ARE SEEDLINGS REASONABLE SURROGATES FOR TREES - AN ANALYSIS OF OZONE IMPACTS ON QUERCUS-RUBRA

The appropriateness of using seedling responses to predict mature tree responses to ozone is questionable considering the long life span of trees. To determine if northern red oak (Quercus rubra L.) seedlings a nd mature trees respond similarly to ozone, 30-year-old trees and two- year-old seedlings were fumigated with subambient ambient, and twice a mbient concentrations of ozone for three growing seasons it using an o pen-top chamber facility. Ozone reduced leaf physiological function of mature trees. However, stem diameter growth and leaf mass of mature t rees were not significantly reduced by ozone. Photosynthesis in seedli ng leaves was slightly reduced by ozone, but seedling growth and bioma ss were unaffected. Mature tree fine-root biomass responded negatively to increasing ozone, while seedlings exhibited increases in biomass. Carbon retention was enhanced in leaves and branches of mature trees b y ozone treatment, while seedlings were unresponsive. Differences in o zone uptake, recurrent flushing and carbon dynamics rather than microc limate may explain differences in ozone sensitivity between seedlings and mature trees. These results indicate that seedlings may not reflec t the ozone sensitivity of larger more physiologically mature trees.