Effects of the fungicide penconazole on the leaf litter associated aquatic mycobiome in artificial stream channel and flask experiments

Aquatic fungi play a key role in the turnover of organic matter in freshwater ecosystems, such as leaf litter in streams. Even though agriculturally applied fungicides that reach streams through spray drift or surface runoff may endanger the important functions of these organisms, potential effects of fungicides on the diversity of a complex fungal community are still understudied. We used metabarcoding of fungal DNA to investigate composition changes in a natural leaf litter associated aquatic mycobiome in artificial stream channels and flasks treated with 250 µg/L of the fungicide penconazole. Treated samples were compared with control samples from untreated systems and samples from a reference stream over 21 days. Our results show that differences in community composition between fungicide treated and control samples were weak for leaves that were preconditioned for two weeks in the reference stream prior to exposure. Apart from treatment effects on fungal biomass (in terms of ergosterol content), only the read numbers of two key taxa indicated an abundance shift that was probably induced by the fungicide. In contrast, strong diversity effects were observed during the following long-term recolonization (85 days) of sterilized leaves under penconazole stress, in which the occurrences of key taxa were significantly reduced in fungicide treated stream channels. Our results imply that DNA metabarcoding can be particularly effective to detect changes in fungal communities during the colonization of leaf litter, a crucial process for the following decomposition and the conservation of fungal diversity.