Shifts in soil microbial resource limitation along a natural gradient of EcM tree dominance in a subtropical montane forest

The status of microbial resource limitation plays a central role in regulating ecosystem carbon (C) and nutrient cycle. Tree mycorrhizal associations are increasingly known to regulate soil biogeochemical processes due to their contrasting nutrient acquisition strategies and litter quality, while their effectS on saprotrophic microbial resource limitation remain poorly understood. In this study, we collected soil samples from 35 plots with a natural gradient of EcM tree dominance (defined as the proportion of EcM tree basal area relative to the all trees) in a subtropical montane forest. A full factorial C, nitrogen (N) and phosphorus (P) addition experiment were conducted to infer soil microbial resource limitation based on the responses of microbial growth. The activities of exocellular enzyme were also determined to explore the possible links between ecoenzymatic stoichiometry and microbial resource limitation. C addition induced a systematic increase of microbial growth, and C plus P addition elicited even stronger responses in all soils, suggesting that microbial growth in this subtropical forest was primarily limited by C and secondarily limited by P. With increasing EcM tree dominance, microbial C limitation showed no significant trend, while the secondary P limitation decreased. Ecoenzymatic stoichiometry could not reliably represent soil microbial resource limitation along the gradient of EcM tree dominance. In addition, the variation in microbial secondary P limitation was positively associated with leaf P content and soil N availability, but negatively associated with the proportion of labile P and the relative abundance of phosphate-solubilizing microorganisms. These findings highlight the mycorrhizal association can shift soil microbial secondary P limitation in subtropical forest, which may have implications for the maintenance of forest productivity and soil C sequestration potential.