Evidence is provided for an internal CO₂ sink in forest soils, that may have a potential impact on the global CO₂-budget. Lowered CO₂ fraction in the soil atmosphere, and thus lowered CO₂ release to the aboveground atmosphere, is indicated in high N-deposition areas. Also at forest edges, especially of spruce forest, where additional N-deposition has occurred, the soil CO₂ is lowered, and the gradient increases into the closed forest. Over the last three decades the capacity of the forest soil to maintain the internal sink process has been limited to a cumulative supply of approximately 1000 and 1500 kg N ha⁻¹. Beyond this limit the internal soil CO₂ sink becomes an additional CO₂ source, together with nitrogen leaching. This stage of “nitrogen saturation” is still uncommon in closed forests in southern Scandinavia, however, it occurs in exposed forest edges which receive high atmospheric N-deposition. The soil CO₂ gradient, which originally increases from the edge towards the closed forest, becomes reversed.