- Nitrogen Fixation by Bacteria – Converting inert atmospheric nitrogen (N2)into biologically available forms such as ammonia (NH3), nitrates, or nitrites
- Nitrification by Bacteria – Converting ammonia to nitrite and then to nitrate
- Assimilation by Plants – Absorbing nitrogen from the soil and incorporating them in the plant and animal bodies
- Ammonification by Decomposers – Converting the dead organic nitrogen of plants or animals back into ammonia
- Denitrification by Denitrifiers – Reducingnitrates or nitrites and releasing gaseous nitrogen What role do bacteria play in the nitrogen cycle? Nitrogen fixation – Performed by two different groups of bacteria – a) symbiotic nitrogen fixers like Rhizobium, which keep a close association with the host leguminous plant, and b) free-living, non-symbiotic bacteria like Azotobacter. Both these group of bacteria use specific enzymes to complete the biological nitrogen fixation process by the following reaction – N2 + 8 H+ + 8 e− → 2 NH3 + H2 Nitrification – Performed by nitrifying bacteria in two steps – i) Ammonia-oxidizing bacteria such as Nitrosomonas species perform oxidation of ammonia to nitrite by the following reaction – 2NH4+ + 3O2 + 8 e− → 2 NO2– + 4H2 + 2H2O ii) Nitrite-oxidizing bacteria such as Nitrobacter species perform oxidation of nitrite (NO2–) to nitrate (NO3–) by the following reaction – 2 NO3– + O2 → 2 NO3–
Burning of Fossil FuelsUse of Nitrogen-Containing Fertilizers
