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

Abstract. Methane (CH 4 ) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May-October 2008) cumulative CH 4 emission of 2.4 (EC) and 3.7 g CH 4 m −2 (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km 2 , the chamber measured flux data yielded a regional flux estimate of 6.7 g CH 4 m −2 yr −1 . Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 g CH 4 m −2 yr −1 were the most dominant CH 4 -emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH 4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH 4 release pathway from wetlands to the atmosphere was plantmediated diffusion through aerenchyma, a process that discriminates against 13 C-CH 4 . The CH 4 released to the atmosphere was lighter than that in the surface porewater, and δ 13 C in the emitted CH 4 correlated negatively with the vascular plant cover (LAI). The mean value of δ 13 C obtained here for the emitted CH 4 , −68.2 ± 2.0 ‰, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH 4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1 • C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH 4 -emitting wet surfaces.

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 up-scaling 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 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 2.4 m pixel-sized Quickbird satellite image. The good agreement of the CO₂ balances for the EC footprint based on the different methods (−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 annual CO₂ balance for the study region was −67 to −41 g C m⁻². 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 future will have great impact on the regional CO₂ balance

In this study, we use the coupled photosynthesis-stomatal conductance model of Collatz Thomas Friborg* et al. (1991) to simulate the current canopy carbon dioxide exchange of a heterogeneous Mathias Herbst † tundra ecosystem in European Russia. For the parameterization, we used data obtained Torbjörn Johansson* and from in situ leaf level measurements in combination with meteorological data from 2008. The modeled CO 2 fluxes were compared with net ecosystem exchange (NEE), measured