Effects of Elevated O3 and CO2 on Biomass and Antioxidant System in Needles of Armand Pine

Using open top chambers, effects of elevated O₃ (80 nmol mol^-1) and CO₂ (700 μmol mol^-1), alone and in combination, were studied on young armand pine (Pinus armandii Franch.) trees. Current-year needles were collected after a growth season in all the treatments. No marked changes were found in the needles under elevated CO₂ exposure alone. Needles biomass was significantly decreased by elevated O₃, and the decrease was lower in the needles concomitantly exposed to elevated CO₂. Hydrogen peroxide and malondialdehyde contents increased significantly in the needles under elevated O₃ exposure, but the O₃-induced increase was alleviated by elevated CO₂. Elevated O₃ remarkably reduced ascorbate content and enhanced activities of superoxide dismutase and ascorbate peroxidase, and these changes was all alleviated by elevated CO₂. The results suggest that elevated CO₂ ameliorated O₃-induced oxidative stress in the needles of armand pine. Consequently, needles biomass was less affected at high O₃ and CO₂ in combination than at high O₃ alone. This protection of CO₂ against O₃ stress was achieved hardly by enhancing antioxidant capability.