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 ºF. Rainfall has increased in some regions and decreased in others. And human actions have more than doubled inputs of biologically available nitrogen. Elevated atmospheric CO2 increases plant growth in many experiments, but most past experiments studied impacts of CO2 alone or in combination with one other factor. The results of the Carnegie-led experiment reveal new dimensions of ecosystem responses to global change. In the California grassland studied by this team, elevated CO2 suppresses plant growth in many treatments, especially treatments where growth at normal CO2 is fastest. Field noted, "When we look at impacts of realistic global changes on whole ecosystems, we see a broad range of responses. We do not yet know whether responses will be similar in other ecosystems, but our wide range of treatments helps open the door to understanding global-change impacts on ecosystems not yet studied."
Rebecca Shaw | EurekAlert!
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