Abstract: Leaf traits could reflect plant adaptation strategies to environmental changes. In this study, we measured photosynthetic efficiency and leaf traits of Ligustrum lucidum under Pb stress and analyzed their relationships, aiming to understand the adaptive strategies of L. lucidum to Pb stress. Two-year-old L. lucidum was treated with four Pb concentrations (0, 300, 600, 1800 mg·kg^-1, designated as CK, L1, L2 and L3, respectively). The results showed that net photosynthetic rate (P_n) was significantly reduced by 37.66%, 57.73%, and 77.47% under L1, L2, and L3 treatments, respectively. The maximum photochemical efficiency (F_v/F_m) of L. lucidum was only decreased significantly by 6.25% and 12.50% in L2 and L3, respectively. Specific leaf area (SLA), chlorophyll (Chl), chlorophyll a (Chla), chlorophyll b (Chlb), leaf phosphorus (TP), leaf nitrogen (TN), and nitrogen to phosphorus ratio (N/P) were significantly decreased. However, the intracellular CO₂ concentration (C_i) and carbon to nitrogen ratio (C/N) were significantly increased in Pb treatments. Carbon to phosphorus ratio (C/P) was significantly increased under L2 and L3 treatments. Stomatal conductance (G_s) and leaf thickness (LT) were significantly decreased under L3 treatment. SLA and Chl were significantly correlated with the leaf traits except LT. N/P was significantly correlated with the leaf traits except G_s and C_i. Results of structural equation modeling showed that gas exchange and Chl directly affected photosynthetic efficiency, while leaf phenotype and chemical elements had indirect effects. Principal component analysis verified the adaptability of the leaf economics spectrum in L. lucidum under Pb stress, which belonged to the end of slow investment return in the leaf economics spectrum.

Key words: Pb stress, leaf trait, photosynthetic efficiency, leaf economics spectrum, Ligustrum lucidum.