Ninety percent of the earth's fixed nitrogen is produced by biological fixation each year. Fixation requires energy and is summed up by the following two chemical equations. 2 NH 3 These chemical processes are performed by mutualistic bacteria that generally live on the roots of plants, as well as cyanobacteria and some free living bacteria. These amino acids are then oxidized to form water, carbon dioxide, and ammonia. The ammonia plays an important role in the ecosystem, including being absorbed into plant roots, and passing through the food chain.
Nitrification involves the oxidation of ammonia into nitrate and nitrite, giving off energy.
Two types of bacteria, nitrosomonas and nitrobacters, use nitrates and nitrites respectively as energy sources. Denitrification is the reduction of nitrates to gaseous N 2 by fungi and certain bacteria which are facultative anaerobes. These are organisms which in the absence of oxygen will use nitrates as a hydrogen acceptor, thereby releasing N 2 into the atmosphere.