An intimate relationship between a plant and a microorganism
Nitrogen is one of the elements essential to life since it is present in DNA (the blueprint of life) as well as in proteins (cell constituents characteristic of every living being). In gaseous form, nitrogen constitutes 79 % of the atmosphere but most living creatures cannot assimilate it. However, certain bacteria, present in soil, can chemically reduce atmospheric nitrogen (N2). The bacteria transform nitrogen into ammonia which can be assimilated by plants and which can then circulate up the food chain from plants to herbivores and from herbivores to carnivores. A few legumes and certain shrubs, such as the specked alder, have developed symbiotic relationships with these microorganisms (e.g., Rhizobium leguminosarum). They provide them with sugars and carbohydrates and receive, in return, the nitrogen required for their metabolism.