Carbon dioxide balance of subarctic tundra from plot to regional scales.

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 Cm^-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 2.4m pixel-sized Quick- Bird satellite image. The good agreement of the CO₂ balances for the EC footprint based on the different measuring techniques (-105 to -81 g Cm^-2 vs. -79 g Cm^-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 Cm^-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. [ABSTRACT FROM AUTHOR]