Contrasted effects of increased N and CO₂ supply on two keystone species in peatland restoration and implications for global change

<b>1</b> Significant areas of temperate bogs have been damaged by peat harvesting but may regenerate. These secondary mires, if well managed, may act as strong C sinks, regulate hydrology and buffer regional climate. <br> <b>2</b> The potential effects of bog regeneration will, however, depend on the successful establishment of the principal peat formers –<i>Sphagnum</i> mosses. The influence of hydrology and microclimate on <i>Sphagnum</i> re-growth is well studied but effects of elevated CO2 and N deposition are not known. <br> <b>3</b> We carried out two <i>in-situ</i> experiments in a cutover bog during three growing seasons in which we raised either CO₂ (to 560 p.p.m.) or N (by adding NH₄NO₃, 3 g m⁻² year⁻¹). The two treatments had contrasting effects on competition between the initial coloniser <i>Polytrichum strictum</i> (favoured by high N) and the later coloniser <i>Sphagnum fallax</i> (favoured by high CO₂). <br> <b>4</b> Such changes may have important consequences for bog regeneration and hence for carbon sequestration in cutover bogs, with potential feedback on regional hydrological and climatic processes.