Genotypic variation in response of quaking aspen (Populus tremuloides) to atmospheric CO2 enrichment

Enriched atmospheric CO2 alters the quantity and quality of plant productio n, but how such effects vary among plant genotypes is poorly known. We eval uated the independent and interactive effects of CO2 and nutrient availabil ity on growth, allocation and phytochemistry of six aspen (Populus tremuloi des Michx) genotypes. One-year-old trees, propagated from root cuttings, we re grown in CO2-controlled glasshouses for 64 days, then harvested. Foliage was analyzed for levels of water, nitrogen, stal ch, phenolic glycosides a nd condensed tannins. Of seven plant growth/allocation variables measured, four (biomass production, stem growth, relative growth rate and root:shoot ratio) exhibited marginally to highly significant CO2 x genotype interactio ns. CO2 enrichment stimulated growth of some genotypes more than others, an d this interaction was itself influenced by soil nutrient availability. In addition, enriched CO2 increased the magnitude of the among-genotype varian ce for four of the growth/allocation variables. Of six foliar chemical cons tituents analyzed, CO2-mediated responses of two (the phenolic glycoside tr emulacin and condensed tannins) varied among genotypes. Moreover, enriched CO2 increased the magnitude of among-genotype variance for four of the chem ical variables. Given the importance of these growth and chemical character istics to the biological fitness of aspen, this research suggests that proj ected atmospheric CO2 increases are likely to alter the genetic structures and evolutionary trajectories of aspen populations.