Studying the cumulative and long-term effects of fipronil, propyzamide and flutriafol on soil microbial functions and community composition: from laboratory to field scale

With the repeated pesticide applications in current agricultural practices, the effect of pesticides in soil may have long lasting effects on the non-targeted microorganisms. Most studies have investigated the effect of pesticides on laboratory basis, but the long-term field effects are largely unknown. In this study we assessed the ecotoxicological effects of fipronil, propyzamide and flutriafol on the soil microbial enzymatic activities (alpha-1,4-glucosidase, beta-1,4-glucosidase, beta-D-cellobiohydrolase, beta-xylosidase, beta-1,4-N-acetyliglucosaminidase, L-leucine aminopeptidase and phosphatase), potential nitrification, the absolute abundance of functional genes (nifH, archaeal and bacterial amoA, chiA, cbhl and phosphatase), the absolute abundance and diversity of total bacteria and fungi, and diversity of ammonia oxidizing microorganisms after repeated applications in laboratory and field settings. Our results showed that both propyzamide and flutriafol affected the soil microorganisms in a similar manner, with propyzamide being more prominent. The fipronil had the least effects in soil microbial functions and community in both laboratory and field studies. The most marked pesticide effects were observed in the field enzymatic activities, with significant inhibitory effects observed at the end of the two-year field study following annual pesticide applications. The pronounced effects from propyzamide and flutriafol were observed in the soil bacterial, fungal, ammonia oxidizing archaeal and bacterial community composition after the first application, but the effects were transient following the second application. However, the bacterial and fungal community structure remained significantly different between propyzamide treated soil and the control. With the recovery of community composition following second application, the microorganisms may be resilient to the pesticide applications, but the inhibitory effects on soil enzymatic activities and the community structural differences indicated that the microbial composition and performance might be altered, especially by the herbicide propyzamide. Overall, our results provide crucial information, useful in pesticide risk assessment.