First defense mechanisms of ornamental species suitable for urban green spaces in China exposed to ozone

High concentrations of tropospheric ozone (O3) represent a serious problem in the Northern Hemisphere, especially in hot spots as urban areas of China. In this study, the first defense mechanisms (i.e., stomatal behavior and morphology, ascorbate regulations) of three widely-used ornamental plant species (Cotinus coggygria Scop., Rosa chinensis Jacq., Tagetes erecta L.) to O3 were evaluated to test the suitability of these species for utilization in urban green spaces (UGS). Seedlings were exposed to (i) ambient air (AA), (ii) AA+60 ppb O3 (AA+60), and (iii) AA+120 ppb O3 (AA+120) for 60 (C. coggygria and R. chinensis) or 32 days (T. erecta), 9 h d−1. Considering the different physiological responses and O3 sensitivity among the species, data of the present study reveal that: (i) O3-induced stomatal closure observed in the three species was not an avoidance-strategy given the lack of a significant relation between gs and O3 fluxes into the leaves, a feature that confirm the strong negative effects of O3 on the photosynthetic metabolism previously reported; and (ii) stomatal morphology, as well as ascorbate regulations, seem to play a pivotal role in the responses of the investigated species to O3”. Overall, our study highlights the importance of investigating the first defense mechanisms adopted by plants to cope with urban environmental stresses, in order to direct a correct management of UGS.