Effects of pyraclostrobin, metalaxyl-M, trichloroisocyanuric acid and thiodiazole copper on soil physicochemical properties and bacterial diversity, community structure and function

Non-target microorganisms in soil are very important for the restoration of soil fertility and the safety of soil microecosystem. Currently, the effects of the bactericides, pyraclostrobin and metalaxyl-M, for the control of tobacco black shank disease and bactericides, trichloroisocyanuric acid and thiodiazole copper, for the control of tobacco bacterial wilt disease on soil microecology are still unclear. In this study, high-throughput sequencing technology was used to analyze the diversity, community structure and function of soil bacteria in tobacco fields after root-irrigation with pyraclostrobin, metalaxyl-M, trichloroisocyanuric acid and thiodiazole copper. The results showed that treatment with trichloroisocyanuric acid and thiodiazole copper significantly increased soil organic matter content, ammonium nitrogen content, and electrical conductivity, while reducing bacterial abundance and diversity. Pyraclostrobin and metalaxyl-M enhanced Actinobacteria abundance by 15.2% (p < 0.05) but reduced Proteobacteria and Acidobacteria by 8.7% and 6.3%, respectively, with no significant changes in overall community diversity (Shannon index, p > 0.1). Functional prediction analysis showed that trichloroisocyanuric acid and thiodiazole copper could increase the relative abundance of metabolic functional genes in soil bacterial communities. This study has laid a solid foundation for the environmental behavior and scientific use of pyraclostrobin, metalaxyl-M, trichloroisocyanuric acid and thiodiazole copper in soil.