Gas Exchange and Antioxidative Compounds in Young Beech Trees under Free-Air Ozone Exposure and Comparisons to Adult Trees

Stuttgart

2007

S. 288-297

4 Abb., 3 Tab., 52 Lit. Ang.

Unselbständiges Werk

200144116

Three-year-old beech (Fagus sylvatica) seedlings growing in containers were placed into the sun and shade crown of a mature beech stand exposed to ambient (1 œ~ O3) and double ambient (2 œ~ O3) ozone concentrations at a free-air exposure system (œgKranzberg Forstœh, Germany). Pigments, ı¿-tocopherol, glutathione, ascorbate, and gas exchange were measured in leaves during 2003 (a drought year) and 2004 (an average year). Sun-exposed seedlings showed higher contents of antioxidants, xanthophylls, and ıÀ-carotene and lower contents of chlorophyll, ı¿-carotene, and neoxanthin than shade-exposed seedlings. In 2003 sunexposed seedlings showed higher contents of carotenoids and total glutathione and lower net photosynthesis rates (Amax) compared to 2004. O3 exposure generally affected the content of chlorophyll, the xanthophyll cycle, and the intercellular CO2 concentration (ci). Seedlings differed from the adjacent adult trees in most biochemical and physiological parameters investigated: Sun exposed seedlings showed higher contents of ı¿-tocopherol and xanthophylls and lower contents of ascorbate, chlorophyll, neoxanthin, and ı¿-carotene compared to adult trees. Shade exposed seedlings had lower contents of xanthophylls, ı¿-carotene, and ı¿-tocopherol than shade leaves of old-growth trees. In 2003, seedlings had higher Amax, stomatal conductance (gs), and ci under 2 œ~ O3 than adult trees. The results showed that shade acclimated beech seedlings are more sensitive to O3, possibly due to a lower antioxidative capacity per O3 uptake. We conclude that beech seedlings are uncertain surrogates for adult beech trees.