Organ-Specific Physiological and Metabolic Differentiation in Celery (Apium graveolens L.) to Supplemental Blue Light in Controlled Environment Agriculture

Optimizing spectral quality is a key strategy in controlled environment agriculture (CEA) to enhance both productivity and nutritional quality in horticultural crops. In this study, we investigated the organ-specific physiological and metabolic responses of celery (Apium graveolens L. cv. Dayehuang) to supplemental blue light at three intensities (10, 20, and 30 μmol·m−2·s−1 with red/blue light ratios of 0.76, 0.68, and 0.60, respectively) in a plant factory with artificial lighting. Results showed that a moderate red/blue light ratio of 0.68 significantly enhanced chlorophyll accumulation, PSII quantum efficiency, and net photosynthetic rate, resulting in the highest shoot biomass without inducing photoinhibition. Leaf tissues showed marked increases in flavonoids and total phenolics, while petioles exhibited elevated soluble sugar levels and favorable modulation of volatile compound profiles. Antioxidant enzyme activities, particularly superoxide dismutase and peroxidase, were also enhanced with a moderate red/blue light ratio of 0.68, contributing to improved oxidative stress defense. Composite indices, including functional yield index and antioxidant performance index, confirmed that a moderate red/blue light ratio of 0.68 achieved the optimal trade-off between biomass production and nutritional enhancement. These findings reveal distinct organ-specific responses to supplemental blue light and underscore the value of spectral fine-tuning to simultaneously promote both source (leaf) and sink (petiole) performance in celery grown under CEA systems.