EFFECT OF LEAF-LITTER EXCLUSION ON MICROBIAL ENZYME-ACTIVITY ASSOCIATED WITH WOOD BIOFILMS IN STREAMS

Leaf litter inputs have been excluded from 1 of 2 1st-order streams at Coweeta Hydrologic Laboratory, North Carolina since August 1993 to ex amine the bottom-up effects of resource reduction on stream ecosystems . As part of the larger project, we studied the effect of litter exclu sion on the extracellular enzyme activity and fungal biomass of wood b iofilms in the presence and absence of leaf litter. Replicate strips o f wood veneer were incubated in both streams for 28, 58, and 86 d. Erg osterol content (to estimate fungal biomass), the activity of 5 lignoc ellulose-degrading enzymes, acid phosphatase activity, breakdown rates , and % organic matter were determined when the veneer strips were col lected. Hydrolytic enzyme activity and wood breakdown rates in the lit ter-excluded stream were significantly higher than in the reference st ream. Enzyme activities of all hydrolytic enzymes were highly correlat ed with each other. Measurement of relative activities of selected ext racellular enzymes comparing carbon and nutrient acquisition suggested nutrient imitation of heterotrophic biofilms in the reference stream. Microbial activity of wood biofilms was significantly altered by the exclusion of leaf litter, and hydrolytic enzyme activity, as an indica tor of carbon cycling, was higher on wood in streams without leaf litt er.