Abstract. The temperature sensitivity of soil organic carbon decomposition is critically important in determining the rate of future climate change because soils store 2–3 times the amount of atmospheric carbon. Of particular controversy is the question, whether temperature sensitivity differs between young or labile and old or more stable carbon pools. Contrasting hypotheses are currently supported. Depending on assumptions, identical data have been used to endorse contradicting hypotheses. Ambiguities in experimental methodology have so far limited corroboration of any particular hypothesis. Here, we show in a clear-cut approach that differences in temperature sensitivity between young and old carbon are negligible. Using the change in stable isotope composition in transitional systems from C3 to C4 vegetation, we were able to directly distinguish the temperature sensitivity of carbon differing several decades in age. Compared to previously followed approaches, we were able to identify release of much older carbon, un-natural conditions of long-term incubations were avoided and no arguable curve-fitting was employed. Our results demonstrate that feedbacks of the carbon cycle on climate change are driven equally by young and old soil organic carbon.
In situ
incubations highlight the environmental constraints on soil organic carbon decomposition
