Effects Of Mine Water Discharge On Extracellular Enzyme Activity And Microbial Community Structure In Desert Grassland Soil

A large amount of untreated high salinity mine water discharged after mining directly enters the soil,which will cause salinization of the surrounding soil and greatly affect the spatial distribution of soil physical and chemical properties.However,the process and mechanism of the influence of mine water discharge on the structure and diversity of soil microbial community are still unclear,especially the research on the effect of long-term open storage of mine water on the extracellular enzyme activity and soil microbial characteristics in desert grassland is lacking.In this study,the desert grassland in the mine water discharge area of underground Coal Mine in Ningxia an arid and sandy area was taken as the research object,and the soil physical and chemical factors,microbial biomass,extracellular enzyme activity and microbial community characteristics in 0-10,10-20 and 20-30 cm soil layers along the waterfront,coastal land and natural areas of the mine water discharge lake were studied.Combined with the habitat characteristics of soil abiotic and biological factors,the changing characteristics of soil microbial community structure and diversity and the main influencing factors in desert grassland under the disturbance of mine water were revealed.The main results show that:(1)Mine water discharge had different effects on soil physical and chemical properties.Soil salinity,water content,electrical conductivity and organic carbon content decreased from the waterfront to the coastal land and natural area with distance.However,the soil pH value increased from the waterfront to the coastal land and the natural area with the distance.The changes of total nitrogen and total phosphorus content are similar,which are significantly lower in the coastal land than in the waterfront and natural area.However,mine water had little effect on soil available phosphorus,nitrate nitrogen and ammonium nitrogen.The soil water content increased significantly with the increase of soil depth,and it was higher in 20-30 cm soil layer.The content of soil available phosphorus decreased significantly with the increase of soil depth,and it was lower in 20-30 cm soil layer.The content of soil organic carbon is the lowest in 20-30 cm soil layers in the waterfront and coastal land areas,and other soil physical and chemical factors change little in different soil layers.(2)Mine water discharge had different effects on soil microbial biomass carbon,nitrogen and phosphorus.Microbial biomass phosphorus content in the waterfront area is significantly higher than that in the coastal land and natural area.The contents of microbial biomass carbon and nitrogen in 0-10 cm soil layer in the waterfront and coastal land are significantly lower than those in the natural area.Mine water significantly reduced the ratio of soil microbial biomass carbon to soil organic carbon,which was lower in the waterfront area,and the soil nutrient loss was higher,which reduced the soil quality.The contents of soil microbial biomass carbon and nitrogen changed greatly in different soil layers in the coastal land and natural areas,and decreased significantly with the increase of soil depth,with the lowest contents in 20-30 cm soil layer.The ratio of soil microbial biomass carbon to soil organic carbon in the coastal and natural areas is significantly different in different soil layers.Soil total nitrogen,salt and available phosphorus are the main factors affecting soil microbial biomass C,N and P in the study area.(3)Mine water discharge significantly increased the activities of soil β-1,4-glucosidase,alkaline phosphatase,β-N-acetylglucosaminidase and leucine aminopeptidase,and the activities of the four soil enzymes were the highest in the waterfront area.The activities of β-1,4-glucosidase,β-Nacetylglucosamine and leucine aminopeptidase were significantly different in different soil layers.Bothβ-1,4-glucosidase and β-N-acetylglucosaminidase decreased with the increase of soil depth,with the lowest activity in 20-30 cm soil layer.However,the activity of alkaline phosphatase gradually increased with the increase of soil depth,with the highest activity in 20-30 cm soil layer.(4)Mine water discharge had significant effects on soil extracellular enzyme stoichiometric vector length,vector angle,(NAG+LAP):ALP(enzyme N:P)and BG:ALP(enzyme C:P),but had significant effects on BG:(NAG+LAP)(enzyme C:N)had less effect.The vector angle change of enzyme stoichiometry indicated that soil microorganisms in the study area were mainly limited by P.Redundancy analysis showed that soil water content,salinity,organic carbon and available phosphorus were the main factors affecting the activity of extracellular enzymes in the soil in the study area and the enzyme stoichiometric ratio.(5)Mine water changed the soil environment of the desert steppe,affecting both the structure and diversity of the microbial community.Mine water discharge significantly changed the community composition of soil bacteria and fungi,and had a significant impact on the relative abundance of soil bacteria and fungi at the phylum level.The main dominant bacteria phylum in the waterfront area are:Actinobacteria,Proteobacteria and Firmicutes.The main dominant bacteria phylum in the coastal land and natural areas are:Actinobacteria,Proteobacteria and Chloroflexi.The main dominant fungi phylum in the waterfront area are:Ascomycota,Chytridiomycota and Rozellomycota.The main dominant fungi phylum in the coastal land and natural areas are:Ascomycota,Basidiomycota and Mortierellomycota.At the class level,the bacteria with relatively high relative abundance in waterfront areas are Alphaproteobacteria,Gammaproteobacteria and Bacilli;the relatively high relative abundance in coastal land and natural areas are:Actinobacteria,Alphaproteobacteria,and Thermoleophilia.The fungi with relatively high relative abundance in the waterfront,coastal land and natural area are:Sordariomycetes and Dothideomycetes.At the bacterial genus level,the main dominant bacterial genera in the waterfront,coastal land and natural areas are:norank_f_norank_o_norank_c_MB-A2-108,the main dominant fungal genera in the waterfront area is unclassified_k_Fungi,and the main dominant fungal genera in the coastal land area is:Preussia,the main dominant fungal genus in the natural area is:unclassified_p_Ascomycota.(6)The diversity and richness of soil bacteria and fungi in the waterfront were significantly lower than those in the natural area,further indicating that mine water had a significant impact on the richness and diversity of soil bacteria and fungi.Salt inhibited the growth of soil bacteria and fungi,but at the same time promoted the enrichment of halophilic bacteria in the study area.The richness and diversity of soil bacteria and fungi in different soil layers were less different.RDA analysis showed that soil salinity,water content,organic carbon,pH and β-N-acetylglucosaminidase were the main factors affecting the diversity of soil bacterial and fungal communities in the study area.