The Degradation Of Atrazine And Microbial Diversity Characteristics Of This Process In Submerged Plant Rhizosphere

Atrazine is a common persistent toxic pollutant,because of its stable nature,long half-life,making its high residual in soil conditions.Atrazine in the soil enters into the water due to leaching and surface runoff.Atrazine will be immobilized by sediments while the sediments adsorb it.Meanwhile,atrazine has been detected in sediments frequently.Therefore,it is necessary to study the restoration of the sediment.Rhizoremediation is considered to be the most potential technology,the chemistry and biochemistry behavior of organic pollutants in the submerged plant rhizosphere sediment is the main mechanism,microbial diversity as indicators are very important in monitoring sediment changes and reflect the environmental stresses,for the further understanding of soil/sediment microbial community state is also very useful.This research selected two submerged plant: Potamogeton crispus L and Myriophyllum spicatum L,to explored the specific degradation behavior of atrazine in different submerged plant rhizosphere and characteristics of sediment microbial diversity.The main results were as follows:(1)Add 2 mg/kg atrazine to the sediment of Nanhu Lake,carry out atrazine degradation experiment respectively.At 60 d: in the system of P.crispus,the residual concentration of atrazine in atrazine plant treatment(AT-P,rhizosphere)and Atrazine treatment(AT,non-rhizosphere)were 0.43 and 0.60 mg/kg,the degradation rate were78.63 and 70.01% respectively.There are significant differences between the two treatments(p < 0.05).In the system of M.spicatum,the residual concentration of atrazine in AT-P(rhizosphere)and AT(non-rhizosphere)were 0.126 and 0.323 mg/kg,the degradation rate are 93.69 and 81.75% respectively.There are significant differences between the two treatments(p < 0.05).The degradation rate of M.spicatum was higher than P.crispus.The atrazine degradation products of different treatments in these two systems were hydroxylatrazine.The content of hydroxylatrazine reduce gradually over time and the hydroxylatrazine content in AT-P treament(rhizosphere)was higher than AT treatment(non-rhizosphere).In these two systems,the content of soluble organic carbon and degradation rate of atrazine had no significant correlation,but the basic trend was same.It means that DOC content is relatively high and the atrazine degradation rate is also relatively high.The soluble ammonium nitrate nitrogen and soluble nitrogen present decline trend during the experiment and the content of AT-P treatment(rhizosphere)is higher than AT treatment(non-rhizosphere).(2)In these different treatment of two system,the activity of dehydrogenase presents rising trend with the time passed;the number of bacteria presents rising trend with thetime passed,and was as following order: AT-P treatment > CK-P treatment > AT treatment.Rhizosphere effect made adaption microorganisms to pollutants strengthen or microorganisms was able to take advantage of exogenous pollutants as carbon source and nitrogen source,thus improved the dehydrogenase activity indirect and promoted the degradation of atrazine.Selected three strains that could growth with only nitrogen source atrazine from sediment,the degradation rate of atrazine was 14.49%,60.02% and 13.50%,respectively.(3)Selected the sediment samples from different treatment in M.spicatum system at60 d,used MiSep sequencing technique to measure the microbial diversity.The richness estimators and diversity estimators showed that,the richness of microbial community ordered was as follow: AT-P>CK-P>CK>AT,the diversity of microbial community ordered was as follow: CK-P>AT-P >CK>AT.Compared with another three treatments,community structure analysis shows that the richness of two strains of AT-P treatment had significant higher diversity: Desulfobulbus,Nitrospira,they may be the strains that related with the degradation of atrazine;the richness of two strains of AT treatment have significant diversity with another two treatments: norank_c__OPB35_soil_group,norank_f__Xanthomonadales_Incertae_Sedis,we can conclude that added atrazine to sediment can promoted this two strains growth and breeding.