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.

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 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.

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.

scholarly journals Nitrogen utilization and transformation ofStenotrophomonas maltophiliaW-6 with nitrogen-fixing ability

2018 ◽  
Author(s):  
Shutong Wang ◽  
Yi Xu ◽  
Zhenlun Li
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogen Cycle ◽  
Biological Nitrogen Fixation ◽  
Stenotrophomonas Maltophilia ◽  
Inorganic Nitrogen ◽  
Nitrate Removal ◽  
Nitrogen Utilization ◽  
Purple Soil ◽  
Nitrogen Fixing ◽  
Biological Nitrogen

AbstractStrain W-6 was isolated from the purple soil and successfully identifed asStenotrophomonas maltophiliaand used for the investigation on nitrogen utilization. Strain W-6 was monitored with the ability of biological nitrogen fixation when N2was used for the sole nitrogen source, and yet nitrogenase activity would be inhibited in the presence of extra nitrogen. Moreover, Strain W-6 could utilize NO3−, NO2−and NH4+for cell growth through assimilation, but unable to convert them to atmospheric nitrogen. Meantime, accumulation of nitrite was observed during the nitrate removal process, and the optimal conditions for nitrate removal were temperature of 20°C, shaking speed of 150 rpm, sodium succinate as the carbon source and C/N of 12. The experimental results indicate thatStenotrophomonas maltophiliautilize W-6 could utilize not only N2but also other nitrogen sources directly as its N substance. Therefore, heterotrophicAzotobactermay possess a great significance to nitrogen cycle except in biological nitrogen fixation.ImportanceAzotobacterspp. are found in soils worldwide, with features not simply for the nitrogen fixation, but for the energy metabolism relevant to agriculture. However, the role ofAzotobacterpotential in the function of nitrogen cycle except in biological nitrogen fixation is largely unknown. As such, whether bacteria utilize either inorganic nitrogen or organic nitrogen has remained obscure. The present studies indicate thatStenotrophomonas maltophiliaW-6 could highly efficient utilize nitrate, nitrite and ammonium etc. N substance and detect NH4+as final product. The transport velocities of nitrate-N to nitrite-N was quickly without gaseous nitrogen was produced. We probed the relationship between biological nitrogen fixation and N cycle via N conversion processes byS. maltophiliaW-6 with nitrogen-fixing ability

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.

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.

Enhancing Soil Nitrogen Use and Biological Nitrogen Fixation in Wetland Rice

1995 ◽  
Vol 31 (3) ◽  
pp. 261-278 ◽  
Author(s):  
D. K. Kundu ◽  
J. K. Ladha
Keyword(s):  
Nitrogen Fixation ◽  
Soil Nitrogen ◽  
Biological Nitrogen Fixation ◽  
Field Experiments ◽  
Rice Variety ◽  
Wetland Rice ◽  
Nitrogen Use ◽  
Fertilizer Nitrogen ◽  
Nitrogen Fertility ◽  
Biological Nitrogen

SummaryThe limited fossil fuel reserve available for manufacturing fertilizer nitrogen and the adverse effects of continued use of high fertilizer nitrogen doses on the environment call for a more efficient use of indigenous soil nitrogen. This paper presents several ways of enhancing soil nitrogen use in wetland rice. These involve utilizing nitrogen present in the deeper soil layers, increasing soil nitrogen mineralization rate, decreasing the loss of mineralized nitrogen from the rooting zone, and adjusting rice variety, soil flooding, and transplanting time. To sustain nitrogen fertility and productivity of ricelands, however, the original soil nitrogen levels must be maintained through natural resources like recycled crop residues and enhanced biological N2 fixation. Various ways of stimulating biological nitrogen fixation by both indigenous and exogenous agents are discussed. Since enhancement of soil nitrogen use in rice and maintenance of the original nitrogen level in soil by stimulating biological nitrogen fixation have not been examined together in the field, elaborate field experiments should be conducted to assess the impacts of such combined practices on long-term soil nitrogen fertility and productivity.

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