Helping plants get more nitrogen from the air

2000 ◽  
Vol 8 (2) ◽  
pp. 193-200 ◽  
Author(s):  
Edward C. Cocking
Keyword(s):  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Fossil Fuels ◽  
Crop Yields ◽  
Atmospheric Nitrogen ◽  
Fixed Nitrogen ◽  
Free Living ◽  
World Agriculture ◽  
Biological Nitrogen ◽  
Inoculation Technology

Plants cannot themselves obtain their nitrogen from the air but rely mainly on the supply of combined nitrogen in the form of ammonia, or nitrates, resulting from nitrogen fixation by free-living bacteria in the soil or bacteria living symbiotically in nodules on the roots of legumes. Increased crop yields in the twentieth century required this biological nitrogen fixation to be supplemented increasingly by the use of fixed nitrogen from chemical fertilizers. The development of the Haber–Bosch process for catalytically combining atmospheric nitrogen with hydrogen from fossil fuels to produce ammonia enabled increased crop yields. However, energy and environmental concerns arising from the overuse of nitrogenous fertilizers have highlighted the need for plants to obtain more of their nitrogen from the air by biological nitrogen fixation. New systems are being developed for increased biological nitrogen fixation with cereals and other non-legumes by establishing nitrogen-fixing bacteria within their roots. This new inoculation technology is aimed at significantly reducing the use of synthetic nitrogenous fertilizers in world agriculture.

Nitrogen fixation in the high arctic tundra at Sarcpa Lake, Northwest Territories

1985 ◽  
Vol 63 (5) ◽  
pp. 974-979 ◽  
Author(s):  
Jim D. Karagatzides ◽  
Martin C. Lewis ◽  
Herbert M. Schulman
Keyword(s):  
Nitrogen Fixation ◽  
Northwest Territories ◽  
Acetylene Reduction ◽  
Biological Nitrogen Fixation ◽  
Arctic Tundra ◽  
High Arctic ◽  
Fixed Nitrogen ◽  
Free Living ◽  
Blue Green Algae ◽  
Biological Nitrogen

The acetylene reduction assay was used to examine biological nitrogen fixation in the high arctic tundra at Sarcpa Lake, Northwest Territories (68°32′ N, 83°19′ W). The highest rates of acetylene reduction (9.37 ± 3.19 μmol C2H4 m−2 h−1) were in habitats that had a high density of the legumes Oxytropis maydelliana, O. arctobia, and Astragalus alpinus. Nitrogen fixation in the wet soils along the shore of a small lake was similar (8.87 ± 4.35 μmol C2H4 m−2 h−1) because of the blue-green alga Nostoc, which associates with mosses. Free-living blue-green algae and lichens made insignificant contributions to the total nitrogen fixation budget because they were uncommon and fixed nitrogen at a slower rate. Nitrogen-fixing lichens in the area included Stereocaulon arenarium and S. rivulorum. It is concluded that legumes have a significant input to the biological nitrogen fixation budget at Sarcpa Lake.

Biological and ecological aspects of nitrogen fixation by free-living micro-organisms

1969 ◽  
Vol 172 (1029) ◽  
pp. 367-388 ◽  
Keyword(s):  
Nitrogen Fixation ◽  
Soil Fertility ◽  
Biological Nitrogen Fixation ◽  
Higher Plants ◽  
Symbiotic Association ◽  
Free Living ◽  
Blue Green Algae ◽  
Ecological Aspects ◽  
Micro Organisms ◽  
Biological Nitrogen

Biological nitrogen fixation is a characteristic of certain micro-organisms, which may be free-living or occur in symbiotic association with higher plants. The purpose of this paper is to summarize some of the biological and ecological aspects of nitrogen-fixation by free-living forms. Biochemical aspects have been reviewed in other contributions to this discussion by Drs Wilson, Burris, and Cox & Fay. Nitrogen fixation by heterotrophic micro-organisms has been considered by Jensen (1965); nitrogen fixation by blue-green algae by Fogg & Stewart (1965), and by Stewart (1966, 1969), while Moore (1966) has evaluated the contribution of nitrogen-fixing micro-organisms to soil fertility.

First steps in biological nitrogen fixation

1969 ◽  
Vol 172 (1029) ◽  
pp. 319-325 ◽  
Keyword(s):  
Nitrogen Fixation ◽  
Subject Matter ◽  
Biological Nitrogen Fixation ◽  
Atmospheric Nitrogen ◽  
Human Interest ◽  
Biochemical Component ◽  
The Subject ◽  
Biological Nitrogen

Since abstracts of the papers in this discussion have been circulated, I assume that it is unnecessary to explain that the title does not refer to the biochemical steps that result in the fixation of atmospheric nitrogen, but to the well-known saying that ‘a child must learn to walk before it runs’. As an introduction to the summaries of present day research, it seems worth-while to furnish a perspective of some of the events that led to the modern studies that have been made possible by the development of cell-free systems capable of fixing N 2 . This contribution will be limited primarily to those steps that are most closely related to the subject matter of the biochemical papers on the programme. This choice is dictated, not only because of the limits of time but also because these papers represent the area of my own research interests and, presumably, then, the area of my greatest competency. Alone, perhaps this would not be enough, but if the personal participation that furnishes background dealing with items of human interest and errors—observations that never get into the published works—is added, it should suffice. Other aspects in the field are represented in the discussion by the contributors of the afternoon portion of the programme; but having heard three of these recently, I am confident that these papers, too, will have a biochemical component.

scholarly journals Soil nitrogen response to shrub encroachment in a degrading semiarid grassland

2018 ◽  
Author(s):  
Thomas Turpin-Jelfs ◽  
Katerina Michaelides ◽  
Joel A. Biederman ◽  
Alexandre M. Anesio
Keyword(s):  
Nitrogen Fixation ◽  
Soil Nitrogen ◽  
Biological Nitrogen Fixation ◽  
Inorganic Nitrogen ◽  
Shrub Encroachment ◽  
Shrub Cover ◽  
Prosopis Velutina ◽  
Free Living ◽  
Semiarid Grassland ◽  
Biological Nitrogen

Abstract. Transitions from grass- to shrub-dominated states in drylands by woody plant encroachment represent significant forms of land cover change with the potential to alter the spatial distribution and cycling of soil resources. Yet an understanding of how this phenomenon impacts the soil nitrogen pool, which is essential to primary production in arid and semiarid systems, is poorly resolved. In this study, we quantified how the distribution and speciation of soil nitrogen, as well as rates of free-living biological nitrogen fixation, changed along a gradient of increasing mesquite (Prosopis velutina Woot.) cover in a semiarid grassland of the Southwestern US. Our results show that site-level concentrations of total nitrogen remain unchanged with increasing shrub cover as losses from intershrub areas (sum of grass and bare-soil cover) are proportional to increases in soils under shrub canopies. However, despite the similar carbon-to-nitrogen ratio and microbial biomass of soil from intershrub and shrub areas at each site, site-level concentrations of inorganic nitrogen increase with shrub cover due to the accumulation of ammonium and nitrate in soils beneath shrub canopies. Using the acetylene reduction assay technique, we found increasing ratios of inorganic nitrogen-to-bioavailable phosphorus inhibit rates of biological nitrogen fixation by free-living soil bacteria. Consequently, we conclude that shrub encroachment has the potential to significantly alter the dynamics of soil nitrogen cycling in dryland systems.

The fixed nitrogen sensitivity of biological nitrogen fixation in salt marshes sediments from the northeastern United States

2020 ◽  
Author(s):  
Romain Darnajoux ◽  
Rei Zhang ◽  
Katja Luxem ◽  
Xinning Zhang
Keyword(s):  
Nitrogen Fixation ◽  
Salt Marshes ◽  
Biological Nitrogen Fixation ◽  
Nitrogenase Activity ◽  
Inorganic Nitrogen ◽  
Ammonium Concentration ◽  
Desulfovibrio Vulgaris ◽  
Fixed Nitrogen ◽  
Sulfate Reducing ◽  
Biological Nitrogen

<p>Biological nitrogen fixation, the main input of fixed N into ecosystems, converts inert N<sub>2</sub> gas into bioavailable ammonium in an energetically costly reaction catalyzed by the prokaryotic metalloenzyme nitrogenase.  The high ATP and reductant requirements of N<sub>2</sub> fixation explain why this process is highly regulated in diazotrophs, with the presence of ammonium inhibiting nitrogenase expression and activity. Yet, several reports of N<sub>2</sub> fixation in ammonium- and nitrate-rich (10 to 300 µM) benthic environments challenge our understanding of a key environmental sensitivity of N<sub>2</sub> fixation. Field studies point to heterotrophic sulfate reducers as the likely diazotrophs in these benthic settings, but the fixed N sensitivity of sulfate-reducing diazotrophs is not well understood due to a dearth of culture studies. Additionally, assays of N<sub>2</sub> fixation in incubations rarely involve parallel measurements of dissolved inorganic nitrogen, possibly leading to experimental bias in favor of detecting activity under ammonium-replete initial conditions.</p><p>To help reconcile the environmental results, we investigate the ammonium sensitivity of N<sub>2</sub> fixation using the acetylene reduction assay and <sup>15</sup>N<sub>2</sub> tracer methods in i) the model sulfate-reducing diazotroph, <em>Desulfovibrio vulgaris</em> str. Hildenborough (DvH), ii) four enrichment cultures from salt marsh sediments of New Jersey, and iii) slurry incubations of sediments collected from three northeastern salt marshes. In all instances, we found that ammonium strongly inhibits biological nitrogen fixation, with nitrogenase activity only detectable when ammonium concentration is below a threshold of 10 µM (slurry incubation) or 2 µM (pure cultures, enrichments). Amendment of ammonium quickly inhibits nitrogen fixation and nitrogenase activity only resumes  once ammonium is depleted to the threshold level. Ammonium additions to actively fixing samples show complete inhibition of N<sub>2</sub> fixation within several hours post-addition. </p><p>Our measurements of the ammonium sensitivity of benthic N<sub>2</sub> fixation are consistent with the traditional understanding of nitrogen fixer metabolism and with early findings of Postgate et al. (1984) demonstrating that N<sub>2</sub> fixation by the sulfate reducer <em>Desulfovibrio gigas</em> is inhibited by ammonium levels that exceed 10 µM. These results help clarify a long-standing paradox in benthic nitrogen cycling. We suggest that prior observations of N<sub>2</sub> fixation at elevated ammonium levels could reflect methodological artifacts due to very fast depletion of ammonium during activity assays, legacy N<sub>2</sub> fixation activity associated with incomplete inhibition by ammonium, or spatial heterogeneity. Further work to standardize fixed N sensitivity assays could help with cross-study comparisons and with clarifying inconsistencies in our understanding of how environmental fixed nitrogen levels control nitrogen fixation.</p>

The current and potential contribution of asymbiotic nitrogen fixation to nitrogen requirements on farms: a review

2001 ◽  
Vol 41 (3) ◽  
pp. 447 ◽  
Author(s):  
I. R. Kennedy ◽  
N. Islam
Keyword(s):  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Potential Contribution ◽  
Free Living ◽  
Biological Potential ◽  
Asymbiotic Nitrogen Fixation ◽  
Microbial Strains ◽  
The Many ◽  
Short Time ◽  
Biological Nitrogen

Significant levels of biological nitrogen fixation from sources other than nodulated legumes have become a tantalizing prospect for decades. Since the benefit to agriculture of nitrogen fixation from nodulated legumes was established, there have been widespread efforts to promote the use of various asymbiotic diazotrophic bacteria to fix extra nitrogen in soil. Despite much optimism by scientists and farmers, this prospect remains to be realised. Recently, the prospect has been pursued with renewed enthusiasm and several commercialised products have appeared. What are the reasons for this fresh enthusiasm? Are the new products based on realistic assessments of their biological potential? Why has it taken so long to advance to a stage where there is still only limited evidence that verifies hope becoming reality? This review assesses the current contribution from asymbiotic nitrogen fixation and re-assesses the prospects for greater contributions from this source. Among the many aspects of this multi-faceted subject that will be considered are: (i) the range of free-living microbial strains currently contributing to signficant asymbiotic nitrogen fixation; (ii) the significance of nitrogen-fixing microbes naturally associated with plants; (iii) the significance of endophytic systems and their role in sugarcane and other Gramineae; (iv) the possibility of extending this range by introducing new strains or discovering new systems capable of contributing additional nitrogen fixation. The case will be made that conditions providing a sustainable contribution for more than a short time are usually missing in such systems so that spontaneous biological nitrogen fixation is usually transient. It will be argued further that if all the positive factors controlling spontaneity at the biothermodynamic level are exploited, significant biological nitrogen fixation may soon be achieved in some of these systems on farms.

scholarly journals Soil nitrogen response to shrub encroachment in a degrading semi-arid grassland

2019 ◽  
Vol 16 (2) ◽  
pp. 369-381 ◽  
Author(s):  
Thomas Turpin-Jelfs ◽  
Katerina Michaelides ◽  
Joel A. Biederman ◽  
Alexandre M. Anesio
Keyword(s):  
Nitrogen Fixation ◽  
Microbial Biomass ◽  
Soil Nitrogen ◽  
Biological Nitrogen Fixation ◽  
Inorganic Nitrogen ◽  
Shrub Cover ◽  
Prosopis Velutina ◽  
Free Living ◽  
Biological Nitrogen ◽  
Semi Arid

Abstract. Transitions from grass- to shrub-dominated states in drylands by woody plant encroachment represent significant forms of land cover change with the potential to alter the spatial distribution and cycling of soil resources. Yet an understanding of how this phenomenon impacts the soil nitrogen pool, which is essential to primary production in arid and semi-arid systems, is poorly resolved. In this study, we quantified how the distribution and speciation of soil nitrogen, as well as rates of free-living biological nitrogen fixation, changed along a gradient of increasing mesquite (Prosopis velutina Woot.) cover in a semi-arid grassland of the southwestern US. Our results show that site-level concentrations of total nitrogen remain unchanged with increasing shrub cover as losses from inter-shrub areas (sum of grass and bare-soil cover) are proportional to increases in soils under shrub canopies. However, despite the similar carbon-to-nitrogen ratio and microbial biomass of soil from inter-shrub and shrub areas at each site, site-level concentrations of inorganic nitrogen increase with shrub cover due to the accumulation of ammonium and nitrate in soils beneath shrub canopies. Using the acetylene reduction assay technique, we found increasing ratios of inorganic nitrogen to bioavailable phosphorus inhibit rates of biological nitrogen fixation by free-living soil bacteria. Overall, these results provide a greater insight into how grassland-to-shrubland transitions influence the soil N pool through associated impacts on the soil microbial biomass.

Biological nitrogen fixation associated with tropical pasture grasses

2001 ◽  
Vol 28 (9) ◽  
pp. 837 ◽  
Author(s):  
Veronica M. Reis ◽  
Fábio B. dos Reis Jr ◽  
Diego M. Quesada ◽  
Octávio C. A. de Oliveira ◽  
Bruno J. R. Alves ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Fossil Fuels ◽  
Pennisetum Purpureum ◽  
N Accumulation ◽  
Fast Growing ◽  
15N Enrichment ◽  
Pasture Grasses ◽  
High Yields ◽  
Biological Nitrogen

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 The semi-humid or humid tropics are ideal for the production of large quantities of biomass from fast-growing C4 grasses, but high yields normally require large quantities of fertiliser, especially N, which has a very high input from fossil fuels (natural gas). A program has been started recently to use elephant grass (Pennisetum purpureum Schum.) to substitute firewood as a fuel and also to make charcoal for iron production. In this case, any large N fertiliser additions would mean that the yield of bio fuel per unit of fossil fuel invested would be detrimentally affected. In this study, we report on the potential for the selection of genotypes of fast-growing C4 tropical grasses of the genera Pennisetum and Brachiaria for their capacity to obtain N inputs from plant-associated biological nitrogen fixation (BNF). Fourteen genotypes each of Brachiaria and Pennisetum were screened for BNF contributions by growing them in 15N-labelled soil. In the case of the Pennisetum, after a suitable cutting height for the crop had been selected, there were large differences in dry matter production, N accumulation and 15N enrichment. The differences in 15N enrichment between genotypes were statistically significant and BNF inputs were estimated as high as 41% of accumulated N. In the study on Brachiaria genotypes, potential inputs of BNF seemed lower. Only one or two genotypes of B. brizantha and B. ruziziensis obtained more then 20% of their N from BNF. The N2-fixing bacteria that were most commonly associated with shoots and roots the Pennisetum genotypes were of the genus Herbaspirillum, but predominantly of a recently described new species. The Brachiaria spp. from three different sites (Rio de Janeiro, Goânia, Bahia) were predominately colonised by Azospirillum spp., most of the isolates being of the species Azospirillum amazonense. Very few Herbaspirilla were isolated from these plants.

Role of microRNAs in the legume - rhizobium nitrogen fixing symbiosis

2019 ◽  
Author(s):  
◽  
Nhung Thi Huyen Hoang
Keyword(s):  
Transcription Factor ◽  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Nodule Development ◽  
Atmospheric Nitrogen ◽  
Ammonia Production ◽  
Nitrogen Fixing ◽  
Nodule Number ◽  
Biological Nitrogen

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Nitrogen is a macronutrient that is critical for plant growth and development because it provides the building blocks of nucleic acids, proteins, chlorophyll, and energy- transfer compounds, such as ATP. Although 78% of the atmosphere is diatomic nitrogen, this form is inert and unavailable to plants due to the strong nitrogen-nitrogen triple bond. Plants can only absorb nitrogen in the forms of NH4+ or NO3-. Most of the inorganic nitrogen available to crop plants is provided through fertilizers synthesized based on the Haber-Bosch process. This process converts atmospheric nitrogen (N2) into ammonia (NH3) by a reaction with hydrogen (H2) using a metal catalyst (iron) under high temperatures (~500 [degrees]C) and high pressures (150-300 bar). Ammonia production by this method consumes a lot of energy, which is derived from burning fossil fuels. Synthetic ammonia production by the Haber-Bosch process causes losses of biodiversity through eutrophication, soil acidification and global increase in N2O atmospheric concentration, which is the third most significant greenhouse gas. An alternative approach to provide a sustainable nitrogen source to plants without causing such damage to the environment is through biological nitrogen fixation between legume species and Rhizobium bacteria. The symbiotic interaction between legume plants and rhizobia results in the formation of root nodules, specialized organs within which rhizobia convert atmospheric nitrogen into ammonia for plant consumption. In return, the legume host plants provide rhizobia with photosynthate as a carbon source for their growth. The legume - Rhizobium symbiosis is a sophisticated process that requires numerous regulators including the 20-24 nucleotide-long microRNAs which negatively regulate the expression of their target messenger RNAs. In my study, we provide two examples that demonstrate the significant role of microRNAs in the symbiotic interplay between soybean, an important legume crop, and rhizobia. In the first example, our results suggest that gma-miR319i functions as a positive regulator of nodule number during the soybean - Bradyrhizobium symbiosis by targeting the TCP33 transcription factor. Overexpression and CRISPR/cas9-mediated gene mutation of gma-miR319i increased and reduced nodule number after rhizobial inoculation, respectively. gma-miR319i and TCP33 showed an inverse expression pattern in different stages of nodule development. TCP33 modulated nodule development in a gma-miR319i dependent manner. The expression of gma-miR319i and TCP33 was differentially regulated in one soybean mutant line that exhibits a hypernodulation phenotype. In the second example, we further investigated the mechanism by which two identical microRNAs, gma-miR171o and gma-miR171q, function in modulating the spatial and temporal aspects of soybean nodulation. Although sharing the identical mature sequence, gma-miR171o and gma-miR171q genes are divergent and show unique, tissue-specific expression patterns. The expression levels of the two miRNAs are negatively correlated with that of their target genes. Ectopic expression of these miRNAs in transgenic hairy roots resulted in a significant reduction in nodule formation. Both gma-miR171o and gma-miR171q target members of the GRAS transcription factor superfamily, namely GmSCL-6 and GmNSP2. Besides those two above-mentioned examples, we were able to generate and characterize an enhancer trap insertional mutant of the NODULATION SIGNALING PATHWAY 2 (NSP2) gene which is the target gene of Gma-miR171 and also an important regulator of nodulation. Overall, our study shows the importance of microRNAs in the regulation of nitrogen-fixing symbiosis. Our results contribute to efforts to fully understand the molecular mechanisms controlling the legume - Rhizobium interaction. Our ultimate hope is that the information gained through my studies can lead to an increased utilization of biological nitrogen fixation for sustainable agriculture and environment protection.

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