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Interactive Effects of Elevated CO2 and Ozone on Scots Pine
Kainulainen, P., Holopainen, J.K. and Holopainen, T.  1998.  The influence of elevated CO2 and O3 concentrations on Scots pine needles: Changes in starch and secondary metabolites over three exposure years.  Oecologia 114: 455-460.

What was done
The authors built open-top chambers around Scots pine trees that were about 20-years old and fumigated them with combinations of ambient or CO2-enriched air (645 ppm) and ambient or twice-ambient (20 to 40 ppb) ozone-enriched air for three growing seasons to study the interactive effects of these gases on starch and secondary metabolite production.

What was learned
Elevated CO2 and O3 (ozone) had no significant impact on starch production in Scots pine, even after two years of treatment exposure.  However, near the end of the third year, elevated CO2 alone significantly enhanced starch production in current-year needles, relative to starch concentrations measured in needles of trees grown in ambient CO2.  Neither elevated CO2, O3, nor combinations thereof, had any significant effects on the concentrations of secondary metabolites investigated in this study.

What it means
This paper is important, as it shows the need for long-term studies when investigating tree responses to atmospheric CO2 enrichment.  Whereas no effects of elevated CO2 on starch production were found after two years of treatment exposure, starch concentrations in needles increased significantly in CO2-enriched trees late into the third year of the study.  Thus, long-lived perennial plants, such as trees, clearly require long-term CO2-enrichment studies to elucidate how they will respond to the rising concentration of atmospheric CO2.  With respect to Scots pine, this study suggests they will display increases in starch concentrations in response to the rising CO2 content of the air, which can be mobilized to provide carbohydrates for active plant sinks to increase total tree size and biomass.  In addition, if levels of O3 continue to accumulate in the lower atmosphere, Scots Pine should not display any adverse effects, especially since higher levels of atmospheric CO2 can protect against O3-induced damage.

Reviewed 15 May 1999