This paper investigates the possible contribution of Short Rotation Cultures (SRC) to carbon sequestration in both current and elevated atmospheric CO₂ concentrations ([CO₂]). A dense poplar plantation (1 × 1 m) was exposed to a [CO₂] of 550 ppm in Central Italy using the free-air CO₂ enrichment (FACE) technique. Three species of Populus were examined, namely P. alba L., P. nigra L. and P. × euramericana Dode (Guinier). Aboveground woody biomass of trees exposed to elevated [CO₂] for three growing seasons increased by 15 to 27%, depending on species. As a result, light-use efficiency increased. Aboveground biomass allocation was unaffected, and belowground biomass also increased under elevated [CO₂] conditions, by 22 to 38%. Populus nigra, with total biomass equal to 62.02 and 72.03 Mg ha⁻¹ in ambient and elevated [CO₂], respectively, was the most productive species, although its productivity was stimulated least by atmospheric CO₂ enrichment. There was greater depletion of inorganic nitrogen from the soil after three growing seasons in elevated [CO₂], but no effect of [CO₂] on stem wood density, which differed significantly only among species.