizobia. The proportions of plant N derived from nitrogen fixation were determined using {sup 15}N dilution. Results show that assessment of nitrogen fixation by soybean using the ureide technique should now be possible with the standard curves presented, irrespective of genotype or strain of rhizobia occupying the nodules.

  15. Applying Reversible Mutations of Nodulation and Nitrogen-Fixation Genes to Study Social Cheating in Rhizobium etli-Legume Interaction

    PubMed Central

    Wang, Hui; Zhong, Zengtao; Zhu, Jun

    2013-01-01

    Mutualisms are common in nature, though these symbioses can be quite permeable to cheaters in situations where one individual parasitizes the other by discontinuing cooperation yet still exploits the benefits of the partnership. In the Rhizobium-legume system, there are two separate contexts, namely nodulation and nitrogen fixation processes, by which resident Rhizobium individuals can benefit by cheating. Here, we constructed reversible and irreversible mutations in key nodulation and nitrogen-fixation pathways of Rhizobium etli and compared their interaction with plant hosts Phaseolus vulgaris to that of wild type. We show that R. etli reversible mutants deficient in nodulation factor production are capable of intra-specific cheating, wherein mutants exploit other Rhizobium individuals capable of producing these factors. Similarly, we show that R. etli mutants are also capable of cheating inter-specifically, colonizing the host legume yet contributing nothing to the partnership in terms of nitrogen fixation. Our findings indicate that cheating is possible in both of these frameworks, seemingly without damaging the stability of the mutualism itself. These results may potentially help explain observations suggesting that legume plants are commonly infected by multiple bacterial lineages during the nodulation process. PMID:23922937

  16. Growth-promoting Sphingomonas paucimobilis ZJSH1 associated with Dendrobium officinale through phytohormone production and nitrogen fixation

    PubMed Central

    Yang, Suijuan; Zhang, Xinghai; Cao, Zhaoyun; Zhao, Kaipeng; Wang, Sai; Chen, Mingxue; Hu, Xiufang

    2014-01-01

    Growth-promoting Sphingomonas paucimobilis ZJSH1, associated with Dendrobium officinale, a traditional Chinese medicinal plant, was characterized. At 90 days post-inoculation, strain ZJSH1 significantly promoted the growth of D. officinale seedlings, with increases of stems by 8.6% and fresh weight by 7.5%. Interestingly, the polysaccharide content extracted from the inoculated seedlings was 0.6% higher than that of the control. Similar growth promotion was observed with the transplants inoculated with strain ZJSH1. The mechanism of growth promotion was attributed to a combination of phytohormones and nitrogen fixation. Strain ZJSH1 was found using the Kjeldahl method to have a nitrogen fixation activity of 1.15 mg l−1, which was confirmed by sequencing of the nifH gene. Using high-performance liquid chromatography-mass spectrometry, strain ZJSH1 was found to produce various phytohormones, including salicylic acid (SA), indole-3-acetic acid (IAA), Zeatin and abscisic acid (ABA). The growth curve showed that strain ZJSH1 grew well in the seedlings, especially in the roots. Accordingly, much higher contents of SA, ABA, IAA and c-ZR were detected in the inoculated seedlings, which may play roles as both phytohormones and ‘Systemic Acquired Resistance’ drivers. Nitrogen fixation and secretion of plant growth regulators (SA, IAA, Zeatin and ABA) endow S. paucimobilis ZJSH1 with growth-promoting properties, which provides a potential for application in the commercial growth of D. officinale. PMID:25142808

  17. Applying reversible mutations of nodulation and nitrogen-fixation genes to study social cheating in Rhizobium etli-legume interaction.

    PubMed

    Ling, Jun; Zheng, Huiming; Katzianer, David S; Wang, Hui; Zhong, Zengtao; Zhu, Jun

    2013-01-01

    Mutualisms are common in nature, though these symbioses can be quite permeable to cheaters in situations where one individual parasitizes the other by discontinuing cooperation yet still exploits the benefits of the partnership. In the Rhizobium-legume system, there are two separate contexts, namely nodulation and nitrogen fixation processes, by which resident Rhizobium individuals can benefit by cheating. Here, we constructed reversible and irreversible mutations in key nodulation and nitrogen-fixation pathways of Rhizobium etli and compared their interaction with plant hosts Phaseolus vulgaris to that of wild type. We show that R. etli reversible mutants deficient in nodulation factor production are capable of intra-specific cheating, wherein mutants exploit other Rhizobium individuals capable of producing these factors. Similarly, we show that R. etli mutants are also capable of cheating inter-specifically, colonizing the host legume yet contributing nothing to the partnership in terms of nitrogen fixation. Our findings indicate that cheating is possible in both of these frameworks, seemingly without damaging the stability of the mutualism itself. These results may potentially help explain observations suggesting that legume plants are commonly infected by multiple bacterial lineages during the nodulation process.

  18. [Carbon storage and carbon fixation during the succession of natural vegetation in wetland ecosystem on east beach of Chongming Island].

    PubMed

    Mei, Xue-Ying; Zhang, Xiu-Feng

    2007-04-01

    Vegetation is an important biological factor in the ecological succession of wetland, and the main factor affecting the carbon storage and carbon fixation in wetland ecosystem. By the methods of field survey and lab analysis, this paper studied the carbon storage and carbon fixation during the succession of wetland vegetation on east beach of Chongming Island, and the results showed that there existed greater differences in the existing carbon storage and its allocation in wetland vegetation at its different succession stages. The existing carbon storage of the pioneer plant Scirpus mariqueter was much less than that of Phragmites australis, only accounted for about 13% of the latter. The underground rhizome of P. australis and the aboveground part of S. mariqueter were the main sites of existing carbon storage. P. australis at the later succession stage of wetland vegetation had a stronger capability of carbon fixation than S. mariqueter at the earlier succession stage of the vegetation, with the values being (1.63 +/- 0.39) kg x m(-2) x a(-1) and (0.63 +/- 0.28) kg x m(-2) x a(-1), respectively, suggesting that during the succession of S. mariqueter community to P. australis community, the carbon fixation capability of the wetland ecosystem became stronger.

  19. Persistence of biological nitrogen fixation in high latitude grass-clover grasslands under different management practices

    NASA Astrophysics Data System (ADS)

    Tzanakakis, Vasileios; Sturite, Ievina; Dörsch, Peter

    2016-04-01

    Biological nitrogen fixation (BNF) can substantially contribute to N supply in permanent grasslands, improving N yield and forage quality, while reducing inorganic N inputs. Among the factors critical to the performance of BNF in grass-legume mixtures are selected grass and legume species, proportion of legumes, the soil-climatic conditions, in particular winter conditions, and management practices (e.g. fertilization and compaction). In high latitude grasslands, low temperatures can reduce the performance of BNF by hampering the legumés growth and by suppressing N2 fixation. Estimation of BNF in field experiments is not straightforward. Different methods have been developed providing different results. In the present study, we evaluated the performance of BNF, in a newly established field experiment in North Norway over four years. The grassland consisted of white clover (Trifolium repens L.) and red clover (Trifolium pretense L.) sawn in three proportions (0, 15 and 30% in total) together with timothy (Pheum pretense L.) and meadow fescue (Festuca pratensis L.). Three levels of compaction were applied each year (no tractor, light tractor, heavy tractor) together with two different N rates (110 kg N/ha as cattle slurry or 170 kg N/ha as cattle slurry and inorganic N fertilizer). We applied two different methods, the 15N natural abundance and the difference method, to estimate BNF in the first harvest of each year. Overall, the difference method overestimated BNF relative to the 15N natural abundance method. BNF in the first harvest was compared to winter survival of red and white clover plants, which decreased with increasing age of the grassland. However, winter conditions did not seem to affect the grassland's ability to fix N in spring. The fraction of N derived from the atmosphere (NdfA) in white and red clover was close to 100% in each spring, indicating no suppression of BNF. BNF increased the total N yield of the grasslands by up to 75%, mainly due to high

  20. Facultative nitrogen fixation by canopy legumes in a lowland tropical forest.

    PubMed

    Barron, Alexander R; Purves, Drew W; Hedin, Lars O

    2011-02-01

    Symbiotic dinitrogen (N(2)) fixation is often invoked to explain the N richness of tropical forests as ostensibly N(2)-fixing trees can be a major component of the community. Such arguments assume N(2) fixers are fixing N when present. However, in laboratory experiments, legumes consistently reduce N(2) fixation in response to increased soil N availability. These contrasting views of N(2) fixation as either obligate or facultative have drastically different implications for the N cycle of tropical forests. We tested these models by directly measuring N(2)-fixing root nodules and nitrogenase activity of individual canopy-dominant legume trees (Inga sp.) across several lowland forest types. Fixation was substantial in disturbed forests and some gaps but near zero in the high N soils of mature forest. Our findings suggest that canopy legumes closely regulate N(2) fixation, leading to large variations in N inputs across the landscape, and low symbiotic fixation in mature forests despite abundant legumes.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. A Trait-Based Model for Understanding Rates, Patterns, and Ecological Consequences of Microbial Nitrogen Fixation in High-Latitude Terrestrial Ecosystems

    NASA Astrophysics Data System (ADS)

    Cheng, Y.; Riley, W. J.; Tang, J.; Bouskill, N.

    2014-12-01

    Nitrogen limitation constrains primary productivity in high-latitude terrestrial ecosystems. In these ecosystems, Biological Soil Crusts (BSCs) fix the majority of nitrogen and are therefore the dominant nitrogen source to the surrounding soil. Understanding the distribution of nitrogen fixing microorganisms and the constraints on the rate at which nitrogen is fixed is important for reducing uncertainty in predictions of carbon-climate feedbacks. However, few models take into account the environmental, ecological, and energetic constraints on nitrogen fixation. Here we present and discuss a model representing the spatial distribution and activity of nitrogen-fixing and non-fixing microorganisms. We represent a number of functional guilds with different traits associated with resource acquisition (e.g., carbon, nitrogen, phosphorus, and molybdenum) and environmental optima (e.g., light, moisture, and temperature). The model spatially resolves the distribution of nitrogen-fixers or non-nitrogen-fixers across nutrient gradients and demonstrates seasonality in fixation rates. An important aspect of the structure of the model is the inclusion of resource acquisition investments that strongly constrains the distribution of BSCs and impacts the rates of nitrogen fixation at the ecosystem level. Reducing the uncertainty associated with predictions of the fate of high-latitude soil carbon fluxes will require a mechanistic understanding of the nitrogen cycle under a changing climate. This model can significantly contribute to that goal.

  3. Nitrite fixation by humic substances: Nitrogen-15 nuclear magnetic resonance evidence for potential intermediates in chemodenitrification

    USGS Publications Warehouse

    Thorn, K.A.; Mikita, M.A.

    2000-01-01

    Studies have suggested that NO2/-, produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic matter to form trace N gases, including N2O. To gain an understanding of the nitrosation chemistry on a molecular level, soil and aquatic humic substances were reacted with 15N-labeled NaNO2, and analyzed by liquid phase 15N and 13C nuclear magnetic resonance (NMR). The International Humic Substances Society (IHSS) Pahokee peat and peat humic acid were also reacted with Na15NO2 and analyzed by solid-state 15N NMR. In Suwannee River, Armadale, and Laurentian fulvic acids, phenolic rings and activated methylene groups underwent nitrosation to form nitrosophenols (quinone monoximes) and ketoximes, respectively. The oximes underwent Beckmann rearrangements to 2??amides, and Beckmann fragmentations to nitriles. The nitriles in turn underwent hydrolysis to 1??amides. Peaks tentatively identified as imine, indophenol, or azoxybenzene nitrogens were clearly present in spectra of samples nitrosated at pH 6 but diminished at pH 3. The 15N NMR spectrum of the peat humic acid exhibited peaks corresponding with N-nitroso groups in addition to nitrosophenols, ketoximes, and secondary Beckmann reaction products. Formation of N-nitroso groups was more significant in the whole peat compared with the peat humic acid. Carbon-13 NMR analyses also indicated the occurrence of nitrosative demethoxylation in peat and soil humic acids. Reaction of 15N-NH3 fixated fulvic acid with unlabeled NO2/- resulted in nitrosative deamination of aminohydroquinone N, suggesting a previously unrecognized pathway for production of N2 gas in soils fertilized with NH3.Studies have suggested that NO2-, produced during nitrification and denitrification, can become incorporated into soil organic matter and, in one of the processes associated with chemodenitrification, react with organic

  4. Restriction Endonuclease and nif Homology Patterns of Bradyrhizobium japonicum USDA 110 Derivatives With and Without Nitrogen Fixation Competence †

    PubMed Central

    Mathis, James N.; Kuykendall, L. David; Elkan, Gerald H.

    1986-01-01

    DNAs from Bradyrhizobium japonicum USDA 110 derivatives that differ in nitrogen-fixing ability produced similar electrophoretic patterns with five different restriction enzymes. Our data support the hypothesis of common ancestry for these derivatives. Derivatives I-110 and L1-110 differed as much as 100-fold in acetylene reduction activity when they were tested with several soybean cultivars in both greenhouse and field experiments. While possessing nodulating ability, derivative L1-110 is deficient in symbiotic nitrogen-fixing ability, whereas derivative I-110 is symbiotically competent. Hybridization of nifDK and nifH probes from B. japonicum to Southern blots of restricted DNAs from strain USDA 110 derivatives produced similar patterns. This finding indicates similar structural gene organization for both derivative I-110 and derivative L1-110 and implies that the difference in symbiotic nitrogen fixation is probably not due to structural gene rearrangements. However, our hybridization data do not rule out the possibility of differences in expression of structural nif genes or alterations in the structure or expression of other genes required for symbiotic nitrogen fixation. Images PMID:16347007

  5. Growth, nitrogen fixation, yield and kernel quality of peanut in response to lime, organic and inorganic fertilizer levels.

    PubMed

    Basu, Manisha; Bhadoria, P B S; Mahapatra, S C

    2008-07-01

    The aim of this investigation was to study the effect of different levels of chemical fertilizers alone and in combination with farmyard manure and lime on growth, nitrogen fixation, yield and kernel quality of peanut in an acid lateritic soil. Five fertilization levels viz., no chemical fertilizer (CF) (F0), CF @ 20:40:30 (F1), CF @ 40:80:60 (F2) kg ha(-1) NPK, F1 +2.5 t ha(-1) FYM (F3) and F2 +5 t ha(-1) FYM (F4) with and without liming (2 t ha(-1)) were tested. Results revealed that integrated application of FYM+CF at F3 level significantly (P0.05) improved the nitrogen content of nodules (12.4%), kernel yield (19.3%), mineral composition, oil content (4.8%), protein content (28.2%) and hydration coefficient (11.6%) of kernels over sole CF at F1 level. Maximum level of CF or FYM+CF though improved the population of symbiotic nitrogen fixing bacteria in the peanut rhizosphere, however, could not improve nitrogen fixation, yield and kernel quality.

  6. High levels of heterogeneity in diazotroph diversity and activity within a putative hotspot for marine nitrogen fixation

    PubMed Central

    Messer, Lauren F; Mahaffey, Claire; M Robinson, Charlotte; Jeffries, Thomas C; Baker, Kirralee G; Bibiloni Isaksson, Jaime; Ostrowski, Martin; Doblin, Martina A; Brown, Mark V; Seymour, Justin R

    2016-01-01

    Australia's tropical waters represent predicted ‘hotspots' for nitrogen (N2) fixation based on empirical and modelled data. However, the identity, activity and ecology of diazotrophs within this region are virtually unknown. By coupling DNA and cDNA sequencing of nitrogenase genes (nifH) with size-fractionated N2 fixation rate measurements, we elucidated diazotroph dynamics across the shelf region of the Arafura and Timor Seas (ATS) and oceanic Coral Sea during Austral spring and winter. During spring, Trichodesmium dominated ATS assemblages, comprising 60% of nifH DNA sequences, while Candidatus Atelocyanobacterium thalassa (UCYN-A) comprised 42% in the Coral Sea. In contrast, during winter the relative abundance of heterotrophic unicellular diazotrophs (δ-proteobacteria and γ-24774A11) increased in both regions, concomitant with a marked decline in UCYN-A sequences, whereby this clade effectively disappeared in the Coral Sea. Conservative estimates of N2 fixation rates ranged from <1 to 91 nmol l−1 day−1, and size fractionation indicated that unicellular organisms dominated N2 fixation during both spring and winter, but average unicellular rates were up to 10-fold higher in winter than in spring. Relative abundances of UCYN-A1 and γ-24774A11 nifH transcripts negatively correlated to silicate and phosphate, suggesting an affinity for oligotrophy. Our results indicate that Australia's tropical waters are indeed hotspots for N2 fixation and that regional physicochemical characteristics drive differential contributions of cyanobacterial and heterotrophic phylotypes to N2 fixation. PMID:26613341

  7. High levels of heterogeneity in diazotroph diversity and activity within a putative hotspot for marine nitrogen fixation.

    PubMed

    Messer, Lauren F; Mahaffey, Claire; M Robinson, Charlotte; Jeffries, Thomas C; Baker, Kirralee G; Bibiloni Isaksson, Jaime; Ostrowski, Martin; Doblin, Martina A; Brown, Mark V; Seymour, Justin R

    2016-06-01

    Australia's tropical waters represent predicted 'hotspots' for nitrogen (N2) fixation based on empirical and modelled data. However, the identity, activity and ecology of diazotrophs within this region are virtually unknown. By coupling DNA and cDNA sequencing of nitrogenase genes (nifH) with size-fractionated N2 fixation rate measurements, we elucidated diazotroph dynamics across the shelf region of the Arafura and Timor Seas (ATS) and oceanic Coral Sea during Austral spring and winter. During spring, Trichodesmium dominated ATS assemblages, comprising 60% of nifH DNA sequences, while Candidatus Atelocyanobacterium thalassa (UCYN-A) comprised 42% in the Coral Sea. In contrast, during winter the relative abundance of heterotrophic unicellular diazotrophs (δ-proteobacteria and γ-24774A11) increased in both regions, concomitant with a marked decline in UCYN-A sequences, whereby this clade effectively disappeared in the Coral Sea. Conservative estimates of N2 fixation rates ranged from <1 to 91 nmol l(-1) day(-1), and size fractionation indicated that unicellular organisms dominated N2 fixation during both spring and winter, but average unicellular rates were up to 10-fold higher in winter than in spring. Relative abundances of UCYN-A1 and γ-24774A11 nifH transcripts negatively correlated to silicate and phosphate, suggesting an affinity for oligotrophy. Our results indicate that Australia's tropical waters are indeed hotspots for N2 fixation and that regional physicochemical characteristics drive differential contributions of cyanobacterial and heterotrophic phylotypes to N2 fixation.

  8. High cell-specific rates of nitrogen and carbon fixation by the cyanobacterium Aphanizomenon sp. at low temperatures in the Baltic Sea.

    PubMed

    Svedén, Jennie B; Adam, Birgit; Walve, Jakob; Nahar, Nurun; Musat, Niculina; Lavik, Gaute; Whitehouse, Martin J; Kuypers, Marcel M M; Ploug, Helle

    2015-12-01

    Aphanizomenon is a widespread genus of nitrogen (N2)-fixing cyanobacteria in lakes and estuaries, accounting for a large fraction of the summer N2-fixation in the Baltic Sea. However, information about its cell-specific carbon (C)- and N2-fixation rates in the early growth season has not previously been reported. We combined various methods to study N2-fixation, photosynthesis and respiration in field-sampled Baltic Sea Aphanizomenon sp. during early summer at 10°C. Stable isotope incubations at in situ light intensities during 24 h combined with cell-specific secondary ion mass spectrometry showed an average net N2-fixation rate of 55 fmol N cell(-1) day(-1). Dark net N2-fixation rates over a course of 12 h were 20% of those measured in light. C-fixation, but not N2-fixation, was inhibited by high ambient light intensities during daytime. Consequently, the C:N fixation ratio varied substantially over the diel cycle. C- and N2-fixation rates were comparable to those reported for Aphanizomenon sp. in August at 19°C, using the same methods. High respiration rates (23% of gross photosynthesis) were measured with (14)C-incubations and O2-microsensors, and presumably reflect the energy needed for high N2-fixation rates. Hence, Aphanizomenon sp. is an important contributor to N2-fixation at low in situ temperatures in the early growth season.

  9. Impact of the ahas transgene for herbicides resistance on biological nitrogen fixation and yield of soybean.

    PubMed

    Hungria, Mariangela; Nakatani, André Shigueyoshi; Souza, Rosinei Aparecida; Sei, Fernando Bonafé; de Oliveira Chueire, Ligia Maria; Arias, Carlos Arrabal

    2015-02-01

    Studies on the effects of transgenes in soybean [Glycine max (L.) Merr.] and the associated use of specific herbicides on biological nitrogen fixation (BNF) are still few, although it is important to ensure minimal impacts on benefits provided by the root-nodule symbiosis. Cultivance CV127 transgenic soybean is a cultivar containing the ahas gene, which confers resistance to herbicides of the imidazolinone group. The aim of this study was to assess the effects of the ahas transgene and of imidazolinone herbicide on BNF parameters and soybean yield. A large-scale set of field experiments was conducted, for three cropping seasons, at nine sites in Brazil, with a total of 20 trials. The experiment was designed as a completely randomized block with four replicates and the following treatments: (T1) near isogenic transgenic soybean (Cultivance CV127) + herbicide of the imidazolinone group (imazapyr); (T2) near isogenic transgenic soybean + conventional herbicides; and (T3) parental conventional soybean (Conquista) + conventional herbicides; in addition, two commercial cultivars were included, Monsoy 8001 (M-SOY 8001) (T4), and Coodetec 217 (CD 217) (T5). At the R2 growth stage, plants were collected and BNF parameters evaluated. In general, there were no effects on BNF parameters due to the transgenic trait or associated with the specific herbicide. Similarly, at the final harvest, no grain-yield effects were detected related to the ahas gene or to the specific herbicide. However, clear effects on BNF and grain yield were attributed to location and cropping season.

  10. Data-based assessment of environmental controls on global marine nitrogen fixation

    NASA Astrophysics Data System (ADS)

    Luo, Y.-W.; Lima, I. D.; Karl, D. M.; Deutsch, C. A.; Doney, S. C.

    2014-02-01

    There are a number of hypotheses concerning the environmental controls on marine nitrogen fixation (NF). Most of these hypotheses have not been assessed against direct measurements on the global scale. In this study, we use ~ 500 depth-integrated field measurements of NF covering the Pacific and Atlantic oceans to test whether the spatial variance of these measurements can be explained by the commonly hypothesized environmental controls, including measurement-based surface solar radiation, mixed layer depth, average solar radiation in the mixed layer, sea surface temperature, wind speed, surface nitrate and phosphate concentrations, surface excess phosphate (P*) concentration and subsurface minimum dissolved oxygen (in upper 500 m), as well as model-based P* convergence and atmospheric dust deposition. By conducting simple linear regression and stepwise multiple linear regression (MLR) analyses, surface solar radiation (or sea surface temperature) and subsurface minimum dissolved oxygen are identified as the predictors that explain the most spatial variance in the observed NF data, although it is unclear why the observed NF decreases when the level of subsurface minimum dissolved oxygen is higher than ~ 150 μM. Dust deposition and wind speed do not appear to influence the spatial patterns of NF on global scale. The weak correlation between the observed NF and the P* convergence and concentrations suggests that the available data currently remain insufficient to fully support the hypothesis that spatial variability in denitrification is the principal control on spatial variability in marine NF. By applying the MLR-derived equation, we estimate the global-integrated NF at 74 (error range 51-110) Tg N yr-1 in the open ocean, acknowledging that it could be substantially higher as the 15N2-assimilation method used by most of the field samples underestimates NF. More field NF samples in the Pacific and Indian oceans, particularly in the oxygen minimum zones

  11. Efficient Inactivation of Symbiotic Nitrogen Fixation Related Genes in Lotus japonicus Using CRISPR-Cas9

    PubMed Central

    Wang, Longxiang; Wang, Longlong; Tan, Qian; Fan, Qiuling; Zhu, Hui; Hong, Zonglie; Zhang, Zhongming; Duanmu, Deqiang

    2016-01-01

    The targeted genome editing technique, CRISPR/Cas9 system, has been widely used to modify genes of interest in a predictable and precise manner. In this study, we describe the CRISPR/Cas9-mediated efficient editing of representative SNF (symbiotic nitrogen fixation) related genes in the model legume Lotus japonicus via Agrobacterium-mediated stable or hairy root transformation. We first predicted nine endogenous U6 genes in Lotus and then demonstrated the efficacy of the LjU6-1 gene promoter in driving expression of single guide RNAs (sgRNAs) by using a split yellow fluorescence protein (YFP) reporter system to restore the fluorescence in Arabidopsis protoplasts. Next, we chose a customized sgRNA targeting SYMRK (symbiosis receptor-like kinase) loci and achieved ~35% mutagenic efficiency in 20 T0 transgenic plants, two of them containing biallelic homozygous mutations with a 2-bp deletion near the PAM region. We further designed two sgRNAs targeting three homologous leghemoglobin loci (LjLb1, LjLb2, LjLb3) for testing the possibility of generating multi-gene knockouts. 20 out of 70 hairy root transgenic plants exhibited white nodules, with at least two LjLbs disrupted in each plant. Compared with the constitutively active CaMV 35S promoter, the nodule-specific LjLb2 promoter was also effective in gene editing in nodules by hairy root transformation. Triple mutant knockout of LjLbs was also obtained by stable transformation using two sgRNAs. Collectively, these studies demonstrate that the CRISPR/Cas9 system should greatly facilitate functional analyses of SNF related genes in Lotus japonicus. PMID:27630657

  12. Efficient Inactivation of Symbiotic Nitrogen Fixation Related Genes in Lotus japonicus Using CRISPR-Cas9.

    PubMed

    Wang, Longxiang; Wang, Longlong; Tan, Qian; Fan, Qiuling; Zhu, Hui; Hong, Zonglie; Zhang, Zhongming; Duanmu, Deqiang

    2016-01-01

    The targeted genome editing technique, CRISPR/Cas9 system, has been widely used to modify genes of interest in a predictable and precise manner. In this study, we describe the CRISPR/Cas9-mediated efficient editing of representative SNF (symbiotic nitrogen fixation) related genes in the model legume Lotus japonicus via Agrobacterium-mediated stable or hairy root transformation. We first predicted nine endogenous U6 genes in Lotus and then demonstrated the efficacy of the LjU6-1 gene promoter in driving expression of single guide RNAs (sgRNAs) by using a split yellow fluorescence protein (YFP) reporter system to restore the fluorescence in Arabidopsis protoplasts. Next, we chose a customized sgRNA targeting SYMRK (symbiosis receptor-like kinase) loci and achieved ~35% mutagenic efficiency in 20 T0 transgenic plants, two of them containing biallelic homozygous mutations with a 2-bp deletion near the PAM region. We further designed two sgRNAs targeting three homologous leghemoglobin loci (LjLb1, LjLb2, LjLb3) for testing the possibility of generating multi-gene knockouts. 20 out of 70 hairy root transgenic plants exhibited white nodules, with at least two LjLbs disrupted in each plant. Compared with the constitutively active CaMV 35S promoter, the nodule-specific LjLb2 promoter was also effective in gene editing in nodules by hairy root transformation. Triple mutant knockout of LjLbs was also obtained by stable transformation using two sgRNAs. Collectively, these studies demonstrate that the CRISPR/Cas9 system should greatly facilitate functional analyses of SNF related genes in Lotus japonicus.

  13. Organization and regulation of the genes for nitrogen fixation in Rhodopseudomonas capsulata

    SciTech Connect

    Haselkorn, R.

    1989-05-01

    The research carried out over the past two years with DOE support has led to the elucidation of the complete nucleotide sequence of three genes required for the transcription of the genes for nitrogen fixation in Rhodobacter capsulatus. These genes are called nifR1, nifR2 and nifR4 in R. capsulatus. They were found to be homologous to ntrC, ntrB and ntrA in Klebsiella, respectively. Genetic analysis of ammonia-constitutive (NiF{sup c}) mutants of R. capsulatus, isolated using a nifH::lac fusion, showed that ammonia repression involves components of the adenylylation cascade (e.g., the glnB gene) as in Klebsiella. Oxygen control of nif gene expression was linked to the degree of DNA supercoiling by showing that inhibitors of DNA gyrase prevent nif gene expression. Attempts to relate the degree of supercoiling or of gyrase activity in R. capsulatus to the oxygen level have been inconclusive. The gene encoding the DNA gyrase B subunit of R. capsulatus was cloned. The genes encoding the two large subunits of R. Capsulatus RNA polymerase were cloned, mapped and partially sequenced. The nif genes and the glnA gene are being physically mapped on the R. capsulatus chromosome using pulsed field electrophoresis to separate large segments of the bacterial chromosome. A start was made on the purification of R. capsulatus RNA polymerase. A system for expressing genes in R. capsulatus was applied to nifR4; analogous constructions will be made for nifR1, nifR2 and nifA.

  14. The use of nickel to probe the role of hydrogen metabolism in cyanobacterial nitrogen fixation.

    PubMed

    Pederson, D M; Daday, A; Smith, G D

    1986-01-01

    The hydrogenase activities of the heterocystous cyanobacteria Anabaena cylindrica and Mastigocladus laminosus are nickel dependent, based on their inability to consume hydrogen with various electron acceptors or produce hydrogen with dithionite-reduced methyl viologen, after growth in nickel-depleted medium. Upon addition of nickel ions to nickel-deficient cultures of A. cylindrica, the hydrogenase activity recovered in a manner which was protein synthesis-dependent, the recovery being inhibited by chloramphenicol. We have used the nickel dependence of the hydrogenase as a probe of the possible roles of H2 consumption in enhancing nitrogen fixation, and particularly for protecting nitrogenase against oxygen inhibition. Although at the usual growth temperatures (25 degrees for A. cylindrica and 40 degrees for M. laminosus), the cells consume H2 vigorously in an oxyhydrogen reaction after growth in the presence of nickel ions, we have not found that the reaction confers any significant additional protection of nitrogenase, either at aerobic pO2 (for both organisms) or at elevated pO2 (for A. cylindrica). However, at elevated temperatures (e.g., 40 degrees for A. cylindrica and 48 degrees for M. laminosus) a definite protective effect was observed. At these temperatures both organisms rapidly lost acetylene reduction activity under aerobic conditions. When hydrogen gas (10%) was present, the cells retained approximately 50% of the nitrogenase activity observed under anaerobic conditions (argon gas phase). No such protection by hydrogen gas was observed with nickel-deficient cells. Studies with cell-free extracts of A. cylindrica showed that the predominant effect of temperature was not due to thermal inactivation of nitrogenase.

  15. Isolation of a Rhizobium phaseoli cytochrome mutant with enhanced respiration and symbiotic nitrogen fixation.

    PubMed Central

    Soberón, M; Williams, H D; Poole, R K; Escamilla, E

    1989-01-01

    Cultured cells of a Rhizobium phaseoli wild-type strain (CE2) possess b-type and c-type cytochromes and two terminal oxidases: cytochromes o and aa3. Cytochrome aa3 was partially expressed when CE2 cells were grown on minimal medium, during symbiosis, and in well-aerated liquid cultures in a complex medium (PY2). Two cytochrome mutants of R. phaseoli were obtained and characterized. A Tn5-mob-induced mutant, CFN4201, expressed diminished amounts of b-type and c-type cytochromes, showed an enhanced expression of cytochrome oxidases, and had reduced levels of N,N,N',N'-tetramethyl-p-phenylenediamine, succinate, and NADH oxidase activities. Nodules formed by this strain had no N2 fixation activity. The other mutant, CFN4205, which was isolated by nitrosoguanidine mutagenesis, had reduced levels of cytochrome o and higher succinate oxidase activity but similar NADH and N,N,N',N'-tetramethyl-p-phenylenediamine oxidase activities when compared with the wild-type strain. Strain CFN4205 expressed a fourfold-higher cytochrome aa3 content when cultured on minimal and complex media and had twofold-higher cytochrome aa3 levels during symbiosis when compared with the wild-type strain. Nodules formed by strain CFN4205 fixed 33% more N2 than did nodules formed by the wild-type strain, as judged by the total nitrogen content found in plants nodulated by these strains. Finally, low-temperature photodissociation spectra of whole cells from strains CE2 and CFN4205 reveal cytochromes o and aa3. Both cytochromes react with O2 at -180 degrees C to give a light-insensitive compound. These experiments identify cytochromes o and aa3 as functional terminal oxidases in R. phaseoli. PMID:2644201

  16. Conservation of symbiotic nitrogen fixation gene sequences in Rhizobium japonicum and Bradyrhizobium japonicum.

    PubMed Central

    Masterson, R V; Prakash, R K; Atherly, A G

    1985-01-01

    Southern hybridization with nif (nitrogen fixation) and nod (nodulation) DNA probes from Rhizobium meliloti against intact plasmid DNA of Rhizobium japonicum and Bradyrhizobium japonicum strains indicated that both nif and nod sequences are on plasmid DNA in most R. japonicum strains. An exception is found with R. japonicum strain USDA194 and all B. japonicum strains where nif and nod sequences are on the chromosome. In R. japonicum strains, with the exception of strain USDA205, both nif and nod sequences are on the same plasmid. In strain USDA205, the nif genes are on a 112-megadalton plasmid, and nod genes are on a 195-megadalton plasmid. Hybridization to EcoRI digests of total DNA to nif and nod probes from R. meliloti show that the nif and nod sequences are conserved in both R. japonicum and B. japonicum strains regardless of the plasmid or chromosomal location of these genes. In addition, nif DNA hybridization patterns were identical among all R. japonicum strains and with most of the B. japonicum strains examined. Similarly, many of the bands that hybridize to the nodulation probe isolated from R. meliloti were found to be common among R. japonicum strains. Under reduced hybridization stringency conditions, strong conservation of nodulation sequences was observed in strains of B. japonicum. We have also found that the plasmid pRjaUSDA193, which possess nif and nod sequences, does not possess sequence homology with any plasmid of USDA194, but is homologous to parts of the chromosome of USDA194. Strain USDA194 is unique, since nif and nod sequences are present on the chromosome instead of on a plasmid as observed with all other strains examined. Images PMID:4008441

  17. The interactive effects of temperature and light on biological nitrogen fixation in boreal forests

    USDA-ARS?s Scientific Manuscript database

    • Plant productivity is predicted to increase in northern latitudes due to climate warming; however, this may depend on whether biological N-fixation also increases. We evaluated how variation in temperature and light affect N-fixation by two boreal feather mosses, Pleurozium schreberi and Hylocomi...

  18. Estimation of nitrogen yields and loads from basins draining to Long Island Sound, 1988-98

    USGS Publications Warehouse

    Mullaney, J.R.; Schwarz, G.E.; Trench, E.C.T.

    2002-01-01

    Monitoring data on total nitrogen concentrations and streamflow were used to estimate annual nonpoint nitrogen loads for 1988?98 at 28 monitoring sites and 26 unmonitored basins that drain to Long Island Sound. The estimated total nitrogen yields at monitoring sites were used with basin characteristics and ancillary data to develop a multiple-linear regression equation to estimate nonpoint nitrogen yields from monitored and unmonitored basins. The estimated nonpoint nitrogen load to Long Island Sound from the basins studied ranged from 21 million pounds in water year 1995 to 50 million pounds in water year 1990. Statistically significant regression variables include time, population density, annual mean runoff (minus wastewater return flow), pointsource nitrogen yields, percentage of basin area classified as urban/recreational grasses, percentage of the basin classified as agricultural land, and the ratio of deciduous to total forest area. Nonpoint nitrogen loads from monitored and unmonitored basins were computed using the regression equation by setting the point-source nitrogen yields and wastewater return variables to zero, and incorporating streamflow information from index stations in or near unmonitored basins. Nonpoint nitrogen load information obtained through use of this equation was summarized by six Long Island Sound management zones. Estimates of nonpoint nitrogen loads from these basins can be improved by additional sampling, and by developing data on nitrogen loads from municipal wastewater-treatment facilities outside of Connecticut, compiling information on annual interbasin diversions of flow, studying instream losses of nitrogen, and analyzing the processing and storage of atmospheric nitrogen in different forest types.

  19. Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosm experiment (New Caledonia lagoon)

    NASA Astrophysics Data System (ADS)

    Berthelot, H.; Moutin, T.; L'Helguen, S.; Leblanc, K.; Hélias, S.; Grosso, O.; Leblond, N.; Charrière, B.; Bonnet, S.

    2015-07-01

    In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. In this study, we deployed large in situ mesocosms in New Caledonia in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON), i.e., whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (PO43-) in order to prevent phosphorus (P) limitation and promote N2 fixation. The diazotrophic community was dominated by diatom-diazotroph associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C for the last 9 days (P2) of the experiment. N2 fixation rates averaged 9.8 ± 4.0 and 27.7 ± 8.6 nmol L-1 d-1 during P1 and P2, respectively. NO3- concentrations (< 0.04 μmol L-1) in the mesocosms were a negligible source of N, indicating that N2 fixation was the main driver of new production throughout the experiment. The contribution of N2 fixation to PP was not significantly different (p > 0.05) during P1 (9.0 ± 3.3 %) and P2 (12.6 ± 6.1 %). However, the e ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e ratio = POCexport/PP) was significantly higher (p < 0.05) during P2 (39.7 ± 24.9 %) than during P1 (23.9 ± 20.2 %), indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10 ± 0.02 μmol L-1) was not significantly different (p > 0.05) from the total amount of PON exported (0.10 ± 0.04 μmol L-1), suggesting a rapid and probably direct export of the

  20. Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosms experiment (New Caledonia lagoon)

    NASA Astrophysics Data System (ADS)

    Berthelot, H.; Moutin, T.; L'Helguen, S.; Leblanc, K.; Hélias, S.; Grosso, O.; Leblond, N.; Charrière, B.; Bonnet, S.

    2015-03-01

    In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. Here we deployed in New Caledonia large in situ mesocosms in order to investigate (1) the contribution of N2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON) i.e. whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (P) in order to prevent P-limitation and promote N2 fixation. The diazotrophic community was dominated by diatoms-diazotrophs associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N2-fixing cyanobacteria UCYN-C the 9 last days (P2) of the experiment. N2 fixation rates averaged 9.8 ± 4.0 and 27.7 ± 8.6 nM d-1 during P1 and P2, respectively. NO3- concentrations (< 40 nM) in the mesocosms were a negligible source of N indicating that N2 fixation was the main driver of new production all along the experiment. The contribution of v fixation to PP was not significantly different (p > 0.05) during P1 (9.0 ± 3.3%) and P2 (12.6 ± 6.1%). However, the e ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e ratio = POCexport/PP) was significantly higher (p < 0.05) during P2 (39.7 ± 24.9%) than during P1 (23.9 ± 20.2%) indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10 ± 0.02 μM) was not significantly different (p > 0.05) from the total amount of PON exported (0.10 ± 0.04 μM), suggesting a rapid and probably direct export of the recently fixed N2 by the DDAs. During P2, both PON concentrations

  1. Contrasted Reactivity to Oxygen Tensions in Frankia sp. Strain CcI3 throughout Nitrogen Fixation and Assimilation

    PubMed Central

    Ghodhbane-Gtari, Faten; Hezbri, Karima; Ktari, Amir; Sbissi, Imed; Beauchemin, Nicholas; Gtari, Maher; Tisa, Louis S.

    2014-01-01

    Reconciling the irreconcilable is a primary struggle in aerobic nitrogen-fixing bacteria. Although nitrogenase is oxygen and reactive oxygen species-labile, oxygen tension is required to sustain respiration. In the nitrogen-fixing Frankia, various strategies have been developed through evolution to control the respiration and nitrogen-fixation balance. Here, we assessed the effect of different oxygen tensions on Frankia sp. strain CcI3 growth, vesicle production, and gene expression under different oxygen tensions. Both biomass and vesicle production were correlated with elevated oxygen levels under both nitrogen-replete and nitrogen-deficient conditions. The mRNA levels for the nitrogenase structural genes (nifHDK) were high under hypoxic and hyperoxic conditions compared to oxic conditions. The mRNA level for the hopanoid biosynthesis genes (sqhC and hpnC) was also elevated under hyperoxic conditions suggesting an increase in the vesicle envelope. Under nitrogen-deficient conditions, the hup2 mRNA levels increased with hyperoxic environment, while hup1 mRNA levels remained relatively constant. Taken together, these results indicate that Frankia protects nitrogenase by the use of multiple mechanisms including the vesicle-hopanoid barrier and increased respiratory protection. PMID:24987692

  2. New, national bottom-up estimate for tree-based biological nitrogen fixation in the US

    EPA Science Inventory

    Nitrogen is a limiting nutrient in many ecosystems, but is also a chief pollutant from human activity. Quantifying human impacts on the nitrogen cycle and investigating natural ecosystem nitrogen cycling both require an understanding of the magnitude of nitrogen inputs from biolo...

  3. Nitrogen fixation is not the only trait that determines the success of tropical legumes during secondary succession

    NASA Astrophysics Data System (ADS)

    Gei, Maria G.; Powers, Jennifer S.

    2017-04-01

    Legumes trees are well represented throughout the entire precipitation gradient of tropical forests. Many of these species are able to fix atmospheric dinitrogen through symbiosis and offer a mechanism to overcome nitrogen limitation typical of initial stages of secondary forest succession. While it is often assumed the success of legumes is linked to their fixation ability, the variation of other functional traits within this large group has received considerably less attention. Here we assessed legume abundance in secondary forest plots in 42 Neotropical chronosequences (the 2ndFOR network) that span a broad gradient of precipitation regimes and identified those traits that are favored in distinct successional environments. Our main finding is that in young secondary dry forests (5-20 years), legumes that have the potential to fix nitrogen and have small leaflet size become exceptionally abundant (up to 17-99% relative basal area). We suggest that in those species, reduced leaf area could help regulate leaf temperature and minimize water loss, and the cost of reduced total leaf area may be compensated by high photosynthetic rates maximized with nitrogen obtained through fixation. Overall, our study underscores great functional heterogeneity within tropical legumes, which likely translates into diverse biogeochemical cycles. In addition, these results provide a useful framework for active restoration of degraded areas, as it identifies a group of species that accumulate carbon at fast rates under warm and dry environments, conditions that are expected to become more common in the tropics.

  4. Site-specific recombination of nitrogen-fixation genes in cyanobacteria by XisF-XisH-XisI complex: structures and models

    PubMed Central

    Golden, James W.; Pascual, Jaime; Xu, Dong; Cheltsov, Anton

    2014-01-01

    Nitrogen fixation is an important process that converts atmospheric gaseous nitrogen, a form plants cannot utilize, into ammonia that can be easily assimilated. Large serine recombinase XisF (fdxN element site-specific recombinase), together with controlling factors XisH and XisI, plays a critical role in the expression of nitrogen fixation genes of certain Anabaena and Nostoc species of cyanobacteria. All three proteins are required to excise the fdxN DNA element from the chromosome in differentiating heterocysts for the expression of nitrogen fixation related genes. We report the first crystal structures of XisH and XisI proteins, both adopting novel protein folds. Based on the analysis of their sequences and structures, we propose that XisH and XisI proteins function as endonucleases and recombination directionality factors (RDFs), respectively. PMID:25179344

  5. Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres

    NASA Technical Reports Server (NTRS)

    Chameides, W. L.; Walker, J. C. G.

    1981-01-01

    A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10 to the 17th molecules/J, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10 to the 17th molecules/J while the HCN yield is small. The implications for the evolution of life are discussed.

  6. Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres

    NASA Technical Reports Server (NTRS)

    Chameides, W. L.; Walker, J. C. G.

    1981-01-01

    A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10 to the 17th molecules/J, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10 to the 17th molecules/J while the HCN yield is small. The implications for the evolution of life are discussed.

  7. Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres.

    PubMed

    Chameides, W L; Walker, J C

    1981-12-01

    A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH4, CO2, CO, N2, H2, and H2O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10(17) molecules J-1, but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10(17) molecules J-1 while the HCN yield is small. The implications for the evolution of life are discussed.

  8. Growth and nitrogen fixation in Lotus japonicus and Medicago truncatula under NaCl stress: nodule carbon metabolism.

    PubMed

    López, Miguel; Herrera-Cervera, Jose A; Iribarne, Carmen; Tejera, Noel A; Lluch, Carmen

    2008-04-18

    Lotus japonicus and Medicago truncatula model legumes, which form determined and indeterminate nodules, respectively, provide a convenient system to study plant-Rhizobium interaction and to establish differences between the two types of nodules under salt stress conditions. We examined the effects of 25 and 50mM NaCl doses on growth and nitrogen fixation parameters, as well as carbohydrate content and carbon metabolism of M. truncatula and L. japonicus nodules. The leghemoglobin (Lb) content and nitrogen fixation rate (NFR) were approximately 10.0 and 2.0 times higher, respectively, in nodules of L. japonicus when compared with M. truncatula. Plant growth parameters and nitrogenase activity decreased with NaCl treatments in both legumes. Sucrose was the predominant sugar quantified in nodules of both legumes, showing a decrease in concentration in response to salt stress. The content of trehalose was low (less than 2.5% of total soluble sugars (TSS)) to act as an osmolyte in nodules, despite its concentration being increased under saline conditions. Nodule enzyme activities of trehalose-6-phosphate synthase (TPS) and trehalase (TRE) decreased with salinity. L. japonicus nodule carbon metabolism proved to be less sensitive to salinity than in M. truncatula, as enzymatic activities responsible for the carbon supply to the bacteroids to fuel nitrogen fixation, such as sucrose synthase (SS), alkaline invertase (AI), malate dehydrogenase (MDH) and phosphoenolpyruvate carboxylase (PEPC), were less affected by salt than the corresponding activities in barrel medics. However, nitrogenase activity was only inhibited by salinity in L. japonicus nodules.

  9. Arbuscular Mycorrhiza Stimulates Biological Nitrogen Fixation in Two Medicago spp. through Improved Phosphorus Acquisition.

    PubMed

    Püschel, David; Janoušková, Martina; Voříšková, Alena; Gryndlerová, Hana; Vosátka, Miroslav; Jansa, Jan

    2017-01-01

    Legumes establish root symbioses with rhizobia that provide plants with nitrogen (N) through biological N fixation (BNF), as well as with arbuscular mycorrhizal (AM) fungi that mediate improved plant phosphorus (P) uptake. Such complex relationships complicate our understanding of nutrient acquisition by legumes and how they reward their symbiotic partners with carbon along gradients of environmental conditions. In order to disentangle the interplay between BNF and AM symbioses in two Medicago species (Medicago truncatula and M. sativa) along a P-fertilization gradient, we conducted a pot experiment where the rhizobia-treated plants were either inoculated or not inoculated with AM fungus Rhizophagus irregularis 'PH5' and grown in two nutrient-poor substrates subjected to one of three different P-supply levels. Throughout the experiment, all plants were fertilized with (15)N-enriched liquid N-fertilizer to allow for assessment of BNF efficiency in terms of the fraction of N in the plants derived from the BNF (%NBNF). We hypothesized (1) higher %NBNF coinciding with higher P supply, and (2) higher %NBNF in mycorrhizal as compared to non-mycorrhizal plants under P deficiency due to mycorrhiza-mediated improvement in P nutrition. We found a strongly positive correlation between total plant P content and %NBNF, clearly documenting the importance of plant P nutrition for BNF efficiency. The AM symbiosis generally improved P uptake by plants and considerably stimulated the efficiency of BNF under low P availability (below 10 mg kg(-1) water extractable P). Under high P availability (above 10 mg kg(-1) water extractable P), the AM symbiosis brought no further benefits to the plants with respect to P nutrition even as the effects of P availability on N acquisition via BNF were further modulated by the environmental context (plant and substrate combinations). As a response to elevated P availability in the substrate, the extent of root length colonization by AM fungi was

  10. Arbuscular Mycorrhiza Stimulates Biological Nitrogen Fixation in Two Medicago spp. through Improved Phosphorus Acquisition

    PubMed Central

    Püschel, David; Janoušková, Martina; Voříšková, Alena; Gryndlerová, Hana; Vosátka, Miroslav; Jansa, Jan

    2017-01-01

    Legumes establish root symbioses with rhizobia that provide plants with nitrogen (N) through biological N fixation (BNF), as well as with arbuscular mycorrhizal (AM) fungi that mediate improved plant phosphorus (P) uptake. Such complex relationships complicate our understanding of nutrient acquisition by legumes and how they reward their symbiotic partners with carbon along gradients of environmental conditions. In order to disentangle the interplay between BNF and AM symbioses in two Medicago species (Medicago truncatula and M. sativa) along a P-fertilization gradient, we conducted a pot experiment where the rhizobia-treated plants were either inoculated or not inoculated with AM fungus Rhizophagus irregularis ‘PH5’ and grown in two nutrient-poor substrates subjected to one of three different P-supply levels. Throughout the experiment, all plants were fertilized with 15N-enriched liquid N-fertilizer to allow for assessment of BNF efficiency in terms of the fraction of N in the plants derived from the BNF (%NBNF). We hypothesized (1) higher %NBNF coinciding with higher P supply, and (2) higher %NBNF in mycorrhizal as compared to non-mycorrhizal plants under P deficiency due to mycorrhiza-mediated improvement in P nutrition. We found a strongly positive correlation between total plant P content and %NBNF, clearly documenting the importance of plant P nutrition for BNF efficiency. The AM symbiosis generally improved P uptake by plants and considerably stimulated the efficiency of BNF under low P availability (below 10 mg kg-1 water extractable P). Under high P availability (above 10 mg kg-1 water extractable P), the AM symbiosis brought no further benefits to the plants with respect to P nutrition even as the effects of P availability on N acquisition via BNF were further modulated by the environmental context (plant and substrate combinations). As a response to elevated P availability in the substrate, the extent of root length colonization by AM fungi was

  11. The novel regulatory ncRNA, NfiS, optimizes nitrogen fixation via base pairing with the nitrogenase gene nifK mRNA in Pseudomonas stutzeri A1501.

    PubMed

    Zhan, Yuhua; Yan, Yongliang; Deng, Zhiping; Chen, Ming; Lu, Wei; Lu, Chao; Shang, Liguo; Yang, Zhimin; Zhang, Wei; Wang, Wei; Li, Yun; Ke, Qi; Lu, Jiasi; Xu, Yuquan; Zhang, Liwen; Xie, Zhihong; Cheng, Qi; Elmerich, Claudine; Lin, Min

    2016-07-26

    Unlike most Pseudomonas, the root-associated bacterium Pseudomonas stutzeri A1501 fixes nitrogen after the