What was done
The authors grew 2-year-old saplings of paper birch (Betula papyrifera Marsh.) and 3-year-old saplings of sugar maple (Acer saccharum Marsh.) in well-watered and fertilized 16-L pots from early May until late August in glasshouse rooms maintained at either 400 or 700 ppm CO2.

What was learned
The whole-plant biomass of paper birch was increased by 55% in the CO2-enriched glasshouse rooms, while that of sugar maple was increased by 30%.  Condensed tannins, on the other hand, were unaltered in sugar maple but increased by 27% in paper birch in the CO2-enriched treatment.

What it means
The growth benefits conferred by elevated CO2 in this experiment are obvious.  To this observation the authors add that "the higher condensed tannin concentrations that were present in the birch fine roots may offer these tissues greater protection against soil-borne pathogens and herbivores."

Another important implication of CO2-induced increases in plant concentrations of condensed tannins is that the eating of such tannin-enhanced plant materials can reduce methane emissions from grazing ruminants and thereby lower the potential for global warming, as described in our Editorial of 7 August 2002.  Within this context, it is interesting to note that Parsons et al. report that CO2-induced increases in fine root concentrations of total phenolics and condensed tannins have also been observed in warm temperate conifers by King et al. (1997), Entry et al. (1998), Gebauer et al. (1998) and Runion et al. (1999), as well as in cotton by Booker (2000).

References
Booker, F.L.  2000.  Influence of carbon dioxide enrichment, ozone and nitrogen fertilization on cotton (Gossypium hirsutum L.) leaf and root composition.  Plant, Cell and Environment 23: 573-583.

Entry, J.A., Runion, G.B., Prior, S.A., Mitchell, R.J. and Rogers, H.H.  1998.  Influence of CO2 enrichment and nitrogen fertilization on tissue chemistry and carbon allocation in longleaf pine seedlings.  Plant and Soil 200: 3-11.

Gebauer, R.L., Strain, B.R. and Reynolds, J.F.  1998.  The effect of elevated CO2 and N availability on tissue concentrations and whole plant pools of carbon-based secondary compounds in loblolly pine.  Oecologia 113: 29-36.

King, J.S., Thomas, R.B. and Strain, B.R.  1997.  Morphology and tissue quality of seedling root systems of Pinus taeda and Pinus ponderosa as affected by varying CO2, temperature, and nitrogen.  Plant and Soil 195: 107-119.

Runion, G.B., Entry, J.A., Prior, S.A., Mitchell, R.J. and Rogers, H.H.  1999.  Tissue chemistry and carbon allocation in seedlings of Pinus palustris subjected to elevated atmospheric CO2 and water stress.  Tree Physiology 19: 329-335.