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 -1000 ppm both in forcing and half-forcing culture regardless of growth stage, suggesting that the CO2 enrichment largely exceeding 1000 ppm was not effective. Although the photosynthetic rate was saturated at 1000μmol m-2 s-1 under 400 ppm 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 20oC under 400 ppm CO2, but it continued to increase up to 30oC under 1000 ppm 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 1000 ppm. 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 -1000 ppm in the greenhouse without ventilation during the day.