DO3SE model applicability and O3 flux performance compared to AOT40 for an O3-sensitive tropical tree species (Psidium guajava L. 'Paluma')

Phytotoxic ozone (O-3) levels have been recorded in the Metropolitan Region of So 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 (DO3SE)) 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, POD0 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 DO3SE model for 'Paluma' is applicable in the MRSP as well as in temperate regions and may contribute to future directives.