The toxic effects of tropospheric ozone concentrations on plants have been reported primarily for ecosystems from the northern hemisphere with a mediterranean, temperate or boreal climate. In the southern hemisphere with its tropical climate, the impact of ozone on natural ecosystems and cash crops is still mostly unknown. The principal objectives in this project are to analyze and validate leaf injury by ozone stress in native C3 (Astronium graveolens, Anacardiaceae; Croton floribundus, Euphorbiaceae; Piptadenia gonoacantha, Fabaceae) as well as cultivated C4 (sugar cane) widespread tree and herbaceous species from the Mata Atlantica and cultivated areas in southern Brazil and to relate the structural responses to tropical climate as well as species specificities. The phytotoxic potential of ozone stress is evaluated by means of controlled exposure experiments as well as field surveys. Ozone-like injury in foliage is validated using different methods in light and electron microscopy. In addition to verifying the impact of ozone on representative species of Southern Brazil, the results should indicate whether the approaches and criteria used in regions at higher latitude are also valid in the case of tropical environments. They will also shed light on the similarities and differences between C3 and C4 plant species regarding the structural responses to ozone stress.