Limited direct impacts of precipitation changes on microbial resource limitation in a moderately saline-alkaline desert steppe

Abstract. While soil enzyme C:N:P ecological stoichiometry is known to be sensitive to precipitation changes in acidic to slightly alkaline grasslands, its response to long-term precipitation changes in moderately to severely saline-alkaline desert steppes remain unclear. In these ecosystems, the triple stress of soil water limitation, nutrient poor, and salinity-alkalinity complicates enzyme response, especially under extreme regimes. Based on a precipitation manipulation experiment (50% reduction, 30% reduction, ambient, 30% increase, 50% increase) initiated in 2014 in a moderately saline-alkaline desert steppe in northwestern China, this study assesses microbial resource limitation and identifies their driving factors by monitoring the monthly dynamics of soil extracellular enzyme C:N:P stoichiometry after 9-year treatment. Enzyme stoichiometry showed limited responses to both reduced and increased precipitation (P > 0.05). However, when responses did occur, they varied depending on the direction and intensity of the precipitation change, as well as the specific index examined. Similarly, enzyme vector length and angle were minimally affected by altered precipitation, with phosphorus being the primary limitation for microbes. The variation in vector length and angle was primarily explained by plant traits and microbial stoichiometry, respectively. Precipitation changes altered vector length and angle by modifying soil properties (moisture, NH₄⁺-N concentration, pH), plant traits (diversity, carbon concentration, C:P), and microbial stoichiometry (carbon content, C:N, C:P). Rather than exerting a direct effect on microbial resource limitation, altered precipitation indirectly influenced it through modifying soil resource availability, plant diversity, and the carbon-linked stoichiometry of both plants and microbes.