Which two distinct microbial processes are responsible for the release of fixed nitrogen as dinitrogen gas $\left(\mathrm{N}_2\right)$ to the atmosphere?

Denitrification is a chemical process in which nitrates in the soil are reduced to molecular nitrogen $\left(\mathrm{N}_2\right)$ which is released into the atmosphere. It is done by denitrifying bacteria like Pseudomonas. Anaerobic oxidation of ammonium $\left(\mathrm{NH}_4\right)$ also releases nitrogen in the atmosphere. Related Theory Anammox (anaerobic ammonium oxidation), which is a reaction that oxidizes ammonium to dinitrogen gas using nitrite as the electron acceptor under anoxic conditions, was an important discovery in the nitrogen cycle.