Soil contribution to carbon budget of Russian forest

The flux of CO2 from the soil to the atmosphere – soil respiration (RS), is one of the least known components of the terrestrial carbon cycle. RS depends on many factors and varies substantially in time and space. High uncertainty of RS flux valuation leads to a wide range of reported carbon budget estimates for Russian forests. We developed a modeling system for assessing soil carbon stock and heterotrophic soil respiration based on a possible maximum of relevant input indicators. The most comprehensive databases of RS in situ measurements focused on Northern Eurasia (780 records for the region) has been used. A statistical model for assessing RS of Russian forests and its separation in autotrophic and heterotrophic parts were elaborated based on in situ measurements, climate parameters, soil and land cover datasets. The spatial resolution of the model is 1 km2. Russian forest soil accumulated 144.5 Pg C (or 17.6 kg C m-2) in 1 m depth, including 8.3 Pg C (or 1.0 kg C m-2) in the labile topsoil organic layer. The total heterotrophic soil respiration (RH) flux for the Russian forest is estimated at 1.7 Pg C yr-1 (206 g C m-2 yr-1) that comprises 65% of Net Primary Production (NPP) and together with NPP is one of two major components of the net ecosystem carbon balance comprising on average 546 Tg C yr-1 (66 g C m-2 yr-1) for 2007-2009. Interannual variability or RH in 1996-2005 was estimated at 4.1% for forests of the whole country and typically from 5-11% for large individual regions with an average linear trend +0.2% per year. The uncertainty of annual average of RH was estimated at 8% (confidential interval 0.9).