Components of forest soil CO2 efflux estimated from Δ14C values of soil organic matter

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 understand if a soil is a net sink or source of carbon. The heterotrophic component of the CO2 efflux was estimated for 11 forest sites as the ratio between the carbon stocks of different SOM pools and previously published (Delta C-14 derived) turnover times. The autotrophic component, including root and root-associated respiration, was calculated by subtracting the heterotrophic component from total soil chamber measured CO2 efflux. Results suggested that, on average, 50.4 % of total soil CO2 efflux was derived from the respiration of the living roots, 42.4 % from decomposition of the litter layers and less than 10 % from decomposition of belowground SOM. The Delta C-14 method proved to be an efficient tool by which to partition soil CO2 efflux and quantify the contribution of the different components of soil respiration. However the average calculated heterotrophic respiration was statistically lower compared with two previous studies dealing with soil CO2 efflux partitioning (one performed in the same study area; the other a meta-analysis of soil respiration partitioning). These differences were probably due to the heterogeneity of the SOM fraction and to a sub-optimal choice of the litter sampling period.