DO 3 SE model applicability and O 3 flux performance compared to AOT40 for an O 3 -sensitive tropical tree species ( Psidium guajava L. ‘Paluma’)

Phytotoxic ozone (O 3 ) levels have been recorded in the Metropolitan Region of São Paulo (MRSP). Flux-based critical levels for O 3 through stomata have been adopted for some northern hemisphere species, showing better accuracy than with accumulated ozone exposure above a threshold of 40 ppb (AOT40). In Brazil, critical levels for vegetation protection against O 3 adverse effects do not exist. The study aimed to investigate the applicability of O 3 deposition model (Deposition of Ozone for Stomatal Exchange (DO 3 SE)) to an O 3 -sensitive tropical tree species ( Psidium guajava L. ‘Paluma’) under the MRSP environmental conditions, which are very unstable, and to assess the performance of O 3 flux and AOT40 in relation to O 3 -induced leaf injuries. Stomatal conductance ( g s ) parameterization for ‘Paluma’ was carried out and used to calculate different rate thresholds (from 0 to 5 nmol O 3 m −2 projected leaf area (PLA) s −1 ) for the phytotoxic ozone dose (POD). The model performance was assessed through the relationship between the measured and modeled g sto . Leaf injuries were analyzed and associated with POD and AOT40. The model performance was satisfactory and significant ( R 2 = 0.56; P < 0.0001; root-mean-square error (RMSE) = 116). As already expected, high AOT40 values did not result in high POD values. Although high POD values do not always account for more injuries, POD 0 showed better performance than did AOT40 and other different rate thresholds for POD. Further investigation is necessary to improve our model and also to check if there is a critical level of ozone in which leaf injuries arise. The conclusion is that the DO 3 SE model for ‘Paluma’ is applicable in the MRSP as well as in temperate regions and may contribute to future directives.