Arctic regions contain large amounts of stored soil carbon and comprise huge areas of discontinuous vegetation. The potential for feedback effects on possible changing climatic conditions through altered source/sink action for atmospheric CO2 is therefore an important issue in tundra regions. In this study we investigate environmental controls on CO2 evolution rates in Arctic soils through observations along a Eurasian transect of tundra sites and comparative experiments in northern Sweden and northeast Greenland. Among factors potentially controlling decomposition rates in Eurasian wet and mesic tundra temperature and depth of the water table significantly influenced the CO2 efflux, while thaw depth, soil nitrogen, and organic matter concentrations explained very little of the variation in fluxes. The minor importance of the soil N status in controlling decomposition rates was confirmed in experiments in which N and P was added in a factorial manner at a subarctic heath and a high-Arctic drained fen. Phosphorus decreased the CO2 emissions, while the combined N and P treatment increased the emissions in the subarctic. These effects were not reproduced in the high Arctic. The results support most assumptions in current decomposition models on the soil climatic controls on decomposition rates in the Arctic. ¿ 1998 American Geophysical Union