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: The actual levels of N2 fixation attained by legume and non-legume associations are reviewed and their role as a source of N in tropical and sub-tropical agriculture is assessed.
Abstract: Inputs of biologically fixed N into agricultural systems may be derived from symbiotic relationships involving legumes and Rhizobium spp., partnerships between plants and Frankia spp. or cyanobacteria, or from non-symbiotic associations between free-living diazotrophs and plant roots. It is assumed that these N2-fixing systems will satisfy a large portion of their own N requirements from atmospheric N2, and that additional fixed N will be contributed to soil reserves for the benefit of other crops or forage species. This paper reviews the actual levels of N2 fixation attained by legume and non-legume associations and assesses their role as a source of N in tropical and sub-tropical agriculture. We discuss factors influencing N2 fixation and identify possible strategies for improving the amount of N2 fixed.
366 citations
TL;DR: The minor contribution by nitrogen fixation to the overall nitrogen economy of the sea is not consistent with the supposition that nitrogen is the primary limiting nutrient and suggests that factors other than nitrogen availability limit phytoplankton growth rates.
Abstract: Cyanobacteria of the genus Oscillatoria (Trichodesmium) account for annual inputs of nitrogen to the world's oceans of about 4.8 x 10(12) grams while benthic environments contribute 15 x 10(12) grams. The sum of these inputs is one-fifth of current estimates of nitrogen fixation in terrestrial environments and one-half of the present rate of industrial synthesis of ammonia. When the total of all nitrogen inputs to the sea is compared with estimated losses through denitrification, the marine nitrogen cycle approximates a steady state. Oceanic nitrogen fixation can supply less than 0.3 percent of the calculated demand of marine phytoplankton. The minor contribution by nitrogen fixation to the overall nitrogen economy of the sea is not consistent with the supposition that nitrogen is the primary limiting nutrient and suggests that factors other than nitrogen availability limit phytoplankton growth rates.
363 citations
TL;DR: The results suggest that in 75% of the global ocean, iron availability limits nitrogen fixation by Trichodesmium, and it is suggested that iron fluxes will be even more limiting in the coming century.
Abstract: Iron availability is suggested to be a primary factor limiting nitrogen fixation in the oceans. This hypothesis is principally based on cost‐benefit analyses of iron quotas in the dominant nitrogen-fixing cyanobacteria,Trichodesmium spp., in the contemporary oceans. Although previous studies with Trichodesmium have indicated that iron availability enhanced nitrogen fixation and photosynthesis, no clear relationship has been reported between cellular iron quotas and nitrogen fixation. We re-examined the proposed link between iron availability and nitrogen fixation in laboratory isolates and natural populations collected from coastal waters north of Australia. In laboratory cultures grown under iron-limiting conditions, we measured a decline in cellular iron quotas, photochemical quantum yields, the relative abundance of photosystem I to photosystem II reaction centers, and rates of nitrogen fixation. Nitrogen fixation displayed a critical threshold of the dissolved sum of total inorganic Fe species ([Fe 9]) of ca. log[Fe9] 52 9.7. Field populations of Trichodesmium, collected during bloom conditions, showed high iron quotas consistent with high nitrogen fixation rates. Using seasonal maps of aeolian iron fluxes and model-derived maps of surface water total dissolved Fe, we calculated the potential of nitrogen fixation by Trichodesmium in the global ocean. Our results suggest that in 75% of the global ocean, iron availability limits nitrogen fixation by this organism. Given present trends in the hydrological cycle, we suggest that iron fluxes will be even more limiting in the coming century.
362 citations
TL;DR: Roles for leghemoglobins in oxygen transport and buffering are indicated and proved for the first time that plant hemoglOBins are crucial for symbiotic nitrogen fixation.
357 citations
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357 citations