RESUMO
In southern Brazil, the recent increase in tropospheric ozone (O3) concentrations poses an additional threat to the biodiverse but endangered and fragmented remnants of the Atlantic Forest. Given the mostly unknown sensitivity of tropical species to oxidative stress, the principal objective of this study was to determine whether the current O3 levels in the Metropolitan Region of Campinas (MRC), downwind of São Paulo, affect the native vegetation of forest remnants. Foliar responses to O3 of three tree species typical of the MRC forests were investigated using indoor chamber exposure experiments under controlled conditions and a field survey. Exposure to 70ppb O3 reduced assimilation and leaf conductance but increased respiration in Astronium graveolens while gas exchange in Croton floribundus was little affected. Both A. graveolens and Piptadenia gonoacantha developed characteristic O3-induced injury in the foliage, similar to visible symptoms observed in >30% of trees assessed in the MRC, while C. floribundus remained asymptomatic. The underlying structural symptoms in both O3-exposed and field samples were indicative of oxidative burst, hypersensitive responses, accelerated cell senescence and, primarily in field samples, interaction with photo-oxidative stress. The markers of O3 stress were thus mostly similar to those observed in other regions of the world. Further research is needed, to estimate the proportion of sensitive forest species, the O3 impact on tree growth and stand stability and to detect O3 hot spots where woody species in the Atlantic Forest are mostly affected.
Assuntos
Florestas , Ozônio/efeitos adversos , Folhas de Planta/fisiologia , Árvores/fisiologia , Brasil , Folhas de Planta/efeitos dos fármacos , Árvores/efeitos dos fármacos , Clima TropicalRESUMO
In the Metropolitan Region of Campinas (MRC), Brazil, high levels of primary pollutants contribute to ozone (O3) formation. However, little is known regarding the O3 effects in the tropics. Objectives in this study were to characterize the present levels of O3 pollution and to evaluate the relevance of current concentration-based indices for assessing the phytotoxic potential of O3. Changes in O3 concentrations and precursors at 5 monitoring stations within towns of MRC were analyzed. The daily O3 profile was typical for urban sites and showed little yearly variation. Given the permanently foliated forest canopy, yearly rather than seasonal O3 indices were thus more appropriate for estimating the effective ozone dose. With yearly SUM00, SUM60 and AOT40 of 156, 16 and 14 ppm h and confirmed by evidence of O3 injury in foliage, oxidative stress in the MRC has reached levels high enough to affect trees from the Atlantic Semi-deciduous Forest.