DIFFERENTIAL PHOTOSYNTHETIC RESPONSE OF 2 MEDITERRANEAN SPECIES (ARBUTUS-UNEDO AND VIBURNUM-TINUS) TO SULFUR-DIOXIDE

The responses of young plants of Arbutus unedo and Yiburnum tinus to l ong-term (80120 days) exposure of sulphur dioxide were investigated Co nstant levels of the pollutant of 25 and 60 ppb were supplied to the p lants, in comparison to charcoal-filtered air. At regular intervals, t he photosynthetic responses were analyzed on fully expanded leaves dev eloped during the fumigation. No visible symptoms were detected on the leaves of the treated plants. The photosynthetic activity and growth of A. unedo was markedly reduced in connection to a partial stomatal c losure. In V. tinus, CO2 assimilation did not change although stomatal conductance significantly decreased at the end of treatment. A mechan ism of repair was supposed. Results are discussed on the basis of natu ral drought stress resistance of plants typical of mediterrannean envi ronments. (C) 1998 Elsevier Science Ltd.