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Enzymatic Activities in Coniferous Leaf Litter¹

ABSTRACT

Assays for measuring the activities of cellulase, xylanase, mannase, amylase, ß-glucosidase, invertase, and protease employing buffered suspensions of ground coniferous and deciduous leaf litter exhibited zero-order kinetics. Only a small percentage of the whole-litter activities of invertase (3%), ß-glucosidase (3%), and protease (1%) were extractable into 0.05M potassium acetate, pH 5.0; however, extractable activities of cellulase and xylanase represented from 39 to 174% of the whole-litter activities indicating their soluble exocellular nature. Extractable protease and amylase activities were best correlated (r=0.65 and 0.65, respectively) with the average daily rates of CO₂ evolution in a group of 90 leaf litter samples equally representing 18 coniferous species. Enzymatic activities were readily detectable in extracts of all samples but classification of the samples by species provided little differentiation in the distribution of either enzymatic activities or rates of CO₂ evolution. Mannase, cellulase, and xylanase activities were well-correlated with each other (r=0.88) in all samples. Assays at-tempting to measure a pool of readily-metabolizable substances in litter by extractable reducing substances, ninhydrin-positive substances, glucose, and phenolics failed to show correlation coefficients > 0.41 with rates of CO₂ evolution. Addition of D-(+)-catechin to litter extracts, up to levels equivalent to those observed in the group of samples, did not inhibit any carbohydrase thus suggesting the lack of inhibition of litter-decomposing enzymes by the concentrations of phenolics present in these coniferous leaf litters.

¹ Contribution from Corvallis Environ. Res. Center, USEPA, Corvallis, Oreg.

² National Research Council Resident Research Associate, U.S. EPA, Corvallis Environ. Res. Center, Corvallis, OR 97330. Present address: Environmental Sciences Division, Oak Ridge National Laboratory, Post Box X, Oak Ridge, TN 37830.

Received for publication November 13, 1979. Accepted for publication February 29, 1980.