Increasing precipitation reshapes alpine plant–microbial nutrient partitioning and enhances ecosystem carbon and nitrogen retention

Abstract Precipitation change is an important component of the ongoing climate change and substantially influences terrestrial nutrient and carbon (C) dynamics. However, the mechanisms by which increasing precipitation affects plant–microbial nitrogen (N) assimilation and ecosystem C and N retention remain unclear. Using isotopic tracing along a manipulated precipitation gradient in a water‐ and nutrient‐limited alpine ecosystem, we investigated how increasing precipitation alters plant nutrient strategies, plant–microbial N partitioning and ecosystem C and N retention. Increased precipitation enhanced plant and microbial N assimilation, ecosystem N retention and plant C fixation. However, these effects were not consistent across ecosystem components. Increasing precipitation progressively promoted grass‐forb ratio and community‐level acquisitive root traits, whereas mycorrhizal colonization was greatest at intermediate precipitation. Plant biomass C and N accumulation remained responsive across a broader portion of the precipitation gradient than did microbial N assimilation, thereby shifting plant–microbial N partitioning. Structural equation modelling indicated that the plant pathway plays a stronger role than the microbial pathway in mediating the effects of increasing precipitation on ecosystem N retention and C fixation. Our findings suggest that ecosystem responses to increasing precipitation depend on how different biotic components respond and interact. Synthesis : Increasing precipitation reshapes plant–microbial nutrient partitioning and ecosystem C and N retention in alpine ecosystems. Our findings highlight the need to account for non‐linear and contrasting responses among different ecosystem components when predicting the consequences of future climate change for alpine ecosystem functioning. This work contributes to providing a basis for tracking how alpine ecosystems may reorganize under future climate change.