CARBON PARTITIONING AND ALLOCATION IN NORTHERN RED OAK SEEDLINGS AND MATURE TREES IN RESPONSE TO OZONE

Northern red oak (Quercus rubra L.) seedlings and trees differ in thei r response to ozone. Previous work reported reductions in net photosyn thesis, carboxylation efficiency and quantum yield of mature tree leav es, whereas seedling processes were unaffected by the same ozone expos ure. To further characterize differences in ozone response between see dlings and mature trees, we examined carbon partitioning and allocatio n in 32-year-old trees and 4-year-old seedlings of northern red oak af ter exposure to subambient (seasonal SUM00 dose (sum of all hourly ozo ne exposures) = 31 ppm-h), ambient (SUM00 dose = 85 ppm-h) and twice a mbient (SUM00 dose = 151 ppm-h) ozone concentrations for three growing seasons. For mature trees, ozone exposure decreased foliar starch par titioning, increased starch partitioning in branches and increased C-1 4 retention in leaves. In contrast, starch partitioning in leaves and branches, and foliar C-14 retention in seedlings were unaffected by oz one exposure, but soluble carbohydrate concentrations in coarse and fi ne roots of seedlings were reduced. Differences in carbohydrate demand between seedlings and mature trees may underlie the higher leaf ozone uptake rates and greater physiological response to ozone in mature no rthern red oak trees compared with seedlings.