Study On The Microbial Community Driving The Change Of Soil Organic Carbon In Huixian Karst Wetland

The dynamic change of wetland soil organic carbon(SOC)has not only become one of the hot issues in the study of terrestrial ecosystem carbon cycle,soil carbon sequestration and global climate change,but also attracted much attention in the study of terrestrial ecosystem degradation / restoration.Guilin Huixian karst wetland is the largest natural wetland which is at present known as the largest scale karst areas in middle and low latitudes and low altitudes in China and even the world.In recent years,due to the influence of human activities,the soil degradation is becoming more and more serious.It is of great significance to understand the dynamic changes of SOC and the microbial communities driving the changes of SOC in karst wetland under the states of natural degradation and human disturbance.In this dissertation,three states of Guilin Huixian karst wetland soils,i.e.native wetland,naturally degraded wetland and reclaimed farmland wetland soils were selected.Based on the 16S/ITS2 high-throughput sequencing technology and stable isotope probe technology,the temporal and spatial variation characteristics of microbial community composition and abundance,soil enzyme activities,and SOC and its components were compared in the three states of Huixian karst wetland soils.The soil microbial groups closely related to the changes of organic carbon components were analyzed,and the active microbial groups that may play a real role in the process of fixing inorganic carbon to SOC in the soil carbon sequestration of Huixian karst wetland were preliminarily revealed.The main results are as follows.(1)The soil organic carbon components,related physicochemical properties and soil enzyme activity characteristics in different states of Huixian karst wetland had obvious differences caused by the influence of natural degradation or human disturbance,but their characteristics were different with seasons.The contents of SOC,easily oxidized organic carbon(EOC),microbial biomass carbon(MBC)and particulate organic carbon(POC)were significantly higher in autumn than those in the other three seasons(P<0.05).The vertical distribution characteristics of organic carbon components and soil water content(SWC)in the three states of karst wetland,native,naturally degraded and reclaimed farmland wetland,all decreased with the increase of soil depth.The activities of soil carbonic anhydrase and cellulase had significant differences among karst wetland soils of different states(P<0.05).(2)The species composition of soil microbial community was similar in Huixian karst wetland in different states,but the relative abundance of some dominant species was significantly different.For prokaryotic microbial community,Desulfobacterota is the indicator species in reclaimed wetland.In summer and autumn,the relative abundance of Nitrospira,Nitrospiraceae,Nitrosomonadaceae and Nitrosopumilaceae was higher in the naturally degraded wetland soil.For the fungal community,Sordariales and Staphylotrichum were the indicator species in the native wetland soil,and Eurotiales and Magnaporthaceae were the indicator species in the reclaimed farmland wetland soil.(3)The soil prokaryotic microbial groups closely related to the changes of soil organic carbon components were Anaeromyxobacter,Bacillus,Bryobacter,Flavisolibacter,Gemmatimonas,Haliangium,etc.The soil fungal groups mainly include Clonostachys,Fusarium,Talaromyces,Conlarium,Westerdykella,Ascobolus,Chaetomium,Polyschema,Debaryomyces,Aspergillus,etc.Soil enzymes closely related to the change of soil organic carbon components of wetland were sucrase and carbonic anhydrase.(4)The results of DNA-SIP combined with 16 S rRNA high-throughput sequencing analysis showed that the active microbial groups involved in the utilization of inorganic carbon in Huixian karst wetland soils were consistent with the analysis results of PLFA-SIP.The main groups were Thermotogae,Firmicutes,Bacteroidetes,Synergistetes,Proteobacteria,Rokubacteria,Actinobacteria,Acidobacteria and Gemmatimonadetes.The above results provide a theoretical basis for in-depth study and exploration of microbial resources that play an important role in soil carbon sequestration in karst wetlands,which can be used to improve soil carbon sequestration capacity of karst wetlands and repair wetland degraded soils.