Effect Of Tree Species Richness On Soil Microbial Diversity In A Planted Mixed Forest In South Subtropical Region,Guangxi,China

Soil microbial communities are important components of soil ecosystem,that participate in organic matter decomposition,nutrient cycling and energy conversion,and they play important roles in maintaining the productivity,function and stability of ecosystem.The comosition and struture of soil microbial communities can be affected by forest vegetation,while the relationship between the above and below ground ecosystem diversity remains unclear.Such diversity relationship between vegetation and soil microbial community has been studied extensively in grasslands and natural forest ecosystems.However,it is unclear how the diversity of tree species affects the composition and structure of soil microbial communities in the planted forest ecosystem with multiple tree species.Therefore,in order to explore how the composition and structure of soil microbial communities change with the tree species richness in mixed plantations,we conducted experiment in mixed forest ecosystem of multiple tree species formed by natural restoration after artificial block afforestation in south subtropical region.Tree cluster experiment with tree species gradient from 1 to 10 tree species was set.Through soil physicochemical analysis and microbial high-throughput sequencing,the changes of soil physicochemical properties,composition and diversity of soil microbial communities in0-10 cm soil layer with different tree species diversity gradient were determined,the influencing factors of soil microbial community structure were analyzed,and the influencing mechanism of tree species diversity increasing on soil bacterial and fungal community composition and diversity in south subtropical plantations were explored.The main results are as follows:(1)The increase of tree species richness increased the content of nitrogen and phosphorus in soil.Soil bulk density,pH,soil total nitrogen,soil organic matter,aromatic carbon and the biomass,carbon,and carbon nitrogen ratio of litter and fine root were significantly correlated with tree species richness.Tree species diversity significantly affected soil carbon nitrogen ratio,carbonyl carbon,undecomposed litter carbon,fine root carbon and fine root carbon nitrogen ratio.(2)Increasing tree species richness did not significantly affect the number of soil bacterial OTU numbers.In the study area,Acidobacteria and Proteobacteria were dominated in the soil bacterial community.The Chao1 index of soil bacteria increased significantly with the increase of tree species richness.The Chao1 index of soil bacterial community was significantly correlated with soil pH,soil organic matter,soil ammonium nitrogen,soil carbon/nitrogen ratio,fine root biomass.Increasing tree species richness changed the composition of soil bacterial community in the study area.Soil pH,soil nitrate nitrogen and alkyl carbon,aromatic carbon significantly affected soil bacterial community structure.(3)Increasing tree species richness did not significantly affect the number of soil fungal OTU numbers.In the study area,Ascomycota and Basidiomycota were dominated in the soil fungal community.The Faith' s PD index of soil fungal community increased obviously with tree species richness.The soil fungal Faith' s PD index was significantly correlated with soil pH,soil carbon/nitrogen ratio,fine root biomass,fine root carbon/nitrogen ratio.Increasing tree species richness changed the composition of soil fungal community in the study area.Soil organic carbon,soil nitrate nitrogen,O-alkyl carbon,and fine root biomass were the main factors affecting the soil fungal community structure.