Photosynthesis, Morphology, Yield, and Phytochemical Accumulation in Basil Plants Influenced by Substituting Green Light for Partial Red and/or Blue Light

Abstract

Green light penetrates deeper into the plant canopy because of its high transmittance and reflectance, and may potentially increase light interception and whole-canopy photosynthesis, whereas red and blue light is absorbed primarily by upper leaves. Moreover, green light induces shade avoidance responses and regulates secondary metabolism in plants. In this study, we investigated the effects of substituting partial red and/or blue light with green light on plant growth and development in basil (Ocimum basilicum) ‘Improved Genovese Compact’ (green) and ‘Red Rubin’ (purple) plants. There were four treatments: one combined red and blue (R&B) light treatment, R76B24 [the proportion of red (R) and blue (B) light was 76% and 24%, respectively]; and three green (G) light treatments—R44B24G32, R74B16G10, and R42B13G45—with green light proportions of 32%, 10%, and 45%, respectively. The experiment was conducted in a growth room and the photosynthetic photon flux density (PPFD) of all treatments was set at 220 μmol·m−2·s−1 with a 16-h photoperiod. Plants were subirrigated as needed using a nutrient solution with an electrical conductivity (EC) of 2.0 dS·m−1 and a pH of 6.0. The net photosynthetic rate (Pn) in lower leaves was unaffected by green light treatments in green basil plants, whereas in purple basil plants it increased by 59% and 45% under treatments R44B24G32 and R74B16G10, respectively, compared with the combined R&B light. In green basil plants, treatments R44B24G32 and R42B13G45 induced stem elongation, but green light treatments showed no effects on petiole elongation, leaf expansion, leaf thickness, or plant yield. In purple basil plants, treatments R44B24G32 and R42B13G45 induced stem elongation and decreased leaf thickness and plant yield, but only the R42B13G45 treatment induced petiole elongation, and green light treatments showed no effects on leaf expansion. Concentrations of anthocyanin, phenolics, and flavonoids, and antioxidant capacity in green basil leaves showed no differences between treatments R76B24 and R44B24G32, but decreased under treatments R74B16G10 and R42B13G45. Concentrations of phenolics and flavonoids, and antioxidant capacity in purple basil leaves showed no differences between treatments R76B24 and R74B16G10, but decreased under treatments R44B24G32 and R42B13G45. Combining plant yield, nutritional values, and the working environment for growers, a white light with low green light proportion (≈10%) is recommended for basil production in a controlled environment.