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How do trees prevent dehydration?

March 10, 2014

How do trees prevent dehydration?

At first glance, some of the potted saplings in Brett Wolfe’s shade house look dead. They’re not—at least for the moment

At first glance, some of the potted saplings in Brett Wolfe’s shade house look dead. They’re not—at least for the moment. One, a cuipo (Cavanillesia platanifolia) has gone six months without a drop of H2O. “All I have to do is water it again and it’ll come right back,” said Wolfe, tapping its still-living stem. The thirsty seedling is part of a study aimed at predicting how changes in drought frequency and severity—possible outcomes of climate change—will impact tropical forests.

Wolfe, a Ph.D. student at the University of Utah, is trying to untangle the various ways drought-tolerant trees endure extended dry spells. Strategies vary. Some use water they stored during the rainy season. Others shed their leaves, slowing or ceasing photosynthesis by entering a kind of tropical hibernation. The roots probably implement drought-survival tactics as well. These include shedding fine roots, shrinking root size, and producing a waxy barrier around them—all which reduce potential water loss to dried earth.

“All six species I’m working with are responding to drought in completely different ways,” said Wolfe, whose seedlings vary in terms of traits like wood density and deciduousness. They all share a common mission: avoid hydraulic failure and/or carbon starvation (which are both as fatal as they sound) until the rain returns.

“There is a really big push to figure out how drought kills trees,” said Wolfe. “We have to understand how trees are responding to drought in order to understand how they respond when droughts change. Once we figure that out, we can better predict which species are going to be able to survive.”

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