Fungi have been demonstrated to play key roles in mediating energy flow in the detritus-based food chains in streams. Until recently, however, there have been no methods available that would allow determination of instantaneous growth rates of fungi in any environment. Consequently, quantitative data concerning fungal production or flow of energy through the fungal community are not available. A method for estimating instantaneous growth rates of natural fungal communities by determining rates of incorporation of 14C-acetate into ergosterol was recently described. The proposed studies are designed to adapt and evaluate this method for use on the leaf-decomposing fungal communities in streams. Laboratory studies will establish optimum conditions for the incorporation of acetate into ergosterol and determine factors for converting incorporation rates into growth rates of individual fungal species. Laboratory studies of individual species growing on leaf material will be used to compare estimates of growth rates and production determined by the 14C-acetate method with production estimates determined independently from changes in fungal biomass, respiration and conidium production. The method will then be used to estimate growth rates and production of fungal communities during the decomposition of leaves in two streams that differ in water chemistry. These results will be compared with other measures of activity including total microbial respiration, total microbial biomass and sporulation rates of stream fungi. These studies will contribute to the assessment of a new method that has the potential to make a significant impact on our understanding of fungal activities in the environment and should contribute needed information concerning the productivity of fungi in streams.
