Fungi

Abstract

Fungal diversity in freshwater habitats exceeds 2000 species. Representatives of all major taxonomic groups of fungi are present in freshwater environments though ascomycetes and mitosporic fungi of ascomycetous affinities are the most common fungi on coarse particulate organic matter (CPOM). Freshwater fungi produce extracellular enzymes that degrade all major plant polymers. Consequently, fungi are important decomposers of plant litter in freshwater ecosystems and serve as key mediators in the flow of carbon and energy to higher trophic levels (e.g., macroinvertebrates). Fungal biomass and production typically exceed those of bacteria; thus, fungi usually contribute >90% to total microbial biomass and production on CPOM in both lotic and lentic habitats. Fungal biomass associated with plant litter can exceed 23% of total detrital mass, but typically peaks at 10% on leaf litter in streams and standing-dead macrophytes in marshes. Fungi can be quite important in freshwater ecosystems; fungal production may exceed 100 g of C per m 2 per year in some situations. Fungal activity in freshwater habitats depends on carbon quality (lignin) and nutrient content (N and P) of plant litter as well as external factors such as temperature, dissolved nutrients, relative humidity (standing-dead macrophyte litter), and other factors.