An overview of long-term effects of elevated atmospheric CO2concentration on the growth and physiology of birch (Betula pendulaRoth.)

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Abstract
An extensive number of biochemical and physiological measurements were made over the third and fourth years of the growth of birch (Betula pendula Roth.) in elevated CO2. Trees in elevated CO2 had 58% more biomass than trees grown in ambient CO2 although relative growth rate was not affected in the last year of the study. No changes in biomass allocation were observed. Elevated CO2 caused an increase in starch accumulation in the leaves that resulted in a series of feedback mechanisms to re-establish the source-sink balance of the trees. A decrease in Rubisco activity and to a lesser extent in chlorophyll and soluble proteins led to a decrease in the photosynthetic activity. Although the positive CO 2effect on photosynthetic activity was maintained in the field over the whole experiment, the photosynthetic capacity of the trees was reduced by long-term exposure to elevated CO2. Both maximum electron transport capacity (J max) and maximum carboxylation capacity (V emax) were reduced to a similar extent, so the ratio of J max:V cmax was not altered. Root biomass, fine root density and mycorrhizal infection were increased in elevated CO 2. The mycorrhizal species of fungi associated with the trees grown in elevated CO2 were late-successional species whereas the species associated with trees grown in ambient CO2 were early successional species. This lends support to the hypothesis of a CO2 effect on the ontogeny of the trees.

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