Elevated atmospheric carbon dioxide concentration ([CO₂]) stimulates plant growth, but this enhancement varies considerably. It is still uncertain which plant traits are quantitatively related to the variation in plant growth. To identify the traits responsible, we developed a growth analysis model that included primary parameters associated with morphology, nitrogen (N) use, and leaf and root activities. We analyzed the vegetative growth of 44 ecotypes of Arabidopsis thaliana L. grown at ambient and elevated [CO₂] (800 μmol mol⁻¹). The 44 ecotypes were selected such that they were derived from various latitudes and altitudes. Relative growth rate (RGR) and its response to [CO₂] varied by 1.5- and 1.7-fold among ecotypes, respectively. The variation in RGR at both [CO₂]s showed a strong correlation with the variation in leaf N productivity (LNP; growth rate per leaf N),which was also strongly related to photosynthetic N use efficiency (PNUE). The variation in the response of RGR to [CO₂] also showed a strong correlation with the variation in the response of LNP to [CO₂]. Genomic analyses indicated that there was no phylogenetic constraint on inter-ecotype variation in the CO₂ response of RGR or LNP. We conclude that the significant variation in plant growth and its response to [CO₂] among ecotypes reflects the variation in N use for photosynthesis among ecotypes, and that the response of PNUE to CO₂ is an important target for predicting and/or breeding plants that have high growth rates at elevated [CO₂] (Oguchi et al. 2016 Oecologia, 180: 865-876).