Components of forest soil CO2 efflux estimated from Δ14C values of soil organic matter
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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 (Δ14C 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 Δ14C 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.
KeywordsSoil respiration partitioning Carbon-14 isotope Soil organic matter fractions Forest ecosystems
We thank Robbert Hakkenberg, Annett Börner, Gerd Gleixner, Martina Mund, Markus Reichstein, and Susan Trumbore for discussion of results. Thanks are due also to Jens-Arne Subke for the pre-review of the paper and for useful suggestions. This study received funding from the EU-CarboDATA project (contract number EVK2CT-1999-00044) and from the Province of Trento, Italy (grant REM DL1060).
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