What was done
Two-year-old birch (Betula pendula Roth) seedlings were exposed to ambient air of 350 ppm CO2 or air enriched to a CO2 concentration of 700 ppm under conditions of either ambient temperature or ambient temperature plus 3°C for one full growing season in the field in closed-top chambers at the Mekrijarvi Research Station of the University of Joensuu in eastern Finland.  Then, during the middle of the summer, when carbon-based secondary compounds of birch leaves are fairly stable, the authors picked several leaves from each tree and determined their condensed tannin concentrations, along with the concentrations of a number of other physiologically-important substances.

What was learned
The authors report that the concentration of total phenolics, condensed tannins and their derivatives significantly increased in the birch leaves produced in the CO2-enriched air, as has also been observed by Lavola and Julkunen-Titto (1994), Williams et al. (1994), Kinney et al. (1997), Bezemer and Jones (1998) and Kuokkanen et al. (2001).  In fact, the extra 350 ppm of CO2 nearly tripled condensed tannin concentrations in the ambient-temperature air, while it increased their concentrations in the elevated-temperature air by a factor in excess of 3.5.

What it means
These findings are extremely important, for as described in our Editorial of 7 Aug 2002, the presence of condensed tannins in leaves tends to greatly reduce methane emissions from ruminants that feed upon them, which in turn reduces the magnitude of the global warming impetus provided by this powerful greenhouse gas.

References
Bezemer, T.M. and Jones, T.H.  1998.  Plant-insect herbivore interactions in elevated atmospheric CO2, quantitative analyses and guild effects.  Oikos 82: 212-222.

Kinney, K.K., Lindroth, R.L., Jung, S.M. and Nordheim, E.V.  1997.  Effects of CO2 and NO3 availability on deciduous trees, phytochemistry and insect performance.  Ecology 78: 215-230.

Kuokkanen, K., Julkunen-Titto, R., Keinanen, M., Niemela, P. and Tahvanainen, J.  2001.  The effect of elevated CO2 and temperature on the secondary chemistry of Betula pendula seedlings.  Trees 15: 378-384.

Lavola, A. and Julkunen-Titto, R.  1994.  The effect of elevated carbon dioxide and fertilization on primary and secondary metabolites in birch, Betula pendula (Roth).  Oecologia 99: 315-321.

Williams, R.S., Lincoln, D.E. and Thomas, R.B.  1994.  Loblolly pine grown under elevated CO2 affects early instar pine sawfly performance.  Oecologia 98: 64-71.