EFFECTS OF LIGHT QUALITY AND CO₂ CONCENTRATION ON DIURNAL PHOTOSYNTHETIC CHARACTERISTICS OF STRAWBERRY

As photosynthetic efficiency changes with wavelength and CO₂ level, several artificial light sources for strawberry production were tested. Strawberry (Fragaria ×ananassa Duch. ‘Toyonoka’) plants were planted in a growth chamber (25/20°C, 16 h photoperiod, 400 μl L^-1 CO₂), using different T5 lamps (approximately same PPF at 200 μmol m^-2 s^-1), including Warm White (WW, 3000K, R:G:B=43:40:17), Cool White (CW, 6500K, R:G:B=23:40:37), and TLRA (Tubular Lamp with Red Additive, R:G:B=59:29:12) for seven weeks. The diurnal photosynthetic characteristics of net photosynthetic rate, stomatal conductance, and transpiration rate were measured by portable photosynthetic system (LI-6400). The results showed that diurnal photosynthetic characteristics of strawberry were different among treatments. Net photosynthetic rate was the highest under CW lamps and treatment under TLRA lamps was the lowest. The peak value of net photosynthetic rate appeared after 5, 7 and 3 hours of exposure to WW, CW and TLRA lamps, respectively. The diurnal variation of net photosynthetic rate was a single-peak curve under WW and CW lamps and a double-peak curve under TLRA lamps. There was a significant midday depression when plants were exposed to TLRA lamps for 9 hours. Our results showed that spectral quality during light period affected the diurnal pattern of photosynthetic characteristics. We also compared the photosynthetic characteristics at elevated 1200 μl L^-1 CO₂ concentration used of different light quality lamps. The effect of light quality on photosynthesis characteristics changed with CO₂ concentration. The highest photosynthetic rate and plant growth were again under CW lamp irradiation. No significant midday depression was found when plants were exposed to TLRA lamps at elevated CO₂. Elevated CO₂ treatment resulted in increased plant photosynthesis under all tested light treatments and altered the effect of spectral quality on the diurnal photosynthetic characteristics of strawberry.