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 CO 2 (700 ppm) and/or O 3 (80 ppb) fumigation in (open top chamber) OTC. Our results suggest that elevated CO 2 alleviated the damaging influence of elevated O 3 on photosynthesis in the four urban tree species. Both Q. mongolica and P. armandii showed photosynthetic acclimation after long-term treatment under elevated CO 2 . The combined effect of elevated CO 2 and O 3 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 CO 2 , indicating that elevated CO 2 is able to totally or partly alleviate the harmful effects of elevated O 3 on urban tree species.