Soil CO2 efflux (RS) is an important component of forest ecosystem carbon budgets and net ecosystem CO2 exchange, but little is known about RS and its components in temperate forests in Northeastern China, an area with a large extent of forest. We measured RS along with soil temperature (Ts) and soil moisture (WS)at a 10 cm depth over a 4-year period from 2004 to 2007 in six common forest types in the region. The autotrophic (RA) and heterotrophic (RH) components of soil CO2 efflux were separated with trenched plots. Stem CO2 efflux (ES) was also measured in 2007 in five forest types. Our objectives were to (1) examine the magnitude of RA and RH and the interannual patterns in the ratio of RA/RH in the six forest types and (2) examine correlations between RA and Es.
Results/Conclusions
Annual mean RS and RH ranged from 1.77 to 4.37 μmolCO2 m-2 s-1 and 1.16 to 2.74 μmolCO2 m-2 s-1 in the six forests from 2004 to 2007, respectively. The apparent Q10 for RS and RH ranged from 2.16 to 3.87 and 2.97 to 4.64 respectively. In all six forest types, RS and RH were better predicted by Ts and WS in the dormant season than the growing season, indicating that additional factors such as growth, internal CO2 and assimilate transport became more important contributors to RS during the growing season. RH was the dominant contributor to RS in three forest types. There was a negative linear relationship between RA/RH and soil moisture. The differences in Ts and WS between trenched and control plots decreased during consecutive three years. There was a positive correlation between mean Es and mean RA, suggesting that the relative importance of xylem transport of root-respired-CO2 may change with environmental conditions. We concluded that vegetation type, root-derived CO2 diffusion and transport, and associated carbon metabolism of temperate forests should be considered in assessing and modeling RS and its components.