Thinning Caused Differences Of Microbial Characteristics In Rhizosphere Soil Of Chinese Fir Plantation

The rhizosphere is an active interface for material cycle and energy conversion among plant-soil ecosystems,and is characterized by higher density of microorganisms.However,there is a lack of available information about the effects of thinning on the rhizosphere environment.Therefore,the present study investigated the rhizosphere microbial activity and community structure under different thinning intensity,including CK(0%),LIT(30%),MIT(50%)and HIT(70%),in 31-year-old Chinese fir(Cunninghamia lanceolata [Lamb.] Hook)plantation at Lishui Tree Farm,and analyzed its relationship with vegetation characteristics and soil properties,with the aim of discussing the response mechanism of rhizosphere microorganisms to thinning.The main results were as follows:(1)Thinning decreased litterfall biomass and its carbon and nitrogen content,while increased root biomass and its carbon and nitrogen content.MIT is beneficial to improve the nutrient availability of rhizosphere soil.The contents of water,total nitrogen,water-soluble organic carbon and available phosphorus in rhizosphere soil increased by 12.7%,9.4%,87.1% and 2.9%,respectively.Pearson correlation analysis showed that the nutrient content of rhizosphere soil was closely related to litterfall and root characteristics.(2)Rhizosphere microbial activity showed positive rhizosphere effect,which was 1.04-1.24 times higher than that in bulk soil,and was significantly affected by thinning.MIT and HIT significantly increased the rhizosphere microbial biomass carbon and nitrogen contents by 16.3% and 8.9%,58.9% and 32.9%,respectively.The response of rhizosphere soil enzyme activity to thinning varied with the type of enzyme.Thinning significantly reduced invertase activity,but increased the activities of acid phosphatase,dehydrogenase and urease in the rhizosphere soil.The changes in ?-glucosidase and peroxidase activities after thinning were not significant.Rhizosphere microbial activity was significantly correlated with the contents of soil water,organic carbon,total nitrogen and water-soluble organic carbon,and the characteristics of litterfall and root.(3)Thinning increased the alpha diversity of rhizosphere bacterial community by 10.0%,16.4% and 13.7%,respectively.The composition of rhizosphere bacterial community was changed after thinning,in which Proteobacteria,Actinobacteria,Acidobacteria,and Chloroflexi were dominant bacteria.HIT significantly reduced the abundance of Actinobacteria,while increased Chloroflexi.In addition,the rhizosphere bacterial community also differed at genus and OTU level.For example,the abundance of norank_c_JG37-AG-4was decreased significantly in LIT and MIT,but was increased significantly in HIT.RDA analysis showed that the change of rhizosphere bacterial community was driven by total potassium.(4)The rhizosphere fungal community was more sensitive to thinning than bacteria,and the alpha diversity of fungi was reduced after thinning.Zygomycota,Basidiomycota,and Ascomycota are dominant fungi.The abundance of Ascomycota was significantly reduced after thinning.With the increase of thinning intensity,the abundance of Basidiomycota tended to decrease first and then increased,while the Zygomycota showed an opposite trend.At genus and OTU level,the differences in rhizosphere fungal community under different thinning intensities were more significant.For example,HIT significantly increased the abundance of Geminibasidium,which was 6.7 times higher than that in CK.The main factors affecting rhizosphere fungal community were the contents of water-soluble organic carbon,available nitrogen,total potassium,litter nitrogen and root C/N.(5)Compared with bacteria,the difference in fungal community between rhizosphere and bulk soil was more significant,and the difference was even greater at the finer classification level.The rhizosphere fungi detected 2044 OTUs,including 7 phyla,25 classes,68 orders,137 families,236 genera,and 365 species,whereas only 709 OTUs was detected in the bulk soil,including 7 phyla,19 classes,and 53 orders,105 families,166 genera and 244 species.Conclusively,the results showed that thinning significantly affected the rhizosphere microbial activity and community structure by changing soil properties and the input of litter and roots.These changes may influence the carbon distribution pattern and nutrient cycling process of underground ecosystems.The findings could be crucial for elucidating the microbial mechanism of rhizosphere ecological processes responding to thinning.