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Long-Term Effects of Elevated CO2 on Carbon-Based Secondary and Structural Compounds in Plant Leaves
Penuelas, J., Castells, E., Joffre, R. and Tognetti, R.  2002.  Carbon-based secondary and structural compounds in Mediterranean shrubs growing near a natural CO2 spring.  Global Change Biology 8: 281-288.

What was done
The authors sampled leaves of three species of shrub growing near and away from CO2-emitting springs in Pisa, Italy, to determine the long-term effects of elevated atmospheric CO2 concentrations - 700 ppm (near) vs. 360 ppm (away from) - on foliar concentrations of carbon-based secondary and structural compounds.

What was learned
Elevated CO2 had very few long-term significant effects on foliar concentrations of lignin, cellulose, hemicellulose, lipids, phenolics and total nonstructural carbohydrates.  In fact, the few significant effects that were observed varied by compound and plant species.  Thus, there were no generally-applicable effects of elevated CO2 on carbon-based secondary compounds.

What it means
As the air's CO2 content rises, the results of this study suggest that elevated levels of atmospheric CO2 will likely have little impact on foliar carbon-based secondary compound concentrations.  Indeed, the authors say that "the overall carbon-based secondary structural compound concentrations did not increase in the CO2 spring site."

It is difficult to understand fully why the concentrations of these carbon-based secondary compounds did not increase more generally with atmospheric CO2 enrichment, since many other studies have observed CO2-induced changes in plant digestibility and amenability to decomposition.  Nevertheless, in light of their results, the authors urge caution in attributing such changes to rising atmospheric CO2 concentrations.

Reviewed 5 June 2002