Structural and functional responses of leaf-associated fungal communities to chemical pollution in streams

International audienceThe decomposition of allochthonous plant litter is a key ecological process in forested streams, involving the lignolytic activities of aquatic fungi. In this study we investigated the relationship between water pollution (by a mixture of nutrients, metals and pesticides) and the biomass, structure and enzyme activities of leaf‐associated fungal communities.The experiment was performed through a microcosm approach by comparing fungal communities from a less‐polluted upstream site to a more‐polluted downstream site in the agricultural basin of the Auzon stream (Puy‐de‐Dôme region, Centre France). The resistance as well as the ability of these fungal communities to recover from pollution was also assessed through a translocation experiment.Results showed a lower laccase activity and higher band richness in fungal communities from the downstream site comparing to the upstream site, which can partially be explained by the greater pesticide toxicity and concentration of dissolved organic carbon of downstream waters.Specifically, a negative relationship between laccase activity and nitrate concentration was observed, irrespectively of the studied site, whereas the relationship between nitrate and phenol oxidase/peroxidase appeared much weaker.The translocation experiment evidenced (1) a fast decrease in laccase activity concomitant with a shift in fungal structure after stress exposure, and (2) a recovery ability in terms of laccase activity and fungal community structure 2 weeks after stress removal.This study underlines the sensitivity of leaf‐associated fungal communities in terms of laccase activity and community structure to variations in chemical stress, as well as their ability to recover once the stress is removed. This study highlights the potential use of laccase as an indicator of chemical pollution of streams