Performance of Different Lettuce Cultivars Grown Hydroponically Under Fluorescent and Light-Emitting Diode Light Growth Conditions

Lettuce (Lactuca sativa L.) is one of the most consumed fresh vegetables in the United States. However, lettuce production is heavily limited to California and Arizona, posing a high risk to the supply chain. Hydroponic production is a soilless cultivation method and provides a sustainable alternative to growing lettuce in the field. Light is a critical factor in plant development, and light quality highly affects plant morphogenesis. The goals of this study were 2-fold, with the first to investigate the growth of 26 lettuce cultivars under a hydroponic system supplemented with fluorescent light to determine adaptability. Subsequently, the second goal was to determine how light-emitting diodes (LEDs) affect lettuce plant morphology and photosynthesis compared with fluorescent light for four lettuce cultivars. Results showed that 23 of 26 lettuce cultivars were grown successfully using a hydroponic system. However, lettuce grown under fluorescent light experienced stem elongation—a morphological response to low-light conditions known as shade avoidance syndrome. Stem elongation decreased significantly under LED light, whereas other morphological characteristics remained relatively the same between the two light treatments. Although there were no differences in dry weight and leaf area, the carbon assimilation rate increased significantly in lettuce cultivars Coastal Star, Muir, Green Butter, and Rouge d’Hiver when treated with LED light. Correspondingly, intercellular carbon dioxide (CO2) decreased in these four lettuce cultivars under the LED light treatment. Our study results indicate that LED light increased photosynthetic activity and reduced stem elongation to enhanced lettuce quality.