Decomposition of Decadally Cycling Soil Organic Carbon is Sensitive to Warming

Abstract:

There is a dearth of studies investigating the temperature sensitivity of decomposition for decadally cycling soil organic carbon (SOC) (the dominant component of total soil carbon stocks and the most relevant to global change) mostly due to methodological constraints, which is a major issue for research on the potential link between global warming and the current global carbon cycle. We tackled this issue by using two ¹³C-labeled soils with decadal timescales and a much improved measuring system in a long-term incubation experiment. Results indicated that the temperature sensitivity (as measured by Q₁₀ values) of SOC >23 years was significantly (P<0.001) higher (approximately 45% greater) than SOC <23 years for one soil, and that the temperature sensitivity of SOC >55 years was significantly (P<0.001) higher (approximately 80% greater) than SOC <55 years for the other soil. Furthermore, the temperature sensitivity of decomposition for SOC >23 years or >55 years was substantially higher than that for the entire SOC stocks which was apparently dominated by the fast cycling SOC with turnover times in the range of days to a few years. Because of the use of the improved methods, our data were clearly beyond the reasonable doubt as indicated by the low experimental errors. Overall, these results imply that the decomposition of decadally cycling SOC is highly sensitive to temperature change and vulnerable to loss caused by global warming.