Which two distinct microbial processes are responsible for the release of fixed nitrogen as dinitrogen gas (N2) to the atmosphere?
- Aerobic nitrate oxidation and nitrate reduction
- Decomposition of organic nitrogen and conversion of dinitrogen to ammonium compounds
- Enteric fermentation in cattle and nitrogen fixation by Rhizobium in root nodules of legumes
- Anaerobic ammonium oxidation and denitrification
Answer
(4) Anaerobic ammonium oxidation and denitrification
Solution
Fixed nitrogen returns to the atmosphere as N2 by:
(i) Denitrification — nitrate is reduced to N2 by bacteria such as Pseudomonas and Thiobacillus (as per NCERT).
(ii) Anaerobic ammonium oxidation (anammox) — NH4+ + NO2- N2 + 2H2O.
Nitrogen fixation and ammonification do the opposite (add fixed nitrogen).
Answer: (4)