Effects Of Different Pathways Of Carbon Input On Soil Microbial Community Structure In Chinese Climate Transition Zone

Soil microorganisms play an important role in terrestrial ecosystem processes,such as soil carbon?C?cycle,and nutrient transformation.Soil microorganisms are essential for maintaining the function of terrestrial ecosystems.Forests are one of the major ecosystems over the world and carbon storage in forests accounts for almost half of the total land C pool.Forests are sensitive in response to global environmental change.Studies on soil microorganisms in forests have been attracting great research efforts in recent years.Litter and root inputs are major sources of soil C pool in terrestrial ecosystems.The two pathways of C inputs influence on the processes of soil C cycling.Litter and root exudates regulate the composition of soil microbial communities by changing soil physical and chemical properties.Hence,how soil physicochemical properties drive the response of composition and structure of microbial community to C inputs will improve our understanding for terrestrial C cycling.In order to explore the effects of litter and roots on soil microbial community structure in differentforest types,litter and roots treatments?control,litter addition,litter removal,root exclusion,litter addition and root exclusion,litter removal and root exclusion?were examined in 40-year-old coniferous,broad-leaved and coniferous-broad-leaved mixed forests in subtropical-warm temperate transition regions of China.Phospholipid fatty acid?PLFA?was used to investigate the effects of litter and roots on soil microbial community structure.Redundancy analysis was used to determine the relationship between PLFAs and soil properties?such as pH,soil organic C?.Across the three forest types,litter addition and removal had no effect on soil total organic C,totalnitrogen?N?and pH.Litter addition increased soil ammonium N and nitrate N content.Litter removal decreased soil moisture,pH,nitrate N,ammonium N,total organic C,microbial biomass C and N.Root exclusion reduced soil ammonium N,total organic C and N,microbial biomass C and N.Litter addition had no effect on soil microbial abundance and biomass.Litter removal had neutral effect on soil microbial abundance but reduced total microbial biomass and fungal biomass by 11.8 nmol g^-1 and 0.24 nmol g^-1.Further analysis showed that bacterial biomass showed no response to litter removal but fungal biomass was depressed under litter removal.Root exclusion reduced the abundance of fungi,bacteria and arbuscular mycorrhizal fungi by 0.69 nmol g^-1,0.78 nmol g^-1,and 0.02 nmol g^-1,respectively.Root exclusion significantly decreased soil microbial biomass C and N by 16.24%and 19.93%,respectively.Both the two pathways of C input showed no impact on the ratio of Gram-negative and Gram-negative bacteria.Redundancy analysis showed that soil physical chemistry properties mainly drive the response of microbial community structure to root exclusion.The results suggest that root exclusion,rather litter addition or removal,play a more important role on soil microbial community structure.The findings help to mechanistically understand and predict the relationships C cycle and soil microbial community structure in forests.