| Northeast China is the main area of maize planting.Atrazine is a commonly used herbicide in corn field,which results in a large amount of atrazine entering the black soil farmland ecosystem.It is a great threat to the quality of black soil.To ensure the safety of agricultural production and solve the problem of atrazine in the soil environment and eliminate the potential threat to the environment has become an urgent problem to be solved.At present,in-situ bioremediation is considered to be the most effective way to remove atrazine from soil.In addition,it is reported that humic acid,an important component of soil,plays a role in the regulation of microbial activity.Aiming at the above problems and research progress,we discussed the biological mechanism of atrazine degradation by strain DNS10 which was isolated from the laboratory,during humic acid added.The preparation and optimization of carrier materials containing humic acid and functional strains were studied.In order to provide the necessary technical support and theoretical basis for in situ bioremediation of atrazine contaminated farmland soil,the application of functional microbial agents in the field was discussed.The main research contents and conclusions are summarized as follows:This paper focuses on the response characteristics of atrazine degrading strain DNS10 under exogenous humic acid addition.The effects of different amounts of additive(100 mg·L-1-800 mg·L-1)on the growth and degradation ability of strain DNS10 were determined.On the basis of this,the regulation of humic acid on the expression of degrading gene was studied by the method of quantitative PCR.The results showed that the addition of humic acid could promote the growth of DNS10 and increase the degradation rate of atrazine.When the concentration of humic acid was 400 mg·L-1,strain DNS10 was able to completely degrade atrazine in solution with initial concentration of 100 mg·L-1 at about 36 h.However,the control treatment without humic acid addition was still about 15.82% atrazine residue in the solution.Humic acid could promote the expression of atrazine degradation gene in strain DNS10.After 36 h culture,the expression of trz N was increased by 6.58 times compared with control treatment.The RNA-Seq sequencing technique was used to investigate the differences of the key functional genes of the strain DNS10 before and after the addition of humic acid,and then to explore the effect of humic acid addition on the GO function and the gene KEGG pathway of DNS10.The results showed that there was a difference in the expression of 140 genes in the strain DNS10 after the addition of humic acid.Among them,there were 78 up-regulated genes and 62 down regulated genes.GO enrichment analysis of differentially expressed genes,found that arginine biosynthesis,family glutamine biosynthesis of amino acids and arginine metabolism related genes were up-regulated,which may help to improve the strain for atrazine tolerance,promote bacterial growth.KEGG enrichment analysis results are consistent with the results of GO enrichment analysis.In order to apply the degrading bacteria in the process of soil remediation,we can construct and optimize the carrier to protect the degrading bacteria.The attapulgite,bentonite and cheap high humic acid content as carrier material,carrier material and construction optimization of strain DNS10 by the orthogonal method.The results show that survival rate of strain DNS10 was highest?68.48%?when the ratio of carriers for peat 1 g: attapulgite 0.5g: bentonite 1 g,at room temperature for 30 days.In addition,the mention carrier to the strain DNS10 showed better UV protection,after UV irradiation for 80 min,the survival rate of functional strains in the carrier can still be maintained above 60%.Two better effect treatments and DNS10 was selected to study on soil remediation.The results show that the fast atrazine biodegradation in soil is peat 1 g: attapulgite 0.5g: bentonite 1 g.The 28 day,soil atrazine degradation rate was 95.89%.Through the QPCR study of atz B and atz C in soil,after the addition of A2B2C3,the expressions of atz B and atz C were better than those of other treatments.By pot culture,study the corn in the uncontaminated soil?blank?,atrazine contaminated soil?pollution?and the addition of contaminated soil remediation inocula?repair?in seedling growth,leaf chlorophyll content,MDA content and atrazine distribution in Maize seedling.The results showed that after 21 days of cultivation,the biomass of maize seedlings was significantly lower than that of blank treatment.Similar to biomass,atrazine accumulation in roots and leaves of maize was greater than that of stems in all treatments.Atrazine decreased the chlorophyll content of maize seedling leaves.In the 21 days,the chlorophyll content in the leaves of pollution treatment was decreased by 4.58% and 3.32%,respectively,and the effect on chlorophyll a was more obvious than that of blank and restoration.It was only the blank and the content of repair treatment was 87.59% and 94.67%,respectively.Compared with the pollution treatment,atrazine content in root,stem and leaf was decreased by 22.29%,43.21% and 31.82%,respectively.With the optimization of peat,attapulgite and bentonite as the main matrix,the herbicide atrazine degrading bacteria DNS10 as the active component of the prepared microbial inoculants prepared in farmland soil as fertilizer application,soil treatment can increase the rate of reduction of long residual herbicide atrazine,while significantly increased maize yield.When the inoculum dosage of 10 kg·mu-1,the most significant yield increasing effect the yield increased by 13.92%.In addition,microbial agents could also increase the content of organic matter,ammonium nitrogen and available potassium.By pure culture,microbial agents was not only in improving crop yield,but also significant changes in soil microbial flora,indigenous microbial key function increased significantly,such as the number of key microbial nitrogen fixing bacteria,ammonia oxidizing bacteria and nitrifying bacteria in the soil nitrogen cycle.Compared with the soil without the addition of inoculum,the number of culturable bacteria could be increased by 266.67%,190.91% and 520.75%,respectively.The high-throughput technology was used to research the influence of agent for soil microbial community structure.Agents can improve the diversity of soil bacterial community structure,the main bacteria in Phylum level was Proteobacteria,Acidobacteria and Bacteroidetes,Firmicutes,Planctomycetes,Lactococcuspiscium and Chloroflexi.With the addition of atrazine,the bacteria of Firmicutes in soil increased obviously.The results of PCA analysis showed that the main factors causing the change of microbial community structure could be the addition of atrazine and microbial agents. |
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