What was done
Seedlings of twenty-nine well watered and fertilized white spruce (Picea glauca (Moench) Voss) genotypes were grown in 2.83-liter pots filled with a mixture of peat and vermiculite between 10 May and 23 September 2006 in glasshouse compartments maintained at either ambient (370 ppm) or elevated (740 ppm) atmospheric CO2 concentrations, after which plant performance was assessed by measuring final plant height, basal stem diameter and total biomass production, including roots.

What was learned
Mycroft et al. determined, in their words, that "depending upon genotype, the increase in biomass at elevated CO2 as a percentage of that at ambient CO2 ranged from 23% to 108%, while increases in height ranged from 4% to 48%," and that "in the case of stem diameter, the effect of elevated CO2 varied from a non-significant decrease of 6% to an increase of 32% depending upon genotype."

What it means
The four researchers write that "similar to previous studies (e.g. Bazzaz et al., 1995; Lindroth et al., 2001; Moya et al., 1998; Steinger et al., 1997; Volk and Korner, 2001)," they discovered "significant genotype x CO2 interactions for size-related traits." In addition, they note that their CO2-induced biomass increases (+23% to +108%) were of a similar range as those obtained by Mohan et al. (2004) for red maple (0% to +93%) and by Wang et al. (2000) for quaking aspen (-29% to +94%). These several observations suggest that highly-CO2-responsive genotypes of a wide variety of earth's plants -- from food crops to lumber crops -- could well be selected to take advantage of their genetic ability to optimize their growth in response to projected future increases in the air's CO2 content.

References
Bazzaz, F.A., Jasienski, M., Thomas, S.C. and Wayne, P. 1995. Microevolutionary responses in experimental populations of plants to CO2-enriched environments: Parallel results from two model systems. Proceedings of the National Academy of Sciences 92: 8161-8165.

Lindroth, R.L., Roth, S. and Nordheim, E.V. 2001. Genotypic variation in response of quaking aspen (Populus tremuloides) to atmospheric CO2 enrichment. Oecologia 126: 371-379.

Moya, T.B., Ziska, L.H., Namuco, O.S. and Olszyk, D. 1998. Growth dynamics and genotypic variation in tropical, field-grown paddy rice (Oryza sativa L.) in response to increasing carbon dioxide and temperature. Global Change Biology 4: 645-656.

Mohan, J.E., Clark, J.S. and Schlesinger, W.H. 2004. Genetic variation in germination, growth and survivorship of red maple in response to subambient through elevated atmospheric CO2. Global Change Biology 10: 233-247.

Steinger, T., Lavigne, C., Birrer, A., Groppe, K. and Schmid, B. 1997. Genetic variation in response to elevated CO2 in three grassland perennials - a field experiment with two competition regimes. Acta Oecologica 18: 263-268.

Volk, M. and Korner, C. 2001. Genotype x elevated CO2 interaction and allocation in calcareous grassland species. New Phytologist 151: 637-645.

Wang, X., Curtis, P.S., Pregitzer, K.S. and Zak, D.R. 2000. Genotypic variation in physiological and growth responses of Populus tremuloides to elevated atmospheric CO2 concentration. Tree Physiology 20: 1019-1028.