The idea of an oak or a spruce tree taking a snooze seems a bit bizarre. But for the first time, scientists have observed physical changes in trees that correspond in some ways to sleep in humans and animals, or at least to our day-night rhythm.
Researchers from Austria, Finland and Hungary used laser scanners to scan two trees and scrutinize a cloud of millions of different points across their surface area. From that, they learned that trees actually move overnight, a phenomena that scientists dating back to Charles Darwin have observed in smaller plants.
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"Our results show that the whole tree droops during night which can be seen as position change in leaves and branches", Eetu Puttonen, a researcher from the Finnish Geospatial Research Institute, explained in a press release. "The changes are not too large, only up to 10 centimeters for trees with a height of about 5 meters, but they were systematic and well within the accuracy of our instruments."
To filter out effects from weather and location, the researchers studied one tree in Finland and another far away in Austria, under calm conditions with no wind. The leaves and branches drooped gradually, with the droopiest position achieved a couple of hours before sunrise. In the morning, the trees regained their original rigidity within a few hours.
But Another researcher, András Zlinszky of Hungary's Centre for Ecological Research, said that the drooping effect probably is caused by the loss of internal water pressure within the tree's cells, a phenomenon called turgor pressure.
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"It means branches and leaf stems are less rigid, and more prone to drooping under their own weight," Zlinsky told the British publication New Scientist.
Turgor pressure is influenced by photosynthesis, which stops once the sun goes down, Zlinsky explained.
The study was published recently in Frontiers in Plant Science.