Effect And Mechanism Of Earthworms On Soil Atrazine Degradation

As a kind of triazine herbicide, atrazine(ATR) was widely used in the world. However, as a typical organic pollutant, its impact on ecological environment and human health issues is also increasingly serious. The activity of earthworms could improve the physico-chemical and the microbial properties. Therefore, earthworms have a great potential in remediation of soil polluted by organic pollutants. Choosing two ecological earthworms(Eisenia foetida and Amynthas robustus Perrier) as the experimental organisms, we set up an artificial simulation experiment in this study. The effect of earthworms on soil ATR degradation and pathway of ATR degradation was studied using high performance liquid chromatography(HPLC). Soil chemical and microbiological characteristics ware analyzed to explore the mechanism of the influence of earthworms on ATR degradation. Then stable isotope probing(SIP) coupled with high-throughput sequencing(HTS) was applied to reveal the functional microorganisms involved in the soil ATR degradation processes. Besides, traditional microbial identification method was used to screen ATR degradation bacteria, preparing for the field application. These researches will provide theoretical basis and technical support for enriching and developing the biological remediation techneques of organic polluted soil. The results and conclusions are shown as below:1. Via the degradation effect experiment, we found that the residual of ATR in Sn Ee and Sn Ea significantly lower than that in CKn after 14 days, and the ATR residual in Sn Ea was lower than that in Sn Ee always. The results indicated that two ecological earthworms have promoting effect on soil ATR degradation, and the degradation effect of Amynthas robustus Perrier is better than Eisenia foetida.2. By monitoring the degradation products of ATR, we found that the production of hydroxyatrazine(HYA) and deethylatrazine(DEA) in Sn Ee and Sn Ea significantly higher than that in CKn before 14 days, and the same and opposite effect respectively for deisopropylatrazine(DIA) and HYA after 14 days. This shows that earthworms significantly promote the formation of HYA and DEA by the early stage, and later significantly promote the formation of DIA and the transformation of HYA, so as to affect the biological degradation pathway of ATR.3. The main chemical and microbiological properties of the contaminated soil were determined, we found that the p H, microbial biomass carbon, nitrogen and soil respiration in Sn Ee and Sn Ea higher than that in CKn during the incubation period. Principal components analysis was carried out between these indexes and ATR, we have summarized earthworms promote the degradation of ATR by increasing soil p H, microbial biomass and microbial activity.4. We combining DNA-SIP with HTS to explore the functional microorganisms associated with degradation of ATR in soil. The results showed that the main functional microorganisms are Kaistobacter, Rhodanobacter, Rhodoplanes, Ramlibacter, Pseudonocardia and Planctomyces.5. Enrichment culture method was used to select dominant degradation strains from contaminated soil, and three strains with ATR as the sole nitrogen source were screened out. Combine morphological, physiological and biochemical characteristics with 16 S r DNA, we identified the degradation bacteria Bacillus megaterium, Citrobacter amalonaticus and Brevibacterium halotolerans. They have good potential for soil remediation.