Influence of TiO₂ foliar spray application on photosynthesis and chlorophyll fluorescence of strawberry during low light intensity season in a greenhouse

This study was carried out to investigate the influence of TiO₂ foliar spray application on photosynthesis and chlorophyll fluorescence of strawberry plants during low ambient sunlight season in a greenhouse. Strawberry plants were treated with TiO₂ foliar spray application on February 7 and photosynthesis related parameters were measured 4 times; on February 8, 18, 29 and on March 9. All measurements were performed between 10 and 12 o'clock. The ambient sunlight intensity in the greenhouse was much lower in early part (from February 8 to 18) of the experimental period than in the latter half (from February 28 to March 9). Under low sunlight intensity condition, the photosynthetic rate and stomatal conductance of strawberry leaves was higher with TiO₂ treatments compared to the untreated control. However, under high sunlight intensity (>1,000 µmol m^‑2 s^‑1) condition, photosynthesis decreased with TiO₂ treatments. The transpiration rate of leaves was significantly increased with TiO₂ treatments compared to the control. Chlorophyll fluorescence parameters, such as Fo, Fm, and Fv/Fm showed a high trend with TiO₂ treatments, while NPQ, R_fd, and q_p were higher in the control. Regardless of the TiO₂ treatments, chlorophyll fluorescence parameters, except for Fo, showed a tendency to decrease in high sunlight intensity condition on March 9 compared to February 28. In addition, the amount of photosynthetic pigment increased with treatment of 100 mg kg^‑1 TiO₂. In conclusion, TiO₂ foliar spray application is suggested to be effective for low sunlight intensity season in strawberry cultivation to improve photosynthetic efficiency of the plants.