Strong ecological but weak evolutionary effects of elevated CO₂ on a recombinant inbred population of Arabidopsis thaliana

• Increases in atmospheric CO₂ concentration have an impact on plant communities by influencing plant growth and morphology, species interactions, and ecosystem processes. These ecological effects may be accompanied by evolutionary change if elevated CO₂ (eCO₂) alters patterns of natural selection or expression of genetic variation. • Here, a statistically powerful quantitative genetic experiment and manipulations of CO₂ concentrations in a field setting were used to investigate how eCO₂ impacts patterns of selection on ecologically important traits in Arabidopsis thaliana; heritabilities, which influence the rate of response to selection; and genetic covariances between traits, which may constrain responses to selection. • CO₂ had strong phenotypic effects; plants grown in eCO₂ were taller and produced more biomass and fruits. Also, significant directional selection was observed on many traits and significant genetic variation was observed for all traits. However, no evolutionary effect of eCO₂ was detected; patterns of selection, heritabilities and genetic correlations corresponded closely in ambient and elevated CO₂ environments. • The data suggest that patterns of natural selection and the quantitative genetic parameters of this A. thaliana population are robust to increases in CO₂ concentration and that responses to eCO₂ will be primarily ecological.