Differential sensitivity of four urban tree species to elevated O3

Tropospheric ozone (O-3) 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 O-3 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 O-3 (80 ppb) simulated by using open top chambers (OTCs). The results showed that Q. mongolica was more sensitive to elevated O-3 than G. biloba. P. armandii was most tolerant to O-3 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 O-3, and decreasing by 51.0%, 48.5%, 38.2% and 44.9%, respectively. Elevated O-3 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. tabulaeforrnis after 60 days of fumigation (P < 0.05). Compared to the ambient air control, elevated O-3 significantly increased the emission rates of volatile organic compounds (VOCs) from four tree species. VOCs emission rate increased to the highest level (327.2 mu g g(-1) h(-1)) in Q. mongolica after 60 days of O-3 fumigation. Our results provide a helpful recommendation in creating urban forest ecosystems considering ozone response and VOC emissions. (C) 2015 Elsevier GmbH. All rights reserved.