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: Nitrogen fixation activity appeared to be inversely related to the ability of shipworms to obtain combined-nitrogen compounds in their diet, and could be a significant source of nitrogen for shipwornms and perhaps other oceanic organisms that ingest terrestrial plant material.
Abstract: Nitrogen fixation is associated with four shipworl species A bacterium capable of fixing nitrogen under anaerobic conditions and of liquefying cellulose in culture has been isolated from the gut of one species High fixation rates (up to 15 micrograms of nitrogen per milligram dry weight per hour), which resulted in a doubling of cellular nitrogen in as little as 14 days, was associated with Teredora malleolus from the Sargasso Sea Three species from coastal waters were assayed, and of these juveniles showed the highest fixation rates Nitrogen fixation activity appeared to be inversely related to the ability of shipworms to obtain combined-nitrogen compounds in their diet It could be a significant source of nitrogen for shipwornms and perhaps other oceanic organisms that ingest terrestrial plant material
69 citations
TL;DR: Using reported and estimated crop yield and protein concentration with published estimates of soil N mineralization and atmospheric N deposition, spatial patterns of symbiotic N 2 fixation for soybean and alfalfa are estimated across the Mississippi River Basin, the largest in North America.
Abstract: Human activities have increased the amount of earth's reactive N, resulting in significant improvements in crop yield and animal production but also in environmental degradation and ecosystem disruption in some areas. For example, agriculture has been cited as a major source of N that contributes to hypoxia in the Gulf of Mexico. Although other sources of N have been well characterized in large ecosystem studies, the contribution of legume crops to the N cycle has not. Furthermore, the role legumes play in reducing excess N is not widely recognized. Symbiotic N 2 fixation is a facultative process that is reduced by plant N uptake from other sources. Using reported and estimated crop yield and protein concentration with published estimates of soil N mineralization and atmospheric N deposition, we estimated spatial patterns of symbiotic N 2 fixation for soybean [Glycine max (L.) Merr.] and alfalfa (Medicago sativa L.) across the Mississippi River Basin, the largest in North America. We estimate that alfalfa haylage adds about 20% to total production of dry alfalfa hay and increases total land area in alfalfa by about 11% over that reported in the Census of Agriculture. Our analysis shows wide ranges in N 2 fixation (0 to 185 kg N ha -1 for soybean and 45 to 470 kg N ha ' for alfalfa), reasonable mean rates (84 kg N ha -1 for soybean and 152 kg N ha -1 for alfalfa), and suggests that about 2.9 million Mg of fixed N is harvested annually in these two cultivated legumes.
69 citations
TL;DR: Nitrite, the product of bacteroid nitrate reductase, may not play a role in the inhibitory effect of nitrate on nitrogen fixation activities of legume root nodules, but the degree of inhibition on the fixation activity by nitrate varied in different legume-Rhizobium combinations.
Abstract: The effect of nitrate on symbiotic nitrogen fixation by root nodules of cowpea (Vigna unguiculata L., Walp., cv. California Blackeye) and lupine (Lupinus augustifolius L., cv. Frost) plants inoculated with nitrate reductase-expressing and nitrate reductase-nonexpressing Rhizobium strains were examined. Nitrate reductase of Rhizobium bacteroids in the nodules of cowpea and lupine reduced nitrate to nitrite. Both cowpea and lupine nodules accumulated nitrite when grown in the presence of 15 millimolar nitrate and induced by Rhizobium strains which express nitrate reductase activity (Rhizobium sp. 32H1 and 127E15). The nitrogen fixation (acetylene reduction) activities of cowpea and lupine nodules were inhibited by nitrate whether the nodules were induced by Rhizobium strains that express (Rhizobium sp. 32H1 and 127E15) or do not express (Rhizobium sp. 127E14 and R. lupini ATCC 10318) nitrate reductase activity. These findings indicate that nitrite, the product of bacteroid nitrate reductase, may not play a role in the inhibitory effect of nitrate on nitrogen fixation activities of legume root nodules. However, the degree of inhibition on the fixation activity by nitrate varied in different legume-Rhizobium combinations.
69 citations
TL;DR: The results were so clear-cut that it appeared likely that more conventional procedures using growing cultures on a low-nitrogen medium with a light inoculum and analysis by the Kjeldahl method would readily detect fixation by this organism, and independent tests have confirmed this prediction.
Abstract: The results from a series of studies concerned with the influence of molecular hydrogen on biological nitrogen fixation (Wilson, 1940) led to the suggestion that hydrogenase, the enzyme activating H2, was associated in some way with the nitrogen-fixing enzyme system. Although obscure in the symbiotic combination of leguminous plant and Rhizobium (Wilson, Burris, and Coffee, 1943), the association was so noteworthy with Azotobacter that it suggested that any organism possessing hydrogenase might be a potential nitrogen fixer. At that time we tested three organisms using N5 as a tracer: Escherichia coli; Proteus vulgaris, Hoberman's (1942) strain that catalyzes the hydrogen-exchange reaction; and Scenedesmus, Gaffron's (1944) strain that, with appropriate treatment, switches from photosynthesis to photoreduction. This limited survey revealed no new nitrogen-fixing agents, but recently Gest and Kamen (1949a,b) and Kamen and Gest (1949) have provided a most interesting example in Rhodospirillum rubrum, a nonsulfur purple bacterium. Because of the significance of their findings, we undertook to check their more important observations. On their invitation2 we first made a joint experiment testing the ability of a heavy suspension of the organism to fix N'5. The results were so clear-cut that it appeared likely that more conventional procedures using growing cultures on a low-nitrogen medium with a light inoculum and analysis by the Kjeldahl method would readily detect fixation by this organism. Independent tests in our three laboratories have confirmed this prediction. The results from typical experiments are summarized in table 1. The medium consisted of KH2P04, 2.0 g; MgSO4c7H20, 0.2 g; DL-malic acid, 3.5 g; Difco yeast extract, 0.2 g; biotin, 20 ,ug; trace metals (plus Mo) according to Hutner (1946); distilled water to 1 liter after the pH was brought to 7 with 6 N KOH. The inoculum was 2 per cent by volume of a culture grown on a similar medium (0.8 g sodium citrate added and the quantity of yeast extract doubled). Incubation was from 3 to 6 days at 25 C. Light was from a 200-watt mazda bulb about 30 inches from the cultures. Accompanying growth of the organism was an increase in alkalinity, but the pH seldom exceeded 8.0 at harvest. Little or no growth was noted anaerobically in the dark; aerobically, both in dark and light, growth was definite but apparently restricted to the combined nitrogen
69 citations