1. Nitrogen cycle : This consiss of following steps,
Nitrogen fixation.
(i) Di-= nitrogen molecule from the atmosphere progressively gets reduced by addition of a pair of hydrogen atoms to form Ammonia.
(ii) Nitrogen fixation process requires nitrogenae enzyme complex minerals (Mo,Fe and S) anaerobic condition ATP electron and glucose 6 phosphate as `H^+` donor.
(iii) Nitrogenase enzyme is active only in anaerobic condition. To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen (iv) Nitrogen fixing bacteria in root nodules appears pinkish due to the presence of this leghaemoglobin pigment.
Overall equation :
`N_2+8e^-+8H+16ATPto2NH_3+H_2+16ADP+16P_i`
2. Nitrification.
`NH_3^+` Ammonia is converted into Nitrite
`(NO_2^-)` by nitrosomonas bacterium . Nitrite
`(NO_2^-)` is then converted into Nitrate `(NO_3^-)` by nitrobacter bacterium. `2NH_3^++3O_2overset("Nitrosomonas")to2NO_2^(-)+2H^++2H_2O`
`2NO_2^(-)+O_2overset("Nitrobacter")to2NO_3^-`
3. Nitrate assimilation.
The process by which nitrate is reduced to ammonia is called nitrate assimilation and occurs during nitrogen cycle
`NO_3^(-)overset("Nitrate reductase")underset(Mo)toNO_2^-`
`NO_2^(-)overset("Nitrate reductase")underset(Cu,Fe)toNH_3^+`
4. Ammonification :
Decomposition of organic nitrogen from dead plants and animals into ammonia is called ammonification . organisms involved in this process are bacillus remosus and bacillus vulgaris.
5. Denitrification:
Nitrates in the soil are converted back into atmospheric nitrogen by a process called denitrification . Bacteria involved in this process are pseudomonas, Thiobacillus and bacillus subtilis.
`underset((NO_3^-))"Nitrate"overset("Pseudomonas")tounderset((N_2))"Molecular nitrogen"`
