Effects of Light and Temperature on Photosynthetic Enhancement by High CO₂ Concentration of Strawberry Cultivar Tochiotome Leaves under Forcing or Half-Forcing Culture

Abstract

CO₂ enrichment is widely used to raise the photosynthetic rate and to improve a yield and quality of the strawberry cultivated in Tochigi prefecture. In this study, we investigated the effect of CO₂ concentration on leaf photosynthesis under several light and temperature conditions. Strawberry cultivar Tochiotome was cultivated in pots under forcing and half-forcing culture. The apparent photosynthetic rates in leaves were measured with a portable photosynthesis measurement system. The CO₂-photosynthesis curves in strawberry leaves were saturated at a CO₂ concentration of 800-1000ppm both in forcing and half-forcing culture regardless of growth stage, suggesting that the CO₂ enrichment largely exceeding 1000ppm was not effective. Although the photosynthetic rate was saturated at 1000Μmol m^-2 s^-1 under 400ppm CO₂, it continued increasing over 1000Μmol m^-2 s^-1 under 1000 ppm CO₂. Therefore, the effect of the CO₂ enrichment was larger in high intensity light conditions. The photosynthetic rate was not increased by raising the temperature over 20°C under 400ppm CO₂, but it continued to increase up to 30°C under 1000ppm CO₂. Thus, the effect of the CO₂ enrichment is larger under higher temperature conditions. It is concluded that the CO₂ enrichment is effective for the promotion of the photosynthesis when the ventilation time in the morning is delayed, to keep the temperature high, and CO₂ concentration at 800 to 1000ppm. The ventilation should be started at about 12 o’clock when the light intensity is high enough on a fine day. However, on cloudy days, both temperature and light intensity are low, the photosynthetic rate is improved by keeping the temperature high and increasing the CO₂ concentration to 800-1000ppm in the greenhouse without ventilation during the day.