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Interactive Effects of Elevated CO2 and Ozone on Three Deciduous Tree Species
Loats, K.V. and Rebbeck, J.  1999.  Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings.  Environmental Pollution 106: 237-248.

What was done
Seedlings of black cherry (Prunus serotina), green ash (Fraxinus pennsylvanica), and yellow-poplar (Liriodendron tulipifera) were grown for 10 weeks in pots placed within growth chambers subjected to ambient air, air with twice the ambient CO2 concentration, air with twice the ambient ozone concentration, and air with twice the ambient CO2 and ozone concentrations to determine the effects of elevated CO2 and ozone on photosynthesis and growth in these three deciduous tree species.

What was learned
When measured at CO2 growth concentrations, elevated CO2 increased rates of net photosynthesis by 62, 35, and 55% in black cherry, green ash, and yellow-poplar seedlings, respectively, when subjected simultaneously to ambient levels of ozone.  At twice ambient levels of ozone, atmospheric CO2 enrichment continued to stimulate this parameter in the same respective species by an average of 90, 63, and 50%.  Similarly, elevated CO2 significantly increased total biomass by 54, 40, and 29% in black cherry, green ash, and yellow-poplar seedlings, respectively, while elevated ozone had little impact on growth.  In addition, seedlings exposed to both elevated CO2 and ozone concentrations exhibited biomass values that were similar to those of seedlings exposed to elevated CO2 alone.  Thus, atmospheric CO2 enrichment ameliorated the detrimental effects of elevated ozone concentrations on photosynthesis and biomass production in these seedlings; and, oftentimes, the greatest CO2-induced responses occurred under the unfavorable growing conditions produced by the elevated ozone concentration.

What it means
As the air's CO2 content rises, it is likely that black cherry, green ash, and yellow-poplar seedlings will display significant and substantial increases in their photosynthetic rates and biomass production, even under atmospheric conditions characterized by elevated ozone concentrations.  Thus, the deciduous forests of the eastern United States can be expected to increase their carbon sequestration abilities as they continue to produce more biomass in the years ahead.

Reviewed 15 July 2000