Herbinger, K; Then, C; Haberer, K; Alexou, M; Low, M; Remele, K; Rennenberg, H; Matyssek, R; Grill, D; Wieser, G; Tausz, M
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 x O-3) and double ambient (2 x O-3) ozone concentrations at a free-air exposure system ("Kranzberg Forst", Germany). Pigments, alpha-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 antioxiclants, xanthophylls, and beta-carotene and lower contents of chlorophyll, alpha-carotene, and neoxanthin than shade-exposed seedlings. In 2003 sunexposed seedlings showed higher contents of carotenoids and total glutathione and lower net photosynthesis rates (A(max)) compared to 2004. O-3 exposure generally affected the content of chlorophyll, the xanthophyll cycle, and the intercellular CO2 concentration (c(j)). Seedlings differed from the adjacent adult trees in most biochemical and physiological parameters investigated: Sun exposed seedlings showed higher contents of alpha-tocopherol and xanthophylls and lower contents of ascorbate, chlorophyll, neoxanthin, and alpha-carotene compared to adult trees. Shade exposed seedlings had lower contents of xanthophylls, alpha-carotene, and alpha-tocopherol than shade leaves of old-growth trees. In 2003, seedlings had higher Amax, stomatal conductance (g(s)), and c, under 2 x O-3 than adult trees. The results showed that shade acclimated beech seedlings are more sensitive to O-3, possibly due to a lower antioxiclative capacity per O-3 uptake. We conclude that beech seedlings are uncertain surrogates for adult beech trees.
