Components of forest soil CO2 efflux as estimated from 14C values of SOM

The partitioning of the total soil CO2 efflux into its two main components: respiration from roots (and root-associated organisms) and microbial respiration (by means of soil organic matter (SOM) and litter decomposition), is a major need in soil carbon dynamics studies in order to predict the net response of soil carbon stores to climate change. In this study, SOM-derived CO2 efflux was estimated for eleven forest sites as the sum of the ratios between the carbon stocks of different SOM pools and previously published (?14C derived) turnover times. The fraction of soil CO2 efflux derived from recently fixed carbon, including root and root-associated respiration, was calculated by subtracting the SOM-derived respiration component from total soil chamber measured CO2 efflux. Results suggested that, on average, ~ 50 % of total soil CO2 efflux derived from the respiration of the living roots, ~ 40 % from decomposition of the litter layers and less than 10 % from decomposition of belowground SOM;. Estimates of SOM-derived soil CO2 efflux in the current study were rather low compared with other two partitioning datasets However a major problem in the comparison could have been the high spatial variability of soil carbon and related variables