Functional redundancy in leaf-litter-associated aquatic hyphomycetes: Fine sediment alters community composition but hardly decomposer activity

Abstract

The increase in the flow of fine sediments to the aquatic ecosystems (AH), as a consequence of human activities, is a widespread stressor that may alter the structure of biological communities and ecosystem processes. In this study, the effects of sediments (Ø < 2 mm) on the structure (biomass and composition) and activity (decomposer activity and sporulation rate) of litter-associated microorganisms (mainly AH) were investigated. For this, leaf discs of in-stream preconditioned Quercus robur were incubated in microcosms for 30 days under the influence of four different grain-size (<2, 1–0.5, 0.5–0.063, and <0.063 mm) sediments kept in motion. Fine sediments barely altered microbial decomposer activity and did not affect fungal biomass. Meanwhile, the sporulation rate was enhanced by sediments’ presence, the results being grain-size-dependent, and the fungal community composition was affected by the presence of sediments, independently of grain size. These findings evidence the functional redundancy of microbial assemblages involved in leaf litter decomposition in freshwaters.