Synergistic Regulation of Light Intensity and Calcium Nutrition in PFAL-Grown Lettuce by Optimizing Morphogenesis and Nutrient Homeostasis

In plant factory with artificial lighting, precise regulation of environmental and nutritional factors is essential to optimize both growth and quality of leafy vegetables. This study systematically evaluated the combined effects of light intensity (150, 200, 250 μmol/(m2·s)) and calcium supply in the nutrient solution (0.5, 1.0, 1.5 mmol/L) on lettuce morphology, photosynthesis, quality indices, and tipburn incidence. Elevating light from 150 to 200 μmol/(m2·s) significantly enhanced leaf number, area, photosynthetic rate, biomass, and foliar calcium. These gains plateaued at 250 μmol/(m2·s), where tipburn incidence surged to 76.5%. Photosynthetic pigments progressively rose with light intensity. Calcium supply showed limited morphological influence but proved critical under high light (250 μmol/(m2·s)): increasing calcium to 1.5 mmol/L significantly boosted vitamin C and soluble sugars while reducing nitrate accumulation and suppressing tipburn to 12.8%. Elevated calcium also partially compensated for growth and quality limitations under low light through compensatory effects. Results demonstrated light intensity as the dominant factor governing morphogenesis and photosynthetic capacity, these findings establish that coordinated optimization of light and calcium inputs is crucial for simultaneously improving lettuce yield, nutritional quality, and marketability in controlled environments. This study provides both theoretical insights and practical guidance for efficient and safe leafy vegetable cultivation in controlled environments.