Reference
Kelly, J.J., Bansal, A., Winkelman, J., Janus, L.R., Hell, S., Wencel, M., Belt, P., Kuehn, K.A., Rier, S.T. and Tuchman, N.C. 2010. Alteration of microbial communities colonizing leaf litter in a temperate woodland stream by growth of trees under conditions of elevated atmospheric CO2. Applied and Environmental Microbiology 76: 4950-4959.
What was done
For a period of four years (2000-2003), the authors grew twice-weekly-watered six-year-old quaking aspen (Populus tremuloides) clones, two-year-old white willow (Salix alba) clones, and two-year-old sugar maple (Acer saccharum) siblings out-of-doors at the University of Michigan Biological Station in northern Michigan (USA) in open-bottom root boxes enclosed within clear-plastic-wall open-top chambers continuously supplied throughout the growing season (from May until leaf senescence in November) with either ambient-CO2-air (360 ppm) or elevated-CO2-air (720 ppm). Then, at the conclusion of the four-year period, fallen leaves were collected, dried, and analyzed for simple phenolic and condensed tannin concentrations.
What was learned
From Kelly et al.'s tabular results, we calculate that the 360-ppm CO2 increase employed in their study boosted the simple phenolics concentrations of the aspen, maple and willow leaves by 16, 30 and 22%, respectively, while it boosted their condensed tannin concentrations by 60, 85 and 26%, respectively.
What it means
Because of the fact that both foliar phenolics and condensed tannins often enhance plant resistance to herbivore and pathogen attack -- see Phenolics and Tannins in our Subject Index -- plus the fact that ruminants browsing on foliage containing condensed tannins may have a tendency to expel less methane (an important greenhouse gas) to the atmosphere, the increased concentrations of these substances in the leaves of trees grown in CO2-enriched air bodes well for the health of the trees themselves and for people concerned about CO2- and methane-induced global warming.