CO2 exchange and component CO2 fluxes of a boreal Scots pine forest

We studied CO2 fluxes derived from eddy covariance (EC), modelled with a stand photosynthesis model, and upscaled from continuous measurements with chambers in a Scots pine stand. The annual photosynthesis (GPP(EC)) ecosystem respiration (R-e,R-EC) and net CO2 exchange (NEEEC) derived from EC were correlated with each other. Soil CO2 efflux dominated R e for the whole year, most clearly in winter. The relative contributions of the above-ground respiration components were largest in spring and early summer. The respiration components generally followed the seasonal patterns of temperature although temperature-normalised respiration was higher in the growing season than in winter. The respiration components showed parallel decline during drought. Interannual variability in the annual chamber-based CO2 budgets was twice as large as in the EC-based fluxes, the uncertainty in the chamber fluxes was also larger. Using different environmental drivers for estimating R-e from NEEEC affected the annual Re,(EC) and GPP(EC) +/- 4%.