Egli and Korner (1997) rooted eight beech saplings directly into calcareous or acidic soils in open-top chambers and exposed them to atmospheric CO2 concentrations of either 370 or 570 ppm.  Over the first year of their study, the saplings growing on calcareous soil in CO2-enriched air exhibited a 9% increase in stem diameter; and they speculated that this initial small difference may ultimately "cumulate to higher 'final' tree biomass through compounding interest."

And they were right!  At the end of three years of differential CO2 exposure, the trees in the CO2-enriched chambers were experiencing net ecosystem carbon exchange rates that were 58% greater than the rates of the trees in the ambient CO2 chambers, regardless of soil type; while the stem dry mass of the CO2-enriched trees was increased by about 13% over that observed in the ambient-air chambers (Maurer et al., 1999).

In a similar but much shorter experiment, Dyckmans et al. (2000) grew three-year-old seedlings of beech for six weeks in controlled environment chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm, finding that the doubling of the air's CO2 content increased seedling carbon uptake by 63%.  They also noted that the majority of the assimilated carbon was allocated to the early development of leaves, which would clearly be expected to subsequently lead to greater absolute amounts of photosynthetic carbon fixation.

In the two-year study of Grams et al. (1999), beech seedlings grown at ambient CO2 concentrations displayed large reductions in photosynthetic rates when simultaneously exposed to twice-ambient levels of ozone.  However, at twice-ambient CO2 concentrations, twice-ambient ozone concentrations had no negative effects on the trees' photosynthetic rates.  Thus, atmospheric CO2 enrichment completely ameliorated the negative effects of ozone on photosynthesis in this species.

Similarly, Polle et al. (1997) reported that beech seedlings grown at 700 ppm CO2 for two years displayed significantly reduced activities of catalase and superoxide dismutase, which are antioxidative enzymes responsible for detoxifying highly reactive oxygenated compounds within cells.  Their data imply that CO2-enriched atmospheres are conducive to less oxidative stress and, therefore, less production of harmful oxygenated compounds than typically occurs in ambient air.  Consequently, the seedlings growing in the CO2-enriched air were likely able to remobilize a portion of some of their valuable raw materials away from the production of detoxifying enzymes and reinvest them into other processes required for facilitating optimal plant development and growth.

With respect to this concept of resource optimization, Duquesnay et al. (1998) studied the relative amounts of ¹²C and ¹³C in tree rings of beech growing for the past century in northeastern France and determined that the intrinsic water-use efficiency of the trees had increased by approximately 33% over that time period, no doubt in response to the concomitant rise in the air's CO2 concentration over the last 100 years.

In conclusion, as the CO2 content of the air increases, beech trees will likely display enhanced rates of photosynthesis and decreased damage resulting from oxidative stress.  Together, these phenomena should allow greater optimization of raw materials within beech, allowing them to produce greater amounts of biomass ever more efficiently as the atmospheric CO2 concentration increases.

References
Duquesnay, A., Breda, N., Stievenard, M. and Dupouey, J.L.  1998.  Changes of tree-ring δ¹³C and water-use efficiency of beech (Fagus sylvatica L.) in north-eastern France during the past century.  Plant, Cell and Environment 21: 565-572.

Dyckmans, J., Flessa, H., Polle, A. and Beese, F.  2000.  The effect of elevated [CO2] on uptake and allocation of ¹³C and ¹⁵N in beech (Fagus sylvatica L.) during leafing.  Plant Biology 2: 113-120.

Egli, P. and Korner, C.  1997.  Growth responses to elevated CO2 and soil quality in beech-spruce model ecosystems.  Acta Oecologica 18: 343-349.

Grams, T.E.E, Anegg, S., Haberle, K.-H., Langebartels, C. and Matyssek, R.  1999.  Interactions of chronic exposure to elevated CO2 and O3 levels in the photosynthetic light and dark reactions of European beech (Fagus sylvatica).  New Phytologist 144: 95-107.

Maurer, S., Egli, P., Spinnler, D. and Korner, C.  1999.  Carbon and water fluxes in beech-spruce model ecosystems in response to long-term exposure to atmospheric CO2 enrichment and increased nitrogen deposition.  Functional Ecology 13: 748-755.

Polle, A., Eiblmeier, M., Sheppard, L. and Murray, M.  1997.  Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under range of nutrient regimes.  Plant, Cell and Environment 20: 1317-1321.