Leaf injury and gas exchange in Ipomoea nil cv. Scarlett O’Hara, an ozone bioindicator species, in Sao Paulo, Brazil

Ipomoea nil (L.) Roth. cv. ‘Scarlett O’Hara’ was evaluated as a tropical bioindicator species sensitive to ozone (O3). A total of nine field experiments were performed, with 28 days of exposure each. Visible leaf injuries, carbon assimilation (Asat) and stomatal conductance (gs) were quantified and correlated to oscillations in environmental conditions and accumulated ozone exposure over a threshold of 40 ppb h (AOT40). The values of gas exchange and leaf injury continuously varied throughout the study period. Asat and leaf injury (chlorosis) were higher in spring than in others seasons. The gs was higher in autumn. The analyses of the abiotic and biotic variables revealed an opposing trend between the Asat and both leaf injury and AOT40. Ozone levels were moderate and its relationship with gs was inverse. This may be the cause of the moderate injury. ‘Scarlett O’Hara’ is sensitive to O3 and has potential as an O3 bioindicator in sub–tropical regions.