Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas (GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange (NEE) fluxes of CO₂ as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass (RCG) and spring barley (SB) in a plot experiment (n = 3 for each cropping system). The CO₂ flux was partitioned into gross photosynthesis (GP) and ecosystem respiration (R_E). For the data analysis, simple yet useful GP and R_E models were developed which introduce plot-scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the R_E model estimates the proportion of foliar biomass dependent respiration (R_fb) in the total R_E. Annual R_E was 1887 ± 7 (mean ± standard error, n = 3) and 1288 ± 19 g CO₂-C m⁻² in RCG and SB plots, respectively, with R_fb accounting for 32 and 22% respectively. Total estimated annual GP was −1818 ± 42 and −1329 ± 66 g CO₂-C m⁻² in RCG and SB plots leading to a NEE of 69 ± 36 g CO₂-C m⁻² yr⁻¹ in RCG plots (i.e., a weak net source) and −41 ± 47 g CO₂-C m⁻² yr⁻¹ in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO₂ emissions during cultivation. However, in a broader GHG life-cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial.

Rewetting of drained peatlands has been recommended to reduce CO₂ emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO₂ emissions without losing agricultural land. This study quantified the carbon balance (CO₂, CH₄ and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different groundwater levels (GWLs), that is 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO₂ and CH₄ emissions was measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha⁻¹) than drained peat soils (15 Mg ha⁻¹). Also, CO₂ fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than from drained peat soils, but net uptake of CO₂ was higher from rewetted peat soils. Cumulative CH₄ emissions were negligible (0.01 g CH₄ m⁻²) from drained peat soils but were significantly higher (4.9 g CH₄ m⁻²) from rewetted peat soils during measurement period (01 May–15 September 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m⁻² from rewetted and drained peat soils, respectively, indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.