| Simultaneous studies were conducted under differing soil moisture and ambient ozone exposures for seedlings and canopy trees of Prunus serotina Ehrh. (BC), Fraxinus americana L. (WA), and Acer rubrum L. (RM) within a former nursery bed and a natural forested site at Penn Nursery, Bureau of Forestry, Centre County, PA. Simultaneously, gas exchange, ozone-induced foliar injury, leaf water potential, and seedling growth were intensively measured during the seasons of 1998 and 1999 for seedlings and canopy trees. There were no significant differences detected in predawn leaf water potential between canopy trees grown on a natural dry and wet site. Ambient ozone concentrations and their duration were sufficient during both years to induce typical visible foliar ozone injury on black cherry seedlings (0 to 34% total affected leaf area), black cherry canopy trees (0 to 5% total affected leaf area), and red maple seedlings (<1% total affected leaf area). During both seasons, there was a positive correlation between the increasing cumulative ozone uptake and the increasing percent of total affected leaf area by foliar stipple for BC seedlings and canopy trees. Significant variation for stomatal conductance was found across species (P < 0.001), soil moisture (P < 0.05), and sample date ( P < 0.001) among seedlings exposed to similar ozone exposures in 1999 and among canopy trees in 1998 and 1999. Black cherry and WA had similar ozone uptake but only BC developed ozone-induced adaxial stipple for seedlings and canopy trees. There was a significant site effect only for the lower crown leaves of BC seedlings (P < 0.001) and for red maple canopy trees (P < 0.05) when comparing ambient ozone uptake and decreased photosynthetic activity. For seedlings, wet soil conditions favored higher gas exchange and ozone uptake. For canopy trees, the heterogeneous light conditions within the canopy seemed to pose a more dominant influence on leaf gas exchange than the naturally differing soil moisture. The more severely injured BC seedlings grown under wet soil conditions tended to have an increased growth production in height. Although having similar stomatal conductance, BC canopy trees developed later and less severe visible foliar ozone injury than BC seedlings suggesting a more efficient defense or repair system within the leaves of mature trees. (Abstract shortened by UMI.)... |
