Abstract: A hydroponic experiment was conducted to study the effects of exogenous citric acid (0.5 and 5 mmol·L^-1) and oxalic acid (0.5 and 5 mmol·L^-1) on the growth and physiology of Iris lactea var. chinensis  under 100 and 500 mg·L^-1 Pb stress. Comparing with Pb stress alone, adding 5 mmol·L^-1of citric acid promoted the shoot growth of I. lactea var. chinensis significantly. The addition of oxalic acid mitigated the impact of 500 mg·L^-1Pb stress on the root growth of I. lactea  var. chinensis. Adding 0.5 mmol·L^-1of oxalic acid alleviated the 500 mg·L^-1Pb stress on the shoot growth, and increased the root dry mass significantly under 100 and 500 mg·L^-1 Pb stress. The SOD activity in I. lactea var. chinensis  leaves under 100 mg·L^-1Pb stress was increased significantly by adding 0.5 mmol·L^-1of citric acid, and the POD activity of  I. lactea var. chinensis under 100 mg·L^-1 Pb stress was increased significantly by adding 0.5 and 5 mmol·L^-1 of citric acid or 0.5 mmol·L^-1of oxalic acid. The impact of 500 mg·L^-1 Pb stress on the photosynthetic pigments of I. lactea var. chinensis was alleviated by the addition of 5mmol·L^-1 of citric acid or 0.5 mmol·L^-1of oxalic acid. Adding 0.5 and 5 mmol·L^-1of citric acid or 0.5 mmol·L^-1 of oxalic acid reduced the membrane damage of I. lactea var. chinensis leaves under 100 and 500 mg·L^-1 Pb stress.

Key words: Urban forest, Correlation, Growth index, Compounding