Friday, January 13, 2006
BERKELEY – Trees, particularly those with deep roots, contribute to the Earth's climate much more than scientists thought, according to a new study by biologists and climatologists from the University of California, Berkeley.
While scientists studying global climate change recognize the importance of vegetation in removing carbon dioxide from the atmosphere and in local cooling through transpiration, they have assumed a simple model of plants sucking water out of the soil and spewing water vapor into the atmosphere.
The new study in the Amazonian forest shows that trees use water in a much more complex way: The tap roots transfer rainwater from the surface to reservoirs deep underground and redistribute water upwards after the rains to keep the top layers moist, thereby accentuating both carbon uptake and localized atmospheric cooling during dry periods.
The researchers estimate this effect increases photosynthesis and the evaporation of water from plants, called transpiration, by 40 percent in the dry season, when photosynthesis otherwise would be limited.
"This shifting of water by roots has a physiological effect on the plants, letting them pull more carbon dioxide from the atmosphere as they conduct more photosynthesis," said co-author Todd Dawson, professor of integrative biology at UC Berkeley. "Because this has not been considered until now, people have likely underestimated the amount of carbon taken up by the Amazon and underestimated the impact of Amazonian deforestation on climate."
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