Assessing of temperature-sensitivity of decomposition rate of litter and soil organic matter in two forests

To estimate litter and soil organic matter decomposition by using soil temperature at 5 cm in depth, litterbag and soil incubation experiments were conducted. Litterbags, filled with leaf litter obtained from oak and Japanese cedar forests in Rokkasho village, were placed on the soil surface of each forest, and each soil temperature were measured. In another experiment, soil from each forest was incubated at temperatures of 10°C, 20°C, or 30°C for approximately 700 days, and the atmospheric carbon dioxide concentrations in the incubation bottles were analyzed to estimate the amount of carbon dioxide released from the soil at each temperature. The remaining amount of SOM was calculated from the estimated cumulative carbon dioxide release. SOM decomposition rates and their temperature sensitivity were analyzed using a known model with two decomposable compartments with different decomposition rates (an active and an intermediate compartment) and one recalcitrant SOM compartment. The Arrhenius equation was applied with the field soil temperature or incubation temperature as the temperature parameter, and then Q10 and the activation energy of decomposition rate of leaf litter and two SOM compartments were calculated to examine the temperature sensitivity of each decomposition rates. The cedar leaf decomposition rate was estimated to be more sensitive to temperature than oak leaf. The estimated decomposition rate of the active compartment of SOM was more sensitive to temperature than that of the intermediate compartment. These experimental methods make it possible to use the same soil temperature within a forest to predict litter and SOM decomposition rates.