Regulation of the Growth and Activity of Leaf-Decomposing Fungi by Dissolved Nutrients (N and P) in Streams

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9407232 Subberkropp This study is designed to examine the role of dissolved nutrients (N and P) in regulating the growth and activity of leaf-decomposing stream fungi. Most quantitative studies of stream fungal communities have occurred in streams with high nutrient concentrations. Consequently, little is known concerning fungal activities in streams with low nutrient concentrations even though much of our current understanding of stream ecosystem function has come from studies of such systems. Rates of fungal growth and sporulation, concentrations of fungal biomass and fungal production in both hardwater and softwater streams with very low nutrient concentrations will be determined and compared with similar data from streams containing higher nutrient concentrations. Recently, a method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol has been described. This method has been adapted for use with stream fungal communities and will be used on decomposing leaf litter in the study streams. These data, together with determination of ergosterol contents as a measure of fungal biomass will allow estimation of fungal production during leaf degradation and in streams over an annual cycle. Both types of production estimates will be used in the comparative studies mentioned above. The effects of N and P will be measured directly in field experiments in which water flowing through streamside artificial channels will be amended with N, P or both nutrients and the response of fungal communities determined. Organic matter budgets for fungal isolates from nutrient poor and nutrient rich streams growing on leaf litter in environmental simulating laboratory studies will be constructed to determine if fungi exhibit different strategies of resource allocation in response to varying nutrient concentrations. %%% This project will provide the first research effort concentrating on the role of nutrient limitation of fungal community structure and biomass in streams. The PI will be using a novel technique to measure fungal growth rates and community structure.