Because through them plants are able to supply their nitrogen needs and provide this element to humans and other animals whose nitrogen is essential.
Explanation:
Biological nitrogen fixation (BNF) is considered, after photosynthesis, the most important biological process on the planet. It is based on the fact that some microorganisms, known as diazotrophic, are able to break the bond that joins the two atoms of atmospheric nitrogen (N2) into ammonia (NH3), which is assimilable by plants. If the association between these microorganisms and plants is efficient, the fixed N can supply the needs of the plant, eliminating the use of nitrogen fertilizers and thus offering economic and ecological advantages. In addition, through food, plants provide nitrogen to humans and other animals.
