. Annual program report, 1989. Acidic Precipitation in Ontario Study; Acid precipitation (Meteorology); Acid pollution of rivers, lakes, etc; Acid rain. - 14 - vigorous individuals were used for experimentation under the REC system commencing in the spring of 1987. Rooted cuttings of three clones of hybrid poplar were also planted under the REC system to provide shelter for the maples and serve as an additional species to monitor. The trees were subjected to three different SAR treatments (pH , or ) at regular intervals. Non-destructive measurements on the seedlings include: 1. visib
. Annual program report, 1989. Acidic Precipitation in Ontario Study; Acid precipitation (Meteorology); Acid pollution of rivers, lakes, etc; Acid rain. - 14 - vigorous individuals were used for experimentation under the REC system commencing in the spring of 1987. Rooted cuttings of three clones of hybrid poplar were also planted under the REC system to provide shelter for the maples and serve as an additional species to monitor. The trees were subjected to three different SAR treatments (pH , or ) at regular intervals. Non-destructive measurements on the seedlings include: 1. visible injury rating; 2. photosynthesis rates; 3. throughfall and soil leachate chemistry; 4. plant height, stem diameter, leaf number. Destructive sampling of selected seedlings will be made to investigate: 1. pigment content of leaf tissues; 2. physical and chemical changes in roots and foliage; 3. mycorrhizae. Results are expected in 1990. Insect - Acidic Precipitation Much of the more severe dieback of sugar maple in Ontario is associated with defoliation by forest tent caterpillars. Since there is a possible interaction of acidic precipitation with insect defoliation (, acid stressed trees may be preferred hosts of the insect), this possibility is being investigated. Potted sugar maples are subjected to simulated acid rain at two pH's. They are then defoliated to different degrees either mechanically or by controlled insect feeding. The trees are monitored for growth and survival. The preference of the insects for foliage subjected to different acid treatments and the growth rates of the insects on these diets is being examined. The first year of the two-year project has been completed. The limited data presently available showed reduced growth of the tree seedlings following both severe mechanical and insect feeding defoliation. Further experimenta- tion is necessary before conclusions on the interaction of the insects with acid treatments can be reported. B. SOIL STUDIES
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