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-fixingbacteria and algae.
Symbiotic nitrogen-fixingbacteria 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.
共生的固氮菌侵袭宿主植物的根毛，并在此繁殖和促进根瘤的形成、植物细胞和亲密共生细菌的扩大。
3
There was a negative correlation between the nitrogenase activities of nitrogenfixingbacteria in root and that in leaf and stem.