Does hydrological restoration affect greenhouse gases emission and plant dynamics in sphagnum peatlands?

International audienceThe C-sink function of peatlands is mainly controlled by soil waterlogging and Sphagnum moss dominance. La Guette peatland (Sologne, France) was drained for decades by a road ditch resulting in vascular plant (Molinia caerulea) invasion. Hydrological restoration was undertaken in 2014 and vegetation experiments were set up. In both downstream and upstream stations, three treatments (n=4) were conducted: " control " with intact vegetation, " bare peat " , and " Sphagnum " (bare peat seeded with Sphagnum). Our aim was to assess the effect of such actions on plant community diversity and CO 2 /CH 4 fluxes. In each plot, gas fluxes and plant cover were measured. 18 months after the restoration work, " bare peat " and " Sphagnum " plots were quickly colonised by Eriophorum angustifolium (up to 90%), Rynchospora alba (up to 10%), Trichophorum cespitosum (up to 60%). In both stations, control plots functioned as C sinks with lower CH 4 emissions and higher ecosystem respiration compared to the other treatments. However, at peak biomass the latter treatments tended to act as sinks for CO 2 in 2015 than in 2014 suggesting that plant cover, higher in 2015 than in 2014, is a crucial determinant for CO 2 fluxes. Although vegetation colonisation is proceeding fast, two years do not appear to be sufficient to trigger a C sink function in restored peatlands