While end-of-production sole-source lighting at a moderate intensity increased nutrient, water-soluble vitamin, and carotenoid content, the anthocyanin concentration of red leaf lettuce decreased

Authors: BREWER, DEVIN - Michigan State University; WALTERS, KELLIE - University Of Tennessee; Boldt, Jennifer; LOPEZ, ROBERTO - Michigan State University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2026
Publication Date: 2/19/2026
Citation: Brewer, D., Walters, K., Boldt, J.K., Lopez, R. 2026. While end-of-production sole-source lighting at a moderate intensity increased nutrient, water-soluble vitamin, and carotenoid content, the anthocyanin concentration of red leaf lettuce decreased. Frontiers in Plant Science. 7. Article 1699278. https://doi.org/10.3389/fpls.2026.1699278.
DOI: https://doi.org/10.3389/fpls.2026.1699278

Interpretive Summary: Controlled environment agriculture can provide precise growing conditions for crops. Adjusting the growing conditions can alter how fast a crop grows as well as its appearance and quality. Consumers desire red leaf color in lettuce, but it often lacks an intense color when grown indoors. This research aimed to develop a strategy that yielded both high growth and red leaf coloration. Light intensity, rather than light quality, had a greater effect on increasing the red leaf color in lettuce. This information will help growers use controlled environments to produce high yields of red leaf lettuce with desired color and quality attributes.

Technical Abstract: Plants synthesize anthocyanins to counteract oxidative damage from environmental stressors, such as excessive light intensity or exposure to certain wavebands of photosynthetically active radiation (PAR; 400–700 nm) or ultraviolet (UV; 315–400 nm) radiation. In controlled environments (CE), light intensity and quality can be altered and used to improve foliage color by increasing the anthocyanin concentration of crops prior to harvest. Our objectives were to quantify how end-of-production (EOP) sole-source lighting consisting of various combinations of blue (B) and red (R) light affected development, quality, yield, phytochemical [anthocyanins, carotenoids, B and C vitamins], and nutritional concentrations of red leaf lettuce (Latuca sativa). Eleven-day-old seedlings of ‘Barlach’, ‘Rouxai’, and ‘Thurinus’ were transplanted into deep flow hydroponic tanks in a growth chamber with a carbon dioxide (CO2) concentration of 800 µmol·mol-1, day/night temperature set point of 28/21 °C [mean daily temperature (MDT) of 26 °C] under light-emitting diodes (LEDs) that provided a photosynthetic photon flux density (PPFD) of 300 µmol·m'2·s'1 with a light ratio (%) of 19:39:39:3 blue:green:red:far-red (B:G:R:FR) for 17 h·d-1. After 24 days for ‘Thurinus’ and 30 days for ‘Barlach’ and ‘Rouxai’, plants were either left in the same conditions or transferred to growth chambers with a light ratio (%) of 100:0, 75:25, or 50:50 B:R light and a PPFD of 150 µmol·m'2·s'1 for the last 6 to 8 days of production. Shoot fresh mass (SFM) and shoot dry mass (SDM) of ‘Rouxai’ and ‘Thurinus’were negatively influenced by EOP lighting. However, SFM of ‘Barlach’ was not affected by any EOP treatment. Compared to plants not placed under EOP lighting, SFM of ‘Rouxai’ was 16, 17, and 21% lower and SDM was 25, 27, and 29% lower under B:R treatments of 100:0, 75:25, and 50:50, respectively. Similarly, placing ‘Thurinus’ under the 100:0, 75:25, and 50:50 B:R treatments 19, 30, and 28% less SFM and 17, 27, and 25% less SDM, respectively, compared to control plants. Regardless of the EOP treatment, lightness (L*) of ‘Barlach’ and ‘Thurinus’ increased compared to untreated plants. By day 6 of the EOP treatment, L* of ‘Thurinus’ under the 100:0, 75:25, and 50:50 B:R treatments was 13%, 9%, and 12% greater than the control, respectively. EOP sole-source lighting had no effect on the mineral nutrient content of ‘Barlach’. However, mineral nutrient concentrations of ‘Thurinus’ exposed to 100:0 B:R EOP lighting increased by 22% for nitrogen (N), 22% for phosphorus (P), 47% for calcium (Ca), 35% for magnesium (Mg), 24% for sulfur (S), 10% for boron (B), 40% for copper (Cu), 31% for iron (Fe), 25% for manganese (Mn), 50% for molybdenum (Mo), and 38% for zinc (Zn), compared to the control. Plants exposed to EOP treatment generally had increased B and C vitamin concentrations. Vitamin C of ‘Barlach’, ‘Rouxai’, and ‘Thurinus’ increased by 37% to 42%, 36% to 45%, and 49% to 57%, respectively, when exposed to EOP treatment. ‘Rouxai’ developed the greatest total carotenoid concentration under the 100:00 B:R treatment (29% greater than the control). However, ‘Thurinus’ developed the greatest total carotenoid concentration with no EOP treatment. All cultivars had the highest concentrations of violaxanthin, neoxanthin, zeoxanthin, and a-carotene when not exposed to an EOP treatment. ‘Barlach’, ‘Rouxai’, and ‘Thurinus’ accumulated 52 to 68%, 55 to 57%, and 33 to 43% lower anthocyanin concentrations, respectively, than plants not placed under EOP sole-source lighting. Our results indicate that light intensity may have a greater effect than light quality on inducing anthocyanin accumulation in red leaf lettuce.