Effects of low atmospheric CO2 on plants: more than a thing of the past

In recent geological time, atmospheric CO2 concentrations were 25-50% below the current level. Photosynthetic productivity of C-3 plants is substantia lly reduced at these low CO2 levels, particularly at higher temperatures an d during stress. Acclimation of photosynthesis to reduced CO2 levels might compensate for some of this inhibition, but plants have a limited capacity to modulate Rubisco and other photosynthetic proteins following CO2 reducti on. Because of this, low CO2 probably acted as a significant evolutionary a gent, selecting plants adapted to CO2 deficiency. Adaptations to low CO2 mi ght still exist in plants and might constrain responses to a rising CO2 con centration.