Direct and indirect blue light supplementation on growth, pigments, and gas exchange of young arugula plants

It is well-established that the blue (430-460 nm) portion of the visible light spectrum beneficially affects plants, primarily by modulating the relationship between photosynthesis and energy metabolism and promoting chlorophyll accumulation. This study aimed to evaluate the effects of direct blue light supplementation (via LEDs operating at 450 nm) and indirect blue light supplementation (via reflective materials) on the growth, pigment content, and gas exchange of young arugula (Eruca sativa) plants. Four treatments were tested: control (no supplementation); direct blue light via LED; indirect light via light blue laminate; and indirect light via dark blue laminate. The reflective laminates were placed on the cultivation benches, under the plants. Two hypotheses were tested: 1) The LED, with maximum emission at 450 nm, would have similar performance to the dark blue reflective laminate for plants. 2) The shades of blue in the reflective laminates would influence plant performance. Parameters analyzed included shoot fresh matter, shoot dry matter, contents of chlorophyll a, chlorophyll b, total chlorophyll, chlorophyll a/b ratio, carotenoids, total chlorophyll/carotenoid ratio, and gas exchange parameters (internal CO₂ concentration (Ci), net photosynthesis (PN), transpiration (E), stomatal conductance (gs), water use efficiency (PN/E), and instantaneous carboxylation efficiency (PN /Ci)). Results indicated that both blue LED light and dark blue laminate promoted greater accumulation of dry matter and pigments, emerging as the most effective treatments. On the other hand, even though the light blue laminate presented higher light intensity, Chla, Chlb, Total Chl and carotenoids were 19.2%, 18.9%, 19.1%, and 18.89% lower than the control, respectively. For gas exchange, both direct and indirect blue light supplementation led to higher stomatal conductance, transpiration and water use efficiency. However, no statistically significant differences were observed in net A and A/Ci among treatments, suggesting that combinations of light spectra to optimize plant development in controlled environments, maximizing the benefits of blue light for more efficient production.