Carbon dioxide balance of subarctic tundra from plot to regional scales

Abstract. We report here the carbon dioxide (CO₂) budget of a 98.6 km² subarctic tundra area in northeast European Russia based on measurements at two different scales and two independent upscaling approaches. Plot-scale measurements (chambers on terrestrial surfaces, gas gradient method and bubble collectors on lakes) were carried out from July 2007 to October 2008. The landscape-scale eddy covariance (EC) measurements covered the snow-free period of 2008. The annual net ecosystem exchange (NEE) of different land cover types ranged from −251 to 84 g C m⁻². Leaf area index (LAI) was an excellent predictor of the spatial variability in gross photosynthesis (GP), NEE and ecosystem respiration (ER). The plot-scale CO₂ fluxes were first scaled up to the EC source area and then to the whole study area using two data sets: a land cover classification and a LAI map, both based on field data and a 2.4 m pixel-sized QuickBird satellite image. The good agreement of the CO₂ balances for the EC footprint based on the different measuring techniques (−105 to −81 g C m⁻² vs. −79 g C m⁻²; growing season 2008) justified the integration of the plot-scale measurements over the larger area. The regional CO₂ balance based on area-integrated plot-scale measurements was −41 or −79 g C m⁻² yr⁻¹ according to the two upscaling methods, the land cover classification and the LAI map, respectively. Due to the heterogeneity of tundra, the effect of climate change on CO₂ uptake will vary strongly according to the land cover type and, moreover, likely changes in their relative coverage in the future will have great impact on the regional CO₂ balance.