Behavior of plants in elevated CO2 environments are usually used to estimate how plants will respond to gradually increasing concentrations of atmospheric CO2 that presently are occurring. Klironomos et al. (2005) find, however, that just plopping plants into a high CO2 environment may not be the most accurate way to evaluate responses to more gradual increases. They found that fungal species richness was decreased when a fungi community was exposed to an abrupt increase in CO2 but that gradual increases did not result in significant decreased fungal diversity. While they caution against extrapolating such results to more complex plant communities, they call for more research to better understand whether experiments that instantaneously double CO2 will give accurate information about plant behavior for plants experiencing a doubling by gradual increases.
Reference
Klironomos, J.N., M.F. Allen, M.C. Rillig, J. Piotrowski, S. Makvandi-Nejad, B.E. Wolfe, and J.R. Powell, 2005: Abrupt rise in atmospheric CO2 overestimates community response in a model plant-soil system. Nature, 433, 621-624.