What was done
The authors grew quaking aspen (Populus tremuloides Michx.) from seed, and paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) from 2-year-old transplants in controlled environment greenhouses maintained at ambient (387 ppm) or elevated (696 ppm) CO2 concentrations and low or high light availability (half and full sunlight, respectively) until 31 days after mean bud break, at which time leaves of the trees were harvested and analyzed for a number of different phytochemicals, including condensed tannins.

What was learned
Under low light conditions, the CO2-enriched trees exhibited increases in leaf condensed tannin concentrations of approximately 15% (aspen), 37% (birch) and 74% (maple), while under high light conditions the corresponding increases in condensed tannins were approximately 175%, 125% and 91%.

What it means
These findings are extremely important, for as described in our Editorial of 7 Aug 2002, it has recently been demonstrated that condensed tannins found in leaves can greatly reduce methane emissions from ruminants such as sheep, cattle, antelope, bison, buffalo, camel, deer, giraffe, goat, llama, etc. that feed upon them, which thus reduces the global warming impetus provided by this powerful greenhouse gas.