Grazing alters the response of ANPP to precipitation variability in a desert steppe

Precipitation is a pivotal driver of aboveground net primary productivity (ANPP) in grasslands, while grazing regulates ANPP by reshaping plant community structure. However, how grazing regulates grassland responses to precipitation variability remains incompletely understood. Here, we conducted an 18-year field grazing experiment in a desert steppe, combining long-term ANPP monitoring with daily precipitation data. Our results revealed that grazing significantly reduced community ANPP by 31% and forb ANPP by 61%. This reflected a shift from palatable forbs to stress-tolerant grasses, primarily driven by increased abundance of Stipa breviflora. June-July precipitation amount emerged as the primary driver of inter-annual ANPP variability. Critically, significant interactions between grazing and precipitation demonstrated that grazing fundamentally altered these precipitation-ANPP relationships, strengthening the response slope of grasses while weakening that of forbs and the whole community. Although grazing did not significantly alter legacy effects at the community or grass level, it significantly modulated the legacy effect on forb ANPP; previous-year precipitation remained a significant predictor of ANPP across all organizational levels. Grazing-induced phenotypic adjustments in S. breviflora (increased root length and population density) strengthened the coupling between grasses and early- and mid-summer precipitation, even though their precipitation-use efficiency did not differ between treatments. Our findings demonstrate that grazing reorganizes ecosystem sensitivity to climate by shifting plant functional group dominance and key species traits. These findings provide a mechanistic basis for forecasting grassland responses to climate variability and for guiding grazing management under seasonal precipitation forecasts.