Variation of Antioxidant System in Pinus armandii under Elevated O 3 in an Entire Growth Season

Impact of elevated O 3 (80 nmol mol −1 ) was studied on antioxidant system in the previous‐year needles (P‐needles) of Pinus armandii under the background of global climate change. CAT (catalase) did not play an important role in defensing O 3 pollution, as no significant change was observed in its activity in P‐needles exposed to elevated O 3 during the entire growth season. Ascorbate (AsA) was more sensitive to elevated O 3 , as the O 3 ‐induced decrease in its content was observed at Day 45. It suggests that AsA consumption was a crucial way for protecting against O 3 pollution. After 75 days of O 3 exposure, increase in superoxide dismutase and ascorbate peroxidase activities occurred in P‐needles ( p  < 0.05), whereas glutathione reductase activity was significantly increased after 105 days of O 3 treatment ( p  < 0.05). Dehydroascorbate reductase and monoascorbate reductase activities also increased after 75 days of elevated O 3 exposure. However, the elevated antioxidant capability did not suppress the generation of reactive oxygen species, and as a result, increase in malondialdehyde content was noted ( p  < 0.05). Noticeably, no change was observed in electrolyte leakage during the entire growth season under elevated O 3 fumigation. It indicates that O 3 ‐induced oxidative stress was not severe in the needles of P. armandii . In other words, P. armandii has certain tolerance to O 3 pollution.