Beech trees exposed to high CO2 and to simulated summer ozone levels: Effects on photosynthesis, chloroplast components and leaf enzyme activity

Young trees of European beech (Fagus sylvatica L.) were exposed in a phytot ron to different levels of ozone and CO2 under the climatic simulation of o ne vegetation period. High ozone levels were simulated similar to high ozon e concentration in the field (up to 110 ppb), while CO2 was added as 300 pp m to the present level of ca 380 ppm. Our study describes different aspects of photosynthesis from the leaf level to the reactions of selected thylako id components at different harvest times during growth of the beech trees u nder the different fumigation regimes. Ozone effects appeared in the first weeks of the treatment as a stimulation of chlorophyll fluorescence (F-v/F- m), in oxygen production and in ribulose-1,5-bisphosphate carboxylase/oxyge nase activity, while the summer and early autumn harvests showed strong red uctions in these parameters. Only phosphoenolpyruvate carboxylase (PEPcase) activity remained higher under high ozone. The effects of high CO2 appeare d in general as a small stimulation in enzyme activity like PEPcase in spri ng. However, with increasing time of fumigation, reductions of all paramete rs were observed. Especially chlorophylls showed strong reductions under hi gh CO2. The combined treatment with high ozone plus high CO2 resulted mostl y in an amelioration of the negative ozone effects, although control levels were not reached.