Limited role of fungal diversity in maintaining soil processes in grassland soil under concurrent fungicide stress

Abstract Background Fungicides are an effective tool for protecting crops and maintaining a steady food supply. However, as pathogens continue to evolve, it is crucial to prolong the effectiveness of fungicides by delaying resistance development. A key strategy to achieving this is to combine or rotate fungicides with different modes of action. As fungicides lack specificity, they inevitably affect both pathogenic and non-pathogenic fungi when surrounding environments are unintentionally contaminated. Our study aims to investigate the effects of recommended application methods to prevent resistance development, specifically repeated-single fungicide, simultaneous mixture, and sequential applications on non-target soil fungi, and the subsequent impacts on important soil processes. We used fungicides with different modes of action on soil microcosms inoculated with fungi at varying levels of diversity (3, 5, and 8 species) isolated from a protected grassland. Results We found that repeated treatments of individual isopyrazam and prothioconazole differentially inhibited fungal activity. Although mixture applications are considered more protectant against crop pathogen resistance than repeated application, our study revealed stronger negative effects of simultaneous application on saprobic fungi and consequently on soil processes. However, contrary to expectations, higher fungal diversity did not translate to improved soil function under these conditions. Conclusions The simultaneous application of fungicides with different modes of action (MoA) has more pronounced non-target effects on soil compared to the individual or sequential application of fungicides. These non-target effects extend beyond the intended control of pathogenic fungi, impacting saprobic and beneficial soil microbes and the critical processes they drive. When fungicides are applied concurrently, microbial activities in the soil are significantly altered, even in soils with high microbial diversity. Our study emphasizes the importance of carefully considering the unintended consequences of fungicide use in agriculture. As we strive for a secure food supply, it is crucial to investigate the broader environmental impacts of these chemical interventions, including their effects on non-pathogenic fungi and overall soil health.