Simulated patterns of litter decay predict patterns of extracellular enzyme activities

Decomposition is a complex suite of processes that strongly affects the min eralization and immobilization of mineral nutrients. Thus, considerable res earch has focused on gaining a mechanistic understanding of litter decay. M odels of decay vary with respect to detail, but most utilize decay rate coe fficients for particular chemical constituents of litter, derived from empi rical observations of turnover. Recent studies have shown that the activiti es of extracellular enzymes are correlated with decay, and represent instan taneous measures of biochemical processes responsible for the hydrolysis of particular chemical compounds. For these reasons, temporal patterns in tur nover rates for particular litter constituents should correspond to activit y levels of particular degradative enzymes. To test this hypothesis, we mod ified a general model of litter decay (GENDEC) to predict activities of ext racellular enzymes. This was accomplished by viewing turnover rates for car bon fractions of litter (extractive, acid-soluble and acid-insoluble compou nds) as surrogates for the activity levels of relevant extracellular enzyme s (e.g., glucosidase, cellulases, oxidases). The resulting temporal pattern s 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, a lthough existing data are not sufficient to conduct a rigorous quantitative test of this approach. Conversely, assays of extracellular enzymes could b e used to test models of Litter decay with a high degree of chemical and te mporal 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.