Elevated CO₂ increases photosynthesis in fluctuating irradiance regardless of photosynthetic induction state

Leaves are often exposed to fluctuating irradiance, which limits assimilation. Elevated CO₂ enhances dynamic photosynthesis (i.e. photosynthesis in fluctuating irradiance) beyond its effects on steady-state photosynthesis rates. Studying the role of CO₂ in dynamic photosynthesis is important for understanding plant responses to changing atmospheric CO₂ partial pressures. The rise of photosynthesis after a step-wise increase to 1000 μmol m–2 s–1, the loss of photosynthetic induction after irradiance decreases, and rates of photosynthesis during sinusoidal changes in irradiance were studied in tomato (Solanum lycopersicum L.) leaves, using three CO₂ partial pressures (200, 400, and 800 μbar). Initial irradiance was set to 0, 50, 100, and 200 μmol m–2 s–1 to vary the initial induction state. Most responses at 200 μbar were not different from those at 400 μbar. In contrast, CO₂ at 800 μbar increased the relative carbon gain by 12% after an increase in irradiance, decreased the loss of photosynthetic induction by 14%, and increased dynamic photosynthesis during sine waves by 17%, compared with 400 μbar. These effects were additional to steady-state effects of elevated CO₂ on photosynthesis. The enhancement of dynamic photosynthesis rates by elevated CO₂ may therefore additionally increase photosynthesis in a future, CO₂-enriched climate.