Fall Exposure of Beech Saplings (Fagus sylvatica L.) to Ozone and Simulated Acidic Mist: Effects on Gas Exchange and Leachability.

Two yr old beech saplings (Fagus sylvatica L.) were exposed under an early autumn climate to four levels of O3 (10, 40, 75, and 110 nL L-1 O3) with or without preceding simulated acidic mist (pH 3.5). As a first response in gas exchange to O3, stomatal conductance was transiently increased followed by a decline in net photosynthesis. Thus, regarding exposure effects on stomatal behavior, both O3 and acidic mist increased the pollutant flux into the leaf interior. The subsequent impairment of cell permeability consisted of dose-dependent increases in efflux rates of dichlorofluorescein, indicating greater membrane permeabilities. While the efflux rates of Mg and Ca correlated with those of the fluorescent dye, the leachability of K was increased only at the highest O3 levels. Changes in compartmentation of K, Ca, Mg, and S was derived from selective cell wall extraction; thereafter, the exposure to O3 and acidic mist resulted in increased extracellular fractions of these elements