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CO2 vs. Ozone: Responses of Norway Spruce and European Beech Trees
Reference
Liu, X., Kozovits, A.R., Grams, T.E.E., Blaschke, H., Rennenberg, H. and Matyssek, R.  2004.  Competition modifies effects of ozone/carbon dioxide concentrations on carbohydrate and biomass accumulation in juvenile Norway spruce and European beech.  Tree Physiology 24: 1045-1055.

Background
In the words of the authors, "ozone is considered to be one of the air pollutants most detrimental to plant growth and development in both urban and rural environments (Lefohn, 1992; Skarby et al., 1998; Matyssek and Innes, 1999)," as it "reduces the growth and yield of numerous agronomic crops as well as fruit and forest trees (Retzlaff et al., 1997; Fumagalli et al., 2001; Matyssek and Sandermann, 2003)."  In addition, they say that ozone concentrations are "currently two to three times higher than in the early 1900s (Galloway, 1998; Fowler et al., 1999)," and that tropospheric ozone concentrations likely "will remain high in the future (Elvingson, 2001)."

What was done
Liu et al. grew 3- and 4-year-old European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) seedlings for two growing seasons in well-watered and well-fertilized soil in containers located within walk-in phytotrons maintained at either ambient or ambient + 300 ppm CO2 (each subdivided into ambient and double-ambient ozone concentration treatments), in both monoculture and in competition with each other, after the seedlings had been pre-acclimated for one year to either the ambient or elevated CO2 treatment.  At the end of the study, the plants were harvested and fresh weights and dry biomass values were determined for leaves, shoot axes, coarse roots and fine roots, as were carbohydrate (starch and soluble sugar) contents and concentrations for the same plant parts.

What was learned
The authors report that their data did NOT support their initial hypothesis that "prolonged exposure to elevated CO2 does not compensate for the adverse ozone effects on European Beech or Norway spruce."  In fact, they note in their conclusion that ALL "adverse effects of ozone on carbohydrate concentrations and contents were counteracted when trees were grown in elevated CO2."

What it means
These results are certainly good news for the biosphere (and especially for beech and spruce trees), as well as for human enterprises that result in CO2 being emitted to the atmosphere.  In addition to the latter activities having their own "excuse for being," they have the doubly good fortune of producing a byproduct that goes on to fight -- and overcome -- the deleterious consequences of one of the world's most potent air pollutants.

References
Elvingson, P. 2001. For the most parts steadily down. Acid News 3: 20-21.

Fowler, D., Cape, J.N., Coyle, M., Flechard, C., Kuylenstrierna, J., Hicks, K., Derwent, D., Johnson, C. and Stevenson, D. 1999. The global exposure of forests to air pollutants. In: Sheppard, L.J. and Cape, J.N. (Eds.). Forest Growth Responses to the Pollution Climate of the 21st Century. Kluwer Academic Publisher, Dordrecht, The Netherlands, pp. 5032.

Fumagalli, I., Gimeno, B.S., Velissariou, D., De Temmerman, L. and Mills, G. 2001. Evidence of ozone-induced adverse effects on crops in the Mediterranean region. Atmospheric Environment 35: 2583-2587.

Galloway, J.N. 1998. The global nitrogen cycle: changes and consequences. Environmental Pollution 102: 15-24.

Lefohn, A.S. 1992. Surface Level Ozone Exposure and Their Effects on Vegetation. Lewis Publishers, Chelsea, UK.

Matyssek, R. and Innes, J.L. 1999. Ozone - a risk factor for trees and forests in Europe? Water, Air and Soil Pollution 116: 199-226.

Matyssek, R. and Sandermann, H. 2003. Impact of ozone on trees: an ecophysiological perspective. Progress in Botany 64: 349-404.

Retzlaff, W.A., Williams, L.E. and DeJong, T.M. 1997. Growth and yield response of commercial bearing-age "Casselman" plum trees to various ozone partial pressures. Journal of Environmental Quality 26: 858-865.

Skarby, L., Ro-Poulsen, H., Wellburn, F.A.M. and Sheppard, L.J. 1998. Impacts of ozone on forests: a European perspective. New Phytologist 139: 109-122.


Reviewed 24 November 2004