Responses of Sweet Basil to Different Daily Light Integrals in Photosynthesis, Morphology, Yield, and Nutritional Quality

Abstract

Consumption of basil ( Ocimum basilicum) has been increasing worldwide in recent years because of its unique aromatic flavor and relatively high concentration of phenolics. To achieve a stable and reliable supply of basil, more growers are turning to indoor controlled-environment production with artificial lighting due to its high environmental controllability and sustainability. However, electricity cost for lighting is a major limiting factor to the commercial application of indoor vertical farming, and little information is available on the minimum light requirement to produce uniform and high-quality sweet basil. To determine the optimal daily light integral (DLI) for sweet basil production in indoor vertical farming, this study investigated the effects of five DLIs, namely, 9.3, 11.5, 12.9, 16.5, and 17.8 mol·m ⁻²·d ⁻¹ on basil growth and quality. ‘Improved Genovese Compact’ sweet basil was treated with five DLIs provided by white fluorescent lamps (FLs) for 21 d after germination, and gas exchange rate, growth, yield, and nutritional quality of basil plants were measured to evaluate the effects of the different DLIs on basil growth and quality. Results indicated that basil plants grown under higher DLIs of 12.9, 16.5, or 17.8 mol·m ⁻²·d ⁻¹ had higher net photosynthesis, transpiration, and stomatal conductance ( g _S), compared with those under lower DLIs of 9.3 and 11.5 mol·m ⁻²·d ⁻¹. High DLIs resulted in lower chlorophyll (Chl) a+b concentration per leaf fresh weight (FW), higher Chl a/b ratios, and larger and thicker leaves of basil plants. The shoot FW under DLIs of 12.9, 16.5, and 17.8 mol·m ⁻²·d ⁻¹ was 54.2%, 78.6%, and 77.9%, respectively, higher than that at a DLI of 9.3 mol·m ⁻²·d ⁻¹. In addition, higher DLIs led to higher soluble sugar percent and dry matter percent than lower DLIs. The amounts of total anthocyanin, phenolics, and flavonoids per plant of sweet basil were also positively correlated to DLIs, and antioxidant capacity at a DLI of 17.8 mol·m ⁻²·d ⁻¹ was 73% higher than that at a DLI of 9.3 mol·m ⁻²·d ⁻¹. Combining the results of growth, yield, and nutritional quality of sweet basil, we suggest a DLI of 12.9 mol·m ⁻²·d ⁻¹ for sweet basil commercial production in indoor vertical farming to minimize the energy cost while maintaining a high yield and nutritional quality.