Abstract
Four light treatments (W: white light; EOD-B: end-of-day enhanced blue light; EOD-FR: end-of-day supplementary far-red light; EOD-UV: end-of-day supplementary ultraviolet-A light) were designed to explore the effects of end-of-day (EOD) lightings (30 min before dark period) on leaf color, biomass and phytochemicals accumulation in two lettuce cultivars (Lactuca sativa cv. ‘Red butter’ and ‘Green butter’) in artificial light plant factory. EOD-FR stimulated the plant and shoot biomass of two cultivars, and EOD-B suppressed the growth of ‘Red butter’ but induced higher biomass in ‘Green butter’. EOD lightings generated brighter, greener and yellower leaf in ‘Red butter’ at harvest, but the highest lightness and the deepest redness of ‘Green butter’ leaf were observed in the middle growth stage. ‘Red butter’ had prominent higher contents of chlorophylls and carotenoids, while these pigments showed less sensitivity to the interaction of cultivars and EOD lightings. EOD lightings impeded the accumulation of anthocyanin in two cultivars, except EOD-UV slightly increased the anthocyanin contents in ‘Green butter’. EOD-UV strengthened the antioxidant capability of ‘Green butter’, but EOD lightings had different effects on the antioxidant and nutritional compound contents in two lettuce cultivars.
Highlights
The increasing world population combined with decreasing arable land provide an excellent opportunity for the development of plant factory in urban areas
Regarding ‘Red butter’, the EOD-UV and end-of-day far-red (EOD-FR) clusters were the closest to each other in terms of measured parameter responses, and they were equidistant from cluster W (Figure 9a)
Cluster EOD-B was considerably separated from the other three clusters: EOD-B decreased the fresh and dry weight of plant and shoot; increased the root-shoot ratio; and led to higher contents of VC, carotenoids, nitrates, total phenolic compounds (TPC), and total flavonoids (TF) compared to W, EOD-FR, and EOD-UV, contributing to separate the EOD-B cluster from the others (Figure 9a)
Summary
The increasing world population combined with decreasing arable land provide an excellent opportunity for the development of plant factory in urban areas. Lettuce is rich in natural pigments like anthocyanins, carotenoids and chlorophylls, and nutritional compounds such as vitamin C, proteins, and phenolics [1,2]. These phytochemicals contribute to the leaf color and/or the flavor of lettuce plant, and benefit human health. When the light environment (light quality, quantity, directionality, and photoperiod) changes, these photoreceptors can switch forms or be activated in distinct manners [6,7]. They transduce diverse light signals to modulate the core
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