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.

Nitrogen Metabolism in Plants

Abstract: Although plants or plant parts can be cultured on various organic nitrogen forms, particularly amino acids, under natural conditions the majority of plants depend upon inorganic nitrogen sources. Exceptions to this may be various parasitic and semi-parasitic plants which may be provided with organic nitrogenous nutrients of host origin, and insectivorous plants which partially satisfy their nitrogen demands by utilizing organic nitrogen constituents released by lysis of trapped insects.

Selection of common bean (Phaseolus vulgaris L.) for N2 fixation at different levels of available phosphorus under field and environmentally-controlled conditions

Abstract: Phosphorus is one of several factors which affect N2 fixation and along with N, is a principal yield-limiting nutrient in many regions of the world. Since the legume plant is an essential partner in symbiotic N2 fixation, knowledge of host genotype variability for this process at different levels of P availability will be useful when breeding bean cultivars for enhanced N2 fixation. The objective of this study was to obtain common bean (Phaseolus vulgaris L.) lines able with enhanced ability to support biological N2 fixation under different levels of available phosphorus. Experiments were conducted in a growth room using a sand-alumina system to provide different levels of available P and in the field on a low-N soil. In the growth room studies, P availability strongly affected plant growth and traits related to N2 fixation. No significant interaction was detected for P levels × bean lines, indicating that bean lines performed similarly at both high and low P levels. Total shoot N was used as a direct and indirect measure of N2-fixation potential under growth room (N-free media) and field (low-N soil) conditions, respectively. Based on this criterion, two of the 41 and 54 inbred backcross lines of a segregating population evaluated in the growth room and the field, respectively, contained greater shoot N content than the recurrent parent and N shoot contents similar to the donor parent. Variability of N2 fixation under low available P was observed, and high N2 fixing and high yielding progeny lines were detected.

Microbial Phototrophic, Heterotrophic, and Diazotrophic Activities Associated with Aggregates in the Permanent Ice Cover of Lake Bonney, Antarctica

Abstract: The McMurdo Dry Valley lakes, Antarctica, one of the Earth's southernmost ecosystems containing liquid water, harbor some of the most environmentally extreme (cold, nutrient-deprived) conditions on the planet. Lake Bonney has a permanent ice cover that supports a unique microbial habitat, provided by soil particles blown onto the lake surface from the surrounding, ice-free valley floor. During continuous sunlight summers (Nov.–Feb.), the dark soil particles are heated by solar radiation and melt their way into the ice matrix. Layers and patches of aggregates and liquid water are formed. Aggregates contain a complex cyanobacterial–bacterial community, concurrently conducting photosynthesis (CO2 fixation), nitrogen (N2) fixation, decomposition, and biogeochemical zonation needed to complete essential nutrient cycles. Aggregate-associated CO2- and N2-fixation rates were low and confined to liquid water (i.e., no detectable activities in the ice phase). CO2 fixation was mediated by cyanobacteria; both cyanobacteria and eubacteria appeared responsible for N2 fixation. CO2 fixation was stimulated primarily by nitrogen (NO3 −), but also by phosphorus (PO4 3−). PO4 3− and iron (FeCl3+ EDTA) enrichment stimulated of N2 fixation. Microautoradiographic and physiological studies indicate a morphologically and metabolically diverse microbial community, exhibiting different cell-specific photosynthetic and heterotrophic activities. The microbial community is involved in physical (particle aggregation) and chemical (establishing redox gradients) modification of a nutrient- and organic matter-enriched microbial ``oasis,'' embedded in the desertlike (i.e., nutrient depleted) lake ice cover. Aggregate-associated production and nutrient cycling represent microbial self-sustenance in a microenvironment supporting ``life at the edge,'' as it is known on Earth.

Nitrogen fixation in the rhizosphere of rice

Abstract: THE discovery of nitrogen-fixing activity associated with the rhizosphere of non-leguminous plants such as tropical grasses, rice and maize has provoked considerable interest1–9. Discrepancies in the measurements of this nitrogen-fixing activity by the acetylene reduction assay in different conditions prompted us to develop a modified assay system. We report here the use of this assay to find significant differences in the rates of acetylene reduction associated with the rhizosphere of 50 different strains of rice. This suggests that the rice plant genotype influences the association with nitrogen-fixing bacteria in its rhizosphere.