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Differential Responses of Aspen Genotypes to Elevated CO2
Reference
Dickson, R.E., Coleman, M.D., Pechter, P. and Karnosky, D.  2001.  Growth and crown architecture of two aspen genotypes exposed to interacting ozone and carbon dioxide.  Environmental Pollution 115: 319-334.

What was done
The authors grew two aspen (Populus tremuloides) clones - one tolerant (clone 216) and one sensitive (clone 259) to ozone - for three months in open-top chambers located in Michigan, USA.  Some chambers received atmospheric CO2 concentrations of 350 ppm while others received 700 ppm, with and without exposure to ambient and twice-ambient levels of atmospheric ozone, to study the interactive effects of these parameters on this deciduous tree species.

What was learned
Elevated ozone exposure tended to decrease plant growth parameters in both clones, with greater reductions occurring in the ozone-sensitive clone 259.  Simultaneous exposure to elevated CO2 concentrations generally alleviated the growth reducing effects of ozone in the ozone-tolerant clone 216, but not in the ozone-sensitive clone.  Elevated ozone exposure, for example, reduced total plant dry weight by 28 and 42% in clones 216 and 259, respectively.  When concomitantly fumigated with elevated CO2 concentrations, ozone-induced reductions in total plant dry weight were only 4% in clone 216, while they were still 39% in clone 259.

What it means
As the tropospheric ozone concentration continues to rise, it will likely cause differential reductions in regenerating aspen clone productivity and growth that varies with genotype.  If the CO2 content of the air continues to increase over this same time period, it will likely alleviate ozone-induced growth reductions in clones that have an inherent genetic tolerance for ozone.  However, elevated CO2 may have little or no effect on ameliorating ozone-induced growth reductions in ozone-sensitive aspen clones.  Therefore, in order to achieve maximum growth rates, wood production and carbon sequestration in aspen plantations under future environmental conditions, tree farmers should select for and plant ozone-tolerant clones, which will respond much more favorably to increases in the air's CO2 and ozone concentrations.


Reviewed 9 January 2002