Response of stress indicators and growth parameters of Tibouchina pulchra Cogn. exposed to air and soil pollution near the industrial complex of Cubatao, Brazil

The present study was performed in the vicinity of the industrial complex o f Cubatao, Sao Paulo, Brazil, in order to evaluate the response of 'manaca da serra' Tibouchina pulchra Cogn. (Melastomataceae), a common species of s econdary Atlantic Rain Forest vegetation, to the impact of complex air poll ution. Emphasis was given to changes of biochemical parameters such as asco rbic acid concentration, peroxidase activity, contents of water-soluble thi ols, pH of leaf extract and buffering capacity. These plant factors are oft en used as early indicators of air pollution stress. Field experiments incl uded sampling of leaves from mature trees in areas with different air pollu tion load (passive monitoring), exposure of saplings cultivated in uniform soil at these areas (active monitoring) and a study on the combined effects of contaminated soil and air pollution. In general, metabolic response of saplings was more accentuated than that of mature trees. Leaf extract pH an d buffering capacity showed no or only small alterations in plants exposed to industrial emissions. In contrast, air pollution resulted in a distinct decrease in ascorbic acid contents and an increase in peroxidase activity a nd thiol concentrations in leaves. Cultivation of saplings in soil types fr om contaminated regions frequently caused the same modifications or enhance d the effects produced by air pollution. Growth analysis of exposed sapling s demonstrated that a change of the relationship between above-ground and b elow-ground plant parts was the most obvious effect of air pollution and so il contamination. The experiments showed that even T. pulchra, a species co nsidered resistant to air pollution, suffers metabolic disturbances by the present ambient air and soil quality. Although biochemical and physiologica l alterations were not related to a certain air pollution type, they could be used to estimate the overall pollution load and to map zones with differ ent air quality. (C) 2000 Elsevier Science B.V. All rights reserved.