Fungal Decomposers of Plant Litter in Aquatic Ecosystems

Abstract

Fungi are ubiquitous in aquatic ecosystems. They are important decomposers of plant litter in marshes and streams, and act as important intermediaries of carbon flow to higher trophic levels. Representatives of all major fungal phyla have been reported from aquatic habitats, although ascomycetes and their anamorphs (mostly hyphomycetes) dominate fungal communities in plant litter. Aquatic fungi possess the enzymatic capabilities to degrade the major plant constituents, with the possible exception of lignin. Fungi typically surpass bacteria in terms of both biomass and production associated with standing dead plant shoots in marshes and submerged leaf litter in streams. Peak fungal biomass in these systems usually constitutes 5–10% of the litter mass but can be as high as 15–23%. At the ecosystem scale, fungal production may exceed 100 g C m–2 year–1 in some habitats. The interplay of internal (e.g. litter carbon quality and nutrient concentration) and external factors (e.g. temperature, dissolved nutrients) regulates fungal activity which, in turn, controls rates of litter decomposition. To what extent fungi assume similar importance in aquatic habitats other than marshes and streams is poorly documented.