EFFECTS OF SIMULATED ACID-RAIN ON NEEDLE WETTABILITY AND RAIN RETENTION BY 2 SITKA SPRUCE (PICEA-SITCHENSIS) CLONES

The effect of simulated rain acidity (pH 2.6, 3.4, 4.2, and 5.6) on wettability and rain retention was investigated for elongating needles on stecklings of two Sitka spruce (Picea sitchensis) (Bong.) Carr) clones over an 11-week period. There were highly significant differences in contact angle between pH treatments, clones, and sample dates. Contact angles on needles of both clones exposed at pH less-than-or-equal-to 4.2 were significantly smaller than those on needles exposed at pH 5.6. Needles from both clones exposed to simulated rain at pH less-than-or-equal-to 4.2 retained significantly more simulated rain containing sodium fluorescein. These changes to needle surface properties following realistic exposure to simulated acid rain could have important consequences for processes occurring at the phylloplane, such as ion exchange.