Shifts in soil ammonia‐oxidizing community maintain the nitrogen stimulation of nitrification across climatic conditions

Abstract

Anthropogenic nitrogen (N) loading alters soil ammonia￢ﾀﾐoxidizing archaea (AOA) and bacteria (AOB) abundances, likely leading to substantial changes in soil nitrification. However, the factors and mechanisms determining the responses of soil AOA:AOB and nitrification to N loading are still unclear, making it difficult to predict future changes in soil nitrification. Herein, we synthesizeￂﾠ68 field studies around the world to evaluate the impacts of N loading on soil ammonia oxidizers and nitrification. Across a wide range of biotic and abiotic factors, climate is the most important driver of the responses of AOA:AOB to N loading. Climate does not directly affect the N￢ﾀﾐstimulation of nitrification, but does so via climate￢ﾀﾐrelated shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N￢ﾀﾐavailability and moisture. AOB play a dominant role in affecting nitrification in dry climates, while the impacts from AOA can exceed AOB in humid climates. Together, these results suggest that climate￢ﾀﾐrelated shifts in soil ammonia￢ﾀﾐoxidizing community maintain the N￢ﾀﾐstimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading.