Propagation light intensity influences yield, morphology, and phytochemistry of purple-leaf butterhead lettuce (Lactuca sativa)

Abstract

Lettuce (Lactuca sativa) is an economically important leafy green produced in controlled environment agriculture (CEA). Optimization of lighting conditions is a crucial factor for sustainable production of high-quality lettuce in CEA systems. This study aimed to determine the effects of propagation light intensity (60, 100, 200, 400, and 600 μmol m−2 s−1, 24-h photoperiod) on harvestable yield, morphology, carotenoids, chlorophylls, and anthocyanins of purple-leaf butterhead 'Teodore' lettuce at transplant (14 days after showing) and harvest (21 days after transplanting in a greenhouse environment). We observed a 275 % increase in shoot fresh mass in seedlings grown under 600 μmol m−2 s−1 compared to those under 60 μmol m−2 s−1, and a 163 % improvement persisted through harvest. The HPLC quantification demonstrated that all carotenoids, including violaxanthin, neoxanthin, zeaxanthin, antheraxanthin, lutein, α-carotene, and total carotenoid content and/or concentration increased in lettuce seedlings as light intensities increased from 60 to 400 or 600 μmol m−2 s−1 (5.4–35.9 or 52.7 mol m−2 d−1 DLI). A similar increasing trend was also observed for chlorophyll accumulation. Anthocyanin concentration and content increased with increasing propagation light intensity, but no differences persisted through harvest. Overall, differences in most phytonutrient concentrations and contents persisted through harvest; carotenoid content trends were similar to those at transplant, but carotenoid and chlorophyll concentration trends were somewhat opposite with quadratic decreases as light intensity increased. The results indicate that propagation light intensity could be used as an effective and sustainable strategy to improve the harvestable yield and nutritional quality of lettuce grown in CEA.