Denitrification

Denitrification is reduction of oxidized nitrogen compounds to gaseous products through the sequence nitrate, nitrite, nitric oxide, nitrous oxide and molecular nitrogen. In many microorganisms it supports anaerobic respiration when oxygen is scarce. Different organisms can perform different portions of the sequence; release of nitrous oxide does not imply complete conversion to molecular nitrogen.

Denitrification removes biologically available nitrogen from an ecosystem, whereas nitrification oxidizes reduced nitrogen. Disappearance of nitrate alone cannot distinguish gaseous loss from uptake by plants. Measurements using isotope labelling and mass spectrometry can trace nitrogen into both nitrogen gas and nitrous oxide, connecting the nitrogen cycle to an experimentally measured gas balance.^[ref]