Effects of sample size and temperature on coarse woody debris respiration from Quercus variabilis logs

Abstract

Measuring coarse woody debris (CWD) respiration (R _CWD) may have advantages over other approaches in determining CWD decomposition rates to accurately estimate forest carbon budgets and effects of warm temperatures on decomposition; however, studies on R _CWD are insufficient. The R _CWD from Quercus variabilis logs of different sizes (e.g., different surface area to weight ratios or weights) was measured under homogeneous conditions by using a closed-chamber system with a non-dispersive infrared sensor. The size effect on R _CWD measured on a weight or volume basis was not significant, but it was significant on a surface area basis. This indicates that R _CWD on a weight or volume basis would be a reliable measure, regardless of the size and cross-sectional area effects, while R _CWD on a surface area basis must vary geometrically according to the change in sample size. R _CWD did not change significantly over time until 122 h after sampling. An exponential model with a Q ₁₀ of 2.34 was fitted only at temperatures below 22.6 °C because R _CWD was suppressed at high temperatures due to constantly decreasing moisture. Instead, a logistic model was applied for all temperatures. The annual R _CWD and the decay rate constant were estimated to be 53.4 g C kg⁻¹ year⁻¹ and 0.107 year⁻¹, respectively. The decomposition rate estimate through R _CWD might not correspond to that using the mass loss approach. It remains uncertain whether the methodological differences may lead to potential errors in measuring the actual CWD decomposition rate; therefore, a multiple approach study for CWD decomposition should be conducted.