Which two distinct mictobial processes are responsible for the release of fixed nitrogen as dinitrogen gas (N) to the atmosphere?

Options

(a) Anaerobic ammonium oxidation, and denitrification
(b) Aerobic nitrate oxidation, and nitrite reduction
(c) decomposition of organic nitrogen, and conversion of dinitrogen to ammonium compounds
(d) Enteric fermentation in cattle, and nitrogen fixation by Rhizobium in root nodules of legumes.

Correct Answer:

Anaerobic ammonium oxidation, and denitrification

Explanation:

In the global nitrogen cycle, bacterial denitrification is recognised as important process that converts fixed nitrogen to atmospheric nitrogen gas, N₂. In marine nitrogen cycle, anaerobic oxidation of ammonium coupled to nitrate reduction, contributes substantially to N₂-production in marine sediments.