Study On Stability Of Soil Ecological Function And Microbial Regulation Mechanisms Under The Single And Combined Pollution Of Heavy Metal And Antibiotic

With the deepening of industrialization and urbanization in China,soil pollution is becoming more and more serious.Currently,the situation of agricultural environment needs to be improved urgently and the quality and safety of agricultural products need to be paid more attention because various pollutants entering into the soil.Among pollutants,heavy metals and antibiotics are two of the important pollution types in farmland soil.An analogue incubation experiment was conducted In this study,doxycycline(DOX,0,8,15 mg·kg^-1)and copper(Cu,0,100,400 mg·kg^-1)were chosen as the representative antibiotic and heavy metal,respectively,adding into the soil as exogenous pollutants to show the effects on soil ecosystem of antibiotic and\or heavy metal from the point of view of microorganism and molecule.This study systematically selected the indicators of soil ecosystem which include soil ecological functional stability,microbial community structure,microbial function and genetic abundance of microbial tolerance to pollutants,to illustrate the effects on soil ecosyetem functional stability and microbial of pollutants.In addition,this study comprehensively discussed the interaction relationships among soil ecosystem functional stability,the microbial function,community structure and the relative abundance of ARGs in soil system,for hopefully construct a microbial early warning system for the soil contaminated by heavy metals and\or antibiotics,and provide a theoretical basis for soil remediation and risk assessment.This study suggested the addition of different concentrations of DOX and\or Cu might have complicated and multi-directional effects on soil ecosystem.?1?For the stability of soil ecological function based on quantitative analysis of microbial respiration intensity,the single and combined pollution of DOX and Cu can significantly inhibit soil microbial respiration intensity during the incubation period.The combined addition of DOX and Cu showed a synergistic inhibition on soil resistance,resilience and stability,and the inhibition intensity increased with the increase of the concentration of Cu or DOX.However,under the condition of combined pollution of 400 mg kg^-1 Cu and 8 mg kg^-1 DOX,the addition of high concentration of DOX could alleviate the inhibition of copper on soil stability.Additionally,for one same type of pollution condition,its resilience is bigger than the corresponding resistance,this means the pollution perturbation can stimulate the ability of soil to repair its existing quality,resulting in the later stage of cultivation microbial respiratory intensity is greater than the initial stage of pollution,so as to maintain the long-term stability of the soil system.At the same time,a three-dimensional linear model between DOX,Cu concentration and soil stability was established,and the formula is:Sb=23.558-0.022 Conc._Cu-0.516 Conc._DOX?R²=0.672,p<0.05?.?2?Soil catalase,urease and invertase activities were used to indicate the changes of soil microbial function under single and combined pollution of heavy metals and antibiotics.It was found that DOX and\or Cu pollution stress generally promoted urease activity,inhibited sucrase and catalase activity,and the inhibition intensity corresponded to catalase activity was more strongly than that of sucrase activity.In addition,correlation analysis showed that there was a significant negative correlation between the concentration of copper and catalase activity,urease activity,and a significant negative correlation between urease activity and invertase activity.?3?The intrinsic diversity of soil microbial and the diversity of soil bacterial community structure were characterized by OUTs and their annotated taxonomies,Chao1 index,PD whole tree and Shannon,etc.It was found that soil microbial community structure changed greatly with the type,concentration and cultivation time of pollutants.Within the range of ecosystem remediation capacity,adding pollutants into soil leading to which tended to increase the diversity of microbial community structure,and the increase of microbial community structure diversity resulted from the combined pollution of Cu and DOX was more obvious than that of single pollution.In addition,combined the increased microbial community structure diversity with the significant weakened microbial respiration intensity of polluted soil,this study can conclude that the addition of pollutants may lead to more diverse composition of soil microorganisms,but the respiration activity of kinds of microbial is lower than before.?4?The relative abundance of four antibiotic resistance genes?ARGs??tetA,tetC,tetG and tetW?was used to characterize the tolerance of microorganisms to pollutants.The total relative abundance of these four resistance genes decreased first and then increased,probably resulted from the soil system needed about 7-15 days to adapt to aging after adding pollutants.The pre-existing resistance genes in the soil would transfer first after the change of living environment and at this time,the exogenous antibiotics had not yet induced resistance gene,resulting in the relative abundance of resistance genes decreased first.When at the later stage of culture,the addition of antibiotics could induce the resistance genes and promote the relative abundance of antibiotic resistance genes.Compared with other treatments,the addition of high concentration of Cu and DOX could significantly increase the abundance of resistance genes in the medium and later stage of culture,especially the relative abundance of tet A and tetW.In addition,adding high concentration of Cu could improve the ability of DOX to induce antibiotic resistance genes,increase the relative abundance of tet gene.