Scientists have discovered that elevated atmospheric CO2 (carbon dioxide) can suppress plant growth when increases of this important greenhouse gas are combined with a broad suite of already-occurring environmental changes. According to Christopher Field, project leader and director of the new Department of Global Ecology of the Carnegie Institution of Washington, "We are now getting a much richer picture of ecosystem responses to global environmental changes, and the traditional view that elevated CO2 always stimulates plant growth simply isn't correct." The research is published in the December 6, 2002, issue of Science.

Many past studies of global-change impacts on plants and ecosystems have focused on responses to increases in atmospheric CO2. But realistically, global changes are much more than just elevated CO2. They include global warming, altered rainfall, and increases in biologically available nitrogen compounds produced during fossil-fuel combustion. These other global changes can have major impacts on plants and ecosystems. A new study by scientists at the Carnegie Institution of Washington, the Nature Conservancy, and Stanford University shows, for the first time, how these other global changes alter the response of a natural ecosystem to increased atmospheric CO2. According to lead author Rebecca Shaw, "In the third year of the experiment, plant growth increased in the plots treated with CO2 alone, as in many other experiments. It also increased in plots exposed to the other global changes--warming, increased precipitation, and fertilizing with nitrogen --alone or in combination. But, when we added carbon dioxide, the effect of the other treatments was suppressed. The elevated CO2 in this situation pushed the response back toward the initial conditions."

Over the last hundred years, the concentration of CO2 in the atmosphere has increased by more than 30%. The planet has warmed by about 1 F. Rainfall has increased in some r
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Contact: Rebecca Shaw
shaw@globalecology.stanford.edu
415-793 5921
Carnegie Institution
5-Dec-2002

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