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.

Symbiotic specificity of tropical tree rhizobia for host legumes

Abstract: Summary • The host range and specificity is reported of a genetically diverse group of rhizobia isolated from nodules of Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban. • Nodule number and nitrogen content was measured in seedlings of herbaceous and woody legume species after inoculation with rhizobial strains isolated from tropical soils, to establish symbiotic effectiveness groups for rhizobial strains and their hosts. • Specificity for nodulation and N2 fixation varied greatly among the legumes. Symbionts of all four legumes exhibited a wide range of promiscuity and symbiotic effectiveness with isolates of S. sesban having the narrowest host range. N2 fixation varied greatly; although some strains fixed large amounts of N2 with more than one host, none was effective with all hosts. Rhizobial isolates of C. calothyrsus, G. sepium and L. leucocephala were able to effectively cross-nodulate each others’ hosts as well as a number of other species. • The complex nature of cross-nodulation relationships between diverse rhizobial strains and legume hosts is highlighted. Host plants inoculated with effective rhizobial strains showed better nitrogen use efficiency than plants supplied solely with mineral nitrogen.

Regulation of nitrogen-fixation by different nitrogen sources in the marine non-heterocystous cyanobacterium Trichodesmium sp. NIBB1067

Abstract: The effect of various nitrogen sources on the synthesis and activity of nitrogenase was studied in the marine, non-heterocystous cyanobacterium Trichodesmium sp. NIBB1067 grown under defined culture conditions. Cells grown with N2 as the sole inorganic nitrogen source showed light-dependent nitrogenase activity (acetylene reduction). Nitrogenase activity in cells grown on N2 was not suppressed after 7 h incubation with 2 mM NaNO3 or 0.02 mM NH4Cl. However, after 3 h of exposure to 0.5 mM of urea, nitrogenase was inactivated. Cells grown in medium containing 2 mM NaNO3, 0.5 mM urea or 0.02 mM NH4Cl completely lacked the ability to reduce acetylene. Western immunoblots tested with polyclonal antisera against the Fe-protein and the Mo−Fe protein, revealed the following: (1) both the Fe-protein and the Mo−Fe protein were synthesized in cells grown with N2 as well as in cells grown with NaNO3 or low concentration of NH4Cl; (2) two bands (apparent molecular mass of 38 000 and 40 000) which cross-reacted with the antiserum to the Fe-protein, were found in nitrogen-fixing cells; (3) only one protein band, corresponding to the high molecular mass form of the Fe-protein, was found in cells grown with NaNO3 or low concentration of NH4Cl; (4) neither the Fe-protein nor the Mo−Fe protein was found in cells grown with urea; (5) the apparent molecular mass of the Fe-protein of Trichodesmium sp. NIBB1067 was about 5000 dalton higher than that of the heterocystous cyanobacterium, Anabaena cylindrica IAM-M1.

Influence of different Sinorhizobium meliloti inocula on abundance of genes involved in nitrogen transformations in the rhizosphere of alfalfa (Medicago sativa L.)

Abstract: Summary Inoculation of leguminous seeds with selected rhizobial strains is practised in agriculture to ameliorate the plant yield by enhanced root nodulation and nitrogen uptake of the plant. However, effective symbiosis between legumes and rhizobia does not only depend on the capacity of nitrogen fixation but also on the entire nitrogen turnover in the rhizosphere. We investigated the influence of seed inoculation with two indigenous Sinorhizobium meliloti strains exhibiting different efficiency concerning plant growth promotion on nitrogen turnover processes in the rhizosphere during the growth of alfalfa. Quantification of six target genes (bacterial amoA, nirK, nirS, nosZ, nifH and archaeal amoA) within the nitrogen cycle was performed in rhizosphere samples before nodule formation, at bud development and at the late flowering stage. The results clearly demonstrated that effectiveness of rhizobial inocula is related to abundance of nifH genes in the late flowering phase of alfalfa. Moreover, other genes involved in nitrogen turnover had been affected by the inocula, e.g. higher numbers of amoA copies were observed during flowering when the more effective strain had been inoculated. However, the respective gene abundances differed overall to a greater extent between the three plant development stages than between the inoculation variants.

Soybean nodulation and nitrogen fixation in response to soil compaction and surface straw mulching

Abstract: Soil compaction affects nodulation and nitrogen fixation of soybean (Glycine max (L.) Merr.). The effects of compaction can be mediated by straw mulch applied at soil surface. To test these hypotheses a field experiment was carried out in 2008 on a Haplic Luvisol (south-eastern Poland). We grew soybean in treatments with different soil compaction levels: non-compacted (NC), moderately compacted (MC) (3 tractor passes) and strongly compacted soil (SC) (5 tractor passes). Each compaction level had treatments without and with surface chopped straw mulch at the rate of 0.5 kg m−2. Nodulation was evaluated by measurements of nodule-size distribution, number, weight, and diameter of nodules and symbiotic nitrogen fixation – by measurement of nitrogenase activity, nitrogen content in leaves, protein content in seeds and seed yield. Soil measurements included bulk density and nitrogen content in the form of N-NO3 and N-NH4. In general, nitrogenase activity decreased with increasing soil compaction level. At every compaction level, the nitrogenase activity was higher in the mulched when compared to the unmulched soil. Soil compaction and mulching enhanced the contribution of large nodules, those greater than 0.41 cm and dry weight of individual nodules. Total nodule number and weight decreased in sequence: moderately, strongly and non-compacted soil. Mulch influenced nitrogenase activity and nodulation to a higher extent than compaction. An optimum soybean response in terms of seed and protein yields was observed under mulched MC and the worst – under unmulched SC. Both N content in leaves and nitrate content in soil were lower in mulched than in unmulched soil, irrespective of compaction. Bulk density and N-NO3 increased with soil compaction level and N-NH4 remained nearly unchanged. Therefore, our results supported the hypotheses that soil compaction affects nodulation and nitrogen fixation, and that compaction can be mediated by straw mulch. Further studies are needed to assess variability related with different soil and weather conditions.