S08 - Session O1 - Adding green or far-red light to an optimized red and blue LED light spectrum

Authors: Laura Carotti *, Giuseppina Pennisi, Alessandro Pistillo, Guido Evangelista, Loris Mazzaferro, Ivan Paucek, Giorgio Gianquinto, Francesco Orsini

In vertical farms with artificial lighting, the management of light spectrum represents an opportunity to regulate plant growth, morphology, and pigmentation. Red and blue spectral regions are among the wavebands most used in horticulture since they perform well both in terms of photosynthetic performances and energy efficiency. On the other hand, also green and far-red lights were recently shown to play a role on overall crop photosynthesis. In this research, the effect of adding green or far-red light to an optimized red and blue spectrum has been explored. Plants of green and red lettuce ( Lactuca sativa ) were grown for 25 days in a growth chamber. Plants were supplied with four LED light treatments (each replicated three times in light insulated compartments) under a constant PPFD of 250 µ mol m -2 s -1 . Light treatments included a control treatment (RB3) composed of an optimized red and blue light spectrum (R:B ratio of 3), a green added spectrum (RB3G), where the red and blue spectrum was partially substituted by 50 µ mol m -2 s -1 of green light, a far-red added spectrum (RB3Fr) where 50 µ mol m -2 s -1 of far-red light was added and, finally, a white light (W). From 13 to 25 days after sowing, destructive measurements (fresh and dry weight, leaf area) were performed every 2-3 days, while leaf pigmentation was also assessed at the final harvest. Dry weight, fresh weight and leaf area of green lettuce were significantly increased when supplied with either RB3Fr and W spectrum. In both green and red lettuces, the leaf pigmentation was significantly altered by the lighting treatments. Growth analysis was applied in order to assess if and how plant would differently react to the light spectrum according to the different developmental stage reached. It appears that the use of dynamic growth strategies (modulating light spectral components along the crop growth) may represent an important strategy in vertical farms to optimize yield and preserve desirable plant quality while maximizing energy use efficiency.