Objective To determine the effects of different phosphorus supply levels on physiological activity of Phoebe bournei seedling leaf under natural low temperature.

Method Single factor pot experiment was set up with eight phosphorus levels, and following fertilization the seedlings were left under natural low temperature. Photosynthetic and other physiological indexes of the leaves were measured and analyzed. Cold resistance of the seedlings was assessed by principal component analysis.

Result Under natural low temperature environment, all the positive and negative indexes indicated clear and gradual trend with the increase of phosphorus levels. net photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO₂ concentration(Ci), transpiration rate(Tr), water use efficiency(WUE), proline content and SOD activity of P. bournei seedling leaf peaked at a phosphorus level of 30 mg phosphorus per seedling, and their values were 3.09 μmol·m^-2·s^-1, 0.023 mol·m^-2·s^-1, 350.18 μmol·mol^-1, 0.32 mmol·m^-2·s^-1, 9.69, 41.58 μmol·g^-1 and 332.03 U·g^-1, respectively. At the same phosphorus level, MDA content (3.77 μg·g^-1) and stomatal limitation value (Ls, 0.34) were the second lowest. The highest cold resistance score was obtained at a phosphorus level of 30 mg per seedling based on principal component analysis.

Conclusion The optimum phosphorus level is 30 mg per seedling for improving cold resistance of P. bournei seedlings.