Responses Of Soil Organic Carbon Mineralization To Drying-rewetting Events After Long-term Drought In A Subtropical Forest

With the continuous intensification of global climate change,global precipitation patterns have changed significantly,resulting in increases in extreme drought events.Soil water content is the main driving factor regulating soil organic carbon mineralization.It has been demonstrated in previous research that short-term dryingrewetting events could stimulate soil organic carbon mineralization,accelerating soil carbon dioxide emissions.However,how terrestrial soil organic carbon mineralization responds to drying-rewetting events under long-term drought is still poorly understood.This deficiency greatly hinders our understanding and prediction of terrestrial soil carbon decomposition process in the future climate change.In this study,we thus collected soils from a subtropical forest that experienced 7-year longterm extreme drought(70% reduction of throughfall)to explore how long-term drought regulates responses of subtropical forest soil carbon mineralization to dryingrewetting events by adjusting soil water content in microcosm incubation experiments.The main results are as follows:(1)The responses of soil organic carbon mineralization to drying-rewetting events was reduced by long-term drought in a subtropical forest.Specifically,the cumulative organic carbon mineralization of subtropical forest soil under long-term drought significantly decreased by 21.8%,27.9% and 27.4% compared with the control soil during the first,second and fourth drying-rewetting events,respectively.This results indicate microbial adaptation of soil organic carbon mineralization to long-term drought in forests.(2)For the subtropical forest soil under long-term drought,the change of microbial community structure is the main mechanism regulating soil organic carbon mineralization in response to drying-rewetting events.Specifically,drying-rewetting events influenced soil organic carbon mineralization by altering fungal,gram-positive bacterial and actinomycete communities.For the control soil,drying-rewetting events influenced soil organic carbon mineralization by regulating soil ammonium nitrogen content and fungal community.(3)Soil organic carbon mineralization under long-term drought had different responses to drying-rewetting events of different intensities in subtropical forest.In specific,responses of soil organic carbon mineralization to drying-rewetting events of high,medium and low intensities was 33.1%,25.1% and 23.7% lower than that of control soil,respectively.For the soil under long-term drought,the intensities of drying-rewetting events regulated soil organic carbon mineralization by indirectly influencing soil microbial biomass carbon,actinomycete and gram-positive bacterial communities.The intensities of drying-rewetting events regulated the organic carbon mineralization in the control soil by indirectly influencing soil nitrogen content and fungal community.In summary,this study investigated the responses of soil carbon mineralization to drying-rewetting events in a subtropical forest after long-term drought,and explored the important role of soil biotic and abiotic factors in response to different soil moisture fluctuations.The results deepened our understanding of the response of soil organic carbon decomposition to drying-rewetting events and elucidate the mechanisms of soil carbon mineralization responding to drying-rewetting events under long-term drought.These findings can provide data supports for further studies on the response of soil organic carbon mineralization to global changes and for accurate simulation of carbon cycling by terrestrial ecosystem models.