Effects of the fungicide azoxystrobin and wastewater effluent on leaf-associated fungal communities and a key amphipod shredder

Abstract Freshwater ecosystems receive a constant influx of pollutants affecting all levels of biological organisation. We assessed the impacts of wastewater and the fungicide azoxystrobin on two trophic levels: the shredder Gammarus fossarum and leaf-associated fungal communities. Gammarus fossarum and Fagus sylvatica -leaves were exposed to stream water, wastewater, and both water types spiked with 40 µg/L azoxystrobin. For G. fossarum we determined the feeding rate and the respiratory electron transport system (ETS) activity, while the effects on fungal communities were investigated by measuring biomass, community composition, and sporulation rate, the latter serving as a measure of reproductive output. A significant decrease in feeding rate from stream water to wastewater with azoxystrobin was observed. ETS activity declined over time across all treatments, except in wastewater with azoxystrobin. Fungal biomass and community composition were not affected by azoxystrobin nor by wastewater, but the presence of G. fossarum increased the reproductive output. This study suggests that the combination of two stressors negatively affects G. fossarum , while the shredder itself positively affects the reproduction of leaf-associated fungi. By assessing the impact of fungicides in natural and polluted water, this research expands our understanding of pollutant-driven ecosystem shifts and their cascading effects on different trophic levels.