Soil extracellular enzyme stoichiometry reveals the nutrient limitations of soil microbial metabolism under precipitation changes in Ningxia desert steppe of China

Soil microbial communities and extracellular enzyme activity in arid ecosystems are highly sensitive to precipitation changes, yet their metabolic responses remain poorly understood. Through a field precipitation experiment in the Ningxia's desert steppe, we found that increased precipitation significantly enhanced C-, N-, and P-acquiring enzyme activities, with extracellular enzyme stoichiometry revealing microbial P limitation. Soil microbial communities were dominated by the phyla Actinobacteriota, Chloroflexi, and Proteobacteria (bacteria) and Ascomycota (fungi) under altered precipitation. Structural equation modeling (SEM) revealed that biotic factors (community structure/diversity) exerted stronger control over metabolic limitations than abiotic factors, with P limitation surpassing C limitation. These findings highlight P availability as a critical constraint on microbial function in arid grasslands. Our study provides actionable insights for grassland restoration, suggesting targeted P fertilization could mitigate microbial nutrient limitations and enhance ecosystem resilience under climate change.