Pelagic-benthic coupling of the microbial food web modifies nutrient cycles along a cascade-dammed river

Cascade dams disrupt the river continuum,altering hydrology,biodiversity and nutrient flux.Describing the diversity of multi-trophic microbiota and assessing microbial contributions to the ecosystem processes are prerequisites for the restoration of these aquatic systems.This study investigated the microbial food web structure along a cascade-dammed river,paying special attention to the multi-trophic relationships and the potential role of pelagic-benthic coupling in nutrient cycles.Our results revealed the discontinuity in bacterial and eukaryotic community composition,functional group proportion,as well as a-diversity due to fragmentation by damming.The high microbial dissimilarity along the river,with the total multi-trophic P-diversity was 0.84,was almost completely caused by species replacement.Synchronization among trophic levels suggests potential interactions of the pelagic and the benthic groups,of which the p-diversities were primarily influenced by geographic and environmental factors,respectively.Dam-induced environmental variations,especially hydrological and nutrient variables,potentially influence the microbial food web via both top-down and bottom-up forces.We proposed that the cycles of carbon,nitrogen and phosphorus are influenced by multi-trophic groups through autotrophic and heterotrophic processes,predator-prey relationships,as well as the release of nutrients mainly by microfauna.Our results advance the notion that pelagic-benthic trophic coupling may intensify the accumulation of organic carbon,ammonium and inorganic phosphorus,thereby changing the biogeochemical patterns along river systems.As a consequence,researchers should pay more attention to the multi-trophic studies when assessing the environmental impacts,and to provide the necessary guidance for the ecological conservation and restoration of the dam-regulated systems.