COS 93-2 - Effects of pesticides on soil microbial temporal dynamics

Abstract: Agrochemicals are a necessary part of modern agriculture and are commonly used throughout the world to protect plants from various pests and to maximize crop yield. The effects of pesticides have long been debated and it is currently unresolved if and how they affect soil microorganisms. Microorganisms play a critical role in agroecosystems and provide a range of services. Thus, the effects of agrochemicals on soil microbial communities are relevant for agricultural sustainability. Here we aimed to assess the impact of commonly used agrochemicals (fungicide, herbicide and insecticide) on bacteria; and fungal dynamics using a longitudinal experiment. We prepared microcosm chambers with 100g of native grassland soil and a diluted agrochemical. The dilutions were decided based on the maximum recommended amount for each pesticide (prothioconazole and tebuconazole, glyphosate, and lambda-cyhalothrin). Microcosms were then sampled at five different timepoints; days 0, 7, 14, 21 and 42. We assessed microbial abundance using quantitative PCR of bacterial 16s rRNA and fungal ITS genes. Illumina MiSeq sequencing was preformed to evaluate microbial diversity and community composition. Except for insecticide-treated soil for bacteria, a trend of decreasing abundance from days 0 to 21, and an increase from 21 to 42 was observed, suggesting a revival of bacterial communities. We found differences in microbial community structure in response to agrochemicals (PERMANOVA p value of 0.0876, 0.0001 for bacteria and fungi respectively) across time points (PERMANOVA p ≤ 0.0001 for both bacteria and fungi), and this difference was more pronounced in fungi. However, considerable changes in community composition were noted for bacteria with Alphaproteobacteria as the most abundant class followed by followed by Vicinamibacteria and Verrucomicrobiae. For herbicide and insecticide treated soils, we found a slight decline in Vicinamibacteria as time increased. For fungi, we recorded an increase in Sordariomycetes along with a decrease in Eurotiomycetes in all treatments. Co-occurrence network analysis showed that the majority of keystone taxa belonged to Actinobacteria. Indicator species analysis for bacteria demonstrated that the Pedosphaeraceae, Gemmataceae, and Entotheonellacae families are indicators for fungicide, herbicide, and insecticide-treated soils respectively. For fungi, the Ramicandelaberaceae and Orbiliaceae familes are indicators for herbicide and insecticide-treated soils, respectively. Overall, fungi were particularly affected by agrochemical applications, while bacteria showed more resilience. As fungal abundance, diversity and community showed significant changes in response to commonly used pesticides our study indicates that such agrochemicals may have consequences for fungi-derived ecosystem services.