CO2 emissions from soil in response to climatic warming are overestimated - The decomposition of old soil organic matter is tolerant of temperature

The storage of organic carbon in soil is predicted to decrease with global warming because the decomposition of organic matter is expected to accelera te relative to the net primary production (NPP) of vegetation. This decreas e would substantially increase the atmospheric CO2 concentration because so il contains twice as much C as the present atmosphere and the decomposed C from soil will be released to the atmosphere. These predictions of the decr ease in soil C storage are, however, largely dependent on the implied assum ption that the decomposition of all soil organic matter is as sensitive to temperature as is the decomposition of young litter. We used measurements o f the amount and age of soil C and the decomposition of litter on temperatu re gradients and a simple model describing soil C dynamics to show that the decomposition of old soil organic matter is resistant to changes in temper ature. Accordingly, in response to climatic warming, we estimate decomposit ion to accelerate significantly less than previously expected, and predict that the C storage of boreal forest soils will increase.