Competition modifies effects of enhanced ozone/carbon dioxide concentrations on carbohydrate and biomass accumulation in juvenile Norway spruce and European beech |
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| Authors: | Liu Xiping Kozovits Alessandra R Grams Thorsten E E Blaschke Helmut Rennenberg Heinz Matyssek Rainer |
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| Institution: | Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-K?hler-Allee 53/54, D-79110 Freiburg, Germany. |
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| Abstract: | Elevated concentrations of carbon dioxide (CO2]) and ozone (O3]) affect primary metabolism of trees in opposite ways. We studied their potential interactions on carbohydrate concentrations and contents. Two hypotheses currently under debate were tested. (1) Stimulation of primary metabolism by prolonged exposure to elevated CO2] does not compensate for the adverse effects of O3 on carbohydrate accumulation and biomass partitioning to the root. (2) Growth in a mixed-species planting will repress plant responses to elevated O3] and CO2] relative to conditions in a monoculture. To this end, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) saplings grown under conditions of intra- and interspecific competition were pre-acclimated for 1 year to ambient or elevated CO2]. In the following 2-year phytotron study, trees were exposed to factorial combinations of ambient and elevated O3] and CO2]. The total carbohydrate content (sugar and starch) of spruce was greater in plants exposed to elevated CO2] than in plants exposed to ambient CO2]. In beech, the opposite response was observed, especially when this species was grown in combination with spruce. Overall, the data did not support Hypothesis 1, because the adverse effects of O3 were counteracted by elevated CO2]. Support for Hypothesis 2 was species-dependent. In beech saplings, reduction of carbohydrates by elevated O3] and stimulation by elevated CO2] were repressed by competitive interaction with spruce. In contrast, in spruce, stimulation of carbohydrates by elevated CO2] was similar in mono- and mixed cultures. Thus Hypothesis 2 was supported for beech but not spruce. We conclude that, in juvenile beech and spruce, a 3-year exposure to elevated CO2] counteracts the adverse effects of O3 on carbohydrate concentrations and contents. For beech, sensitivity to elevated CO2] and O3] was high in monoculture but was largely repressed by interspecific competition with spruce. In contrast, the response of spruce to perturbations of atmospheric chemistry was not significantly affected by either intra- or interspecific competition. |
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