Formation and Release of Nitrous Oxide from Terrestrial and Aquatic Ecosystems

Abstract

Soil nitrogen (N) is in a constant state of flux, moving and changing chemical forms. Nitrification and denitrification are the main processes to remove reactive N (Nr) from the environment. Both are predominantly microbial processes that provide energy to specialized groups of microorganisms. Nitrification oxidizes reduced N, generally NH3 or NH4+to NO3−via nitrite under aerobic conditions. Denitrification is the process under which oxidized N is reduced back into N2 under anaerobic conditions. Autotrophic nitrification and heterotrophic denitrification are the major N2O forming processes in terrestrial and aquatic forming in terrestrial and aquatic ecosystems. Major factors regulating nitrification and denitrification are the availability of reactive N, the availability of reductant (mostly labile organic carbon compounds), and oxygen concentration. These three factors are in turn governed by many other factors such as water content, pH, porosity, and the presence of inhibitory compounds, which may act to cause accumulation of ionic (nitrite) or gaseous (nitric oxide, nitrous oxide) intermediates. It has been estimated that soils under terrestrial ecosystems denitrify {\textasciitilde}124 Tg N year−1 or about 35--40% of total land based reactive N. Arable soils receiving high inputs of N are hot spots for denitrification and dominant sources of anthropogenic N2O emissions.