Research On Preparation Of Microbial Agent And Its Remediation Of Herbicide-Contaminated Soil

In China,in order to increase the grain yield,a large number of chlorimuron-methyl has been used in farmland,which leads to more ecological and environmental problems.The use of microbial technology to remove residual herbicides in soil has the advantages of low cost,almost no harm to the soil environment,excellent treatment effect and in-situ treatment.At present,it is often used as the main technical means of soil ecological environment restoration in China.The vicious competition of indigenous microorganisms and complex environment can reduce the viability and competitiveness of chlorimuron-methyl degrading microorganisms.Therefore,the microbial inoculum technology that can improve the survival rate of soil bacteria and degradation has been paid more and more attention.In this study,a white-rot fungus W-1 was used to degrade chlorimuron-methyl.Corn stalk,chaff,peanut hull and bran were used as carriers to prepare solid microbial agents to remove chlorimuron-methyl.Improve the removal efficiency of solid microbial agents by optimizing fermentation conditions and the ratio of additives.And the preservation stability of microbial agents was analyzed.Laboratory simulation experiments were conducted to detect the actual remediation effect of microbial agents,and the remediation of soil microbial communities by agents was discussed.The main research of this topic is as follows:（1）The effects of four kinds of carriers（corn stalk,peanut hull,chaff and bran）and seven kinds of protective agents（K₂PO₄,Ca₃（PO₄）₂,K₂HPO₄,carboxymethyl cellulose,dextrin and VC）on the growth of W-1 strain were studied.The results showed that corn stalk had no inhibitory effect on the growth of W-1 strain,while the other three vectors inhibited the growth.Therefore,the microbial agent was prepared with corn stalk as carrier,and seven protective agents can promote the growth of W-1 strain.The appropriate drying methods and drying protectants of the microbial agents were explored.The microbial agents were dried under different drying conditions.Finally,the degradation rate of chlorimuron-methyl was measured by high performance liquid chromatography（HPLC）to determine the influence of different drying conditions on the degradation performance of W-1 strain.The results showed that drying at room temperature of 25°C for 24 h in sterile room has little effect on the repair performance of W-1 strain,so it can be used.Among the four protective agents,calcium phosphate has the best performance,and the degradation rate of chlorimuron-methyl by adding this stabilizer is over 70%.The suitable UV protectants（dextrin and VC）were explored.The results showed that 1%dextrin contributed to the degradation of chlorimuron-methyl by W-1strain,which increased by about 10%,while 0.5%and 1%ascorbic acid inhibited it.（2）Analysis of the removal effect of solid microbial agents on chlorimuron-methyl in soil.The results showed that after 20 days,the removal rate of chlorimuron-methyl in each treatment group decreased in order of solid microbial agent,free bacteria and corn straw.Their degradation trend increased rapidly in the first 5 days,and the removal rate of corn stalk group did not change obviously after 5 days.After the 15th day,the removal rate of isolated bacteria group tended to be flat,and there was no greater improvement.However,the degradation rate of solid microbial agent group has been rising all the time in the whole experiment,and the highest removal rate is 84.8%,which is significantly higher than that of free microbial inoculum and corn stalk treatment group.（3）The structure of soil microbial colony and the influence of W-1 strain were discussed.The results showed that the diversity and richness of microbial communities were significantly improved by adding solid microbial agent.The ACE,Chao and Shannon index of bacteria and fungi increased,while Simpson index decreased.Compared with contaminated soil,microbial inoculum improved the diversity of soil microbial flora,among which bacteria increased significantly compared with fungi.Microbial agents improve the diversity of soil microbial flora,among which bacteria are more obvious than fungi.At the phylum classification level,the relative abundance of Chloroflexi and Actinobacteria of bacteria,Ascomycota and Mortierellomycota of fungi increased,while Basidiomycota of fungi decreased.At the level of class classification,the relative abundance of Thermoleophilia of bacteria and Mortierellomycetes,Sordariomycetes and Tremellomycetes of fungi increased.The Alphaproteobacteria,Gammaproteobacteria and KD4-96 of bacteria,Pezizomycetes and Agaricomycetes of fungi decreased.At the level of genus classification,the relative abundance of Norank＿f＿norank＿o＿norank＿c＿KD4-96 of bacteria,Chaetomium,Mortierella,Gibberella,Trichocladium and Fusarium of fungi increased.The Sphingomonas,Arthrobacter and Marmoricola of bacteria,and Geopora and Tomentella of fungi decreased.After 20 days of restoration,the relative abundance of Ascomycota in CK＿L and CK＿L＿J treatment group increased by 6%and 22.8%respectively,and the relative abundance of Chaetomium increased from the initial 0.5%to 31%,which proved that the inoculated fungi successfully colonized in the soil and became the dominant flora in the environment.