An assessment of carbon dioxide exchanges following vascular plant establishment in a constructed boreal watershed

• CO 2 dynamics of planted, native, boreal species +5 years post-construction. • Plant community sequestered CO 2 , even under variable hydroclimatic conditions. • PAR, soil moisture and plant physiology were key drivers of CO 2 fluxes. • Water table position was not a significant environmental control. • CO 2 fluxes comparable to natural and post-disturbance landscapes in the region. The pre-disturbance landscape of the Athabasca Oil Sands Region (AOSR) is comprised of a mosaic of upland-peatland complexes which provide key ecosystem services such as carbon sequestration and biodiversity. As such, these landscapes have become the central focus of recent, mandatory reclamation efforts in the region. Quantifying plant productivity and understanding environmental drivers during early ecosystem development provides important insight into the ecohydrological performance of constructed landscapes. This study examines the carbon dioxide (CO 2 ) dynamics of dominant vascular species of a constructed upland-fen complex using the chamber method. Notably, due to the young stand age of the upland, fluxes of whole trees were able to be measured using a stacked chamber technique. The sedge-dominated fen consists of fresh and salt tolerant species whereas the treed upland is a mix of coniferous and deciduous species with a patchy understory. Results show differences in the timing and amount of carbon sequestration between the two landscapes, as well as between species under varying environmental conditions. Overall, both fresh and salt tolerant species in the fen sequester carbon. Due to the high, stable water table position, net ecosystem exchange (NEE) in the fen was largely controlled by atmospheric conditions. In the upland, coniferous species exhibit more carbon accumulating days throughout the growing season, albeit at a lesser rate than deciduous species. While all four tree species in the upland were carbon accumulating, understory plots fluctuated between a source and sink. As the upland is a drier environment, NEE was driven by both atmospheric and edaphic controls. Assessment of species-specific carbon fluxes during early development provides insight to land managers on plant function along reclamation trajectories and can be applied to future planting prescriptions to ensure long-term reclamation success.