Responses of native broadleaved woody species to elevated ozone in subtropical China.

To assess ozone sensitivity of subtropical broadleaved tree species and explore possible underlying mechanisms, six evergreen and two deciduous native species were exposed to either charcoal-filtered air or elevated O3 (E-O3, ∼150ppb) for one growing season. Initial visible symptoms in deciduous species appeared much earlier than those in evergreen species. The species which first showed visible symptoms also had the largest reductions in biomass. E-O3 induced significant decreases in photosynthesis rate, chlorophyll content and antioxidant capacity but a significant increase in malondialdehyde content in two deciduous species and two evergreen species (Cinnamomum camphora and Cyclobalanopsis glauca). Except C. glauca, however, E-O3 had no significant effects on stomatal conductance (gs), total phenols and ascorbate contents. Difference in O3 sensitivity among all species was strongly attributed to specific leaf mass rather than gs. It suggests that some subtropical tree species will be threatened by rising O3 concentrations in the near future.