CHANGES IN LEVELS OF ALPHA-TOCOPHEROL AND ASCORBATE IN SPRUCE NEEDLESAT 3 LOW MOUNTAIN SITES EXPOSED TO MG2-DEFICIENCY AND OZONE()

The main objective of this study was the comparison of changes in leve ls of a-tocopherol and ascorbate in needles of spruce trees with vario us degrees of damage at three low mountain sites. The ascorbate conten t in needles of spruce trees with various degrees of damage differs in the course of seasons as well as in the absolute level. The antioxida nt status was affected mainly during summer. The content of ascorbate in needles of damaged trees was significantly increased compared to th at of undamaged trees. Despite seasonal and daily fluctuations, the le vel of ascorbate seems to be a good indicator for the degree of damage in the case of symptoms described as montane yellowing. Together with an increasing content of a-tocopherol per chlorophyll, a rise of asco rbate content indicates enhanced oxidative stress in the needles of da maged trees, particularly in summer. Asc/alpha Toc ratios were increas ed in needles of damaged trees. At the studied sites enhanced oxidativ e stress could be caused by the combined action of Mg2(+)-deficiency, high ozone concentrations and high-light intensity, all inducing an in creased production of radicals in combination with a reduced photosynt hetic capacity.