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.

Role of Some of Mineral Nutrients in Biological Nitrogen Fixation

Abstract: Atmospheric nitrogen fixation probably contributes at most about 10% of the total annual yield of fixed nitrogen. The most important source of fixed nitrogen derives from the activity of certain soil bacteria that absorb atmospheric N2 gas and convert it into ammonium. The process of biological nitrogen fixation offers an economical attractive and ecological advantage by of reducing external nitrogen input and improving the quality and quantity of internal resources. Mineral nutrients may influence N2 fixation in legumes and nonlegumes at various stages of the symbiotic process: infection and nodule development, nodule function, and host plant growth. Here, review the basic concepts of mineral nutrition, as well as the importance of mineral nutrients specifically for biological nitrogen fixation in the legume-rhizobia symbiosis. For healthy and vigorous growth, intact plants need to take up from the soil: relatively large amounts of some inorganic elements: ions of nitrogen (N), potassium (K), calcium (Ca), phosphorus (P) and sulphur (S); and, small quantities of other elements: iron (Fe), nickel (Ni), chlorine (Cl), manganese (Mn), zinc (Zn), boron (B), copper (Cu), and molybdenum (Mo). The enhancing effect of low levels of combined nitrogen on N2 fixation in legumes is related to the lag phase between root infection and the onset of N2 fixation. Phosphorus (P) is second only to nitrogen as an essential mineral fertilizer for crop production. At any given time, a substantial component of soil P is in the form of poorly soluble mineral phosphates. A high phosphorus supply is needed for nodulation. When legumes dependent on symbiotic nitrogen receive an inadequate supply of phosphorus, they may therefore also suffer from nitrogen deficiency. Potassium and sulphur are not usually limiting nutrients for nodulated legumes, although a K+ supplement for osmoadaptation has to be considered for growth in saline soils. Among mineral nutrients, B and Ca are undoubtedly the nutrients with a major effect on legume symbiosis. Both nodulation and nitrogen fixation depend on B and Ca2+, with calcium more necessary for early symbiotic events and B for nodule maturation.

Nitrogen fixation by the verrucomicrobial methanotroph ‘Methylacidiphilum fumariolicum’ SolV

Abstract: The ability to utilize atmospheric nitrogen (N2) as a sole nitrogen source is an important trait for prokaryotes. Knowledge of N2 fixation by methanotrophs is needed to understand their role in nitrogen cycling in different environments. The verrucomicrobial methanotroph ‘Methylacidiphilum fumariolicum’ strain SolV was investigated for its ability to fix N2. Physiological studies were combined with nitrogenase activity measurements and phylogenetic analysis of the nifDHK genes, encoding the subunits of the nitrogenase. ‘M. fumariolicum’ SolV was able to fix N2 at low oxygen (O2) concentration (0.5 %, v/v) in chemostat cultures. This low oxygen concentration was also required for an optimal nitrogenase activity [47.4 nmol ethylene h−1 (mg cell dry weight)−1]. Based on acetylene reduction assay and growth experiments, the nitrogenase of strain SolV seems to be extremely oxygen sensitive compared to most proteobacterial methanotrophs. The activity of the nitrogenase was not inhibited by ammonium concentrations up to 94 mM. This is believed to be the first report on the physiology of N2 fixation within the phylum Verrucomicrobia.

Non-symbiotic nitrogen fixation in the rhizospheres of rice, maize and different tropical grasses

Abstract: Nitrogenase activity estimated in the rhizospheres of rice, maize and different tropical grasses grown under controlled laboratory conditions was shown to depend upon plant species. High nitrogenase activity (2000–6000 nmoles C 2 H 4 h −1 g −1 dry root) occurred in rice rhizosphere, this activity being only 10 times lower than that of symbiotic systems; in the rhizosphere of many other grasses grown in a similar way nitrogenase activity was as low as 10 nmoles C 2 H 4 h −1 g −1 dry root. The influence of soil type on nitrogenase activity was impressive; but the exact nature of the factors implicated could not be established. A rather weak flush of nitrogenase activity in the rhizosphere occurred in the early stage of the plant growth; it was probably due to the exudation of compounds from the seed and lasted 2 or 4 days according to the size of the seed. When the plant entered into its intense photosynthetic phase, the nitrogenase activity gradually increased. When the shoots were severed, nitrogenase activity in the rhizosphere ceased. Nitrogenase activity in the rhizosphere responded greatly to light intensity. Extrapolation of these laboratory findings to the field is discussed.

Nitrogen Isotope Distribution as a Presumptive Indicator of Nitrogen Fixation

Abstract: The generally lower 15N/14N ratio of nitrogen-fixing organisms provides an opportunity to screen mixed populations for individuals fixing nitrogen. Samplings of associated California native species, along with the soil on which they were found, show differences in 15N/14N ratios suggesting a capability among some for the fixation of nitrogen. Not all suspected fixers were depleted in 15N, and two saprophytes had significant 15N enrichment. The method shows some promise, but further understanding of fractionation processes is needed before the method can be generally applied.

Exploring the alternatives of biological nitrogen fixation

Abstract: Most biological nitrogen fixation (BNF) results from the activity of the molybdenum nitrogenase (Mo-nitrogenase, Nif), an oxygen-sensitive metalloenzyme complex found in all known diazotrophs. Two alternative forms of nitrogenase, the vanadium nitrogenase (V-nitrogenase, Vnf) and the iron-only nitrogenase (Fe-only nitrogenase, Anf) have also been identified in the genome of some organisms that encode for Nif. It has been suggested that alternative nitrogenases were responsible for N2-fixation on early Earth because oceans were depleted of bioavailable Mo. Results of recent phylogenetic- and structure-based studies suggest, however, that such an evolutionary path is unlikely, and favor a new model for a stepwise evolution of nitrogenase where the V-nitrogenase and the Fe-only nitrogenase are not the ancestor of the Mo-nitrogenase. Rather, Mo-nitrogenase emerged within the methanogenic archaea and then gave rise to the alternative forms suggesting they arose later in response to the availability of fixed N2 and local environmental factors that influenced metal availability. This review summarizes the current state of knowledge on (1) the biochemistry of these complex systems highlighting the common and specific structural features and catalytic activities of the enzymes, (2) the recent progress in defining the discrete set of genes associated to N2-fixation and the regulatory features that coordinate the differential expression of genes in response to metal availability, and (3) the diverse taxonomic and phylogenic distribution of nitrogenase enzymes and the evolutionary history of BNF from the perspective of metal content and metal availability.