Light Intensity Drives Species-Specific Growth and Phytochemical Accumulation in Microgreens

Microgreens are nutrient-dense functional foods whose yield and phytochemical composition can be regulated through light management in controlled-environment agriculture. This study evaluated species-specific responses to light intensity by analysing growth, nutrient uptake, and phytochemical accumulation in carrot, basil, arugula, and radish microgreens grown under LED lighting at four photosynthetic photon flux densities (PPFD: 67, 100, 140, and 174 μmol·m−2·s−1). Drainage pH and electrical conductivity remained stable across treatments, indicating consistent fertigation conditions. Increasing light intensity enhanced water, nitrate, and potassium uptake and promoted biomass accumulation in all species, although responses varied in magnitude. Phytochemical profiles were strongly modulated by irradiance. Intermediate PPFD levels (100–140 μmol·m−2·s−1) generally maximised carotenoid, sterol, and squalene accumulation, whereas lower irradiance (67 μmol·m−2·s−1) increased vitamin C and tocopherol contents, indicating activation of antioxidant defence mechanisms. Principal component analysis showed that species identity was the primary driver of phytochemical variability, with light intensity acting as a secondary modulator. Carrot and basil responded most strongly to intermediate irradiance, while arugula and radish exhibited greater vitamin C accumulation under lower light. These results support the use of species-specific light strategies to optimise microgreen yield and nutritional quality.