Growth Response to Very High CO2 Concentrations

Summary

Plants grown in elevated CO2 environments typically exhibit increased rates of photosynthesis and biomass production. Most of the studies that have established this fact have historically utilized CO2 concentration increases on the order of 300 to 600 ppm. So what happens if the air's CO2 content is super-enriched, to a concentration on the order of 10,000 ppm? Is the effect of the extra CO2 still positive?

................Finally, in an important field study, Fernandez et al. (1998) investigated the effects of even higher CO2 concentrations (some as great as 35,000 ppm) on an herb and a tree growing in the vicinity of natural CO2 springs in Venezuela. These high CO2 concentrations stimulated the photosynthetic rates of both plants in all seasons of the year. In the dry season, this effect was particularly important; for plants exposed to elevated CO2 continued to maintain positive net photosynthetic rates, while those exposed to ambient air a few tens of meters away exhibited negative rates that, if prolonged, would be expected to lead to their eventual demise. The authors noted their work provides "a positive answer to the question of whether increases in carbon assimilation will be sustained throughout the growing season and over multiple seasons." It also demonstrated that high atmospheric CO2 concentrations, even as much as 100 times greater than the current global mean, were not detrimental to the plants investigated. Indeed, they helped them.................