Influence of air pollution on leaf chemistry, herbivore feeding and gall frequency on Tibouchina pulchra leaves in Cubatão (Brazil)

Fully expanded leaves of trees of Tibouchina pulchra were collected at three sites around the industrial complex of Cubatao: the valley of Piloes river (VP), bearing virtually undamaged vegetation; Caminho do Mar (CM), affected mainly by petrochemical industries; and the valley of Mogi river (VM), severely affected by pollution. The amounts of leaf nitrogen, soluble phenols, tannins, lignins and dietary fibers were determined. Leaf area consumed by herbivores and numbers of leaf galls were used to evaluate the influence of fluctuations of those parameters on the leaf damage caused by herbivores. Comparing with the reference site, leaves from VM and CM were shown to have higher amounts of nitrogen and dietary fibers and lower amounts of soluble phenols and tannins. The highest, lowest and intermediate amounts of lignins corresponded, respectively, to CM, VM and reference site. The largest, lowest and intermediate leaf area consumed by herbivores corresponded, respectively, to VM, CM and reference site. The observed percentages of galled leaves were higher at VM and lower at CM in comparison with the reference site. In all sites, the amounts of nitrogen, fibers and lignins in 1997 were higher than in 1996, but the reverse occurred as to the total soluble phenols. Leaf areas consumed by herbivores were not different in 1996 in comparison with 1997, but galled leaf percentages were lower at VM in 1997. Although air pollution damage is evident at the selected sites and certain chemical parameters and leaf herbivory are significantly correlated, the coefficients of explanation in regression analysis are low.