Pollution emissions from a petrochemical complex and other environmental stressors induce structural and ultrastructural damage in leaves of a biosensor tree species from the Atlantic Rain Forest

•Tibouchina pulchra is a Brazilian tree species tolerant to air pollution.•The plants did not show any visible injury.•Microscopic changes associated with oxidative stress were found in leaf tissues.•The microscopic response intensity was different during dry and wet seasons.•Air pollution and climatic oscillations were possible inducers of microscopic changes.

Tibouchina pulchra (Cham.) Cogn., a pioneer tree species commonly found in the Atlantic Rain Forest in southeast Brazil, proved to be a promising biosensor species for indicating the potential effects of air pollution on this type of forest. This study aimed to investigate whether the present levels of nitrogen oxides, sulfur oxides, ozone and particulate matter in industrial and urban areas in the Cubatão region induce structural and ultrastructural changes in this species, to explore the synergy between air pollutants and the effects of other environmental stressors as contributors to microscopic symptoms and to verify whether these changes are seasonally dependent. The field study consisted of exposing potted saplings of T. pulchra in three sites around the petrochemical industry (industrial area), in downtown Cubatão (urban area) and in a site far from the industrial emissions (reference area). An experimental study using open top chambers (OTC) with filtered air and non-filtered air was also carried out to confirm the field results. Four exposure periods of 12 weeks were conducted during the field and the OTC experiments, covering wet and dry periods. The effects were more pronounced in plants exposed in the industrial areas during the dry period, which were confirmed by OTC experiments. Crystal density variations were linearly explained by decreases in NO2, SO2 and the sum of all hourly concentrations of ozone (SUM00), as well as increases in PM10, relative humidity and rainfall. Variations in lipid peroxidation correlated positively with air temperature and SUM00. Tannins and starch grains decreased. Collapsed and sinuous cell walls, dense cytoplasm, invagination of plasma membranes and vacuome were the main effects observed at the structural level. Occurrence of pectic warts, alterations in chloroplasts and numerous vesicles close to the cell walls were the main ultrastructural effects detected. These results confirmed that pollutants and environmental variables acted synergistically to induce oxidative stress in this species, enhancing our understanding of the bioindicator potential of T. pulchra for monitoring complex mixtures of air pollutants in the tropics.