Effect of Leaf Litter Exclusion on Microbial Enzyme Activity Associated with Wood Biofilms in Streams

Abstract

Leaf litter inputs have been excluded from 1 of 2 Ist-order streams at Coweeta Hydro- logic Laboratory, North Carolina since August 1993 to examine the bottom-up effects of resource reduction on stream ecosystems. As part of the larger project, we studied the effect of litter exclusion on the extracellular enzyme activity and fungal biomass of wood biofilms in the presence and absence of leaf litter. Replicate strips of wood veneer were incubated in both streams for 28, 58, and 86 d. Ergosterol content (to estimate fungal biomass), the activity of 5 lignocellulose-degrading enzymes, acid phosphatase activity, breakdown rates, and % organic matter were determined when the veneer strips were collected. Hydrolytic enzyme activity and wood breakdown rates in the litter-excluded stream were significantly higher than in the reference stream. Enzyme activities of all hydrolytic enzymes were highly correlated with each other. Measurement of relative activities of selected extra- cellular enzymes comparing carbon and nutrient acquisition suggested nutrient limitation of hetero- trophic 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 indicator of carbon cycling, was higher on wood in streams without leaf litter.