Seasonal and spatial variability in soil CO₂ efflux rates for a central SiberianPinus sylvestris forest

Abstract

Rates of CO₂ efflux from the floor of a central Siberian Scots pine (Pinus sylvestris) forest were measured using a dynamic closed chamber system and by a eddy covariance system placed 2.5 m above the forest floor. Measurements were undertaken for a full growing season: from early May to early October 1999. Spatial variability as determined by the chamber measurements showed the rate of CO₂ efflux to depend on location, with rates from relatively open areas (“glades”) only being about 50% those observed below or around trees. This was despite generally higher temperatures in the glade during the day. A strong relationship between CO₂ efflux rate and root density was observed in early spring, suggesting that lower rates in open areas may have been attributable to fewer roots there. Continuous measurements with the eddy covariance system provided good temporal coverage. This method, however, provided estimates of ground CO₂ efflux rate rates that were about 50% lower than chamber measurements that were undertaken in areas considered to be representative of the forest as a whole. An examination of the seasonal pattern of soil CO₂ efflux rates suggests that much of the variability in CO₂ efflux rate could be accounted for by variations in soil temperature. Nevertheless, there were also some indications that the soil water deficits served to reduce soil CO₂ efflux rates during mid-summer. Overall the sensitivity of CO₂ efflux rate to temperature seems to be greater for this boreal ecosystem than has been the case for most other studies.