In this study, we tested the hypothesis that elevated [CO2] shortens the cell cycle in meristems of Dactylis glomerata, more in a Portuguese population (38°53′N) than in a Swedish population (63°09′N). In the shoot meristem, the cell cycle shortened to about the same extent (∼ 26%) in both populations exposed to the elevated [CO2] treatment. In the root meristem, the cell cycle shortened by 17% in the Portuguese and by 8% in the Swedish population. However, the proportion of rapidly cycling cells increased in the Portuguese much more than in the Swedish population in both meristems. In the root meristem, there was a 1.86-fold increase in the Portuguese compared with a 1.31-fold increase in the Swedish. In the shoot meristem, the increases were 1.5–3-fold for the Portuguese and 1.2-fold for the Swedish. The data are consistent in showing that a major response to the elevated [CO2] treatment was an increase in the proportion of cells that were cycling and that this was more marked for the Portuguese population. A more general response to the elevated [CO2] treatment was a shortening of the cell cycle regardless of population.