[Effect of exogenous paclobutrazol on the drought resistance of <i>Phoebe bournei</i> seedlings under drought stress].

To clarify the response mechanism of exogenous paclobutrazol on drought resistance in <i>Phoebe bournei</i> 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 <i>P. bournei</i> 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 <i>P. bournei</i> 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 <i>P. bournei</i> seedlings by regulating photosynthetic and antioxidant systems.