Increasing plant species diversity enhances microbial respiration but does not alter its temperature sensitivity in a subtropical forest

Temperature sensitivity of soil microbial respiration is crucial in determining the dynamics of soil organic carbon under global warming. However, the response of temperature sensitivity and the underlying mechanisms to plant species diversity (PSD) remain unknown. Here, soil microbial respiration and its temperature sensitivity were investigated based on an incubation experiment with soils collected in 43 plots covering a natural gradient of PSD as indexed by Shannon-Weiner index ranging from 0.15 to 3.53 in a subtropical karst forest with calcareous soil. Increasing PSD stimulated soil microbial respiration by increasing soil organic carbon, dissolved organic carbon and soil water content but decreasing fungal/bacteria ratio. Nevertheless, PSD had no significant effect on the temperature sensitivity of microbial respiration due to the contrasting effects from soil biotic and abiotic variables. Increasing PSD stimulated temperature sensitivity by enhancing soil pH through increasing exchangeable calcium and magnesium and decreasing poorly crystalline aluminum/iron-oxides, but suppressed temperature sensitivity via decreasing fungal/bacteria ratio though increasing the quantity and recalcitrance of soil organic carbon. Our study, for the first time, provides the mechanisms underlying the response of temperature sensitivity to PSD, which should be considered when assessing the impacts of PSD on soil organic carbon dynamics under climate change.