The answer is nitrogen-fixing bacteria.
Plants
are not able to directly use atmospheric nitrogen. It must be converted into different
form through a nitrogen cycle. In the process of nitrogen
fixation, nitrogen fixing bacteria converts atmospheric nitrogen into
ammonium. In the process of assimilation, plants incorporate
ammonium into proteins.
Some legumes have a symbiotic relationship with bacteria that
live in their root system. These bacteria are called Rhizobia and have
the ability of nitrogen-fixation.
