Abstract: Schinus terebinthifolia (Raddi) is a tropical fast-growing broadleaf tree species in Brazil’s Atlantic Forest, a threatened biodiversity hotspot. The species has socioeconomic importance, is used in forest restoration programs and urban greening. In urban environments, plants are exposed to several abiotic stressors such as atmospheric pollution. Tropospheric ozone (O₃) is one of the main secondary pollutants that affect plant growth and survival. Therefore, determining the critical levels (CL) of phytotoxic O₃ is essential. Ozone risk assessment for S. terebinthifolia is unknown. Forty-five S. terebinthifolia seedlings were cultivated in pots and submitted to five ozone treatments for three months in an O₃-free-air controlled facility. Ozone risk assessment was based on environmental data, measurements of stomatal O₃ uptake and seedling biomass. To find the best model for predicting O₃-induced biomass loss, we tested the accumulated ozone exposure over a threshold of 40 ppb (AOT40) and the phytotoxic ozone dose above a threshold ‘y’ (POD_y) using linear and 116 nonlinear statistical models. POD₁₆ and POD₁₅ when applied with the four-parameter nonlinear logarithmic model “Bragg4” provided the best fit for assessing O₃ risk based on total biomass and leaf biomass, respectively. The species had a 4% biomass loss at 2.56 mmol O3 m⁻² POD16 and in leaf biomass at 3.37 mmol O₃ m⁻² POD₁₅. The results indicate that biomass accumulation was stimulated at low to moderate O₃ levels but reduced at higher levels. Overall, S. terebinthifolia demonstrated a high tolerance to tropospheric O₃.

Key words: Tropical environments, Ozone-stress, Tolerance, Hormetic biomass response, Schinus terebinthifolia