Differential sensitivity of four urban tree species to elevated O3

Tropospheric ozone (O3) is regarded as one of the most wide-spread air pollutants, and it is likely to increase further in many urban areas of the world. Therefore, trees in urban areas are expected to be subjected to increasing elevated O3 stress. In this study, four 4-year-old urban tree species (Ginkgo biloba, Quercus mongolica, Pinus tabulaeformis and Pinus armandii) in the northeast of China were sampled to investigate their physiological responses and sensitivity to elevated O3 (80 ppb) simulated by using open top chambers (OTCs). The results showed that Q. mongolica was more sensitive to elevated O3 than G. biloba. P. armandii was most tolerant to O3 compared to other tree species. Among the four tree species, Q. mongolica showed a highest decrease in foliar weight, branch weight, stem weight and total above-ground biomass under elevated O3, and decreasing by 51.0%, 48.5%, 38.2% and 44.9%, respectively. Elevated O3 decreased net photosynthetic rate (Pn) in leaves of Q. mongolica by 63.4% (P < 0.01) after 90 days of fumigation, and 45.5% (P < 0.01) in needles of P. tabulaeformis after 30 days of fumigation. Superoxide dismutase (SOD) activity in leaves of Q. mongolica is decreased by 31.9% (P < 0.01) after 90 days of fumigation. A significant decrease of SOD activity was observed in P. tabulaeformis after 60 days of fumigation (P < 0.05). Compared to the ambient air control, elevated O3 significantly increased the emission rates of volatile organic compounds (VOCs) from four tree species. VOCs emission rate increased to the highest level (327.2 μg g−1 h−1) in Q. mongolica after 60 days of O3 fumigation. Our results provide a helpful recommendation in creating urban forest ecosystems considering ozone response and VOC emissions.