Effects of elevated carbon dioxide and increased nitrogen deposition on bog vegetation in the Netherlands

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Summary We studied the effects of elevated atmospheric CO2and increased N deposition on the plant species composition of aSphagnum‐dominated bog ecosystem in the Netherlands. Large peat monoliths (surface area 1 m2, depth 0.6 m) with intact bog vegetation were kept outdoors in large containers and were exposed to elevated CO2or increased N deposition for three growing seasons. Elevated CO2conditions (target concentration 560 µmol CO2 mol−1) were created using MiniFACE technology. In a separate experiment, N deposition was increased by 5 g N m−2year−1by adding dissolved NH4NO3at 3 week intervals during the growing season. Elevated atmospheric CO2increased height growth ofSphagnum magellanicum, the dominantSphagnumspecies, in the second and third growing seasons. Vascular plant biomass was not significantly affected by elevated CO2, but growth of species growing close to the moss surface was influenced negatively by the increasedSphagnumheight growth. Elevated CO2did not change allocation to below‐ground plant parts. Adding N increased above‐ground vascular plant biomass. The shallow‐rooted speciesVaccinium oxycoccusresponded most to the increased N deposition.Sphagnumgrowth was significantly reduced in the third growing season. This reduction was likely the result of the increased vascular plant cover, given the observed negative relation between vascular plant cover andSphagnumgrowth. The observed shifts in species composition as a result of species‐specific responses to treatments, and interactions between peat mosses and vascular plants will have important consequences for the sequestration of carbon in the bog ecosystem.