• We quantified seasonal CO2 assimilation capacities for seven dominant vascular species in a wet boreal forest peatland then applied data to a land surface model parametrized to the site (ELM-SPRUCE) to test if seasonality in photosynthetic parameters results in differences in simulated plant responses to elevated CO2 and temperature.
• We collected seasonal leaf-level gas exchange, nutrient content and stand allometric data from the field-layer community (i.e., Maianthemum trifolium), understory shrubs (Rhododendron groenlandicum, Chamaedaphne calyculata, Kalmia polifolia, and Vaccinium angustifolium) and overstory trees (Picea mariana and Larix laricina).
• We found significant interspecific seasonal differences in specific leaf area, foliar nitrogen (N) and photosynthetic parameters (e.g., rates of Rubisco carboxylation (Vcmax25degC), electron transport (Jmax25degC) and dark respiration (Rd25degC), but minimal correlation between foliar N and Vcmax25degC, Jmax25degC or Rd25degC. ELM-SPRUCE was sensitive to the introduction of observed interspecific seasonality in Vcmax25degC , Jmax25degC and Rd25degC, leading to enhanced net primary production (NPP) using seasonal parameters. This pattern was particularly pronounced under higher temperature and elevated CO2.
• In conclusion, our results show that the model’s estimation of boreal ecosystem-level NPP could be significantly improved, especially at elevated temperatures and CO2, by the inclusion of species-specific seasonal parameterization of key photosynthetic parameters.