Did you ever wonder how water gets to the top of trees? Defying physics, water rises even to the top of 300-foot redwoods by the draw of the atmosphere. Almost like sucking on a straw, the atmosphere pulls water upward from the soil, through the plants, where it is lost from leaves in the process known as transpiration.
The continuous flow of water from the soil to the atmosphere is essential for plant life. When water is unavailable in the soil, the plants lose more water than they gain, and they wilt. The tiny pores that allow leaves to lose water close to prevent cell damage. And the process of photosynthesis stops. With watering, some plants can recover.
At any given time, the water in plants is held under some level of tension. Water inside some desert plants is held at a tension in excess of minus 100 atmospheres! In other words, you’d need to apply pressure of more than 100 atmospheres to squeeze water out of their tissues.
Now, an international group of researchers has reported that in most plants, internal tension is usually close to the point where recovery from wilt is impossible. Drop the water availability and the plants—in this case trees—will cease to grow. This suggests that forests worldwide are vulnerable to future droughts that may accompany climate change.
Already, drought has been linked to the die-back of pinyon pine forests in New Mexico. Undoubtedly, some trees will be more vulnerable than others, but widespread tree death is another impact we can expect with the ongoing changes in our global climate.
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For more information, see Choat et al. (2012) in Nature, doi:10.1038/nature11688
Photo, taken on June 18, 2011, courtesy of Ralph Daily via Flickr.
Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.