Nitrogen fixation

About: Nitrogen fixation is a research topic. Over the lifetime, 7940 publications have been published within this topic receiving 232921 citations. The topic is also known as: GO:0009399.

A Model of Nutrient Exchange in the Rhizobium-Legume Symbiosis

Abstract: Rhizobium bacteria and leguminous plants can establish a symbiotic relationship in which photosynthetic products made by the plant supply energy used by Rhizobium to reduce atmospheric dinitrogen (Bergerson, 1982; Verma and Long, 1983). Reduced nitrogen is returned to the plant to complete the exchange. Details of the interaction are not completely understood but it is clear that the relationship has required considerable adaptation by both symbiotic partners. For instance, the low oxygen tension needed to stabilize nitrogenase is preserved by leghemoglobin, a plant-derived protein produced only in the nodule. Unusual forms of glutamine synthetase are found in both the plants and the bacteria (Cullimore et al. 1983; Darrow and Knotts, 1977).

Buckminsterfullerenes: a non-metal system for nitrogen fixation.

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

Nitrogen Fixation by Blue-Green Algae-Lichen Crusts in the Great Basin Desert

Abstract: Blue-green algae-lichen crusts (Atriplex confertifolia, Eurotia lanata, and Artemisia tridentata sites) from the Great Basin Desert have a laboratory potential of fixing atmospheric nitrogen at rates up to 84 g of N ha⁻¹ hour⁻¹. Nitrogen fixation is optimal when the crust is moistened to -⅓ bar pressure, temperature is 19 to 23C, and the light intensity is 200 microeinsteins m⁻² sec⁻¹ with incandescent light. The acetylene reduction technique provided a useful assay to measure in situ nitrogen fixation which was correlated with potential values obtained in the laboratory under optimum conditions. Nitrogen fixation was found to be reduced under desert shrub canopies possibly due to allelopathic effects of the shrubs. Aqueous leaf extracts of desert shrubs significantly inhibited nitrogen fixation. Annual nitrogen fixed was estimated at 10 to 100 kg of N ha⁻¹ year⁻¹, depending upon microenvironmental conditions.

Nitrogen fixation and identification of potential diazotrophs in the Canadian Arctic

Abstract: [1] Global gaseous nitrogen (N2) fixation rates may be underestimated and data is lacking from many regions without conspicuous diazotrophic cyanobacteria, such as cold oceans. We estimated N2 fixation rates at diverse sites in the Canadian Arctic, including the mouth of the Mackenzie River, the offshore Beaufort Sea, Lancaster Sound, Baffin Bay and a river influenced fjord. We also identified potential diazotrophic communities using a targeted survey of the nifH gene. Nitrogen fixation rates ranged from 0.02 nmol N L−1 d−1 in Baffin Bay to 4.45 nmol N L−1 d−1 in the Mackenzie River plume. Sequences recovered from the nifH gene survey belonged mainly to Cluster III, a group of nifH sequences associated with diverse microorganisms, with some α- andγ-proteobacterianifH genes at most sites. Cyanobacteria nifH genes with best matches to Nostocales, which are common in Arctic freshwaters, were recovered from the marine Beaufort Sea. The geographic pattern of N2 fixation rates and nifHgene identities suggest that the Mackenzie River is the source of a diazotrophic community that contributes new nitrogen to the nitrogen-depleted surface waters of the Beaufort Sea. This first record of N2 fixation at high latitudes refines our understanding of the global nitrogen budget.

Nitrogen and phosphorus availability limit N2 fixation in bean

Abstract: Availability of nitrogen (N) and phosphorus (P) might significantly affect N2 fixation in legumes. The interaction of N and P was studied in common bean (Phaseolus vulgaris), considering their effects on nodulation and N2 fixation, nitrate reductase activity, and the composition of N compounds in xylem sap. The effect of N on the uptake of P by plants was estimated by analysing rhizospheric pH and P concentration in xylem sap and in plant shoots. Inoculated bean plants were grown in pots containing perlite/vermiculite in two experiments with different amounts of P and N. In a third experiment, bean plants were grown on two soil types or on river sand supplied with different concentrations of N. At harvest, shoot growth, number of nodules and mass, and nitrogenase activity were determined. Xylem sap was collected for the determination of ureides, amino acids, nitrate and phosphate concentration. At low nitrate concentration (1 mM), increasing amounts of P promoted both nodule formation and N2 fixation, measured as ureide content in the xylem sap. However, at high nitrate concentration (10 mM), nodulation and N2 fixation did not improve with increased P supply. Glutamine and aspartate were the main organic N compounds transported in the xylem sap of plants grown in low nitrate, whereas asparagine was the dominant N compound in xylem sap from plants grown in high nitrate. Nitrate reductase activity in roots was higher than in shoots of plants grown with low P and high N. In both soils and in the sand experiment, increased application of N decreased nodule mass and number, nitrogenase activity and xylem ureides but increased the concentration of asparagine in xylem sap. Increasing P nutrition improved symbiotic N2 fixation in bean only at low N concentrations. It did not alleviate the inhibitory effect of high nitrate concentration on N2 fixation. A decrease in plant P uptake was observed, as indicated by a lower concentration of P in the xylem sap and shoots, correlating with the amount of N supplied. Simultaneously with the specific inhibition of N2 fixation, high nitrate concentrations might decrease P availability, thus inhibiting even further the symbiotic association because of the high P requirement for nodulation and N2 fixation.