The effects of elevated carbon dioxide and warming on photosynthesis and growth in five boreal tree species

Julia M. Hammer, The University of Western Ontario

Abstract

Anthropogenic activities are increasing atmospheric CO₂ concentrations, leading to global warming. Boreal forests absorb and store CO₂ through photosynthesis and growth, yet we have relatively little data on the photosynthetic and growth responses of boreal trees to elevated CO₂ (EC) and warming. I grew seedlings of five North American boreal tree species for one growing season under different CO₂ (410 and 750 ppm) and temperature (ambient, +4, and +8 ºC) conditions, then measured photosynthetic traits and whole-plant biomass. The results were generally consistent across species: photosynthetic capacity (V_cmax and J_max) was unaffected by EC but strongly reduced by warming. Accordingly, net photosynthesis (A_growth) and biomass were stimulated by EC and suppressed by warming. Interactions between growth CO₂ and warming were rare. These findings improve our Earth system models and suggest that photosynthetic CO₂ uptake and growth in well-watered, well-fertilised boreal tree seedlings will be similar under current and future climates.