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.

Oxygen-poor microzones as potential sites of microbial n(2) fixation in nitrogen-depleted aerobic marine waters.

Abstract: 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.

Is the distribution of nitrogen‐fixing cyanobacteria in the oceans related to temperature?

Abstract: Approximately 50% of the global natural fixation of nitrogen occurs in the oceans supporting a considerable part of the new primary production. Virtually all nitrogen fixation in the ocean occurs in the tropics and subtropics where the surface water temperature is 25°C or higher. It is attributed almost exclusively to cyanobacteria. This is remarkable firstly because diazotrophic cyanobacteria are found in other environments irrespective of temperature and secondly because primary production in temperate and cold oceans is generally limited by nitrogen. Cyanobacteria are oxygenic phototrophic organisms that evolved a variety of strategies protecting nitrogenase from oxygen inactivation. Free-living diazotrophic cyanobacteria in the ocean are of the non-heterocystous type, namely the filamentous Trichodesmium and the unicellular groups A-C. I will argue that warm water is a prerequisite for these diazotrophic organisms because of the low-oxygen solubility and high rates of respiration allowing the organism to maintain anoxic conditions in the nitrogen-fixing cell. Heterocystous cyanobacteria are abundant in freshwater and brackish environments in all climatic zones. The heterocyst cell envelope is a tuneable gas diffusion barrier that optimizes the influx of both oxygen and nitrogen, while maintaining anoxic conditions inside the cell. It is not known why heterocystous cyanobacteria are absent from the temperate and cold oceans and seas.

Biology and biochemistry of nitrogen fixation

Abstract: 1 The Biology and Biochemistry of Nitrogen Fixation: A Look Forward (AR Glenn and M Dilworth) 2 Molybdenum Nitrogenase (RW Miller) 3 Alternative Nitrogenases (RN Pau) 4 The Chemistry of Dinitrogen Reduction (RL Richards) 5 Physiological Control of Nitrogenase and Uptake Hydrogenase (FJ Bergersen) 6 Genetics and Regulation of Mo-Nitrogenase (C Elmerich) 7 The Genetics and Regulation of Alternative Nitrogenase (RL Robson) 8 Free-living Diazotrophs (WB Silvester and DR Musgrave) 9 Associative Nitrogen Fixation in Plants (RV Klucas) 10 Ecology of Legume Root Nodule Bacteria (YM Barnet) 11 Recognition and Infection in Legume Nodulation (BWS Sobral et al) 12 Organic and Inorganic Inputs into Legume Root Nodule Nitrogen Fixation (L Rosendahl, AR Glenn and MJ Dilworth) 13 Amonia Assimilation and Export of Nitrogen from the Legume Nodule (CA Atkins) 14 Limitations in the use of Legumes in Agriculture and Forestry (AD Robson and PJ Bottomley) 15 Actinorhizal Plants: (Frankia) - Symbioses (CS Schwintzer and JD Tjepkema) 16 Cyanobacteria and their Symbionts (P Rowell and NW Kerby) 17 Genetic Enhancement of Nitrogen Fixation (DA Phillips)

Nitrogen Fertilization Has a Stronger Effect on Soil Nitrogen-Fixing Bacterial Communities than Elevated Atmospheric CO2

Abstract: Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how N-fixing bacteria will respond to global change factors such as increasing atmospheric CO2 and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO2 conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO2 to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO2, and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO2 and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO2 conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate.