NITROGEN FIXATION

The conversion of elemental nitrogen in the atmosphere (N2) to a reduced form (e.g., ammonia and amino groups of amino acids) that can be used as a nitrogen source by organisms. The process is important since all organisms require a source of nitrogen for nutrition, and N2 cannot be used by the great majority of the biota to satisfy that need. Biological nitrogen fixation is carried out by a variety of organisms; however, those responsible for most of the fixation are certain species of bluegreen algae, the soil bacterium Azotobacter, and the symbiotic association of plants of the legume variety and the bacterium Rhizobium.