LEAF LINER PROCESSING AND EXOENZYME PRODUCTION ON LEAVES IN STREAMS OF DIFFERENT PH

We examined microbial colonization, exoenzyme activity, and processing of leaves of yellow poplar (Liriodendron tulipifera), red maple (Acer rubrum), and white oak (Quercus alba) in three streams on the Alleghe ny Plateau of West Virginia, United States. Leaf packs were placed in streams that varied in their underlying bedrock geology, and therefore in their sensitivity to the high level of acidic precipitation that o ccurs in this region. The mean pH of the streams was 4.3 in the South Fork of Red Run (SFR), 6.2 in Wilson Hollow Run (WHR), and 7.7 in the North Fork of Hickman Slide Run (HSR). Through time, the patterns of m icrobial biomass and exoenzyme activity were generally similar among l eaf species, but the magnitude of microbial biomass and exoenzyme acti vity differed among leaf species. Pectinase activity was greatest in H SR, the most alkaline stream, whereas the activity of exocellulase and xylanase was greatest in WHR and SFR, the intermediate and acidic str eams. This variation in the activity of different exoenzymes was consi stent with published pH optima for these exoenzymes. Variation in proc essing rates, both among leaf species and among streams, seems to be r elated to the level of microbial exoenzyme activity on the leaf detrit us.