Data from: Inorganic fungicides as routinely applied in organic and conventional agriculture can increase palatability but reduce microbial decomposition of leaf litter

1. The application of fungicides is considered an indispensable measure to
secure crop production. These substances, however, may unintentionally
enter surface waters via runoff, potentially affecting the microbial
community. To assess such risks adequately, authorities recently called
for suitable test designs involving relevant aquatic microorganisms. 2. We
assessed the structural and functional responses of leaf-associated
microbial communities, which play a key role in the breakdown of
allochthonous leaf material in streams, towards the inorganic fungicides
copper (Cu) and elemental sulphur (S). These substances are of particular
interest as they are authorized for both conventional and organic farming
in many countries of the world. We used the food-choice of the amphipod
shredder Gammarus fossarum (indicative for microorganism-mediated leaf
palatability) as well as microbial leaf decomposition as functional
endpoints. Moreover, the leaf-associated microbial communities were
characterized by means of bacterial density, fungal biomass and community
composition facilitating mechanistic understanding of the observed
functional effects. 3. While Gammarus preferred Cu-exposed leaves over
unexposed ones, microbial leaf decomposition was reduced by both Cu and S
(up to 30%). Furthermore, Cu-exposure decreased bacterial densities (up to
60%), stimulated the growth of leaf-associated fungi (up to 100%) and
altered fungal community composition, while S did not affect any of the
assessed structural endpoints. 4. Synthesis and applications. We observed
both structural and functional changes in leaf-associated microbial
communities at inorganic fungicide concentrations realistic for surface
water bodies influenced by conventional and organic farming. Our data
hence justify a careful re-evaluation of the environmental safety of the
agricultural use of these compounds. Moreover, inclusion of an
experimental design similar to the one used in the present study in
lower-tier environmental risk assessments of antimicrobial compounds may
aid to safeguard the integrity of aquatic microbial communities and the
functions they provide.