Photosynthetic responses and reproductive ability of strawberry following sunlight application in a plant factory closed system in subtropical Okinawa

Abstract

Sunlight is an abundant source of green energy that gives an energy-saving solution when introduced into a plant factory. However, a limitation point of applying sunlight is that it is unstable on cloudy and rainy days, and it fluctuates by seasons. Aiming to produce strawberry in subtropical areas, we investigated the effects of different light conditions on photosynthetic responses and reproductive ability of strawberry grown in a closed-type plant factory using sunlight (solar plant factory, SPF). The strawberries were grown under two different light conditions [full sunlight (S) or 10% sunlight + fluorescent light (SA)] with a CO2 concentration of 1,200 μmol mol-1 and a relative humidity of 50% ± 10%. The results showed that under long-day conditions, the response of net photosynthetic rate (Pn) of the strawberries leaves to different light levels did not differ between the two light conditions and was equal to that of plants grown in a CO2-enriched greenhouse. However, due to lower light intensity under short-day conditions, the response of Pn of the plants was significantly reduced in S treatment compared with that in SA treatment. Supplemented lighting to stabilize the light intensity showed effectiveness in improving Pn under the short-day conditions. The strawberries grown in SPF showed a high potential to produce flowers and fruits, which were not inferior to those under other controlled environment productions. These results suggest that strawberry production using SPF in the subtropics is practicable, and the limitation of SPF can be overcome by additional lighting utilization.