PROCEEDINGS: Index of Abstracts

OZONE EXPOSURE, UPTAKE, AND RESPONSE OF DIFFERENT-SIZED BLACK CHERRY TREES

Todd S. Fredericksen-1, John M. Skelly-1, Kim C. Steiner-1, and Thomas E. Kolb-2

1-Research Associate, Environmental Resources Research Institute; Professor, Department of Plant Pathology; and Professor, School of Forest Resources, respectively, The Pennsylvania State University, University Park, PA, 16802. 2-Assistant Professor, School of Forestry, Northern Arizona University, Flagstaff, AZ, 86011.

Differences in exposure, uptake and relative sensitivity to ozone between seedling, sapling, and canopy black cherry (Prunus serotina Ehrh.) trees were characterized during two growing seasons in north central Pennsylvania. Open-grown trees of all sizes received a similar amount of ozone exposure. Seedlings had greater foliar ozone injury, expressed as adaxial stipple and early leaf senescence, than larger trees, which was correlated with their higher rates of stomatal conductance and greater rates of ozone uptake. The higher stomatal conductance and ozone uptake of seedlings was proportional to their higher (less negative) predawn xylem water potentials. Seedlings appeared to have some ability to compensate for injury because their free growth habit reduced exposure per unit leaf area compared to larger trees whose leaves were exposed to ozone throughout the entire growing season.