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Effects of Elevated CO2 and O3 on the Reproductive Fitness of Paper Birch Trees
Darbah, J.N.T., Kubiske, M.E., Nelson, N., Oksanen, E., Vaapavuori, E. and Karnosky, D.F. 2007. Impacts of elevated atmospheric CO2 and O3 on paper Birch (Betula papyrifera): Reproductive fitness. The Scientific World JOURNAL 7(S1): 240-246.

What was done
Working at the FACE facility near Rhinelander, Wisconsin (USA), where young paper birch (Betula papyrifera Marsh.) seedlings were planted in 1997 and had been growing since 1998 in open-top chambers maintained at atmospheric CO2 concentrations of either approximately 360 or 560 ppm, as well as at atmospheric ozone (O3) concentrations of either ambient or 1.5 times ambient, the authors - over the 2004-2006 growing seasons - collected many types of data pertaining to flowering, seed production, seed germination and new seedling growth and development.

What was learned
In the words of the six researchers who conducted the work, "elevated CO2 had significant positive effect[s] on birch catkin size, weight, and germination success rate (elevated CO2 increased germination rate of birch by 110%, compared to ambient CO2 concentrations, decreased seedling mortality by 73%, increased seed weight by 17% [and] increased [new seedling] root length by 59%." On the other hand, they found that "the opposite was true of elevated O3 (elevated O3 decreased the germination rate of birch by 62%, decreased seed weight by 25%, and increased [new seedling] root length by [only] 15%."

With respect to this latter point, Darbah et al. note that "the seeds produced under elevated O3 had much less stored carbohydrate, lipids, and proteins for the newly developing seedling to depend on and, hence, the slow growth rate." In addition, they report that "the total number of trees that flowered increased by 139% under elevated CO2 [but only] 40% under elevated O3." Likewise, "with respect to the quantity of flowers produced, elevated CO2 had [a] 262% increase, while that of elevated O3 had [only a] 75% increase compared to the control treatment."

What it means
In concluding the discussion of their results, Darbah et al. say their findings imply that "seedling recruitment [in paper birch] will be enhanced under elevated CO2 but reduced under elevated O3," which is another important reason to hope that the air's CO2 content continues to climb as long as the atmosphere's ozone concentration is in a significantly ascending mode.

Reviewed 15 August 2007