Grant: Discovery Grants Program - Individual

There is a need for new approaches to better understand how fungi contribute to decomposition of plant matter in streams, and the impact that pollution and other anthropogenic changes have on this process. My research program tackles this problem by applying molecular techniques to characterize fungi and their activities.Stream communities depend heavily on imported plant material for energy and food. As much as 90 % can be in the form of autumn-shed leaves falling into streams. These leaves are not acceptable as food until they have been colonized by microorganisms, which raises the nitrogen level of the detritus and breaks down the plant's structural polysaccharides (cellulose, hemiculoses) into subunits that can be digested by invertebrates. Microbial decomposition is thus a key process for primary producers (through release of nutrients) and invertebrate consumers (through conditioning of detritus). In most streams, a specialized group of fungi, the aquatic hyphomycetes, dominate the decomposition of leaves. Their biomass accounts for up to 20% of detrital leaf mass and fungal annual production per stream area is of the same order of magnitude as that of bacteria and macroinvertebrates. A process-oriented approach to decomposition is important for estimates of what will be available for primary producers and upper trophic levels, and standardized measures of decay rates have been proposed as criteria to assess functional stream integrity. Biodiversity studies suggest, however, that these functional aspects have to be complemented by structural (taxonomic) information for understanding and potentially predicting ecosystem responses to environmental change. The proposed research program will identify the main participants in leaf decomposition and estimate their contributions. In addition to aquatic fungi, we will consider other microbial groups such as Chytrids, Oomycetes and Bacteria. Responses of these groups to anthropogenic change (temperature, eutrophication, heavy metal pollution) will be evaluated.