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

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 × O 3 ) and double ambient (2 × O 3 ) ozone concentrations at a free-air exposure system (“Kranzberg Forst”, Germany). Pigments, α-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 β-carotene and lower contents of chlorophyll, α-carotene, and neoxanthin than shade-exposed seedlings. In 2003 sun-exposed 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 CO 2 concentration (c i ). Seedlings differed from the adjacent adult trees in most biochemical and physiological parameters investigated: Sun exposed seedlings showed higher contents of α-tocopherol and xanthophylls and lower contents of ascorbate, chlorophyll, neoxanthin, and α-carotene compared to adult trees. Shade exposed seedlings had lower contents of xanthophylls, α-carotene, and α-tocopherol than shade leaves of old-growth trees. In 2003, seedlings had higher A max , stomatal conductance (g s ), and c i under 2 × O 3 than adult trees. The results showed that shade acclimated beech seedlings are more sensitive to O 3 , possibly due to a lower antioxidative capacity per O 3 uptake. We conclude that beech seedlings are uncertain surrogates for adult beech trees.