Effects of temperature and moisture on carbon respired from decomposing woody roots

Controls of temperature and moisture on root decomposition have not been well studied despite their direct relevance to climate change impacts on root carbon flux. The main objective of this laboratory study was to examine the respiration response of Sitka spruce, Douglas-fir, western hemlock, ponderosa pine, and lodgepole pine decomposing roots (1-3 cm in diameter) to temperature and moisture change. Roots of Sitka spruce, Douglas-fir and western hemlock, and ponderosa pine and lodgepole pine were collected from Cascade Head, H.J. Andrews, and Pringle Falls site, respectively. Dead root respiration increased with temperature and reached the maximum at 30-40 degreesC, and then decreased. Analysis of covariance indicated that the Q(10) of root decomposition rate was influenced significantly (p<0.01) by incubation temperature range 5-40<degrees>C, but not by species, decay class or the direction of temperature change. At 5-10 degreesC, Q(10) averaged 3.99 and then decreased to 1.37 at 30-40 degreesC. Over a range of 5-60 degreesC, Q(10) could be predicted by a single-exponential model using temperature as the independent variable. Analysis of variance showed that the respiration rate of dead roots was significantly (p<0.01) influenced by root moisture, species, and decay class as well as temperature. Dead root respiration increased with root moisture, reached the optimum range when moisture was between 100 and 275% and then decreased. Moreover, there were apparent interactions of root moisture and temperature on root respiration. Our study showed the direction of temperature and moisture change did not significantly influence root respiration, indicating that hysteresis may not occur for the temperature and moisture ranges examined. To better model global climate warming effects on root carbon flux, we suggest a temperature dependent Q(10) function should be incorporated into current root dynamics models. The short-term laboratory incubation approach provided a good way to examine temperature and moisture controls on root decomposition, although we are cautious about long-term mass-loss extrapolations based on these short-term results. (C) 2000 Elsevier Science B.V. All rights reserved.