COMPARISON OF THE RESPONSE OF RED OAK (QUERCUS-RUBRA) SEEDLINGS AND MATURE TREES TO OZONE EXPOSURE USING SIMULATION MODELING

Field studies have determined that the photosynthetic rates of mature northern red oak (Quercus rubra L.) trees are sensitive to ozone expos ure whereas those of seedlings are not. We used a model of tree physio logy to determine the consequences of these differences in photosynthe tic response to carbon allocation and tissue growth in seedlings and m ature trees over a 2-year period. In the seedling simulations at twice ambient ozone, only the total non-structural carbohydrate (TNC) stora ge pool was affected. The effects in the simulated mature tree were mu ch greater, with large decreases predicted for TNC, fine root, leaf, s tem, branch, and coarse root tissues. The model produced many ozone-in duced responses in the mature tree that were similar or consistent wit h observations made in a held study, but the simulations overestimated the effect of twice ambient ozone on root TNC and growth. The discrep ancy between field and simulated results suggests that the field study trees exposed to elevated ozone levels may use carbon at a reduced ra te, particularly through reduced respiration. (C) 1988 Elsevier Scienc e Ltd. All rights reserved.