Direct Effects of Acid Wet Deposition on Photosynthesis, Stomatal Conductance and Growth of Populus cv. Beaupre

Abstract

Poplar cuttings (Populus cv. Beaupre) were grown in a greenhouse and sprayed three times a week with simulated acid rain of pH 4.3 and 3.5 or with de-ionized water (pH 5.6). In August the “old” shoots were cut and “new” shoots developed from two axillary buds. Net photosynthetic rate and stomatal conductance of both leaf sides decreased with decreasing pH both for old and new shoots. The reduction of net photosynthesis is not only due to a decreased stomatal conductance, but also to a decreased residual conductance. Water use efficiency is similar for all treatments. Chlorophyll content of the new shoots and dry/fresh weight ratio are decreased at pH 3.5 and 4.3, specific leaf area is increased and chl a/b ratio is not changed. The reduced chlorophyll content seems to be important for the reduction of net photosynthesis. At the end of the season shoot lenght and dry weight of stem and root were reduced at pH 4.3 and 3.5. No significant change of total leaf area or leaf dry weight is found.