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Photosynthetic Responses of Four Urban Tree Species Exposed to Elevated CO2 and/or Elevated O3

We compared the differences in photosynthesis of four urban tree species (Ginkgo biloba, Pinus tabulaeformis, Quercus mongolica and Pinus armandii) exposed to long-term elevated CO2 (700 ppm) and/or O3 (80 ppb) fumigation in (open top chamber) OTC. Our results suggest that elevated CO2 alleviated the damaging influence of elevated O3 on photosynthesis in the four urban tree species. Both Q. mongolica and P. armandii showed photosynthetic acclimation after long-term treatment under elevated CO2. The combined effect of elevated CO2 and O3 caused the changes including net photosynthetic rates (Pn), stomatal conductance (gs) and chlorophyll content that were more similar to ambient air (CK) or slightly lower than elevated CO2, indicating that elevated CO2 is able to totally or partly alleviate the harmful effects of elevated O3 on urban tree species.