CO2 efflux from soil and snow surfaces was measured continuously in a Japanese cedar (Cryptomeria japonica D. Don) forest in central Japan using an open dynamic chamber system. The chamber opens and closes automatically and records measurements based on an open-flow dynamic method. Between May and December, mean soil CO2 efflux ranged from 1,529 mg CO2 m-2 h-1 in September to 255 mg CO2 m -2 h-1 in December. The seasonal change in CO2 efflux from the soil paralleled the seasonal pattern of soil temperature. No marked diurnal trends in soil CO2 efflux were observed on days without rainfall, whereas significant pulses in soil CO2 efflux were observed on days with rainfall. In this plantation, soil CO2 efflux frequently responded to rainfall. Measurements of changes from litter-covered soil to snow-covered surfaces revealed that CO2 efflux decreased from values of ca. 250 mg CO2 m-2 h-1 above soil to less than 33 mg CO2 m-2 h-1 above snow. Soil temperature alone explained 66% of the overall variation in soil CO2 efflux, but explained approximately 85% of the variation when data from two anomalous periods were excluded. Moreover, we found a significant correlation between soil CO2 efflux and soil moisture (which explained 44% of the overall variation) using a second-order polynomial function. Our results suggest that the seasonality of CO2 efflux is affected not only by soil temperature and moisture, but also by drying and rewetting cycles and by litterfall pulses.
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