Effects of rainfall acidity and ozone on foliar leaching in red spruce (Picea rubens)

The effects of acid rain and ozone on the leaching of chemicals from the ca nopy of red spruce (Picea rubens Sarg.) saplings was measured over a 4-year treatment period. The saplings were exposed to various levels of ozone and to acid rain (pH 3.1, 4.1, and 5.1) using open-top chambers. No effects of ozone treatments on canopy leaching were observed. Significant effects of rainfall pH on canopy leaching of Ca2+ and Mg2+ were observed, and post-hoc analysis indicated that these effects were associated only with the most a cidic treatment (pH 3.1). In the low pH treatment (high NO3- and SO42-) sig nificant canopy retention of both NO3- and SO42- were observed. The observe d increase in base cation leaching flux from the red spruce canopy in the l ow pH treatment was particularly prominent early in the growing season (Jun e) probably reflecting incomplete cuticle formation in the young foliage. A lthough the annual magnitude of extra Ca2+ leaching from the canopy of red spruce trees in the low pH treatment was small relative to the foliar calci um pool (about 10%), if this leaching preferentially depletes a physiologic ally important pool, it may influence tree health.