Although there is 34,500 tons of gaseous nitrogen in the air column above each acre of the earth's surface, this cannot be used by plants until it has been fixed by nitrogen-fixing bacteria and algae.

There was a negative correlation between the nitrogenase activities of nitrogen fixing bacteria in root and that in leaf and stem.

Symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate the formation of root nodules, enlargements of plant cells and bacteria in close association.