Related to but distinct from this question due to the concentrations involved.
While small carbon dioxide concentration increases can positively impact plant growth under some circumstances and at the same time negatively affect it under other circumstances, these changes are relatively small (doubling CO2 from 0.04% to 0.08%).
Is there any research on plants grown at extremely high (>1%) carbon dioxide concentrations in the air, assuming Earth atomspheric pressure? For the purpose of this question, assume that the plants are supplied with pH modifiers such as limestone in the soil to prevent soil acidification.