Microbial dynamics associated with leaves decomposing in the mainstem and floodplain pond of a large river

Aquatic habitats of forested floodplain systems receive large inputs of allochthonous plant litter. We examined the decomposition of, and microbial productivity associated with, leaves of a common floodplain tree, Populus gr. nigra, in the mainstem and floodplain pond of a seventh order river in 2 consecutive years. Litter bags were submerged at both sites, retrieved periodically, and analyzed for litter mass loss, bacterial and fungal biomass, growth rate and production, and sporulation rates of aquatic hyphomycetes. Litter decomposition rates were similar in both sites and years (leaf breakdown coefficients k of 0.0070 to 0.0085 d–1), although microbial dynamics partly differed between sites. Species diversity of aquatic hyphomycetes was lower on leaves submerged in the pond (16 species) than in the river (21 species). Mycelial biomass was also significantly lower in the pond, with values