Growth of five hybrid poplar genotypes exposed to interacting elevated CO2 and O3

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 (O-3), and their interactions are unknown. To study these effects, we exposed five different hybrid Populus clones to increased concentrations of CO2, O-3, and CO2 + O-3 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 O-3 decreased all three of these growth responses. Exposure impact differed among the different plant parts (leaf, stem, and roots) and among the crones. 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 O-3 treatment. The addition of CO2 to the O-3 exposure counteracted the negative impact of O-3 in all plant components except leaf mass (e.g., CO2 + O-3 plant mass equaled control plant mass) in all of the clones. But correspondingly, added O-3 negated increased growth from CO2. Genetic variation in response to atmospheric pollutants must be considered even in closely related genotypes found in Populus culture.