Effect Of Fungicide Tetraconazole Application On Soil Microbial Community

Tetraconazole is a novel triazole fungicide developed by Italy Isagro Co.It is effective in controlling broad-spectrum diseases such as powdery mildew and rust on vegetables,cereals and fruits.However,tetraconazole has a relatively high soil organic carbon binding coefficient and a long half-lives.Most studies have reported that the pesticides having the most significant effect on the soil microbial community were broad-spectrum killing and inhibiting fungicides.To prevent tetraconazole-induced adverse effects on the soil ecosystem,the degradation dynamics and effect of tetraconazole addition on soil microbial communities were accurately evaluated here.It is of great significance for its scientific utilization and environmental risk assessments.Tetraconazole was applied to soil samples with no previous pesticide history at three different levels:the largest recommended field rate(0.33mg/kg dry weight equivalent soil,DW),three times recommended field rate(1.00 mg/kg DW soil)and ten times recommended field rate(3.33 mg/kg DW soil).After being incubated for 7,15,30,45,60 and 90 days,soil sample were collected for the determination of tetraconazole residue and properties with potentiality to indicate soil health such as basal respiration,substrate-induced respiration,microbial biomass carbon,community structure and functional diversity.Results are showed as follows:1.Gas chromatography-tandem mass spectrometry(GC-MS/MS)coupled with QuEChERS method was developed for the determination of tetraconazole,and quantitated by external standards.Average recoveries of tetraconazole in soil at four levels(0.01mgkg-1,0.05mgkg-1,0.5 mgkg-1,5.0mgkg-1)ranged from 80.9%-90.3%with coefficient of variation of 4.2-8.1%.Limit of determination(LOD)for tetraconazole was 0.87?g/kg,limit of quantitation(LOQ)for tetraconazole was 3.57?g/kg.The results of tetraconazole spiked experiment show that this method with small interference,good linearity,accuracy,precision and sensitivity.The residue dissipation experiments indicated that the degradation dynamics of tetraconazole applied at different levels(0.33,1.00,3.33 mg/kg DW soil)in soil followed the first order kinetics model and its half-lives were 69-87 days.2.Tetraconazole significantly decreased the number of soil microbial community as the result of microbial biomass C determination suggested.The activity of basal respiration and substrate-induced respiration were inhibited by tetraconazole application,and it tended to recovery or recovered as the time extension.Both qC02 and QR indicated that the effect of tetraconazole on soil microbial was minor when it was applied at the recommended field concentration(T1),and the higher tetraconazole concentrations(T3 and T10)were harmful to soil microbial.3.Phospholipid fatty acid(PLFA)experiment was conducted to evaluate the effect of tetraconazole on soil microbial community structure.The total PLFA analysis showed that the number or activity of microbial community was significantly decreased in tetraconazole-treatment soil.The ratios of the Gram-negative/Gram-positive(GN/GP)bacteria decreased,and GN decreased more significantly than GP.The ratios of the fungi/bacteria were increased because fungi biomass was increased in tetraconazole-treatment soil,but bacteria biomass was decreased on contrary.Principal component analysis(PCA)indicated that both tetraconazole addition and incubation time had change the structure of soil microbial community obviously,and more significant effect was showed by incubation time.4.BIOLOG Eco plates experiment was used for the evaluation of the effect of tetraconazole addition on soil microbial community functional diversity.The values of average well color development indicated that tetraconazole applied at the largest recommended field rate(T1)decreased substrates utilization of soil microbial temporally and higher application levels(T3 and T10)performed a longer adverse impact.Microbial functional diversity indices analysis showed tetraconazole application significantly decreased the number of the available carbon substrates,increased the richness abundance of common species and decreased the degree of carbon source utilization of microbial communities.In a word,the effect of tetraconazole applied at the recommended field rate on soil microbial was minor,higher-concentration tetraconazole(three or ten folds recommended field rate)decreased soil microbial biomass and activity and change the structure and functional diversity of soil microbial community significantly.