Response Of Soil Microecology To Cadmium And Quinclorac Contamination And Enterobacter Ludwigii EM1 Repair

With the accelerated development of agricultural modernization,farmland soil pollution is increasing,among which heavy metals and organic pesticides are two main types of pollutants.Cadmium is one of the most common and serious heavy metals in the soil.It is highly toxic and has a high risk of migration,can be accumulated through the food chain.Especially in southern China,rice is seriously polluted by cadmium,and cadmium pollution in rice has high concealment.Quinclorac is a selective herbicide for controlling rice stalks,which has a large residual amount in the soil,which causes phytotoxicity in the later crops and often forms a combined pollution with cadmium in the soil.Microbial remediation technology is one of the effective means to solve soil pollution.In this study,the effects of single and combined pollution of cadmium and quinclorac and the EM1 remediation of degrading bacteria on soil microecology were studied from three aspects:soil cultivable microorganisms,soil enzyme activity and bacterial community diversity,and the ecological toxicity of single and combined pollution was explored.Mechanism provides theoretical support for establishing early warning indicators for relevant contaminated soils.The main results are as follows:(1)The number of bacteria and fungi in single and combined cadmium soils increased compared with the control,and the number of actinomycetes decreased.After the addition of EMI,the number of bacteria in the contaminated soil was higher than control.After the addition of cadmium to the single contaminated soil of quinclorac,the number of bacteria and actinomycetes decreased.The addition of quinclorac to the single contaminated soil of cadmium reduces the number of bacteria and increases the number of fungi and actinomycetes.(2)The enzyme activity in cadmium single pollution and quinclorac single contaminated soil respectively showed a decrease and increase compared with the control.After adding EMI,the urease and phosphatase activities of cadmium single contaminated soil increased,and the urease activity of quinclorac contaminated soil decreased.After the addition of cadmium to the single contaminated soil of quinclorac,the enzyme activity decreased.Addition quinclorac to cadmium single contaminated soil reduces the urease activity and increased the activity of sucrase.(3)Composite pollution compared to single pollution,the residual concentration of quinclorac in soil decreased rapidly to 0.10 mg·L-1 on the 5th day,and the cadmium residual concentration in 35 d was higher than single pollution.After the addition of EMI,in the case of composite pollution,the degradation rate of quinclorac was significantly higher than that of single pollution.At 15-35 d,the cadmium residue in the compound contaminated soil was significantly lower than single cadmium pollution.(4)The diversity analysis of soil bacterial community showed that there were significant differences in Alpha diversity,Beta diversity,species composition and community structure similarity.Compared with the control,the chao1 index and the shannon index of each treatment increased to different extents.The difference in community diversity index of quinclorac in single contaminated soil before and after adding EMI was particularly significant.The dominant bacteria with the highest relative abundance in each treatment is the Proteobacteria.Compared with the control,new dominant bacteria(Verrucomicrobia and Planctomycetes)appeared in the single contaminated soil of cadmium and quinclorac,and the dominant bacteria Saccharibacteria disappeared.After EMI repair,the dominant bacteria Verrucomicrobia and Planctomycetes and Nitrospirae in the single contaminated soil of cadmium and quinclorac decreased.A new dominant strain,Saccharibacteria,appeared in all treatments with the addition of EM1.Principal component analysis showed that the bacterial community structure changed significantly after EMI repair.The composite contamination treatment of EM1 repair was closest to the discrete distance of the control,indicating that EM1 can effectively repair the contaminated soil of cadmium and quinclorac.The interaction between bacterial communities is more closely related to single pollution.After adding EMI,the positive correlation between bacteria increases and the negative correlation decreases.