Blue Light Sonata: Dynamic variation of red:blue ratio during the photoperiod differentially affects leaf photosynthesis, pigments, and growth in lettuce

Abstract

Vertical farming (VF) has unparalleled capacity to highly customize plant growth environments. In VF, red and blue LED lights are predominantly used as the two main wavelengths for photosynthesis. For many plants, red light increases biomass, and blue light can increase nutritional content. Because red light is more cost-and energy-efficient to produce than blue light, refined growth recipes are imperative to mutualistically improve efficiency with crop yield and quality. This studys aim was to balance lighting energy-use with growth and nutritional quality by using "dynamic lighting" recipes to reduce durations of high-intensity blue light. Lettuce (Lactuca sativa L.) was grown for 21 days at 220 mol m-2 s-1, receiving one of five R:B ratios (R:B100:0, R:B95:5, R:B89:11, R:B50:50, and R:B0:100) for either the whole 18-hour photoperiod (Whole Day), the first six hours of the photoperiod (Morning), or the last six hours of the photoperiod (Evening). Morning and Evening treatments received low blue (R:B89:11) for the remaining 12 hours of the day. The Morning and Evening high blue treatments had greater fresh weight and leaf area than their respective Whole Day treatments, attributed to reduced instantaneous leaf photosynthesis under high blue. High blue reduced photosynthesis during only the six hours of Morning and Evening treatments, compared to the full impact of static high blue for 18-hour Whole Day treatments. Intriguingly, with only six hours of R:B0:100, Morning and Evening treatments had the same high anthocyanin content as lettuce grown for 18 hours under R:B0:100. Therefore, daily blue light fraction can be reduced by using dynamic treatments to more efficiently promote growth and nutritional quality.