Elevated levels of ground-level ozone threaten terrestrial ecosystems and biodiversity.

Ozone (O₃) sensitivity varies greatly among plant species. Leaf traits such as stomatal conductance, antioxidant capacity and leaf morphology and anatomy may play important roles in controlling this variation, but the relative contributions of each trait remain elusive. In this study, we examined the differences in O₃ sensitivity among 29 deciduous and evergreen woody species used for urban greening in China in an open-top chamber experiment. Elevated O₃ caused visible injury and reductions in net photosynthesis, and these effects differed significantly among species. The deciduous species Sorbaria sorbifolia, Hibiscus syriacus and Fraxinus chinensis were the most sensitive, while evergreen species ranked among the most tolerant. O₃ sensitivity was linked to both low leaf mass per area (LMA) and low leaf area-based antioxidant levels, but not to variation in leaf mass-based antioxidant levels or stomatal conductance. The well-known and easily measured leaf trait LMA thus represents a potentially useful metric for O₃ risk assessment and for selecting appropriate species for urban greening in O₃-polluted areas.