Growth, phytohormone and transcriptome responses of Cunninghamia lanceolata seedlings to different light qualities

Light is the primary energy source for photosynthesis and an important signal regulating seedling growth, hormonal balance, and metabolic adaptation. In this study, seedlings of Cunninghamia lanceolata were grown under six light quality treatments, including white light (WL), blue light (BL), red light (RL), far-red light (FrL), and mixed RL: FrL ratios at 1:1 (1:1L) and 1:2 (1:2L). All treatments were applied at a constant photosynthetic photon flux density of 400 μmol·m^-2·s^-1. The results showed that BL, FrL, and 1:2L significantly promoted stem elongation, whereas RL and 1:1L increased root collar diameter. Hormone assays revealed a clear antagonistic pattern between gibberellic acid (GA₃) and abscisic acid (ABA), with GA₃ contents elevated under BL and FrL but reduced under RL, while ABA showed the opposite trend. Transcriptomic analysis showed that different light spectra regulated the expression of photoreceptors (PHYB, CRY1 and CRY2) and downstream factors (COP1, PIF3, HY5). BL stimulated flavonoid biosynthesis, RL enhanced phenylpropanoid and cell wall related pathways, and FrL induced carotenoid and stilbenoid metabolism. There results indicated that light spectra regulate seedling growth by integrating photoreceptor signaling, hormone dynamics, and secondary metabolism. The study improves our understanding of light responses in gymnosperms and provides a physiological and molecular basis for optimizing nursery light management and afforestation practices.