Abstract: To clarify the response mechanism of exogenous paclobutrazol on drought resistance in Phoebe bournei seedlings, we investigated the effects of spraying different concentrations of paclobutrazol (25, 50, 100 mg·L^-1) on the photosynthetic and antioxidant systems of 2-year-old P. bournei seedlings under drought stress using natural drought method. The results showed that drought stress significantly reduced the photosynthesis and broke the dynamic balance of antioxidant system in P. bournei seedlings. Spraying with different concentrations of paclobutrazol effectively alleviated the negative impacts of drought stress, and enhanced the defense capability of photosynthetic and antioxidant systems, with the 100 mg·L^-1 paclobutrazol treatment being the most effective. Under exogenous 100 mg·L^-1 paclobutrazol treatment, the total chlorophyll in leaves increased significantly, with a maximum increase of 51.9%. The apparent photosynthetic electron transfer rate, photochemical quenching coefficient and actual photochemical quantum yield were significantly increased, with maximum increase of 67.8%, 58.4%, and 59.7%, respectively. The net photosynthetic rate, stomatal conductance and transpiration rate, were enhanced, reaching maximum increase of 65.5%, 65.4%, and 68.6%, respectively. In summary, exogenous 100 mg·L^-1paclobutrazol has the strongest ability to enhance drought resistance of P. bournei seedlings by regulating photosynthetic and antioxidant systems.

Key words: Phoebe bournei, paclobutrazol, drought stress, drought resistance