The Role of Antioxidative Defense in Determining Ozone Sensitivity of Norway Spruce (Picea abies (L.) Karst.) Across Tree Age: Implications for the Sun- and Shade-Crown : 5th International Symposium on Response of Plant Metabolism to Air Pollution and Global Change

2002

3 Abb., 2 Tab., 34 Lit. Ang.

Unselbständiges Werk

5943

200096895

We compared ascorbate contents of current-year Picea abies needles with respect to tree age and crown position. In order to exclude microclimate influences potted seedlings were transferred into the upper canopy of a 45 year-old stand. In the sund- and the shade-crown 100-needle dry weight was significantly lower in seedlings than in adult trees, whereas the opposite was found for specific leaf area. Such age dependent changes in needle morphology also influenced the detocification capacity: In general, the contents of scorbate per unit needle surface area increased with increasing tree age, a fact that could not be observed when needle dry-weight based ascorbate concentrations were compared in both canopy positions. As O3 injury results from the balance between uptake and detocification processes, the overall tree response to O3 can be expressed as the ratio between the amount of potentially available ascorbate and the O3 flux into the needles. Our data show that the contents of the potentially available ascorbate per nmol O3 taken up per second increased with tree age. In general, the amount of potentially available ascorbate per nmol O3 taken up was lower in the shade- than in the sun crown which points towards a higher risk of O3 damage in the shade-crown.