Cultivation of bioenergy crops in rewetted peatland (paludiculture) is considered as a possible land use option to mitigate greenhouse gas (GHG) emissions. However, bioenergy crops like reed canary grass (RCG) can have a complex influence on GHG fluxes. Here we determined the effect of RCG cultivation on GHG emission from peatland rewetted to various extents. Mesocosms were manipulated to three different ground water levels (GWLs), i.e. 0, -10 and -20 cm below the soil surface in a controlled semi-field facility. Emissions of CO 2 (ecosystem respiration, ER), CH 4 and N 2O from mesocosms with RCG and bare soil were measured at weekly to fortnightly intervals with static chamber techniques for a period of 1 year. Cultivation of RCG increased both ER and CH 4 emissions, but decreased the N 2O emissions. The presence of RCG gave rise to 69, 75 and 85% of total ER at -20, -10 and 0 cm GWL, respectively. However, this difference was due to decreased soil respiration at the rising GWL as the plant-derived CO 2 flux was similar at all three GWLs. For methane, 70-95% of the total emission was due to presence of RCG, with the highest contribution at -20 cm GWL. In contrast, cultivation of RCG decreased N2O emission by 33-86% with the major reductions at -10 and -20 cm GWL. In terms of global warming potential, the increase in CH 4 emissions due to RCG cultivation was more than offset by the decrease in N 2O emissions at -10 and -20 cm GWL; at 0 cm GWL the CH 4 emissions was offset only by 23%. CO 2 emissions from ER were obviously the dominant RCG-derived GHG flux, but aboveground biomass yields, and preliminary measurements of gross photosynthetic production, showed that ER could be more than balanced due to the photosynthetic uptake of CO 2 by RCG. Our results support that RCG cultivation could be a good land use option in terms of mitigating GHG emission from rewetted peatlands, potentially turning these ecosystems into a sink of atmospheric CO 2.
