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Effects of Elevated CO2 and O3 on Photosynthesis in European Beech Trees
Reference
Grams, T.E.E, Anegg, S., Haberle, K.-H., Langebartels, C. and Matyssek, R.  1999.  Interactions of chronic exposure to elevated CO2 and O3 levels in the photosynthetic light and dark reactions of European beech (Fagus sylvatica).  New Phytologist 144: 95-107.

What was done
European beech seedlings were grown for one year in glasshouses receiving atmospheric CO2 concentrations of 367 and 667 ppm.  During the following year, in addition to maintaining the same differential CO2 concentrations, seedlings were also exposed to ambient or twice-ambient levels of O3 (ozone) to determine the interactive effects of these two gases on photosynthesis.

What was learned
Elevated CO2 decreased foliar levels of nitrogen and chlorophyll during the second year of the study, as did the combination of elevated CO2 and O3 for chlorophyll, while elevated O3 alone had no significant effects on either of these parameters.  With respect to photosynthesis, however, elevated O3 significantly reduced this process in seedlings grown at ambient atmospheric CO2 concentrations by a factor of approximately three.  In contrast, at elevated CO2 levels, seedlings did not exhibit any photosynthetic reductions due to the presence of enhanced O3 concentrations.  If fact, photosynthesis actually increased for CO2-enriched seedlings, but not significantly, by 8% when simultaneously fumigated with elevated O3.  Thus, these several observations suggest that elevated atmospheric CO2 concentrations can counteract the adverse effects of elevated O3 concentrations on beech seedlings.

What it means
As the CO2 content of the air continues to rise, it is likely that the atmospheric O3 concentration will likewise rise.  Under such atmospheric conditions, European beech trees should be protected from the negative growth-retarding effects of elevated O3 by the increasing CO2 concentration.  Indeed, in the words of the authors, "long-term acclimation to elevated CO2 supply does counteract the O3-induced decline of photosynthetic light and dark reactions."  Moreover, elevated CO2 may actually more than counteract the negative impacts of elevated O3 on beech, thus inducing photosynthetic and growth enhancements in this valuable European species.


Reviewed 15 December 1999