Simulated patterns of litter decay predict patterns of extracellular enzyme activities

Decomposition is a complex suite of processes that strongly affects the mineralization and immobilization of mineral nutrients. Thus, considerable research has focused on gaining a mechanistic understanding of litter decay. Models of decay vary with respect to detail, but most utilize decay rate coefficients for particular chemical constituents of litter, derived from empirical observations of turnover. Recent studies have shown that the activities of extracellular enzymes are correlated with decay, and represent instantaneous measures of biochemical processes responsible for the hydrolysis of particular chemical compounds. For these reasons, temporal patterns in turnover rates for particular litter constituents should correspond to activity levels of particular degradative enzymes. To test this hypothesis, we modified a general model of litter decay (GENDEC) to predict activities of extracellular enzymes. This was accomplished by viewing turnover rates for carbon fractions of litter (extractive, acid-soluble and acid-insoluble compounds) as surrogates for the activity levels of relevant extracellular enzymes (e.g., glucosidase, cellulases, oxidases). The resulting temporal patterns of litter turnover rates generated by the model were similar to observed patterns of enzyme activities. These results demonstrated that traditional modeling approaches may be used to predict patterns of enzyme activities, although existing data are not sufficient to conduct a rigorous quantitative test of this approach. Conversely, assays of extracellular enzymes could be used to test models of Litter decay with a high degree of chemical and temporal resolution, because enzymes catalyze specific reactions and measures of activity levels represent instantaneous rates of degradation. (C) 2000 Published by Elsevier Science B.V. All rights reserved.