GROWTH AND MAINTENANCE RESPIRATION IN LEAVES OF NORTHERN RED OAK SEEDLINGS AND MATURE TREES AFTER 3 YEARS OF OZONE EXPOSURE

A two-component model of growth and maintenance respiration is used to study the response of northern red oak (Quercus rubra L.) seedlings a nd 32-year-old trees to subambient (10 mu mol h; cumulative dose based on 7 h daily mean), ambient (43 mu mol h), and twice-ambient (85 mu m ol h) ozone, The relative growth rates (RGR) of leaves sampled from se edlings and trees were similar across treatments, as were specific lea f respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25.3 mol CO2 kg(-1) leaf dry mass pro duced for seedlings and 21.5 mol kg(-1) for trees, Maintenance coeffic ients ranged from 0.89 to 1.07 mol CO2 kg(-1) leaf dry mass d(-1) for seedlings and from 0.64 to 0.84 mol kg(-1) d(-1) for trees, Neither co efficient was affected by ozone, Leaves sampled throughout the growing season also showed little response of respiration to ozone, This occu rred despite a 30% reduction in net photosynthesis for trees grown at twice-ambient ozone, These results suggest that growth and maintenance respiration in young northern red oak leaves are not affected by ozon e and that in older leaves injury can occur without a parallel increas e in so-called 'maintenance' respiration.