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Response of Silver Birch Trees to Elevated CO2 and Ozone
Eichelmann, H., Oja, V., Rasulov, B., Padu, E., Bichele, I., Pettai, H., Mols, T., Kasparova, I., Vapaavuori, E. and Laisk, A.  2004.   Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2- and O3-enriched atmospheres.  Plant, Cell and Environment 27: 479-495.

What was done
Two silver birch (Betula pendula Roth) clones (K1659 and V5952) were grown in open-top chambers for three years (age 7-9 years) at ambient and double-ambient atmospheric CO2 concentrations, ambient and double-ambient tropospheric O3 concentrations, and double-ambient CO2 and O3 concentrations together.

What was learned
By itself, the 100% increase in atmospheric CO2 concentration increased the average net photosynthetic rates of both silver birch clones by approximately 16%, while the doubled O3 by itself caused a 10% decline in the average photosynthetic rate of clone V5952, but not of clone K1659.  When both trace gases were simultaneously doubled, however, the photosynthetic rate of clone V5952 once again experienced a 16% increase in net photosynthesis, as if the doubled O3 had had no effect when applied in the presence of doubled CO2.

What it means
Once again, we have a situation where atmospheric CO2 enrichment more than completely ameliorates the deleterious effect of ozone pollution on the photosynthetic rate of a plant, in this case, silver birch clone V5952.  See Ozone (Effects on Plants) in our Subject Index for other examples of this phenomenon.

Reviewed 16 June 2004