APPLICATION OF FUNGAL AND BACTERIAL PRODUCTION METHODOLOGIES TO DECOMPOSING LEAVES IN STREAMS

As leaves enter woodland streams, they are colonized by both fungi and bacteria, To determine the contribution of each of these microbial gr oups to the decomposition process, comparisons of fungal and bacterial production are needed. Recently, a new method for estimating fungal p roduction based on rates of [C-14]acetate incorporation into ergostero l was described, Bacterial production in environmental samples has bee n determined from rates of [H-3]leucine incorporation into protein, In this study, we evaluated conditions necessary to use these methods fo r estimating fungal and bacterial production associated with leaves de composing in a stream, During incubation of leaf disks with radiolabel ed substrates, aeration increased rates of fungal incorporation but de creased bacterial production, Incorporation of both radiolabeled subst rates by microorganisms associated with leaf litter was linear over th e time periods examined (2 h for bacteria and 4 h for fungi). Incorpor ation of radiolabeled substrates present at different concentrations i ndicated that 400 nM leucine and 5 mM acetate maximized uptake for bac teria and fungi, respectively. Growth rates and rates of acetate incor poration into ergosterol followed similar patterns when fungi were gro wn on leaf disks in tile laboratory, Three species of stream fungi exh ibited similar ratios of rates of biomass increase to rates of acetate incorporation into ergosterol, with a mean of 19.3 mu g of biomass pe r nmol of acetate incorporated, Both bacterial and fungal production i ncreased exponentially with increasing temperature, In the stream that we examined, fungal carbon production was 11 to 26 times greater than bacterial carbon production on leaves colonized for 21 days.