Ombrotrophic bogs are important long-term sinks for atmospheric carbon. Changes in species composition of the bog plant community may have important effects on carbon sequestration, because peat mosses ( Sphagnum ) contribute more to peat accumulation than vascular plants. The aim of this study was to investigate the effects of elevated atmospheric carbon dioxide (CO 2 ) and increased nitrogen (N) deposition on bog vegetation in the Netherlands, with special attention to the relationship between peat mosses and vascular plants.Three experiments were conducted, one outdoors and two in the greenhouse, in which peat monoliths were exposed to different levels of atmospheric CO 2 and Ndeposition. The outdoor experiment was part of the European BERI project, which used MiniFACE technology for creating elevated CO 2 conditions. The vegetation response in all three experiments was followed for two or three growing seasons. In addition, evapotranspiration and the partitioning of 15 N-labelled Ndeposition among Sphagnum , vascular plants and peat was measured.The results showed, for the first time, that elevated CO 2 benefits growth of Sphagnum , but not necessarily at the cost of vascular plant growth. Increases in vascular plant biomass were non-significant, and were apparently restricted by the faster Sphagnum height growth and/or nutrient limitation. Sphagnum can take advantage of elevated CO 2 because its growth is less nutrient limited than that of vascular plants. Reductions in evapotranspiration at elevated CO 2 in summer would further benefit Sphagnum , as its growth is very sensitive to changes in moisture availability. During three growing seasons of Naddition, the Sphagnum layer became saturated with N, resulting in a larger availability of Nand better growth of vascular plants. After reaching a cover of about 60% vascular plants reduced Sphagnum growth through increased shading.These changes in relative abundances of peat mosses versus vascular plants, in response to treatments and interactions between ...