Study On The Effect Of Metalaxyl Enantiomers On Soil Microorganism

Metalaxyl is a kind of chiral pesticide,which is applied directly to soil as a common root germicide in tobacco.Metalaxyl is unavoidable to affect soil microbes.Studies have shown that the selective behavior of the two enantiomers of metalaxyl in different organisms and environments has a great difference.In this study,the effects of metalaxyl enantiomers on soil microbial activity,community structure diversity and microbial biological function were systematically studied by indoor simulation.This study describes the difference in the effect of metalaxyl enantiomers on soil microbes and the key factors.The results provide a theoretical basis for evaluating the ecological risk and rational use of the enantiomers of metalaxyl.The conclusions are summarized as follows:1.Degradation of metalaxyl enantiomers in soilIn this experiment,the analytical method of metalaxyl enantiomers in soil was established by high performance liquid chromatography-mass spectrometry(HPLC-MS/MS).The degradation rule of soil under indoor cultivation condition was defined.The results showed that the degradation trend of metalaxyl two enantiomers accorded with the first order kinetic equation.The tendency seems to be faster at the first stage and slower then.The half-life of 1 mg/kg R-and S-metalaxyl were 8.05 d and 8.82 d,the half-life of 10 mg/kg R-metalaxyl S-metalaxyl is 9.39 d and 9.96 d,respectively.Compared with Smetalaxyl,R-metalaxyl degraded faster.2.Effects of metalaxyl enantiomers on the overall activity of soil microbesIn this experiment,the effects of metalaxyl enantiomers on soil basal respiration,induced respiration,urease and catalase activity were studied by indoor simulated culture.The results showed that the inhibitory effect of different enantiomers on the overall activity of soil microorganism in the early stage of culture was dose-dependent.The greater the concentration of metalaxyl enantiomers,the more obvious the inhibition effect of soil microbes.The inhibitory effect of high concentration of R-metalaxyl is stronger than S-metalalin for a certain period of time.In the later period of culture,the high concentration of metalaxyl enantiomer activates the overall activity of soil microorganism.Then the activity was slowly recovered to the control level.The effect of metalaxyl enantiomers on the overall activity of soil microbes is not only related to the concentration and time of treatment,but also the stereoselective difference.3.Effects of metalaxyl enantiomers on soil microbial community structureThe effect of metalaxyl enantiomers on soil microbial community structure was studied by using phospholipid fatty acid(PLFA)method.The results showed that metalaxyl enantiomers had inhibitory effect on soil bacteria,fungi,GN and GP bacteria,and there was a dose inhibition relationship.The concentration of metalaxyl enantiomers is the main factor affecting the soil microbial community structure.The higher the concentration is,the stronger the inhibition effect is.The inhibitory effect of R-metalaxyl at the same concentration is stronger than that of S-metalaxyl,and there is a stereoselective difference4.Effects of metalaxyl enantiomers on soil microbial functionThe effects of metalalin enantiomers on the utilization and community function of soil microbial substrates were studied by biolog-eco method.The results showed that the Shannon index,Simpson index and Mclntosh index of soil were significantly changed by metalaxyl enantiomers.The homogeneity of soil microbial population was broken,and the enantiomer treatment of metalalin increased the richness of the dominant population.Concentration of metalaxyl enantiomers is the main factor affecting the structure function of soil microbial community,and there is a dose activation relationship.There is no stereoselective difference between the different enantiomers.5.Effects of metalaxyl enantiomers on root activity and antioxidant enzyme activity of tobacco seedlingsThe root activity of tobacco seedlings was significantly reduced by methodel stress,and the activity of SOD,POD,CAT and MDA content in leaves were increased.The stress effect of 30 mg/L metalaxyl on tobacco seedlings was stronger than that of 10 mg/L.The effects of enantiomers stress on SOD,CAT activity and MDA content have significant stereoselectivity.The effect of R-metalaxyl on SOD in the late stage of 30 mg/L stress is stronger than that of S-metalaxyl.The effect of R-metalaxyl on CAT is stronger than that of S-metalaxyl.The content of MDA under the stress of 10 mg/LR-metalaxyl is higher than that of S-metalaxyl.