Abstract: This study selected eight common tree species as donor materials to prepare leaf extracts at four mass concentrations(5.0, 12.5, 25.0 and 50.0 g/L) with distilled water as the blank control, and systematically investigated their allelopathic effects on Lactuca sativa seed germination, seedling growth, and related physiological indicators. The results showed that:(1) Seed germination parameters were significantly influenced by interactive effects of tree species type, extract concentration, temperature and their interactions, exhibiting temperature sensitivity, species specificity, and integrated allelopathic responses. Temperature emerged as the most critical factor, with allelopathic inhibitory effects at 25℃ being significantly stronger than at 15℃.(2) Based on the mean comprehensive allelopathic coefficient, the top three species with pronounced inhibitory effects on lettuce germination were Salix babylonica(-0.266), Robinia pseudoacacia(-0.238), and Morus alba(-0.216), highlighting the necessity to evaluate allelopathic risks in agroforestry systems.(3) Compared with the blank control, the SPAD values of lettuce seedlings under allelopathic stress all showed a downward trend, the activity of superoxide dismutase(SOD) significantly increased, and root elongation was hindered. The intercellular CO₂ concentration in the treatment groups such as Salix babylonica and Quercus variabilis increased, while the net photosynthetic rate decreased. The final fresh weights of all treatment groups were lower than those of the control. This study comprehensively elucidates the early-stage allelopathic mechanisms of common tree species on lettuce, providing theoretical guidance for optimal tree-species configuration in agroforestry systems in Central China.