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 and 32-year-old trees to subambient (10 μmol h; cumulative dose based on 7 h daily mean), ambient (43 μmol h), and twice-ambient (85 μmol h) ozone. The relative growth rates (RGR) of leaves sampled from seedlings and trees were similar across treatments, as were specific leaf respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25.3 mol CO₂ kg¹ leaf dry mass produced for seedlings and 21.5 mol kg^-1 for trees. Maintenance coefficients 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 coefficient was affected by ozone. Leaves sampled throughout the growing season also showed little response of respiration to ozone. This occurred 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 ozone and that in older leaves injury can occur without a parallel increase in so-called 'maintenance' respiration.