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. [ABSTRACT FROM AUTHOR]