( Sciences. Fung is director of the Berke...)Deep-rooted plants have much greater impact on climate than experts thought

The researchers incorporated these new details into the most widely accepted model of global climate, and found that it accounts for a previously observed but unexplained dip in Amazonian temperature during the dry season.

"Evapotranspiration stays higher than previously expected during the prolonged dry season because of this private reserve of water banked during the wet season by the tap roots," said Dawson. "Just as perspiration cools us off, increased transpiration by trees in June and July explains the drop in temperature in the Amazon."

This effect changes the way the atmosphere heats and cools, and will change the way rain is distributed, he noted. Depending on the extent to which trees elsewhere in the world, especially in Africa and other tropical and extratropical areas, redistribute water in the soil, the impact on global climate could be significant.

"The impact on transpiration is greatest in the Amazon and Congo forests, but our model also shows an impact in the United States and other places that have dry and wet periods," Lee said.

Trees have long been known to lift water from the soil to great heights using a principle called hydraulic lift, with energy supplied by evaporation of water from leaf openings called stomata. Twenty years ago, however, some small plants were found to do more than lift water from the soil to the leaves - they also lifted deep water with their tap root and deposited it in shallow soil for use at a later time, and reversed the process during the rainy season to push water into storage deep underground. Dawson discovered in 1990 that trees do this, too, and to date, so-called hydraulic redistribution has been found in some 60 separate deeply rooted plant spe
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Source:University of California - Berkeley