[masklinn]

The primary limiting factor on plant growth is not generally CO2. You can know that by observing that CO2 is not really what fertilizers concern themselves with.

Water, nitrogen, and micronutrients, tend to be the big issues. Existing plants deal fairly well with around 200~250ppm CO2 because that's been the concentration for the last 20 million years.

[betwixthewires]

For individual ecosystems or individual plants, yes, the limiting factor is nitrogen fixing in the soil. For the global biosphere however, the limiting factor to the creation of biomass (via photosynthesis) is carbon dioxide availability.