This article provides a flow diagram of the nitrogen cycle.
Nitrogen is one of the very important elements in biosphere. It remains in various forms in different environmental components, viz., as gases N2 and NOx; as ions in soil and water NO3, NO2, NH4+, or as organic material or insoluble nitrogenous materials Among these, atmosphere possesses 78% of nitrogen (by volume).
Even though atmosphere has such a high amount of nitrogen, the growth of many organisms is limited by a shortage of nitrogen 1 his shortage occurs because very few organisms can utilize the atmospheric nitrogen (N7) directly. Most plants can absorb this vital nutrient only when it is in the form of nitrites (NO-) nitrates (NOJ) or ammonium ions (NH4+).
Only some selected bacteria-cither in symbiotic or free living state-fix atmospheric nitrogen to NH3 and then utilize the same for amino acid biosynthesis. The animals obtained the nitrogen from-plants as food materials.
The organic nitrogen thus available as extra from plants and animals or dead remains of organisms is decomposed, which may release N2 gas, NOx gas, NO3 or NO2 or NH4+ions. Various processes are thus involved in such cycling of nitrogen from environmental components to biological communities (Fig. 5.21).