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.

Micronutrient effects on cyanobacterial growth and physiology

Abstract: Trace metals play crucial roles in the carbon and nitrogen metabolism of cyanobacteria. Physiological responses to metal limitation and toxicity in culture have shown that iron is important for photosynthesis and energy distribution in the cell while both iron and molybdenum are biochemically involved in nitrate reduction and nitrogen fixation. Nitrogen fixation is also relatively sensitive to copper toxicity. Consequently, factors that affect the supply rate, chemical speciation, or the recycling of trace metals can alter patterns of primary productivity and nitrogen metabolism. Overall, three trace metal dependent processes may contribute towards dominance: efficient use of limiting light, nitrogen fixation, and production of extracellular iron binding compounds.

Elevated atmospheric CO2 and increased nitrogen deposition: effects on C and N metabolism and growth of the peat moss Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) Warnst

Abstract: Sphagnum bogs play an important role when considering the impacts of global change on global carbon and nitrogen cycles. Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) was grown at 360 (ambient) and 700 mu L L-1 (elevated) atmospheric [CO2] in combination with different nitrogen deposition rates (6, 15, 23 g N m(-2) y(-1)), in a short- and long-term growth chamber experiment. After 6 months, elevated atmospheric [CO2] in combination with the lowest nitrogen deposition rate, increased plant dry mass by 17%. In combination with a high nitrogen deposition rate, biomass production was not significantly stimulated. At the start of the experiment, photosynthesis was stimulated by elevated atmospheric [CO2], but it was downregulated to control levels after three days of exposure. Elevated [CO2] substantially reduced dark respiration, which resulted in a continuous increase in soluble sugar content in capitula. Differences in growth response among different nitrogen and CO2 treatments could not be related to measured carbon exchange rates, which was mainly due to interference of microbial respiration. Doubling atmospheric [CO2] reduced total nitrogen content in capitula but not in stems at all nitrogen deposition rates. Reduction in total nitrogen content coincided with a decrease in amino acids, but soluble protein levels remained unaffected. Thus, elevated [CO2] induced a substantial shift in the partitioning of nitrogen compounds in capitula. Soluble sugar concentration was negatively correlated with total nitrogen content, which implies that the reduction in amino acid content in capitula, exposed to elevated [CO2], might be caused by the accumulation of soluble sugars. Growth was not stimulated by increased nitrogen deposition. High nitrogen deposition, resulting in a capitulum nitrogen content in excess of 15 mg g(-1) dw, was detrimental to photosynthesis, reduced water content and induced necrosis. We propose a capitulum nitrogen content of 15 mg g(-1) dw as a possible bioindicator for the detection of nitrogen pollution stress in oligo-mesotrophic peat bog ecosystems. At the lowest nitrogen deposition level, nitrogen recovery was higher than 100%, which indicates substantial dry deposition and/or gaseous nitrogen fixation by bacteria, associated with Sphagnum. Increasing nitrogen deposition rates decreased nitrogen recovery percentages, which indicates reduced efficiency of nitrogen fixation.

Biological Nitrogen Fixation

Abstract: INTRODUCTION 263 DEREPRESSION OF THE NIF GENES 264 ENERGY COST OF N, FIXATION 266 Nitrogenase-Catalyzed H2 Evolution 267 Apparent ATP Requirement 268

The evolution of nitrogen fixation in cyanobacteria

Abstract: Motivation: Fixed nitrogen is an essential requirement for the biosynthesis of cellular nitrogenous compounds. Some cyanobacteria can fix nitrogen, contributing significantly to the nitrogen cycle, agriculture and biogeochemical history of Earth. The rate and position on the species phylogeny of gains and losses of this ability, as well as of the underlying nif genes, are controversial. Results: We use probabilistic models of trait evolution to investigate the presence and absence of cyanobacterial nitrogen-fixing ability. We estimate rates of change on the species phylogeny, pinpoint probable changes and reconstruct the state and nif gene complement of the ancestor. Our results are consistent with a nitrogen-fixing cyanobacterial ancestor, repeated loss of nitrogen fixation and vertical descent, with little horizontal transfer of the genes involved. Contact: db60@st-andrews.ac.uk Supplementary information: Supplementary data are available at Bioinformatics online.

Effect of rhizobia and soil nitrate on the establishment and functioning of the soybean symbiosis in the field

Abstract: The symbiosis of the root-nodules of Bragg soybean [Glycine max (L.) Merrill] and the relative dependence of the plants on symbiotic and soil sources of N were evaluated in an experiment conducted on a vertisol which was high in organic- and mineral-N, free of Rhizobium japonicum, and where poor nodulation was characteristic of inoculated, new sowings. Effective inoculant containing R. japonicum strain CB 1809 was sprayed into the seed bed at three rates of application (10-fold intervals). Increasing rates of inoculant led to greater numbers of rhizobia in the rhizosphere and in the soil, and to improved nodulation. Uninoculated plants did not nodulate. High soil NO-3 (30 ¦g N/g, top 30 cm) did not prevent prompt, abundant colonization of rhizospheres by the bacteria from the inoculant, but nodule initiation was delayed and nodule development was retarded until 42 days after sowing. There was an acceleration in nodule formation and development between 42 and 62 days which coincided with a depletion of NO-3 from the top 60 cm of the soil profile. Nodulated and unnodulated soybeans took up NO-3 at similar times and rates to a soil depth of 90 cm; only unnodulated plants utilized soil NO-3 below 90 cm. Vacuum-extracted stem (xylem) exudate was sampled from plants throughout growth and analysed for nitrogenous solutes. The proportion of ureide-N relative to total-solutes-N in xylem sap was used as an index of symbiotic N2-fixation. The initial increase in concentrations of ureides coincided with the period of accelerated nodule formation and development between 42 and 62 days. Thereafter, there was a progressive increase in ureide concentrations in nodulated plants, and the levels were related to rate of inoculation, extent of nodulation, and to the decline in concentrations of soil NO-3. Ureide concentrations in unnodulated plants remained low throughout. The quantities of NO-3-N and s-NH2- N in xylem sap were not related to nodulation. The differences between treatments in terms of whole-plant N and grain N were less than predicted from the symbiotic parameters. This indicated that soybeans compensated for symbiotic deficiencies by more efficient exploitation of soil N and/or by more efficient redistribution of vegetative N into grain N, and that nodulation and soil NO-3 were interactive and complementary in meeting the N requirements of the crop.