Total and component carbon fluxes of a Scots pine ecosystem from chamber measurements and eddy covariance

Background and Aims Distinguishing between, and quantifying, the different components of ecosystem C fluxes is critical in predicting the responses of ecosystem C cycling to climate change. The aims of this study were to quantify the photosynthetic and respiratory fluxes of a 50-year-old Scots pine (Pinus sylvestris) ecosystem, and to distinguish respiration of branches with needles from that of stems, and that of soil. Methods The CO2 flux of the ecosystem was continuously measured using the eddy covariance (EC) method, and its components (respiration and photosynthesis of a branch with needles, stem and soil surface) were measured with an automated chamber system, from 2001 to 2004. Key Results All values below are chamber based. The average temperature coefficient (Q(10)) of respiration was 2.7. 2.2 and 4.0, respectively, for branch (R-bran), stem (R-stem) and the soil surface (R-soil). Respiration at a reference temperature of 15 degrees C (R-15) was 1.27, 0.49 and 4.02 mu mol CO2 m(-2) ground s(-1) for the three components, respectively. Over 4 years, the annual R-bran, R-stem and R-soil ranged from 196 to 256, 56 to 83 and 439 to 598 g C m(-2) ground year(-1), respectively, with a 4-year average of 227, 72 and 507 g C m(-2) ground year(-1). Annual ecosystem respiration (R-eco) was 731, 783, 909 and 751 g C m(-2) ground year(-1) in years 2001-2004, respectively, gross primary production (GPP) was 922, 1030, 1138 and 1001 g C m(-2) ground year(-1), and net ecosystem production (NEP) was 191, 247, 229 and 251 g C m(-2) ground year(-1). The average contribution of R-bran, R-stem and R-soil to R-eco was 29, 9 and 62%, respectively. Overstorey photosynthesis accounted for 96% of GPP. The average R-eco/GPP ratio was 0.78. Net primary production (NPP) in the 4 years was 469, 581, 600 and 551 g C m(-2) year(-1) respectively, with the NPP/GPP ratio 0.54 averaged over the years. Conclusions Respiration from the soil is the dominant component of ecosystem respiration. Differences between years in R-eco were due to differences in temperature during the growing season. R-soil was more sensitive to temperature than R-bran and R-stem and differences in R-soil were responsible for the differences in R-eco between years.