Bacterial Resilience and Vulnerability to Neonicotinoid Seed Treatments in Soil: Short-Term Community Responses

We explored the short-term impacts of three neonicotinoids (imidacloprid, thiamethoxam, and clothianidin) on soil bacterial community composition and diversity in wheat-planted microcosms. Neonicotinoids were applied as seed treatments, and soil samples were collected over 10 days. Overall alpha diversity metrics showed no significant treatment- or time-dependent shifts; however, post hoc analyses revealed transient, treatment-specific responses at individual sampling time points. Thiamethoxam and clothianidin significantly increased diversity and evenness at early time points, while imidacloprid reduced diversity by Day 10. Clothianidin was also associated with a short-term increase in estimated species richness. Actinobacteriota and Proteobacteria dominated across treatments, with Firmicutes increasing and Bacteroidota declining with time. The minor phylum Methylomirabilota exhibited a significant treatment effect. Sampling day and day-treatment interaction significantly influenced community structure. Mesorhizobium enriched under all neonicotinoids. Imidacloprid enhanced Massilia and suppressed Solirubrobacterales and Chloroflexia. Thiamethoxam enriched Gaiella, Solirubrobacter, and Massilia but suppressed Nitrospira. Clothianidin enriched Solirubrobacter and Lysobacter but suppressed Methyloceanibacter and Nitrospira. Haliangiaceae were positively correlated with sampling days, while Flavobacteriaceae and Microscillaceae were negatively correlated. Yersiniaceae and Solirubrobacteraceae were negatively correlated with imidacloprid and Mycobacteriaceae with thiamethoxam. These findings highlight the need for longer-term and functional investigations into neonicotinoid impacts on soil microbial communities and ecosystem health.