Temperature and moisture dependence of decomposition rates of hardwood and coniferous leaf litter

Abstract

Samples of fresh (autumn) and of year-old (late summer) deciduous forest-leaf litter and humus, and of Douglas fir fine litter and humus, were wetted to known moisture content, nominally between 200 and 40% water (dry basis), and maintained at constant temperatures between 10° and 40°C. Rates of CO 2 production were measured by KOH absorption and titration. Decomposition rate was found to be a linear function of log — (water potential), and to approach a maximum near 40°C. The temperature-dependence was consistent with models based on irreversible heat inactivation of a rate-controlling enzyme, also with Eyring's “absolute reaction rate” theory for reactions controlled by a reversibly inactivated enzyme. Activation energies were 66.8–67.3 kJ mol −1 for litter, and 61.4–67.5 kJ mol −1 for humus decomposition; for enzyme inactivation energies were 150–154 kJ mol −1.