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Abstract

The activity of the extracellular enzymes ß-glucosidase, ß-xylosidase, phosphatase, and leucine-aminopeptidase were measured on the epilithic biofilms of the Breitenbach. Differences in the degradative enzymatic metabolism between microhabitats were observed. V_max values for the four enzymes were higher in the open, higher water velocity site (A), than in the open, low water velocity site (B) and the forested site (C). The higher algal biomass accumulated at site A might provide a higher substrate availability enhancing the hydrolytic capacity of the heterotrophs. A different organic matter source is suggested at site C as a result of the important leaf fall input during the study period (October - November 1995), expressed by the high polysaccharide degradation capacity and a lower ß-xylosidase : ß-glucosidase ratio at this site. On average, turnover times of substrate hydrolysis (T_t) for the four enzymes were: 80 hours (ß-xylosidase), 19 hours (phosphatase), 17 hours (ß-glucosidase) and 5 hours (aminopeptidase) indicating slow recycling of hemicellulosic compounds in contrast to the faster utilization of proteinaceous compounds.