Elevated CO2 Ameliorated the Adverse Effect of Elevated O3 in Previous-Year and Current-Year Needles of Pinus tabulaeformis in Urban Area

The effects of elevated CO2 (700 ppm) and/or elevated O3 (80 ppb) on different-age needles of Pinus tabulaeformis were studied in open top chambers. Elevated CO2 increased needle dry weight, net photosynthetic rate, and maximum quantum yield of photosystem II in previous and current-year needles. Elevated O3 significantly decreased dry weight, net photosynthetic rate, and maximum quantum yield of photosystem II only in previous-year needles. Elevated O3 increased hydrogen and malondialdehyde content in previous-year needles, but did not significantly increase hydrogen peroxide content in current-year needles, which indicated that oxidative stress induced by elevated O3 was more severe in previous-year needles than in current-year needles. Our results showed that the adverse effect of elevated O3 in needles of P. tabulaeformis was ameliorated by elevated CO2.