CO2 and air circulation effects on photosynthesis and transpiration of tomato seedlings

In the daytime, a CO₂ depletion of 10–15% and air circulation of less than 0.5 m s⁻¹ often occur in a naturally ventilated greenhouse during a sunny day with high wind speed (3–5 m s⁻¹). We, therefore, investigated the effects of moderate increase of the CO₂ concentration above the atmospheric level (500–600 μmol mol⁻¹) and air circulation up to 1.0 m s⁻¹ in a growth chamber on the net photosynthetic and transpiration rates of tomato seedlings as the first step. The average net photosynthetic rates were 2.1, 1.8, and 1.6 times higher in the growth chambers with increased CO₂ concentration (500–600 μmol mol⁻¹) and air circulation (1.0 m s⁻¹), increased CO₂ concentration, and increased air circulation, respectively, compared with those in the control (no increase in CO₂ concentration (200–300 μmol mol⁻¹) or air circulation (0.3 m s⁻¹). The transpiration rate increased with increased air circulation, while it decreased with increased CO₂ concentration regardless of air circulation. From the results, we consider that increasing the CO₂ concentration and/or air circulation in ventilated greenhouses up to the outside concentration (350–450 μmol mol⁻¹) and 1.0 m s⁻¹, respectively, can significantly increase the net photosynthetic rate of greenhouse plants.