Raheema Javed
Last Activity: 9 Years ago
Nitrogen-fixing bacteriaare microorganisms present in the soil or in plant roots that change nitrogen gases from the atmosphere into solid nitrogen compounds that plants can use in the soil. That's a mouthful! Let's break this concept down.
Two kinds of nitrogen-fixingbacteriaare recognized: free-living (non-symbiotic) bacteria, including thecyanobacteria(or blue-green algae)AnabaenaandNostocand genera such asAzotobacter,Beijerinckia, andClostridium; and mutualistic (symbiotic) bacteria such asRhizobium, associated with leguminous plants (e.g., various members of thepea family), and certainAzospirillumspecies, associated with cereal grasses.
The symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules the bacteria convert free nitrogen toammonia, which the host plant utilizes for its development. To ensure sufficient nodule formation and optimum growth oflegumes(e.g., alfalfa, beans, clovers, peas, soybeans), seeds are usually inoculated with commercial cultures of appropriateRhizobiumspecies, especially insoilspoor or lacking in the required bacterium.