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Effects of Elevated CO2 on the Lignin and Total Phenolic Concentrations of Cattail and Trembling Aspen Leaves
Reference
Wetzel, R.G. and Tuchman, N.C.  2005.  Effects of atmospheric CO2 enrichment and sunlight on degradation of plant particulate and dissolved organic matter and microbial utilization.  Archiv fur Hydrobiologie 162: 287-308.

Background
As the CO2 content of the air increases, most of earth's vegetation experiences enhanced rates of photosynthetic carbon uptake, which phenomenon commonly leads to increased production of carbon-based secondary compounds, including lignin and total phenolics, which tend to increase plant defense and resistance mechanisms to herbivore and pathogen attack.

What was done
The authors grew well-watered trembling aspen (Populus tremuloides) and cattails (Typha latifolia) for a period of three years in open-bottom root boxes out-of-doors within clear-plastic-wall open-top chambers maintained at either ambient (360 ppm) or elevated (720 ppm) atmospheric CO2 concentrations from early spring through leaf senescence.  During this period, green and naturally-senesced leaves were collected and analyzed for the fractions of leaf mass composed of lignin and total phenolics.

What was learned
In the case of trembling aspen, green leaf material contained 15.0% more lignin and 19.1% more total phenolics when the experimental seedlings were grown in CO2-enriched as opposed to ambient air, while senesced leaf material grown in CO2-enriched air contained 32.8 and 63.2% more of these substances than similar leaves grown in ambient air.  In the case of cattails, green leaf material contained 37.5% more lignin and 27.6% more total phenolics when the plants were grown in CO2-enriched as opposed to ambient air, while senesced leaf material grown in CO2-enrihced air contained 26.5 and 40.6% more of these substances than similar leaves grown in ambient air.

What it means
These findings would seem to suggest that the ongoing rise in the air's CO2 content should strengthen trembling aspen and cattail defense mechanisms and reduce their biomass losses to herbivory, which phenomena should enhance the general health and robustness of these widespread aquatic (cattail) and terrestrial (trembling aspen) plants.

Reviewed 20 July 2005