<P> The conversion of nitrogen gas ( N ) into nitrates and nitrites through atmospheric , industrial and biological processes is called nitrogen fixation . Atmospheric nitrogen must be processed , or `` fixed '' , into a usable form to be taken up by plants . Between 5x10 and 10x10 g per year are fixed by lightning strikes , but most fixation is done by free - living or symbiotic bacteria known as diazotrophs . These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia , which is converted by the bacteria into other organic compounds . Most biological nitrogen fixation occurs by the activity of Mo - nitrogenase , found in a wide variety of bacteria and some Archaea . Mo - nitrogenase is a complex two - component enzyme that has multiple metal - containing prosthetic groups . An example of free - living bacteria is Azotobacter . Symbiotic nitrogen - fixing bacteria such as Rhizobium usually live in the root nodules of legumes ( such as peas , alfalfa , and locust trees ) . Here they form a mutualistic relationship with the plant , producing ammonia in exchange for carbohydrates . Because of this relationship , legumes will often increase the nitrogen content of nitrogen - poor soils . A few non-legumes can also form such symbioses . Today , about 30 % of the total fixed nitrogen is produced industrially using the Haber - Bosch process , which uses high temperatures and pressures to convert nitrogen gas and a hydrogen source ( natural gas or petroleum ) into ammonia . </P>
<P> The conversion of nitrogen gas ( N ) into nitrates and nitrites through atmospheric , industrial and biological processes is called nitrogen fixation . Atmospheric nitrogen must be processed , or `` fixed '' , into a usable form to be taken up by plants . Between 5x10 and 10x10 g per year are fixed by lightning strikes , but most fixation is done by free - living or symbiotic bacteria known as diazotrophs . These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia , which is converted by the bacteria into other organic compounds . Most biological nitrogen fixation occurs by the activity of Mo - nitrogenase , found in a wide variety of bacteria and some Archaea . Mo - nitrogenase is a complex two - component enzyme that has multiple metal - containing prosthetic groups . An example of free - living bacteria is Azotobacter . Symbiotic nitrogen - fixing bacteria such as Rhizobium usually live in the root nodules of legumes ( such as peas , alfalfa , and locust trees ) . Here they form a mutualistic relationship with the plant , producing ammonia in exchange for carbohydrates . Because of this relationship , legumes will often increase the nitrogen content of nitrogen - poor soils . A few non-legumes can also form such symbioses . Today , about 30 % of the total fixed nitrogen is produced industrially using the Haber - Bosch process , which uses high temperatures and pressures to convert nitrogen gas and a hydrogen source ( natural gas or petroleum ) into ammonia . </P>
the microbes or bacteria which converts atmospheric nitrogen into nitrate in the soil is
the microbes or bacteria which converts atmospheric nitrogen into nitrate in the soil is
diazotrophs
diazotrophs