Scientists flush out root cause of how trees lift water

14 September 2008


Despite relying on trees to provide us with oxygen, lock away CO2, provide shade and even building materials and matchsticks we still didn't really know how trees manage to lift water, over a hundred metres, from their roots to the top of the canopy.  Now scientists writing in Nature have taken a leaf out of the contact lens manufacturer's book and used the same material from which soft contact lenses are made to create an artificial tree.

Canadian MapleCornell researchers Tobias Wheeler and Abraham Stroock found that the tiny pores present in the hydrogel were a good facsimile of what goes on in a leaf where water can ooze out from tiny channels running up the stem called xylem and evaporate.  Critically, air can't enter.  As a result the evaporation of water from the leaves puts the water in the stem under tension and because water molecules are naturally sticky due to a process called hydrogen bonding, when water evaporates from the leaves more water molecules are pulled up to replace them.

As a result some of this negative pressure is also transferred to the roots, enabling a plant to pull water in from the soil and up the stem.  This agrees with what biologists had long suspected might be going on but could never prove.  The Cornell team suggest that apart from solving a long-standing mystery their work could also hold the key to the production of artificial trees that could efficiently extract clean water from deep underground to provide drinking supplies.


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