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M. Čater, P. Simončič: PHOTOSYNTHETIC RESPONSE OF YOUNG BEECH (Fagus Sylvatica L.) ... Šumarski list br. 11–12, CXXXIII (2009), 569-576 dimension. Evident changes in distribution of plants and species diversity consequently affect primary producti vity (Callaghan etal. 2004). Several key questions about the future response of beech to expected changes such as temperature increase, redistribution of precipitation and increase of atmospheric CO concentration remain open and without answers. Quotations in literature and research results are in most cases unclear and sometimes even contradictory (Po or ter 1998,Lloyd andFarquhar 1996). Photosynthe sis, the first estimate of net productivity could be measured as the response of plants to different light intensity or the response to different concentration of CO 2 which is entering the system in the controlled environment. In spite of good understanding of processes of carbon dynamics at leaf level in a changed CO 2 environment, it is difficult to make a prognosis of the fu ture response of the whole plant, also because of the short time interval of observations and numerous possible interactions that have not yet been recognized.According toBatič(2007) most changes by the increased amount of atmospheric CO could be expected for C3 2 plants at the beginning of saturation curves, especially for the plants that grow in reduced or minimal light conditions, close to compensation point.Wemay therefore expect most changes in shade tolerant species. The research goal was to define range of photosynthetic response in young beech in dependence of light intensity and different concentration of CO between 2 three canopy conditions (shelter, forest edge and gap) on different forest sites. MATERIALAND METHODS – Materijali i metode Research was performed on 10–15 year old beech trees at five selected natural forest stands: at Kladje and Brička in the Pohorje area, atVrhovo and the karstic- Table 1 Research plots characteristics Tablica 1.Značajkepokusnih ploha dinaric area in Kočevski Rog –at Snežna jama (managed forest) and Rajhenav (virgin forest) (Table 1). Plot Ploha Altitude Nadmorska visina (m) Lat (o) Long (o) Annual precipitation Oborina (mm) Annualaverage air T Prosječna godišnja T(oC) Soiltype Tip tla Growing stock Drvna zaliha (m 3 /ha) Brička 1093 46o28’40’’ 15o15’40’ 1190 9,1 Dystric Cambisol 477 Kladje 1308 46o28’48’’ 15o23’24’’ 1066 9,2 Dystric Cambisol 390 Vrhovo 273 45o48’25’’ 15o18’11’’ 1138 9,4 Acric Luvisol 479 Sn. jama 875 45o39’15’’ 15o01’40’’ 1330 8,3 Rendzic Leptosol 612 Rajhenav 865 45o39’36’’ 15o03’36’’ 1330 8,3 Rendzic Leptosol 992 Both Brička and Kladje belong to the acidophilous beech forest type Luzulo albidae-Fagetum (Urbančič and Kutnar 2006) while Snežna jama and Rajhenav belong to dinaric silver fir and beech forest type Omphalodo- Fagetum (Kutnar andUrbančič2008). At each location a research plot was established 100x100m in size, reaching from complete closure to open sky conditions on all plots with little or no exposure. The gradient of natural light conditions was obtained by selecting young trees under a range of canopy openness. On each fenced plot, for 24 young beech trees in comparable light-intensity conditions, their potential light environment was estimated with hemispherical photos (Anonymous 2003). Fine tuning was applied after pilot analysis, so that the light conditions on all plots were comparable.The parameter used for evaluation of light conditions was the indirect site factor (ISF) (Wagner 1994), which is the relative proportion of diffuse light intensity above a defined plant compared to open/gap conditions, (without shading) in percentage (%). Photos were taken with a digital Nikon Coolpix 990 and calibrated fish-eye lens and analyzed withWinScanopy software. In the process of hemispherical photo analysis the vegetation period was defined for each plot group separately; for the diffuse light distribution a “Standard overcast sky” (SOC) model was applied. For the calculation within the vegetation period, the sun’s position was specified every ten (10) minutes.The solar constant was defined as 1370W/m2, 0.6for atmospheric transmissivity and 0.15 for the proportion of diffuse radiation compared to calculated direct potential radiation.According to light conditions three groups were defined: stand conditions (ISF<20), edge (20 of trees on plots ranged from 40 - 70 cm under stand conditions, from 70–110 cm under edge conditions and from 110–220 cm in open area conditions. In each group, four trees were randomly selected for measurement of photosynthesis. In the same leaves nitrogen 2 concentration [mg/cm] was determined to compare macronutrient status in different light categories (Leco CNS-2000 analyzer) (Anonymous,2007). |