Wetland plant development overrides nitrogen effects on initial methane emissions after peat rewetting

Growing productive wetland species on rewetted peatland (paludiculture) is a promising solution to offset carbon loss from drained peatlands. The inlet of nitrogen (N) rich surface water, a proposed method to improve productivity of vegetation, may affect methane (CH4) emissions. This study aims to compare initial CH4 emissions from newly rewetted peat with different types of vegetation and N loading simulating diffuse N inlet. Diffusive CH4 emissions were measured in peat mesocosms during one growing season. Peat cores were either planted with Typha latifolia or Phragmites australis or they were left bare. Mesocosms received 0, 50, 150 or 450 kg ha−1 year−1 N. Plants affected CH4 emissions from rewetted peat soil, leading to stable fluxes over time of 133 mg m−2 day−1 CH4 at 20 °C. Biomass harvesting lead to a 153% increase of CH4 emissions. With increasing N load, CH4 emissions from mesocosms with Typha and Phragmites decreased up to a load of 150 kg ha−1 N, but this was only significant for the Phragmites treatment. Emissions of unvegetated mesocosms increased with increasing N load but not significantly. In conclusion, our mesocosm study suggests that vegetation can reduce or prevent an increase in CH4 emissions from rewetted peatlands compared to only rewetting, possibly due to an increased oxygenation of the sediments by macrophyte roots preventing excessive CH4 formation, while added N does not provoke great changes in emissions at N concentrations up to 150 kg ha−1.