Vplyv veku na prieduchovú vodivosť a fotosyntézu dubu letného

Increasing age brings along lowering of the tree vitality. Ecophysiological parameters as photosynthesis and its dependence on the concentration of CO2 (A-Ci curves) and light, chlorophyll fluorescence, stomatal conductance and water potential provide information on the physiological vitality of plants. These methods were used to assess the effect of age on the photosynthesis of pedunculate oak (Quercus robur). Two groups of trees were compared, the first group was over 600 years old while the second was less than 30 years old. Gas exchange measurements indicated lower light-saturated photosynthesis of old trees. Using A-Ci curves helped to estimate biochemical limitations of photosynthesis such as Vcmax, Jmax a Rd (maximum rate of carbon carboxylation, maximum electron transport speed and day respiration; respectively), which were similar for both groups of the trees. Chlorophyll fluorescence measurements enabled to estimate dark adapted (Fv/Fm) and light-adapted fluorescence (Fvˈ/Fmˈ). There were no differences between old and young trees in the parameters of chlorophyll fluorescence. However, the stomatal conductance was lower in old than in young trees under unlimited soil water availability. Resulting intercellular concentration of CO2 was lower in old trees, which indicated a lower concentration of CO2 at the sites of carboxylation and lower carbon assimilation rate. On the other hand, higher values of water potential of old trees in the mild drought in summer indicated their better access to soil water. Therefore, maximal stomatal conductance was similar in both groups of trees upon mild drought. Minimum stomatal conductance was higher in old trees. The results suggest that one of the reasons for the lowering of the vitality of old trees is their inability to regulate stomatal conductance, and to optimize carbon assimilation-water loss balance