Response of leaf surfaces and gas exchange to wind stress and acid mist in birch (Betula pubescens)

 This research demonstrates that a leaf’s response to acid mist is dependent on the integrity of the leaf cuticle and that significant differences in the structural and physiological disturbances in leaves can be attributable to different types of wind action. Betula pubescens Ehrh. plants were located at adjacent, but contrasting, sites to create different wind treatments: (i) direct wind action, (ii) indirect wind action and (iii) shelter from wind action (control). In combination with the wind treatments, acidic (pHs 5 and 3) or neutral (pH 7) mists were applied weekly. Wind action significantly increased visible leaf injury, microscopic cuticular lesions and cuticular conductance (g _c ), but reduced photosynthetic rate (P _N ) and stomatal conductance (g _s ) compared to shelter. Wind action combined with acid mist was more injurious than wind action alone, but leaves sheltered from wind action were highly resistant to the damaging effects of acid mist. Direct wind action combined with pH 3 mist resulted in the highest values of g _c and the greatest number of cuticular lesions. By contrast, indirect wind action combined with pH 3 mist induced most visible injury, but relatively low values of g _c and few microscopic cuticular lesions. Acid mist reduced P _N only when leaves had been damaged by wind action. Higher values of g _c were associated both with increases in the area of visible leaf injury and with the number of cuticular lesions. Compensatory increase in P _N of healthy tissue was evident in leaves exposed to combinations of wind action and acid mist. Received: 10 November 1997 / Accepted: 6 March 1998