Effects of silver nanoparticles and nitrile fungicides on soil microbial community structure, metabolic functions, and resistance genes

Nitrile fungicides and silver nanoparticles (AgNPs) are increasingly applied in agriculture, yet their synergistic toxicity to soil ecosystems remains unclear. This study investigated the individual and combined effects of AgNPs and three nitrile fungicides—azoxystrobin, flufenacet, and chlorothalonil—on soil microbial communities, metabolic activities, antibiotic resistance genes, metal resistance genes, and plant physiology. The results showed that the synergistic toxicity of AgNPs with the three nitrile fungicides induced oxidative stress in the maize to varying degrees. Nitrile fungicides alone increased sucrase activity, while AgNPs alone suppressed urease, sucrase, and acid phosphatase. Both treatments promoted dominance of Pseudomonadota , Bacteroidota , and Sphingopyxis . AgNPs specifically enriched Proteobacteria and Myxococcus , causing carbon/nitrogen utilization impediments partially mitigated by nitrile biodegradation. Synergistic exposure redirected nitrile catabolism from the benzoyl-CoA to catechol pathway. AgNPs alone upregulated silver resistance genes and activated antibiotic efflux pumps; synergistic exposure with fungicides suppressed Ag + efflux genes while exacerbating antibiotic efflux activation and weakening links between environmental factors (NH₄ + -N, NO₃ − -N, Ag + ) and resistance genes. These findings reveal the responses of plants and soil microorganisms to co-exposure of nitrile fungicides and AgNPs, and provide insights for assessing the ecological risks of combined application of nanomaterials and pesticides.