Lithological controls on soil microbial resource limitation in subtropical forests of southwest China

Resource constraints on soil microbial metabolism critically influence biogeochemical cycling and ecosystem functioning. However, the drivers and mechanisms underlying soil microbial resource limitation, particularly across broad spatial scales, remain incompletely understood. Here, we investigated patterns of soil microbial resource limitation using enzymatic stoichiometry in subtropical forests developed on two contrasting lithologies (limestone and clastic rock) in southwest China, and explored linkages with climatic, plant, microbial traits (i.e., biomass and community composition measured via qPCR), and soil geochemical factors. Activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes and their stoichiometric ratios differed significantly between lithologies. Vector analysis revealed that soil microbes in clastic rock forests experienced greater C and P limitation, whereas those in limestone forests were more N-limited. Random forest and structural equation modeling identified lithology, rather than climate, as the primary factor regulating microbial resource limitation within this subtropical region, primarily through its influence on soil geochemistry and microbial traits. These findings underscore the predominant role of lithology in shaping soil microbial resource limitation in subtropical forests, with significant implications for understanding nutrient cycling and carbon sequestration in these globally important ecosystems.