Temperature sensitivity of soil carbon decomposition and feedbacks to climate change

Significantly more carbon is stored in the world's soils—including peatlands, wetlands and permafrost—than is present in the atmosphere. Disagreement exists, however, regarding the effects of climate change on global soil carbon stocks. If carbon stored belowground is transferred to the atmosphere by a warming-induced acceleration of its decomposition, a positive feedback to climate change would occur. Conversely, if increases of plant-derived carbon inputs to soils exceed increases in decomposition, the feedback would be negative. Despite much research, a consensus has not yet emerged on the temperature sensitivity of soil carbon decomposition. Unravelling the feedback effect is particularly difficult, because the diverse soil organic compounds exhibit a wide range of kinetic properties, which determine the intrinsic temperature sensitivity of their decomposition. Moreover, several environmental constraints obscure the intrinsic temperature sensitivity of substrate decomposition, causing lower observed ‘apparent’ temperature sensitivity, and these constraints may, themselves, be sensitive to climate. Climatically induced changes in the enormous carbon stocks that occur belowground in soils, peatlands and permafrost could cause important positive or negative feedbacks to climate change. But despite much research, there is still no consensus on the subject: it could go either way. Eric A. Davidson and Ivan A. Janssens review this continuing controversy within the context of current understanding of soil carbon dynamics.