NITROGE CYCLE (Gaseous Cycle)
◇ Apart from carbon, hydrogen and oxygen, nitrogen is the most prevalent element in living organisms.
◇ Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls and many vitamins.
◇ Plants compete with microbes for the limited nitrogen that is available in the soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
◇ Nitrogen exists as two nitrogen atoms (N2) joined by a very strong triple covalent bond (N ≡ N).
◇ In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O).
◇ Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.