High-Intensity Continuous Light from Red-Blue Light-Emitting Diodes Improved Yield, Nutritional Quality and Reactive Oxygen Species Accumulation in Two Leaf-Color Lettuces.

In an environmentally controlled plant factory with LED red-blue light, the effects of conventional light (4R:1B, 200 μmol·m·s, 18/6 h) and continuous light (CL, 24/0 h) with three light intensities (4R:1B, 200, 300 and 400 μmol·m·s, 24/0 h) on yield, nutritional quality, reactive oxygen species (ROS) content and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH) in green-leaf Yidali and purple-leaf Zishan lettuces were investigated. The results showed that the dry and fresh shoot weight of two lettuces exposed to CL tended to increase with light intensity-from 200 to 400 μmol·m·s-compared to conventional light, while the leaf area tended to decrease or remained unchanged. High-intensity CL could significantly increase soluble sugar and reduce the nitrate contents of the two lettuces.