how do plants fulfill the requirement of nitrogen from the atmospere?explain.
Plants cannot utilise nitrogen directly available in atmosphere because nitrogen is an inert element. Nitrogen requirement of plants is fulfilled by nitrogen fixing bacteria. Atmospheric nitrogen is converted to ammonium ion by some bacteria which can by used by the plants. While some of these microorganisms are free-living in soil and water, others exist in a symbiotic association with plants. The process of converting atmospheric nitrogen into ammonium by microorganisms is called nitrogen fixation. The Rhizobium bacteria, form root nodules in most leguminous plants. The bacteria in the root nodules help in fixation of atmospheric nitrogen and help in plant growth. Some nitrogen is also left behind in the soil that may be used by the crops of next season. The carbon requirement of the bacteria is taken care of by the host plant. In other plants including some grasses, the nitrogen fixing bacteria stay close to the roots. The organic matter present in the soil is used by Azotobacter to fix nitrogen. Azospirillum is associated with the roots and functions to fix nitrogen.