Soil warming delays leaf litter decomposition but exerts no effect on litter nutrient release in a subtropical natural forest over 450 days

Litter decomposition is a fundamental ecosystem process, influencing soil carbon storage, nutrient availability, and forest productivity. Climate change may affect litter decomposition and thus nutrient dynamics via altering plant phenology, litter quality, and the composition of soil microbial communities. However, the effects of climate change on litter decomposition are not well understood, especially in tropical and subtropical forest ecosystems, which are less temperature limited. We conducted a manipulative study to assess how soil warming affects litter decomposition rates and its relation to litter chemistry, extracellular enzyme activities, and microbial biomass in an evergreen broad-leaved forest in subtropical China. The temperature at 0-10 cm soil depth was experimentally increased by 4 degrees C, starting from June 2016 to October 2017. Soil warming did not affect litter mass loss during the initial stage (0-270 day), but reduced litter mass loss by 12.9 % at the later stages (days 350 to 450). Structural equation modeling showed that litter moisture content was reduced by warming, but this was not the main effector leading to the reduction in late-stage litter decomposition in the warming treatment. The model suggested that warming reduced litter decomposition rates likely indirectly, through its negative effects on extractable organic carbon and microbial biomass (e.g., microbial carbon and nitrogen), and on litter enzyme activities (a composite variable of beta-glucosidase, cellobiohydrolase, acid phosphatase, and phenoloxidase). These results show that warming may slow down litter carbon cycling, but this subtropical forest ecosystem did not affect litter N and P cycling and soil nutrient availability.