Nitrogen enrichment differentially regulates the response of ecosystem stability to extreme dry versus wet events.

Extreme climate events, such as severe droughts and heavy rainfall, have profound impacts on the sustainable provision of ecosystem functions and services. However, how N enrichment interacts with discrete extreme climate events to affect ecosystem functions is largely unknown. Here, we investigated the responses of the temporal stability (i.e., resistance, recovery, and resilience) of aboveground net primary productivity (ANPP) in an alpine meadow to extreme dry and wet events under six N addition treatments (0, 2, 4, 8, 16, 32 g N m year). We found that N addition had contrasting effects on the responses of ANPP to the extreme dry versus wet events, which resulted in no overall significant effects on ANPP stability across 2015-2019. Specifically, high N addition rates reduced the stability, resistance, and resilience of ANPP in response to extreme drought, whereas medium N addition rates increased ANPP stability and recovery in response to the extreme wet event. The main mechanisms underlying the response of ANPP to extreme drought and wet events were discrepant. Species richness, asynchrony, and dominant species resistance contributed most to the reduction of ANPP resistance to extreme drought, while species asynchrony and dominant and common species resilience contributed most to the decrease of ANPP resilience from extreme drought with N enrichment. The ANPP recovery from the extreme wet event was mainly explained by dominant and common species recovery. Our results provide strong evidence that N deposition mediates ecosystem stability in response to extreme dry and wet events in different ways and modulates the provisioning of grassland ecosystem functions under increasing extreme climate events.