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We determine the carbon balance of Russia, including Ukraine, Belarus and Kazakhstan using inventory based, eddy covariance, Dynamic Global Vegetation Models (DGVM), and inversion methods. Our current best estimate of the net biosphere to atmosphere flux is -0.66 PgCyr-1. This sink is primarily caused by forests that using two independent methods are estimated to take up -0.69PgCyr-1. Using inverse models yields an average net biopshere to atmosphere flux of the same value with a interannual variability of 35% (1σ). The total estimated biosphere to atmosphere flux from eddy covariance observations over a limited number of sites amounts to -1 PgCyr-1. Fires emit 137 to 121 TgCyr-1 using two different methods. The interannual variability of fire emissions is large, up to a factor 0.5 to 3. Smaller fluxes to the ocean and inland lakes, trade are also accounted for. Our best estimate for the Russian net biosphere to atmosphere flux then amounts to -659TgCyr-1 as the average of the inverse models of -653TgCyr-1, bottom up -563TgCyr-1and the independent landscape approach of -761 TgCyr-1. These three methods agree well within their error bounds, so there is good consistency between bottom up and top down methods. The best estimate of the net land to atmosphere flux, including the fossil fuel emissions is -145 to -73TgCyr-1. Estimated methane emissions vary considerably with one inventory-based estimate providing a net land to atmosphere flux of 12.6TgC-CH4yr-1 and an independent model estimate for the boreal and Arctic zones of Eurasia of 27.6TgC-CH4yr-1. [ABSTRACT FROM AUTHOR]

Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be performed through a cross validation of the eddy covariance measurements against ecological inventory estimates of carbon exchanges (Ehman, 2002; Curtis, 2002). Indeed, the widespread presence of ideal conditions for the applicability of the eddy covariance technique, as vast and homogeneous grass vegetation cover over flat terrains (Baldocchi, 2003), make steppes a suitable ground to ensure a constrain to flux estimates with independent methodological approaches. We report about the analysis of the carbon cycle of a true steppe ecosystem in southern Siberia during the growing season of 2004 in the framework of the TCOS-Siberia project activities performed by continuous monitoring of CO2 fluxes at ecosystem scale by the eddy covariance method, fortnightly samplings of phytomass, and ingrowth cores extractions for NPP assessment, and weekly measurements of heterotrophic component of soil CO2 effluxes obtained by an experiment of root exclusion. The carbon balance of the monitored natural steppe was, according to micrometeorological measurements, a sink of carbon of 151.7±30.1 gC m-2, cumulated during the growing season from May to September. This result was in agreement with the independent estimate through ecological inventory which yielded a sink of 150.1 gC m-2 although this method was characterized by a large uncertainty (±130%) considering the 95% confidence interval of the estimate. Uncertainties in belowground process estimates account for a large part of the error. Thus, in particular efforts to better quantify the dynamics of root biomass (growth and turnover) have to be undertaken in order to reduce the uncertainties in the assessment of NPP. This assessment should be preferably based on the application of multiple methods, each one characterized by its own merits and flaws. [ABSTRACT FROM AUTHOR]