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Abstract
The flux (R s) and carbon isotopic composition (δ13C Rs ) of soil respired CO 2 was measured every 2 h over the course of three diel cycles in a Mediterranean oak woodland, together with measurements of the δ13C composition of leaf, root and soil organic matter (δ13C SOM) and metabolites. Simulations of R s and δ13C Rs were also made using a numerical model parameterised with the SOM data and assuming short-term production rates were driven mainly by temperature. Average values of δ13C Rs over the study period were within the range of root metabolite and average δ13C SOM values, but enriched in 13C relative to the bulk δ13C of leaf, litter, and roots and the upper soil organic layers. There was good agreement between model output and observed CO 2 fluxes and the underlying features of δ13C Rs . Observed diel variations of 0.5 ‰ in δ13C Rs were predicted by the model in response to temperature-related shifts in production rates along a ∼3 ‰ gradient observed in the profile of δ13C SOM. However, observed δ13C Rs varied by over 2 ‰, indicating that both dynamics in soil respiratory metabolism and physical processes can influence short-term variability of δ13C Rs .
Acknowledgements
We thank Cathy Besson, Stephan Unger, Joao Banza and Alan Pike for assistance in the field. We also thank Manuela Negreanu for the IRMS work and Max Hill for the assistance with the HPLC analysis. This study was made possible through the EU funded projects: Mediterranean IN Drought (MIND Project No. EVK2-CT-2002-00158) to MM, a Carboeurope-IP salary to LW, a Marie Curie International Fellowship awarded to US (MOIF-CT-2004-2704) and a Ph.D. studentship awarded to CB (MOIF-CT-2004-2704).
Notes
†Originally presented at the JESIUM 2008 Conference (31 August–5 September 2008, Presqu'île de Giens, France).