Effects Of Soil Cadmium,zinc And Fluorine Contamination On Microbial Community Structure,Diversity And The Growth Of Brassica Chinensis L.

Soil heavy metal and fluorine combined pollution near the phosphogypsum stack has be-come one of the global environmental problems that poses a threat to soil ecosystems and hu-man health.However,the ecological effects of soil cadmium（Cd）,zinc（Zn）and fluorine（F）and their interactions in soil-microorganism and soil-plant systems remain unclear.In this study,the spatial distributions and pollution risk of total and available Cd,Zn and F content were analyzed in farmland soil near a phosphogypsum stack.Based on field investigation,the effects of Cd,Zn and F and their interactions on soil microbial diversity and growth,photosynthesis,bioconcentration and translocation of pak choi（Brassica chinensis L.）were quantitatively in-vestigated by quadratic regression orthogonal combination design.The main conclusions were as follows:（1）The mean concentrations of total Cd,Zn and F in soil were 3.22±1.39,346.99±277.04and 961.54±136.24 mg kg^-1,and the over-standard rate were 100%,50%and 88.89%,respec-tively.In terms of spatial distribution,except for water-soluble Cd（Cd＿H₂O）and F extracted by DTPA（F＿DTPA）,the total and other available content of Cd,Zn and F were the highest near the phosphogypsum stack,and decreased gradually from northwest to southeast.In addi-tion,based on Nemerow pollution index and other methods,the soils were seriously polluted,and Cd was the element with the greatest pollution risk in this study area.（2）The contamination of Cd,Zn and F resulted in the decrease of bacterial and fungalαdiversity in potting soil.The quadratic regression orthogonal combination design showed that bacterial and fungal richness and diversity indexes were significantly negatively affected by Zn（P<0.05）,and the Zn-F interaction resulted in a significant decrease in bacterial Shannon di-versity and PD indexes（P<0.05）.However,with the enhancement of Cd-F interaction,theαdiversity index of fungi was significantly increased（P<0.05）.（3）Different abundances of bacteria and fungi responded diversely to soil Cd,Zn and F.The results showed that Zn was the main effect on 6 bacterial phyla including Proteobacteria and the fungus Mortierellomycota under single factor（P<0.05）.For interaction,the enhanced Zn-F interaction significantly increased the relative abundance of bacteria Proteobacteria,Acidobacteriota and fungus Basidiomycota（P<0.05）,while the relative abundance of Verru-comicrobiota decreased significantly（P<0.05）;Cd-Zn interaction had a significant positive effect on the relative abundance of bacteria Verrucomicrobiota and Desulfobacterota（P<0.05）and a significant negative effect on the bacterium Acidobacteriota（P<0.05）;the Cd-F interac-tion resulted in a significant decrease in the relative abundance of bacterium Bacteroidota（P<0.05）,while a significant increase in the relative abundance of the fungus Basidiomycota（P<0.05）.（4）The physiological and biochemical indices of pak choi were restricted under high con-centrations of Cd,Zn and F,including dry weight,plant height and root length,total chlorophyll content,chlorophyll b,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）and intercellular CO₂ concentration（Ci）,protein,soluble sugar,vitamin C and Super-oxide dismutase,peroxidase,catalase and polyphenol oxidase（P<0.05）.（5）Cd,Zn and F and their interactions significantly affected the bioconcentration and translocation of these elements in Brassica chinensis L.（P<0.05）,which could promote the absorption of Cd and transport of Zn and F in Brassica chinensis L.,but limited the absorption of Zn and F and transport of Cd.Notably,bioconcentration factors of Cd(BCF_Cd)and Zn(BCF_Zn)were positively affected by soil Cd and Zn（P<0.05）,and the F translocation factor（TF_f）was significantly affected by soil Cd and F（P<0.05）.Moreover,BCF_Zn was positively affected by Cd-Zn interaction（P<0.05）,but negatively effected by the Zn-F interaction（P<0.05）.In addition,Cd-Zn interaction had a significant positive effect on TF_f（P<0.05）.In conclusion,this study comprehensively evaluated the pollution risks of Cd,Zn and F,and conducted a pot experiment with quadratic regression orthogonal combination design.The interaction model of cadmium,zinc and fluorine on bacterial and fungalαdiversity,and the bioconcentration and translocation of these elements in Brassica chinensis L.was established,which could provide a scientific basis for the ecological risk assessment and ecological effect of phosphogypsum polluted soil.