PHOTOSYNTHETIC RESPONSE OF YOUNG BEECH (Fagus Sylvatica L.) ON RESEARCH PLOTS IN DIFFERENT LIGHT CONDITIONS FOTOSINTETSKI ODZIV MLADIH STABALA BUKVE (Fagus sylvatica L.) NA ODABRANIM PLOHAMA U RAZLIČITIM SVJETLOSNIM UVJETIMA

In view of evident changes in the reaction of European beech (Fagus sylvatica L.) to environmental changes, five plots with young trees of the same age were established and studied on natural beech sites. Beech trees were equally distributed along the light gradient and were divided according to light conditions. The parameter used for evaluation of light conditions was the indirect site factor (ISF) obtained by the WinScanopy analysis. Three groups of canopy – light conditions were defined: stand conditions (ISF<20), edge (2025). In all categories light saturation curves and curves describing dependence between intercellular CO2 concentration in leaves and assimilation rate (A-Ci) were measured under the same fixed parameters (temperature, flow and CO2 concentration, humidity, and light intensity) with Li-6400, to compare responses between different light categories and different plots within comparable light conditions. Differences between canopy, edge and open area responses were confirmed with high significance on all plots as well as between studied forest complexes. On plots from Kočevje region, young beech indicated more shade tolerance, the response to increased light intensity and different CO2 concentration was greater than the response of young beech on Pohorje plots within the same light intensities. Responses of trees on plots in managed and virgin forest were also different: young beech response in virgin forest plot was more shade-tolerant, compared to response of young beech from plots in managed forest.