Degradation Of Azoxystrobin And Its Ecological Effects In Soil After Repeated Application

Because of its continuous cropping and high incidence of diseases and pests,facility agriculture needs high-frequency and heavy use of pesticides.In addition,its relatively closed environment not only causes the pesticide residue problems in soil are more serious,but also affect soil microbial activities and their diversity.In this study,the fungicide azoxystrobin commonly used in vegetable greenhouse was selected as the research object.Azoxystrobin was applied several times under laboratory simulation conditions to study its residual activity in soil and the effects on soil respiration,soil enzyme activity and of soil microbial diversity,in order to provide a scientific basis for the evaluation of the ecological safety of azoxystrobin and its rational use.The results were summarized as follows:1.The degradation of azoxystrobin at the recommended dose(2 mg·kg-1),double the recommended dose(4 mg·kg-1)and five times the recommended dose(10 mg·kg-1)followed a first-order model in soil.The half-lifes of azoxystrobin at 2 mg·kg-1 doses were 10.3,9.3,9.8,8.1 d;The half-lifes of azoxystrobin at 4 mg·kg-1 doses were 12.0,9.3,7.3,6.3 d;The half-lifes of azoxystrobin at 10 mg·kg-1 doses were 15.6,9.2,8.5,7.5 d.The results showed that with the increase of application times,different treatments of azoxystrobin in soil degradation showed an accelerating trend.2.Azoxystrobin repeated four times had no significant effect on soil urease activity.After the first application,azoxystrobin inhibited soil dehydrogenase and neutral phosphatase activity,but there are no significant effect after the follow application.The soil sucrase activity increased by 11.9%,7.0%,8.4%and 15.3%respectively at day 14 after four successive treatment of 10 mg·kg-1 azoxystrobin,no significant effect changes at levels of 2 and 4 mg·kg-1.Soil catalase activity increased by 10.1%at day 14 after the fourth application of 10 mg·kg-1 azoxystrobin,no significant effect on othe treatment.3.The effect of repeated application of azoxystrobin on soil respiration activity was determined by substrate induced respiration method.After the first application of azoxystrobin,the soil respiration activity increased significantly by 10.3%-55.1%,and the increase was positively correlated with the application concentration.After the second application,soil respiration was increased and restored the control level after one day.There was no significant effect of respiration on soil 7 h respiration activity after the third application.On the day 7-14 after the fourth application,Soil respiration activity increased by 4.0%?26.6%.4.The effect of azoxystrobin on the amount of soil microorganisms was determination by plate counting.The results showed that azoxystrobin significantly inhibited the fungi in the soil and the inhibitory effect increased with the increase of the applied concentration.After the first application of azoxystrobin,the number of fungi was inhibited by 30 to 38%,On the day 14 after four successive treatment of azoxystrobin,the inhibition of the number of fungi were 33?47%,25?51%,36?48%and 29?35%.Azoxystrobin significantly inhibited the bacteria in the soil after the first application,and the inhibitory effect have positive correlation with the application concentration.After the second and third application of azoxystrobin,it showed inhibition of bacteria first and then changed to promotion.the effect of azoxystrobin was only promotion after the fourth application,and the effect of promotion decreased with time until it disappears.5.The Amplicon sequencing was used to research the effects of azoxystrobin on soil microbial community.The results showed that repeated application of azoxystrobin changed soil microbial community structure.After the application of azoxystrobin,Proteobacteria,Bacteroidetes and Actinobacteria were dominant bacteria in soil,and Firmicutes changed from inferior bacteria to dominant bacteria group.By analyzing the chao index and the Shannon index,the species richness of the bacteria in soil samples after the first application of azoxystrobin was significantly higher than others.After the first application of azoxystrobin,there was no obvious change in species richness of soil bacteria,but it was significantly affected after the follow three times treatment of azoxystrobin.