Pre-harvest short-term continuous LED lighting improves the nutritional quality and flavor of hydroponic purple-leaf lettuce

Enhancing nutritional and flavor quality has always been a pursuit of growers in the hydroponic production of lettuce in plant factories with artificial lighting (PFALs). While continuous lighting (CL) is a unique lighting mode that promotes plant yield and quality by eliminating the in-darkness period and prolonging the photosynthetic duration of plants, the specific method of CL that takes into account energy conservation is still unclear. In this study, the purple-leaf lettuce variety, 'Zixiangye', was used to investigate the effects of continuous LED lighting with different intensities and durations before harvest on the plant growth and quality of hydroponic lettuce. The results show that pre-harvest short-term CL with LED exerted a positive influence on the dry matter, as well as the nutritional and flavor quality of hydroponic purple-leaf lettuce. CL with increased light intensities (50,100,150 mu mol m- 2 s- 1) and durations (2 days and 4 days) improved the levels of carotenoids, ascorbic acid (AsA), and anthocyanin, accompanied by a decrease in the content of nitrate, where CL of 150 mu mol m-2 s- 1 and 2 days is a better supplemental light condition in the study. Furthermore, 150 mu mol m-2 s- 1 CL gradually improved the nutritional and flavor quality of lettuce within 48 h, by promoting the accumulation of soluble sugar content and decreasing the content of lettuce bitterness, lactucin, and lactucopicrin. In summary, the utilization of pre-harvest short-term continuous LED lighting could improve the nutritional and flavor quality of hydroponic purple-leaf lettuce in PFALs. Our study proposes a light-environment strategy that uses pre-harvest short-term CL to enhance the nutritional quality and flavor of lettuce, which provides theoretical and technical guidance for the energy-efficient production of lettuce in PFALs.