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

Abstract Anthropogenic nitrogen (N) loading alters soil ammonia‐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 synthesize 68 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‐stimulation of nitrification, but does so via climate‐related shifts in AOA:AOB. Specifically, climate modulates the responses of AOA:AOB to N loading by affecting soil pH, N‐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‐related shifts in soil ammonia‐oxidizing community maintain the N‐stimulation of nitrification, highlighting the importance of microbial community composition in mediating the responses of the soil N cycle to N loading.