Seasonal variation in soil CO₂ efflux in evergreen coniferous and broad-leaved deciduous forests in a cool-temperate forest, central Korea

We measured the soil surface CO₂ efflux (R_S) from January 2005 to December 2006 in two neighboring stands in Gwangneung Forest, central Korea: evergreen coniferous forest (Abies holophylla, stand A) and broad-leaved deciduous forest (Quercus-dominated, stand Q). Regarding seasonal variation, R_S rate was low during the winter and early spring months in each stand and peaked in late July [1170 (stand A) and 1130 (stand Q) in 2005, and 1000 (stand A) and 740 (stand Q) mg CO₂ m^-2 h^-1 in 2006]. R_S rate was higher in stand A than in stand Q during most of the growing season. The pattern of summer rainfall differed between 2005 and 2006. R_S rate for both stands was suppressed significantly by the droughts in June 2005 and September 2006. After the heavy rainfall of July 2006, R_S rate was lower than in July 2005 in both stands, but this decrement was much greater in stand Q than in stand A. In midsummer (August) 2006, under higher soil temperature (ST) and lower soil water content (SWC) conditions than in August 2005, R_S rate of stand A was lower than that in August 2005, whereas stand Q showed no marked change. The exponential relationship between ST and R_S accounted for approximately 91-97% of the R_S variability in each stand and in each year. In stand A, the application of a second-order polynomial function indicated a significant correlation between SWC and R_S when the soil was warm (ST > 15°C). Our results suggest that the seasonality of R_S is strongly affected by the pattern of summer rainfall even in an Asia monsoon climate regime. In addition, the vegetation type (i.e., evergreen coniferous forest vs. broad-leaved deciduous forest) plays a significant role in response of R_S to various environmental fluctuations such as drought, heavy rainfall, and hot-dry condition.