Increasing plant species diversity aggravates microbial phosphorus limitation but alleviates microbial carbon limitation in a subtropical forest

Abstract The limitation of microbes by soil organic carbon (SOC), nitrogen (N), or phosphorus (P) is linked with soil microbial activities, so that how change of plant species diversity (PSD) affects microbial resource limitation would partly determine its impacts on SOC dynamics and nutrient cycling. However, the responses of microbial resource limitation to increasing PSD have poorly explored. Here, 45 plots covering a natural gradient of PSD were used to investigate the effects of PSD on microbial resource limitation in a subtropical forest. Extracellular enzymatic stoichiometry along with a laboratory N and P addition experiment was used to determine microbial resource limitation. Contents of microbial biomass C, N and P significantly increased, but C:P and N:P ratios in microbial biomass were unchanged as PSD increased. Soil microbes were co-limited by C and P, but not limited by N across the 45 plots. Increasing PSD did not alter microbial N limitation, alleviated microbial C limitation, and aggravated microbial P limitation. The alleviated microbial C limitation or aggravated microbial P limitation was attributed to increased soil C availability but decreased P availability, which resulted in greater soil C:P and N:P ratios and their imbalance between soil and microbial biomass under higher PSD. Our results highlight the divergent effects of increasing PSD on microbial C and P limitation, and may have high implications for SOC accumulation. Nevertheless, whether the observed patterns are widely applicable needs to be assessed by more investigations, since this study was only conducted in a subtropical forest with calcareous soil.