On the potential CO2 release from tundra soils in a changing climate

About 30% of the carbon in terrestrial ecosystems is stored in northern wet lands and boreal forest regions. Prevailing cold and wet soil conditions ha ve largely been responsible for this carbon accumulation. It has been sugge sted that a warmer and drier climate in these regions might increase the de composition rate and, hence, release more CO2 to the atmosphere than at pre sent. This study reports on the spatial variability and temperature depende nce of the potential carbon release after incubating highly organic soils f rom the European Arctic and Siberia at different temperatures. We found tha t the decay potential, measured as CO2 production in laboratory experiments , differed strongly within and among sites, particularly at higher soil tem peratures. Furthermore, both the decay potential and its temperature respon se decreased significantly with depth in the soil, presumably because the o lder soils at deeper layers contained higher proportions of recalcitrant ca rbon than the younger soil organic matter at the surface. These results hav e implications for global models of potential feedbacks on climate change i nferred from changes in the carbon balance of northern wetlands and tundra. Firstly, because the decay potential of the organic matter varies locally as well as regionally, predictions of how the tundra carbon balance may cha nge will be unreliable if these are based on measurements at a few sites on ly. Secondly, any increase in CO2 production may be transitional as both th e carbon flux and its temperature sensitivity decrease when the most easily degradable organic material near the soil surface has decomposed. Conseque ntly, it is crucial to account for transient responses and regional differe nces in the models of potential feedbacks on climate change from changed ca rbon cycling in northern terrestrial ecosystems. (C) 1999 Elsevier Science B.V.