... ? 2NH + H 16ADP + 16Pi Often the nitrogen fixers live in close association with a specific eukaryotic organism. Although their biomass is small their role in the biosphere is just as important as that of the photosynthetic autotrophs fixing ninety million tons of gaseous nitrogen per year (Jones, 1997). Various photosynthetic bacteria, including Cyanobacteria are the main nitrogen fixers. On land most nitrogen fixation comes from the bacteria associated with the formation of root nodules in certain plants with free-living soil bacteria making only a small contribution. Some bacteria belonging to the genus Rhizobium live in close association with the roots of leguminous seed plants such as peas, soybeans and alfalfa. These bacteria are normally free-living in the soil but when they are close to the root of a legume they infect it. They invade the root hairs and cause the production of an infection thread in the root ...

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