Effects Of Soil Microbial Community On Soil Carbon Mineralization And Its Underlying Mechanisms In Subtropical Forests Under Drought

Frequency and intensity of drought events were increased under the context of global change,with dramatic impacts on soil carbon dynamics.The importance of soil microorganisms in the process of soil carbon sequestration and decomposition has been increasingly emphasized.However,it remains largely unknow how the changes in soil microbial communities and metabolic functions affect the dynamics of soil carbon decomposition in forest under long-term drought.Plant roots provides sufficient energy resources for microorganisms to sustain their growth and extracellular enzyme production.But whether roots input can affect the regulation process of soil carbon decomposition by microorganisms remains unclear.Therefore,this study was based on the experiment site which experienced 7-year long-term extreme drought with rainfall isolation and root exclusion by trenching in a subtropical forest.We systematically studied the effects of drought on soil microbial diversity and community composition through high-throughput amplicon sequencing.Then we explored the microbial regulation of the influence from drought on carbon mineralization through microcosm incubation experiments.The main results are as follows:(1)Drought significantly decreased the activities of acid phosphatase and polyphenol oxidase by 44.0% and 53.9%,reducing microbial biomass,which indicated that drought inhibited microbial activity.The long-term drought reduced the bacterial diversity and the stability of the bacterial network.But there was no effect on the fungal diversity,and the complexity and stability of the fungal network increased under drought.Besides,the relative abundance and α-diversity of saprotroph fungi were significantly higher.This indicated that fungi may be more resistant than bacteria under drought.(2)Drought significantly reduced carbon mineralization of soil with root and root exclusion by 17.9% and 18.9%,respectively.Microbial community played important regulatory roles for drought to reduce soil organic carbon mineralization.For soil with root,the β-diversity of fungi and the α-diversity of saprotroph explained 81% variability of the soil organic carbon mineralization together with significantly negatively correlation simultaneously.For soils with root exclusion,the most important influencing factor of drought inhibiting carbon mineralization was the reduction of relative abundance of microbial network module 1.And the relative abundance of module 1 was significantly positively correlated with acid phosphatase activity.In Module 1,the dominant taxa were Mortierella.Therefore,although Mortierella has a low abundance in the total microbial community,it still impacted the soil carbon decomposition importantly.(3)Plant root input increases nutrient availability under drought,alleviates resource pressure on microorganisms,and increases microbial biomass.Root input increased the differences of microbial network edges and modularity between drought and control.Root significantly reduced the bacterial Y/A strategy by 49.1% under longterm drought,while the fungal community Y/A strategy did not change significantly.These showed that compared with root exclusion,root input can increase microbial activity under drought and enabling bacteria to shift from biomass synthesis to resource acquisition,and bacteria are more sensitive to root input.In addition,the root system affects the regulation process of soil microbial community for carbon mineralization.Compared to root exclusion treatment,root input made the organic carbon mineralization link more strongly to soil physicochemical properties,microbial community,and extracellular enzyme activity.In summary,the stability of fungal communities were stronger than that of bacteria under long-term drought.The increased diversity of saprophytic fungi may be more conducive to the stability of soil carbon pools.The driving force of drought on soil carbon mineralization varies between systems with root and with root and with root exclusion.This study revealed the different responses of key microbial communities and strategies on drought and root exclusion treatment,deepened the understanding of the response of forest soil carbon mineralization to drought and its microbial regulation mechanism,which may improve the accuracy of terrestrial ecosystem models in predicting carbon cycle under global change.