Nitrogen fixation is a key component of the nitrogen cycle, one of the most fundamental cycles in the biosphere. Conversion of atmospheric nitrogen into organic nitrogen compounds can be carried out only by certain bacteria and blue-green algae (cyanobacteria). Some nitrogen fixing bacteria live symbiotically with leguminous plants such as peas, beans, clover, and certain tropical trees in nodules on the plants' roots, while others live independently in the soil and aquatic habitats. By the activity of these microorganisms, the soil is enriched with the nitrogen required for plant growth and...