Can abandoned peatland pasture sequestrate more carbon dioxide from the atmosphere than an adjacent pristine bog in Newfoundland, Canada?

Net ecosystem exchange of carbon dioxide (NEE) and its components, gross primary productivity (GPP) and ecosystem respiration (ER), were compared between a bog and an abandoned peatland pasture within the same peatland complex in western Newfoundland, Canada. Measurements based on the eddy covariance technique from April 2014 to April 2016 were used to examine the influence of agricultural management and abandonment on peatland carbon dioxide (CO2) exchange. NEE, GPP and ER at both sites showed pronounced seasonal variation, peaking near the middle growing season. The maximum net CO2 uptake rate of −28.61 μmol m−2 s−1 and emission rate of 14.39 μmol m−2 s−1 at the pasture were significantly higher than those at the bog (−9.67 μmol m−2 s−1 and 5.50 μmol m−2 s−1, respectively). Daytime average GPP was related to photosynthetic photon flux density and air temperature and the nighttime average ER decreased with soil water content, but increased with surface soil temperature for both sites. Annual NEE of the pasture (−128 ± 60 g C m−2 yr−1 in 2014-15 and −124 ± 56 g C m−2 yr−1 in 2015-16) was considerably larger than that of the bog (−46 ± 36 g C m−2 yr−1 in 2014-15). GPP of 1086 ± 141 g C m−2 yr−1 in 2014-15 and 982 ± 123 g C m−2 yr−1 in 2015-16 and ER of 957 ± 129 g C m−2 yr−1 in 2014-15 and 858 ± 112 g C m−2 yr−1 in 2015-16 at the pasture were approximately twice the magnitude of the corresponding fluxes at the bog. The difference in GPP between the bog and pasture was mainly related to their different aboveground biomass. Higher ER at the pasture was probably related to its lower water table depth, greater substrate availability and higher autotrophic respiration. Unlike previous findings that managed peatlands are large CO2 emitters, our results suggest that abandoned peatland pastures can function like natural grasslands and sequester considerable amounts of CO2 from the atmosphere.