Global Relative Importance of Denitrification and Anammox in Microbial Nitrogen Loss Across Terrestrial and Aquatic Ecosystems

Denitrification and anaerobic ammonium oxidation (anammox) are the major microbial processes responsible for global nitrogen (N) loss. Yet, the relative contributions of denitrification and anammox to N loss across contrasting terrestrial and aquatic ecosystems worldwide remain unclear, hampering capacities to predict the human alterations in the global N cycle. Here, a global synthesis including 3240 observations from 199 published isotope pairing studies is conducted and finds that denitrification governs microbial N loss globally (79.8±0.4%). Significantly, anammox is more important in aquatic than terrestrial ecosystems worldwide and can contribute up to 43.2% of N loss in global seawater. Global maps for N loss associated with denitrification and anammox are further generated and show that the contribution of anammox to N loss decreases with latitude for soils and sediments but generally increases with substrate depth. This work highlights the importance of anammox as well as denitrification in driving ecosystem N losses, which is critical for improving the current global N cycle model and achieving sustainable N management.