Effects of the fungicide tebuconazole on microbial capacities for litter breakdown in streams.

Streams draining agricultural basins are subjected to the input of fungicides which can affect aquatic microbial communities. We analyzed the effect of the fungicide tebuconazole (TBZ) on Alnus glutinosa and Populus nigra litter breakdown by aquatic microorganisms. For six weeks, fungal and bacterial responses were analyzed in indoor stream channels subjected to TBZ-contaminated (33.1±12.4 μg L(-1)) and uncontaminated conditions. Litter breakdown rates decreased in presence of TBZ. The decrease was explained by reductions in microbial biomass development and shifts in community structure. At the same time, TBZ modified the kinetics of β-glucosidase, β-xylosidase and cellobiohydrolase enzymes resulting in lower affinities for cellulose and hemicellulose decomposition in leaves. These alterations were modulated by the litter quality; the greatest structural impairment was observed in Populus whereas Alnus were more affected in terms of leaf breakdown rate. Our results suggest that chronic exposure to TBZ can affect aquatic microbial communities and their capacity to break down leaf litter in streams.