Background
The growth rates of earth's plants are largely determined by the relative magnitudes of carbon gain via photosynthesis and carbon loss via respiration; and although much is known about the effects of atmospheric CO2 enrichment on the first of these phenomena, much less is known about its effects on the second.

What was done
In a study that broached both of these subjects, the authors measured rates of light-saturated net photosynthesis and dark respiration in current-year needles of sun-exposed (3rd whorl) and shaded (6th whorl) parts of the canopies of originally-ten-year-old Norway spruce (Picea abies) trees that were transplanted into native soil (that was given an initial fertilizer treatment) and grown for an additional eight years in the Beskydy Mountains of the Czech Republic within semi-open glass domes having adjustable windows, where the trees were exposed to either the ambient-air CO2 concentration (AC, which varied from 365 to 377 ppm over the course of the long-term experiment) or to an enriched-air CO2 concentration (EC, which was maintained at a steady value of 700 ppm).

What was learned
Based on the graphical representations of Lhotakova et al.'s findings, we calculate that at the end of the eight-year CO2 enrichment experiment there was a CO2-induced increase in light-saturated net photosynthesis of approximately 115% in the trees' sun-exposed needles and about 55% in their shaded needles; and we likewise calculate that there was an approximate 20% decrease in the mean dark respiration rate of the trees' sun-exposed needles and about 40% in their shaded needles.

What it means
In discussing their experimental results, the nine Czech scientists write that "the positive effect of EC on net CO2 assimilation rates, as we observed in juvenile Norway spruce trees in the present study, was also shown in other long-term studies on conifers," citing in this regard Maier et al. (2008), Kosvancova et al. (2009), Crous et al. (2008) and Logan et al. (2009). In addition, they say "it appears that forest trees, including conifers, suppress respiration rates under long-term CO2 enrichment," citing Zhou et al. (2007) and Gonzalez-Meler et al. (2009). And so it is that they therefore conclude that "the observed stimulation of light-saturated net photosynthesis simultaneously with suppressed dark respiration under EC may lead to higher biomass accumulation," as had earlier been observed and reported by Runion et al. (2006) for longleaf pine trees.

References
Crous, K.Y., Walters, M.B. and Ellsworth, D.S. 2008. Elevated CO2 concentration affects leaf photosynthesis-nitrogen relationships in Pinus taeda over nine years in FACE. Tree Physiology 28: 607-614.

Gonzalez-Meler, M.A., Blanc-Betes, E., Flower, C.E., Ward, J.K. and Gomez-Casanovas, N. 2009. Plastic and adaptive responses of plant respiration to changes in atmospheric CO2 concentration. Physiologia Plantarum 137: 473-484.

Kosvancova, M., Urban, O., Sprtova, M., Hrstka, M., Kalina, J., Tomaskova, I., Spunda, V. and Marek, M.V. 2009. Photosynthetic induction in broadleaved Fagus sylvatica and coniferous Picea abies cultivated under ambient and elevated CO2 concentrations. Plant Science 177: 123-130.

Logan, B.A., Combs, A., Myers, K., Kent, R., Stanley, L. and Tissue, D.T. 2009. Seasonal response of photosynthetic electron transport and energy dissipation in the eighth year of exposure to elevated atmospheric CO2 (FACE) in Pinus taeda (loblolly pine). Tree Physiology 29: 789-797.

Maier, C.A., Palmroth, S. and Ward, E. 2008. Short-term effects of fertilization on photosynthesis and leaf morphology of field-grown loblolly pine following long-term exposure to elevated CO2 concentration. Tree Physiology 28: 597-606.

Runion, G.B., Davis, M.A., Pritchard, S.G., Prior, S.A., Mitchell, R.J., Torbert, H.A., Rogers, H.H. and Dute, R.R. 2006. Effects of elevated atmospheric carbon dioxide on biomass and carbon accumulation in a model regenerating longleaf pine community. Journal of Environmental Quality 35: 1478-1486.

Zhou, Y.M., Han, S.J., Zhang, H.S., Xin, L.H. and Zheng, J.Q. 2007. Response of needle dark respiration of Pinus koraiensis and Pinus sylvestriformis to elevated CO2 concentrations for four growing seasons' exposure. Science in China Series D - Earth Sciences 50: 613-619.