Light quality shapes morpho-functional traits and pigment content of green and red leaf cultivars of Atriplex hortensis

Recently the value of red-leaf species as food plants is increasing due to their high content in antioxidant compounds, mainly anthocyanins. Most work has been done on the modulation of light quality to maximise the production of antioxidant compounds in reddish leafy vegetables that mostly adjust the amount of foliar anthocyanins as a reaction to several environmental factors, including light. The aim of this study was to compare the effect of light quality on green- and red-leaf cultivars with a focus on the influence that different light wavelengths have on morpho-functional traits and pigment content. We selected as model plant Atriplex hortensis considering that cultivars with either fully-red or fully-green leaves are available. This species is characterized by the presence of betacyanins, an anthocyanin-homologue pigment known for its antioxidant properties. Plants were grown under four lighting treatments: 100% white light (W), 100% red light (R), red/blue light 50/50 % (RB), and red/green/blue light 33/33/33 % (RGB). All treatments provided a daily light integral (DLI) of 10.8 mol·m‒2·day‒1 over a 12-h photoperiod. Results showed that, in both green and red cultivars, light quality determines changes in morpho-functional traits and the combination of red and blue wavelengths enhances productivity and betacyanin content. In red plants, betacyanin content was two order of magnitude larger than in green plants, was significantly modulated by light quality, and increased according to the increasing percentage of blue wavelengths within the light spectrum. In the framework of enhancing antioxidant compounds in plant food through the adjustment of light spectrum, fully red plants should be considered as more promising than green cultivars.