Combined effects of elevated CO₂ and warmer temperature on limitations to photosynthesis and carbon sequestration in yellow birch.

This article focuses on the combined effects of elevated carbon dioxide (CO₂) concentration and warmer temperature on the photosynthetic traits and growth of yellow birch (Betula alleghaniensis Britt.) seedlings. The study found that treatment with elevated CO₂ (750 μmol mol⁻¹) and temperature (+4 °C) significantly reduced leaf-area-based photosynthetic capacity parameters—including maximum Rubisco carboxylation rate (Vcmax) and maximum photosynthetic electron transport rate (Jmax)—and leaf nitrogen concentration, while increasing total leaf area and biomass. Importantly, the primary photosynthetic limitation shifted from RuBP carboxylation (related to Vcmax) under ambient conditions to RuBP regeneration (related to Jmax) under elevated CO₂ and temperature, indicating a change in the biochemical processes governing photosynthesis. These findings suggest that future models of photosynthesis and growth in boreal trees should account for this shift in limitation and the compensatory increase in leaf area under climate change scenarios.