Respiration and mass loss rates of aspen and pine leaf litter decomposing in laboratory microcosms

Abstract

Respiration rates and mass losses of decomposing pine (Pinus contorta Loud. × P. banksiana Lamb.) and aspen (Populus tremuloides Michx.) leaf litter were compared in laboratory microcosms for a range of temperature and moisture levels. For both litter types, a pair of high-temperature treatments (18, 26 °C) and a pair of low-temperature treatments (2, 10 °C) were distinguishable on the basis of respiration rate, mass loss, shape of the respiration curve, and (for pine) estimated microbial efficiency. Respiration rates in high-temperature treatments showed an initial increase to a wide peak (wider and later at 18 than at 26 °C), followed by a sharp decline; respiration of low-temperature treatments was nearly constant through time or declined slowly. Moisture level (15, 30, or 60 mL∙week−1 watering rate) was less important than temperature in determination of mass losses or respiration rates. Aspen respiration at 18 and 26 °C peaked sooner and declined more rapidly at higher moisture levels than at lower ones; at 2 and 10 °C, higher moisture levels inhibited respiration owing to saturation. Mass loss of pine needles after 153 days decay was a linear function of temperature (R2 = 0.92). The best regression describing mass loss of aspen litter after 130 days decay was a linear function of both temperature and moisture, without interaction (R2 = 0.82). Moisture level became more influential as temperature increased. Researchers are cautioned about the limitations of cumulative respiration curves, and alternatives, such as ANOVA, correlation, and the runs test, are suggested.