Abstract
In this study the influence of chronic free-air ozone exposure and of different meteorological
conditions in the very dry year 2003 and the more humid year 2004 on the antioxidative
system in sun and shade leaves of adult Fagus sylvatica trees were investigated. Contents of ascorbate, glutathione, and α-tocopherol, as
well as chloroplast pigments were determined under ambient (1 × O3 ) and double ambient (2 × O3 ) ozone concentrations. Ozone affected the antioxidative system in June and July,
causing lower ascorbate contents in the apoplastic space, a more oxidized redox state
of ascorbate and glutathione and an increase in pigment contents predominantly in
the shade crown. For all measured parameters significant differences between the years
were observed. In 2004 the redox state of ascorbate and glutathione was in a more
reduced state and leaf contents of α-tocopherol, pigments of the xanthophyll cycle,
β-carotene, lutein, neoxanthin, and α-carotene were lower compared to 2003. Contents
of total glutathione and chlorophyll a + b were increased in the second year. These
results indicate a strong influence of the drought conditions in 2003 on the antioxidative
system of beech overruling the ozone effects. Shade leaves showed lower contents of
ascorbate in both years and the redox states of ascorbate and glutathione were more
oxidized compared to sun leaves. Contents of photoprotective and accessory pigments
generally were enhanced and the de-epoxidation state of the xanthophyll cycle was
lower in the shade compared to the sun crown. Exhibiting less antioxidants shade leaves
seem to be more sensitive against ozone than sun leaves.
Key words
Free-air ozone fumigation - crown position - adult beech trees - ascorbate - glutathione
- α-tocopherol - chloroplast pigments.
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1 These authors contributed equally to the work
kristine.haberer@ctp.uni-freiburg.de
Guest Editor: R. Matyssek
