A wide variety of hybrid poplar clones are being introduced for intensive culture biomass production, but the potential clonal or genotypic response to increasing tropospheric carbon dioxide (CO2), ozone (O3), and their interactions are unknown. To study these effects, we exposed five different hybrid Populus clones to increased concentrations of CO2, O3, and CO2 + O3 in open-top chambers for one growing season and determined growth responses. Exposure to elevated CO2 increased height growth, dry mass, and basal area; exposure to O3 decreased all three of these growth responses. Exposure impact differed among the different plant parts (leaf, stem, and roots) and among the clones. These differences were associated with different growth strategies or carbon allocation patterns inherent in the different clones. The fastest growing clones had the greatest response to O3 treatment. The addition of CO2 to the O3 exposure counteracted the negative impact of O3 in all plant components except leaf mass (e.g., CO2 + O3 plant mass equaled control plant mass) in all of the clones. But correspondingly, added O3 negated increased growth from CO2. Genetic variation in response to atmospheric pollutants must be considered even in closely related genotypes found in Populus culture.