Effects of fungicides on aquatic fungi and bacteria. Effects of fungicides on aquatic fungi and bacteria: a comparison of morphological and molecular approaches from a microcosm experiment

Fungicides are frequently used in agriculture. They can be transported from agricultural areas to the freshwater ecosystems draining agricultural catchments and there, impact freshwater microorganisms and their functions. Therefore, studies studying the impacts on both community composition and functional effects are needed. We examined how fungicides affected leaf-associated fungal and bacterial communities, which are important for the breakdown of organic material. To examine the effects on community composition, we used ITS and 16S metabarcoding and compared this to community composition assessed via the sporulation of aquatic hyphomycetes. While we found a similar number of species with DNA metabarcoding as with sporulation, metabarcoding also enabled the identification of overlooked aquatic hyphomycete taxa and other fungi and could distinguish individual amplicon sequence variants (ASVs) thereby providing greater taxonomic resolution. In line with the sporulation results, metabarcoding neither revealed effects of fungicides on the aquatic hyphomycetes, nor on the whole fungal and bacterial community composition. However, several ASVs showed significant responses to the fungicides, demonstrating that within species genotypes with different tolerance exist. Overall, it appears that the fungicide treatment had little effect on community structure, suggesting that there was minor community turnover, despite having clear effects on functioning.