"Global climate change is strongly linked to the accumulation of greenhouse gases in the atmosphere. In particular, CO2 contributes almost 45-60% to the observed anthropogenic global warming yet has the potential to be captured by trees and stored either in woody biomass or in soils over long time periods. While the above-ground carbon cycle is well constrained, there remain great uncertainties in below-ground carbon cycling. For example, it is currently not known what proportion of carbon, fixed by trees in photosynthesis as CO2, is stored in soil, released back to the atmosphere as CO2 or CH4. We propose to tackle specific key questions about the fate of carbon in forests by taking advantage of existing afforestation experiments in England (main phase) and in Russian Siberia (return phase), by combining new stable isotopes methods and innovative in-growth core approaches. We will enrich tree canopies with 13C-CO2 and track changes in isotopic composition of CO2 evolved from soil using a unique mobile mass-spectrometry lab, available only at the University of York, England. We shall also monitor CH4 fluxes with parallel determination of 13C in CH4. This would allow estimating the gross rates of CH4 production and consumption and for a first time discern the role of fine roots and soil fungi in mediating CH4 flux. Furthermore, the application of N will mimic elevated N deposition, an important global change factor, to predict the response of soil carbon cycle in forests to global climate change. During the return phase we will apply the developed in England in-growth cores to a unique Siberian afforestation experiment, examining the effect of six dominant Siberian tree species on the roles of mycorrhiza and fine roots in carbon fluxes. Overall, the project would 1) greatly advance our knowledge of soil C cycling in forest ecosystems and 2) establish a new cooperative link between researchers of the Institute of Forest in Krasnoyarsk and the University of York"