Internal conductance to CO2 transfer of adult Fagus sylvatica:: Variation between sun and shade leaves and due to free-air ozone fumigation

Two separate objectives were considered in this study. We examined (1) internal conductance to CO2 (g(i)) and photosynthetic limitations in sun and shade leaves of 60-year-old Fagus sylvatica, and (2) whether free-air ozone fumigation affects gi and photosynthetic limitations. gi and photosynthetic limitations were estimated in situ from simultaneous measurements of gas exchange and chlorophyll fluorescence on attached sun and shade leaves of E sylvatica. Trees were exposed to ambient air (1 x O-3) and air with twice the ambient ozone concentration (2x O-3) in a free-air ozone canopy fumigation system in southern Germany (Kranzberg Forest). gi varied between 0.12 and 0.24 mol m(-2) s(-1) and decreased CO2 concentrations from intercellular spaces (C-i) to chloroplastic (C-c) by approximately 55 mu mol mol(-1). The maximum rate of carboxylation (V-cmax) was 22-39% lower when calculated on a C-c basis compared with a C, basis. gi was approximately twice as large in sun leaves compared to shade leaves. Relationships among net photosynthesis, stomata] conductance and gi were very similar in sun and shade leaves. This proportional scaling meant that neither C-i nor C-c varied between sun and shade leaves. Rates of net photosynthesis and stomata] conductance were about 25% lower in the 2 x O-3 treatment compared with 1 x O-3, while V-cmax was unaffected. There was no evidence that gi was affected by ozone. (c) 2006 Elsevier B.V. All rights reserved.