Current availability of CO₂ levels in atmosphere is limiting to all, except 

Current availability of CO₂ levels in the atmosphere is limiting to all, except maize and sugarcane as they are C₄ plants. The C₄ plants show saturation at about 360 μlL^-1 while C3 responds to increased CO₂ concentration and saturation is seen only beyond 450 μlL^-1. Thus, current availability of CO₂ levels is limiting to the C₃ plants.