Effects of Air and CO2 Application within a Strawberry Plant Canopy on Fruit Yield and Dry Matter Production during Summer and Autumn Culture

Strawberries can be categorized into June-bearing and ever-bearing depending on the environmental conditions that determine flower bud initiation. In Japan, the harvest yield and distribution of strawberry fruits during summer and autumn are low because of high temperatures and heavy fruit load. Therefore, cultivation of ever-bearing strawberries is limited to areas with cool summers such as Hokkaido and Tohoku. In this study, we investigated whether air treatment before liquefied carbon dioxide (CO2) application within the strawberry plant canopy could improve CO2 absorption efficiency and increase dry matter production. Four treatments were investigated: application of air within the plant canopy, application of CO2, application of CO2 after air application, and a control. We investigated the CO2 concentration, dry matter production, yield characteristics, individual leaf photosynthesis characteristics, projected leaf area, cumulative light interception, light use efficiency, and fruit quality. The results showed that the local application of only CO2 or Air and, application of CO2 after air application (Air/CO2) treatment within the plant canopy considerably increased the dry matter production. Total fruit yield of Air/CO2 was the highest among all treatments. This is probably because the application of CO2 and air expanded the leaf area, increased cumulative light interception, and improved light use efficiency. In addition, the photosynthetic rate of Air, CO2 and Air/CO2 treatments was higher than that of the control because of higher stomatal conductance. This suggests that local application of liquefied CO2 after air application can effectively increase fruit yield, and that air treatment will improve plant vigor, further increasing strawberry production in summer and autumn.