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CO2 and O3 Effects on Two Silver Birch Clones in Finland

Vapaavuori, E., Holopainen, J.K., Holopainen, T., Julkunen-Titto, R., Kaakinen, S., Kasurien, A., Kontunen-Soppela, S., Kostiainen, K., Oksanen, E., Peltonen, P., Riikonen, J. and Tulva, I. 2009. Rising atmospheric CO2 concentration partially masks the negative effects of elevated O3 in silver birch (Betula pendula Roth). Ambio 38: 418-424.
For a period of three years (1999-2001), Vapaavuori et al. grew 20 initially-seven-year-old individual trees of each of two different silver birch (Betula pendula Roth) clones -- 4 and 80 (V5952 and K1659, respectively, in the Finnish forest genetic register) -- out-of-doors at the Suonenjoki Research Unit site of the Finnish Forest Research Institute within individual open-top chambers maintained at all combinations of (1) ambient CO2 and ambient O3, (2) ambient CO2 and double O3, (3) double CO2 and ambient O3, and (4) double CO2 and double O3, where CO2 treatments were imposed 24 hours per day, and where O3 treatments were imposed for 12, 12 and 14 hours per day in 1999, 2000 and 2001, respectively, throughout the course of which experiment they measured a variety of plant physiological responses to the four different treatments, including net photosynthesis, leaf stomatal conductance, leaf soluble proteins, leaf phenolic compounds, leaf nutrient concentrations, trunk and branch growth, physiology of the foliage and root systems, crown structure, wood properties, and interactions with folivorous insects.

Results indicated that, in general, the negative effects of elevated O3 on the various growth parameters and properties of the trees "were mainly found in ambient CO2," and that elevated CO2 typically "reversed or diminished the effects of elevated O3." Thus, it would appear that in a world where atmospheric O3 concentrations are still a significant scourge of both wild and cultivated plants alike, we can be thankful the air's CO2 molecules are working overtime to heal, or prevent, the damage that is done, or would otherwise be wrought, by the pernicious oxygen triplet.

Archived 7 May 2010