Understanding Nitrifier Denitrification: How far are we?

Abstract:

Nitrifier denitrification is the oxidation of ammonia (NH₃) via hydroxylamine (NH₂OH) to nitrite (NO₂^-) and subsequent reduction of NO₂^- via nitric oxide (NO) to the greenhouse gas nitrous oxide (N₂O) and possibly to dinitrogen (N₂) by autotrophic nitrifiers. Especially in recent years, a lot of research has been conducted on this pathway. Under some conditions, it might dominate the N₂O production from soils. Methods for studying nitrifier denitrification include selective inhibition, stable isotope and isotopomer methods, molecular and modelling approaches. They are applied from pure culture and pot studies to the field scale, trying to improve our knowledge of the conditions and factors controlling nitrifier denitrification. But how far are we? What have we learned so far and what remains to be discovered? With this contribution, I am trying to give an update of our understanding of this less well-known but important pathway.