Effects of CO₂ Enrichment on Yield, Photosynthetic Rate, Translocation and Distribution of Photoassimilates in Strawberry ‘Sagahonoka’

The method of automatically controlling the CO₂ concentration in a greenhouse depending on ventilation was examined in order to efficiently improve the productivity of strawberries under the weather conditions in the northern part of Kyushu in Japan. The effects of CO₂ enrichment on the yields, fruit Brix, and economic value of the strawberry ‘Sagahonoka’ were investigated. In addition, in order to clarify the physiological response of ‘Sagahonoka’ to the CO₂ concentration, the photosynthetic rate, translocation, and photoassimilate distribution rate were measured. It was found that maintaining the CO₂ concentrations above 800 μmol mol−1 and 400 μmol mol−1 during no ventilation and ventilation, respectively, resulted in 25% increases in marketable fruit yields and a 0.2-1.2% higher fruit Brix compared to control, which was kept in 400 μmol mol−1 CO₂ or above all day regardless of ventilation. Additionally, the economic value of ‘Sagahonoka’ was increased. The photosynthetic rate of ‘Sagahonoka’ increased linearly up to 800 μmol mol−1 CO₂, and high CO₂ concentrations affected the distribution for the primary fruit, the most significant sink. It was clarified that CO₂ enrichment at 800 μmol mol−1 for ‘Sagahonoka’ was effective in increasing the photosynthetic rate and distribution of photoassimilates to fruits, and the yields of strawberries could be increased efficiently by automatically controlling the CO₂ concentration depending on ventilation in a southern region of Japan.