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Plant Growth C02 Null*

Posted 12/6/2002 4:20 PM

Study finds more CO2 doesn't always spur plant growth

WASHINGTON (AP) — Global climate change is expected to include a rise in the carbon dioxide level in the atmosphere, and laboratory studies have suggested this will stimulate plants to grow more abundantly. But apparently that is not the whole story.

This happens because plants use carbon dioxide (CO2) to produce plant material. This has led to some suggetioins that while a world with more CO2 may be warmer, plant growth should increase.

Now, tew research in California has found that when other aspects of global climate change are added to the environment of plants, carbon dioxide actually may act as a drag on growth.

The study, appearing this week in the journal Science, mimicked the conditions expected to result from global warming on 128 plots of land in a California grassland. It found that the effects of carbon dioxide, which plants use to produce food, can be either good or bad, depending on other elements of the environment.

"Most studies in the past have just looked at a single element, such as an increase of CO2 or warming temperatures," said Rebecca Shaw, a Carnegie Institution of Washington researcher and first author of the study. "Our study looked at the effects of all the climate change elements" and in all possible combinations.

In the new study, the researchers artificially applied the four major climate change elements at the levels they are expected to achieve by the year 2150 if the current use of fossil fuels world wide is unchanged. These elements include:

atmospheric carbon dioxide, expected to double the current density.

temperature, expected to rise by a degree or more.

nitrogen, deposited in the soil when it is washed from the atmosphere by rain.

precipitation, expected to increase by 50% in some areas.

When carbon dioxide levels alone were increased, plant production increased about eight percent, she said.

"But when carbon dioxide was applied in combination with the other expected changes, we found that the CO2 actually reduced the stimulation that we saw when the other elements were used alone," she said.

For example, when enhanced temperature, nitrogen and water were applied to a plot, the production soared by 84%, she said. But when carbon dioxide was added to this mix, the production dropped by 40%. [There is more water but it is CO2 bound clusters larger than plant pores, like a baby offered a bushel of apples instead of applesauce--RB 021206]

She said the researchers are trying to understand why enriched carbon dioxide is a drag on production in some conditions.

Richard J. Norby, an environmental scientist at the Oak Ridge National Laboratory, said the Stanford study "is a surprise."

"We don't really understand the responses of the plants (in the study)," said Norby, who is doing similar research in his lab. "I think this challenges some of our assumptions about global climate change."

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