Spectral Quality and Infrared Radiation from Supplemental Lighting Shape the Physiology and Phytochemical Profile of Swiss Chard (Beta vulgaris L.)

The transition from High-Pressure Sodium (HPS) to energy-efficient Light-Emitting Diode (LED) supplemental lighting alters the plant thermal environment in controlled environment agriculture (CEA). This study evaluated how three practical supplemental lighting regimes, HPS, LED, and LED supplemented with infrared radiation (LED + IR), influence the physiology, growth, and phytochemical profile of Swiss chard (Beta vulgaris L.). We assessed biomass production, photosynthetic performance, oxidative stress markers (TBARS), and the concentration of primary and secondary metabolites. The LED treatment was superior for biomass production, yielding significant fresh mass while maintaining the lowest leaf nitrate content. Conversely, the addition of IR significantly increased leaf temperature, which suppressed growth but acted as a potent “bio-stress” agent, significantly increasing the total phenolic index. This biofortification, however, significantly decreased photosynthetic pigments (chlorophylls and carotenoids), increased lipid peroxidation (TBARS), and led to the highest accumulation of undesirable nitrates. Our findings reveal a clear growth-defense trade-off, demonstrating that while LED lighting is optimal for maximizing yield and food safety, the targeted application of IR radiation is an effective strategy for enhancing the nutraceutical value of leafy greens, requiring careful management to mitigate negative impacts on growth and quality.