Developmental Stage Shapes Photosynthetic Responses to Light Spectrum and Intensity in Basil Microgreens

Optimizing light management requires understanding how developmental stage and cultivar-specific physiological responses influence plant responses to light. Here, we investigate how developmental stage and cultivar modify photosynthetic responses of basil microgreens to different light spectra and intensities. Green and purple basil were grown under three red-to-blue light ratios (R50:B50, R70:B30, R90:B10) at two light intensities (110 and 160 µmol m^-2 s^-1), and assessed at cotyledon emergence and fully developed cotyledon stages. A clear developmental shift in photosynthetic regulation was observed. At the early stage, treatment-related differences were not statistically resolved, whereas photosynthetic traits showed greater variation at the fully developed cotyledon stage. Cultivars also differed in their physiological profiles: green basil generally showed higher photochemical efficiency (Fv/F_M) and chlorophyll a/b ratios, whereas purple basil showed greater carotenoid investment and energy dissipation, particularly under red-enriched (R90:B10) and higher light intensity conditions. These physiological differences were accompanied by variation in biomass production. Purple basil achieved consistently higher fresh yield across treatments, with maximum production (353.43gm^-2) under R90:B10 at 160 µmol m^-2 s^-1, while green basil maintained more stable but lower yields across light environments. Overall, the results indicate that developmental stage influences the extent to which basil microgreens respond physiologically to light, while cultivar identity contributes to variation in photosynthetic and growth responses. These findings support consideration of developmental stage and cultivar when evaluating light management strategies in controlled environment agriculture.