Carbon Dioxide Fluxes From Downed Log Decomposition Of Major Tree Species In Northeastern China And The Related Factors

Downed log is a conspicuous and important component of forest ecosystems. The CO₂flux from downed logs (R_CWD) is an important component of carbon budgets in forestecosystems with moderate to large amounts of downed logs. In this study, we used an infraredgas exchange analyzer (LI-6400 IRGA) to measure the R_CWD of 11 major tree species in naturalsecondary temperate forests in northeastern China and related environmental factors. Ourspecific objectives were to (1) compare R_CWD, temperature (T_CWD) and water content of downedlogs (W_CWD) for the 11 tree species; (2) quantify the relationships of R_CWD against T_CWD andW_CWD for the species; and (3) examine seasonal dynamics of R_CWD; (4)quantify the effect ofdecay status on R_CWD. The measured R_CWD for Betula platyphylla, Tilia amurensis, Populusdavidiana, Quercus mongolica, Juglans mandshurica, Acer mono, Ulmus propinqua, Fraxinusmandshurica, Pinus koraiensis, Phellodendron amurense and Larix gmelinii averaged 11.41,9.46, 8.63, 7.19, 6.67, 4.86, 3.34, 2.54, 2.30, 2.26 and 2.17μmolCO₂·m^-2·s^-1, respectively. TheR_CWD for the softwood tree species was greater than that for the hardwood tree species, and theR_CWD for the coniferous species tended to be less than that for the broadleaved species. Duringthe measuring period, the T_CWD (except Ulmus propinqua) did not differ significantly amongtree species (p＞0.1), but the W_CWD did (p＜0.001). The R_CWD was significantly affected bytree species, dimension of downed logs, site conditions, and their interactions, but the degree ofthese effects depended on tree species. The T_CWD, W_CWD and their interactions significantly (p＜0.01) influenced the R_CWD, explaining 39.9％～72.9ï¼…of the variations in the R_CWD data. Theseasonality of R_CWD was mainly driven by the T_CWD and showed an overall bell-shaped curvefor all the tree species, while the variations among tree species within a specific season weremainly influenced by W_CWD. To compare the effect of decay status on R_CWD, select three decayclasses from Betula platyphylla and Populus davidiana. CWD decay class (â… ,â…¡,â…¢)significantly affected R_CWD (p＜0.001), Populus davidiana of decay classâ… andâ…¢had asignificantly higher respiration rate than that of decay classâ…¡; the R_CWD of Betula platyphyllaof decay classâ…¢was significantly higher than that of decay classâ… andâ…¡, but R_CWD ofdecay classâ… andâ…¡did not differ The seasonality of R_CWD of different decay classes mainlydriven by the T_CWD.