Topic
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.
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TL;DR: Estimates of transfer of atmospheric derived nitrogen from clover to grass obtained by the natural 15N abundance method were consistently higher than those obtained byThe enriched 15N dilution method, which showed that application of 400 kg N ha-1 significantly reduced dinitrogen fixation, while cutting frequency had no effect.
Abstract: A plant mixture of white clover (Trifolium repens L.), red clover (Trifolium pratense L.), and ryegrass (Lolium perenne L.) was established in the spring of 1991 under a cover-crop of barley. Treatments were two levels of nitrogen (400 and 20 kg N ha-1) and two cutting intensities (3 and 6 cuts per season). Fixation of atmospheric derived nitrogen was estimated by two 15N dilution methods, one based on application of 15N to the soil, the other utilising small differences in natural abundance of 15N.
124 citations
123 citations
TL;DR: It is reported that Phaseolus vulgaris bean seeds naturally carry rhizobia on their testa, which could provide an explanation for bacterial geographical spread and with an improved procedure to detect rhzobia on seeds, it is found that 5 out of 13 Phaseolu vulgarisbean cultivars tested harbor rhizophobia on the seeds.
123 citations
TL;DR: It was concluded that although the grasses recovered different quantities of labelled N, they all obtained virtually the same 15N enrichment in soil derived N.
Abstract: Six pasture grasses, Paspalum notatum cv batatais, P. notatum cv pensacola, Brachiaria radicans, B. ruziziensis, B. decumbens and B. humidicola, were grown in concrete cylinders (60 cm diameter) in the field for 31 months. The soil was amended with either a single addition of 15N labelled organic matter or frequent small (2 kg N. ha-1) additions of 15N enriched (NH4)2SO4. In the labelled fertilizer treatment soil analysis revealed that there was a very drastic change in 15N enrichment in plant-available nitrogen ( 3 - + NH 4 - with depth. The different grass cultivars recovered different quantities of applied labelled N, and evidence was obtained to suggest that the roots exploited the soil to different depths thus obtaining different 15N enrichments in soil derived N. This invalidated the application of the isotope dilution technique to estimate the contribution of nitrogen fixation to the grass cultivars in this treatment. In the labelled organic matter treatment the 15N label in the plant-available N declined at a decreasing rate during the experiment until in the last 12 months the decrease was only from 0.274 to 0.222 atom % excess. There was little change in 15N enrichment of available N with depth, hence it was concluded that although the grasses recovered different quantities of labelled N, they all obtained virtually the same 15N enrichment in soil derived N. Data from the final harvests of this treatment indicated that B. humidicola and B. decumbens obtained 30 and 40% respectively of their nitrogen from N2 fixation amounting to an input of 30 and 45 kg N.ha-1 year-1 respectively.
123 citations
TL;DR: The overall results support the view that, under drought conditions, nitrogen fixation activity in nodules was depressed because demand for fixed N to support growth was lower.
Abstract: Soybean plants [Glycine max (L.) Merr.] were grown in silica sand and were drought stressed for a 4 week period during reproductive development and without any mineral N supply in order to maximize demand for fixed nitrogen. A strain of Bradyrhizobium japonicum that forms large quantities of polysaccharide in nodules was used to determine whether or not the supply of reduced carbon to bacteroids limits nitrogenase activity. A depression of 30-40% in nitrogen content in leaves and pods of stressed plants indicated a marked decline in nitrogen fixation activity during the drought period. A 50% increase in the accumulation of bacterial polysaccharide in nodules accompanied this major decrease in nitrogen fixation activity and this result indicates that the negative impact of drought on nodules was not due to a depression of carbon supply to bacteroids. The drought treatment resulted in a statistically significant increase in N concentration in leaves and pods. Because N concentration and chlorophyll concentration in leaves were not depressed, there was no evidence of nitrogen deficiency in drought-stressed plants, and this result indicates that the negative impact of drought on nodule function was not the cause of the depression of shoot growth. At the end of the drought period, the concentration of carbohydrates, amino nitrogen, and ureides was significantly increased in nodules on drought-stressed plants. The overall results support the view that, under drought conditions, nitrogen fixation activity in nodules was depressed because demand for fixed N to support growth was lower.
123 citations