Previous Experimental Studies of Effects of Atmospheric Carbon Dioxide Concentration on Ecosystems Called into Question


A study just published in Nature, supported by the Canadian Government, the U. S. Department of Energy, and the U. S. National Science Foundation, raises important questions about past scientific research on the ecological effects of changes in atmospheric carbon dioxide (CO2) concentration. The result adds a significant wrinkle to, and may even call into question, decades worth of past research on effects of elevated CO2 concentration on plants and ecosystems. In the past, scientists typically exposed plants and ecosystems to present ambient (350 to 370 ppm) and elevated (550 to 750 ppm) CO2 levels, with the elevated level imposed instantaneously (a step-change increase). On the contrary, the CO2 increase in the Earth s actual atmosphere is occurring gradually (roughly 1-2 ppm per year), and it is possible that ecosystems will respond differently to a gradual CO2 increase than they do to a step-change increase. This possibility has finally been experimentally tested by John Klironomos (University of Guelph), Mike Allen (University of California, Riverside), Matthias Rillig (University of Montana), and their colleagues. These scientists discovered that a more gradual increase in CO2 concentration, carried out over 21 generations of a model plant-soil system, resulted in different effects than an instantaneous increase in CO2 concentration maintained over the same 21 generations. In particular, the step-change increase resulted in significant perturbations to microorganisms living in the soil, while the gradual increase did not.