Light quality influences differently green- and red-leaf plant growth

ABSTRACT: The optimisation of lighting systems is a key issue within many space-oriented research programs on higher plants, such as the European Space Agency programme MELiSSA (Micro-Ecological Life Support System Alternative). LED technology represents a good solution for lighting systems in plant compartment of BLSSs (Bioregenerative Life Support Systems), giving the possibility to combine the different light wavelengths in order to satisfy specific crop requirements and maximise light use efficiency. Red leaf plants have aroused intriguing scientific debates over the last few years to assess and improve their nutritional value as food plants. In most species, red colour in leaves is due to the accumulation of anthocyanins, the red pigment known for its antioxidant properties, to one or a few cell layers. Investigations on the effect of light quality on plant growth of red-leaf cultivars represent a relevant research field. Interestingly, plants grown under different light spectra are reported to modulate the synthesis of various compounds, including anthocyanins. The general aim of our work was to analyse the effect of different light qualities on growth, leaf anatomical and functional traits, eco-physiological parameters and pigment content of Atriplex hortensis L. plants. We cultivated a green- and a red-leaf cultivar of A. hortensis, namely ‘Alba’ and ‘Rubra’ respectively, under four combinations of light wavelengths: white (W), red (R), red-blue (RB), and red-green-blue (RGB). A specific aim was also to evaluate whether and how leaf anthocyanins content varies depending on light spectra with a double scope: a) to analyse their possible role in participating to mechanism for photoprotection together with alterations in leaf eco-physiological and anatomical terms, and b) emphasise their possible role in maximising the nutritional value of red-leaf food plants. The overall results showed different morpho-physiological strategies of acclimation to the different light regimes in the two cultivars, leading to different biomass production in terms of yield and quality. Therefore, in the realization of lighting systems for BLSSs, light recipes designed for green-leaf plants need to be revised to optimize the production of red-leaf crops