Response Of Soil Microbial Community To Tunnels Construction In Karst Areas

While tunnels construction brings convenience to local traffic and economic development,it inevitably has different direct and indirect effects on soil ecosystems.In karst areas,the drainage effect caused by tunnels excavation leads to the leakage of groundwater and the decrease of surface water,which changes soil properties and soil quality,and then affects the diversity,composition and functional metabolism of soil microbial community,leading to changes in the soil ecosystem.In this paper,we focused on soil microbial communities in the tunnels affected and unaffected areas of the Zhongliang Mountain karst trough areas in Chongqing.Based on data of 16 S rDNA sequencing and metagenomic sequencing,the response mechanism of changes in soil microbial diversity,species composition and functional composition under tunnels construction was studied.The main conclusions are as follows:(1)The analyses of soil physical and chemical properties showed that the tunnels construction reduced the soil water content,total nutrient and available nutrient,and increased soil bulk density and soil pH.Compared with the tunnels unaffected areas,soil water content in the tunnels affected areas decreased by 15.47%,and soil pH increased by 5%.In the tunnels affected areas,the contents of soil organic matter,total nitrogen,total phosphorus and total potassium were lower,and the content of soil total phosphorus decreased most obviously by 26.02%;the contents of soil available nitrogen,available phosphorus and available potassium decreased by 6.82%,6.64% and 10.97%,respectively.According to the nutrient grading standard of the second national soil census,the grade of soil total nutrient and available nutrient in the tunnels affected areas decreased,and the soil fertility was generally low.Therefore,after the tunnels construction,the soil environment showed the characteristics of low water content,high pH,and oligotrophic.(2)The 16 S rDNA sequencing technique was used to analyze the composition of soil microbial community.The results showed that the lower soil nutrient content in the tunnels affected areas resulted in the gradual evolution of the soil dominant microbial flora to the microorganisms which were mainly adapted to the low nutrient environment.The relative abundance of Ferrovum was the highest among 78 endemic genera in the tunnels affected areas,and the relative abundance of Thioalkalispyra was the highest among 104 endemic genera in the tunnels unaffected areas.norank_c_Acidobacteria and RB41 were significantly different genera in the total 749 genera in the two regions,and the relative abundance was higher in the tunnels affected areas.The results of redundancy analysis showed that soil available nutrients and pH were important factors affecting the soil microbial community in the Longfeng karst trough areas,indicating that the dominant bacteria in the tunnels affected areas were k-strategist(oligotrophic)microorganisms represented by Acidobacteria,while the dominant bacteria in the tunnels unaffected areas were r-strategist(eutrophic)microorganisms represented by ?-Proteobacteria.(3)Metagenomic sequencing was used to analyze the characteristics of soil microbial functional composition changes,and it was found that with the loss of soil moisture and nutrients in the tunnels affected areas,it was not conducive to microbial metabolic activities and hindered energy metabolism and nutrient cycling.In the function of KEGG(Kyoto Encyclopedia of Genes and Genomes),tunnels construction reduced energy metabolism-related functions such as biosynthesis of amino acids and pyruvate metabolism,and the abundance of glycoside hydrolase in the function of CAZy(Carbohydrate-active enzyme).In particular,the abundance of key enzymes that degrade sugar was reduced,such as ?-glucosidase.The analysis of correlation between environmental factors and microbial functional composition showed that available nitrogen was the main factor affecting soil function in the tunnels affected and unaffected areas,which indicated that with the loss of soil nutrients after the tunnels construction,the activity of soil microbial nutrition and metabolism was decreased.In this paper,molecular biological sequencing technology was applied to analyze the changes of soil microbial community and the characteristics of soil microbial composition and function in the tunnels affected areas.It is of great significance to the protection of ecological environment in karst areas.