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Trees may have a ‘heartbeat’ that is so slow we never noticed it

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From new scientist April 28 2018

TREES aren't as sedate as they seem. Many move their branches up and down at night. The findings hint that the plants are pumping water upwards, and have a slow "pulse".

"We've discovered that most trees have regular periodic changes in shape, synchronised across the whole plant and shorter than a day-night cycle, which imply periodic changes in water pressure," says András Zlinszky of Aarhus University in Denmark.

In a 2017 study, Zlinszky and his colleagues used lasers to scan 22 tree species in windless, lightless conditions to see if the trees' canopies changed shape at night.

In seven species, branches moved up and down by about a centimetre every 3 to 4 hours (Frontiers in Plant Sciencedoi.org/cnp8).

Now Zlinszky and his colleague Anders Barfod at Aarhus have a possible explanation: trees have a "heartbeat", and pump water up from their roots in pulses that last hours.

Previously it was thought that trees just wait for the evaporation of water from leaves to "pull" the water up. "No fluctuations with periods shorter than 24 hours are assumed or explained by current models," says Zlinszky.

Moving the water up in stages may save energy, says Zlinszky. "If water is pumped between sections, only the hydrostatic pressure of an individual section would need to be overcome by transport, not the full pressure resulting from the height of the tree."

It isn't clear how a tree might pump water upwards. Zlinszky and Barfod suggest that the trunk might gently squeeze the water, pushing it up through the xylem: a column of dead cells through which most water moves up the trunk (Plant Signaling and Behaviordoi.org/cnp9).

They say this is supported by studies showing that tree trunks can shrink at night by 0.05 millimetres.

"We suggest a so-far-unknown pumping mechanism," says Barfod.

This article appeared in print under the headline "Trees have a hidden regular 'heartbeat'"

Andy Coghlan

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I wonder who pays for this type of study and why someone would fund it. It's fascinating information but why would someone fund a group of scientists to use lasers to measure trees at night?

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well an apple falling from a tree supposedly inspired the investigation of gravity.... 

‘Maybe sap going up a tree will inspire thoughts on anti-gravity.... :)

Edited by Lance
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