Anthropogenic stress may affect aquatic hyphomycete diversity more than leaf decomposition in a low-order stream

Fungal diversity and microbial decomposition of leaf litter were examined in low-order stream at a reference and an impacted site. The latter, 10 km downstream of the reference site, has high nutrient loads from domestic sewage and agriculture, and increased heavy metal levels in the stream water and sediments. At the polluted site aquatic hyphomycete diversity and sporulation were reduced, whereas fungal biomass and leaf decomposition rate were not. Articulospora tetracladia and Flagellospora sp. were the dominant species at the reference site, and Dimorphospora foliicola was dominant at the polluted site. Biomass of bacteria was higher at the polluted site, but only approached 10% of fungal biomass, indicating that fungi remained the main microbial decomposers. In addition, the results suggest that aquatic hyphomycete communities may respond to stress according to the redundancy model, in which overall function remains stable because increased biomasses of tolerant species compensate for the loss of sensitive species.