Dissipation of herbicides and fungicides in a vineyard soil and responses of bacterial, fungal and protist communities

The effect of pesticide residues on non-target microorganisms in multi-contaminated soils is poorly understood. Here, we examined the dissipation and degradation of a mixture of widely used pesticides in vineyard soil and associated changes of the bacterial, fungal and protistan communities. Laboratory soil microcosms were set at contrasted temperatures (20°C and 30°C) and water contents (20% and 40%) under both sterile and non-sterile conditions. Pesticide dissipation rate constants varied from 27 to >300 days, depending on pesticide properties and the soil conditions. More than 50% of dimethomorph > isoxaben > simazine = atrazine = carbendazim dissipated in soil within 200 days at 20°C and 30°C in both sterile and non-sterile soil experiments. The contribution of biodegradation to the overall pesticide dissipation increased with temperature and water content (up to 79% at 30°C and 40%) for soluble pesticides, ordered from more to less biodegraded, metalaxyl>isoproturon=pyrimethanil>S-metolachlor>carbendazim. Analysis of high-throughput amplicon sequencing showed that temperature and water content affected the taxonomic composition of bacterial, fungal and protist communities, whereas pesticide exposure remained a secondary determinant of community variation. Overall, soil physico-chemical characteristics had a larger impact than pesticides on different taxonomic domains of microorganisms in the vineyard soil. At a finer level of detail, the pesticide mixture had lower effect on bacterial and fungal than on protist communities. Our results emphasize the predominant influence of temperature and soil water content on pesticide dissipation, biodegradation and microbial communities in vineyard soil multi-contaminated with pesticides.