Abstract: By using open top chamber fumigation method, this paper studied the effects of elevated O₃ (≈80 nmol·mol^-1) and CO₂ (≈700 μmol·mol^-1), single and in combination, on the active oxygen metabolism of Quercus mongolica leaves. Elevated O₃ increased the superoxide anion radical (O₂^•) generation rate, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents, and electrolyte leakage (EL) (P<0.05), but decreased the superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities and ascorbate (AsA) content (P<0.05); while elevated CO₂ had no significant effects on the active oxygen metabolism of Q. mongolica leaves. The combination of elevated O₃ and CO₂ had less effects on the O₂^• generation rate, H₂O₂ and MDA contents, and EL, indicating that elevated CO₂ alleviated the oxidative stress of elevated O₃ on Q. mongolica leaves, but increased the SOD, APX, and CAT activities and the AsA and total phenol contents, compared with elevated O₃ (P<0.05), indicating that elevated CO₂ alleviated the negative effects of elevated O₃ on Q. mongolica leaf antioxidant system.

Key words: Quercus mongolica, O₃, CO₂, antioxidant system, total phenol, maize, brassinosteroid, nitric oxide, low temperature, oxidative damage.