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Scientists have detected physical changes in trees during the night, hinting at the possibility that plants go through a day-night cycle just like us.
Most organic beings adapt their behavioral patterns to the rhythm of day and night. Such cycles have been observed in the botanical kingdom before, but experiments so far have been limited to small plants grown in pots. Anybody who has dealt extensively with gardening can attest that flowers continue to open and close in a circadian cycle, even if they’re put in a dark environment. It’s just now however ?that similar behaviour has been observed in fully grown trees in their natural environment.
A multinational team of researchers, backed by the Vienna University of Technology, monitored Birch trees with terrestrial laser scanning. Unlike photographic equipment, lasers are not dependent on light, and their infrared signals allow them to work under the cloak of darkness. Terrestrial laser scanners have been in wide use for the last ten years in engineering, particularly to monitor the structural movement of quarries and mines to determine their safety.
This equipment produces accurate 3D-point clouds, often down to millimeter resolution, providing highly accurate information about the structure and spatial properties of the target.Thanks to this technology, the scientists were able to determine that Birch trees droop their branches as much as 10 centimetres at night. Team member András Zlinszky of the Centre for Ecological Research in Tihany, Hungary, told New Scientist: “It was a very clear effect, and applied to the whole tree,” adding, “No one has observed this effect before at the scale of whole trees, and I was surprised by the extent of the changes.”
The team conducted two separate experiments, one in Finland and the other in Austria. Scans were made at the same time of the year and under similar meteorological conditions between sunset and sunrise, in order to avoid day-time wind.“We’re certain it’s not caused by another effect,” said another team member, Norbert Pfeifer of the Technical University of Vienna in Austria.
The data points to the drooping effect being caused by a loss of internal water pressure inside the cells of the tree, a phenomenon called ‘turgor pressure’. The branches and leaf stems become less rigid because of the pressure difference and thus bend under their own weight.Branches are angled higher throughout the day in order to create less shade for the leaves down below, allowing the tree to grab as much available sunlight as possible. This movement requires a lot of energy, and scientists speculate that the drooping could take place as a way to “rest” and regather strength for the next day.
The next step is to find if this behaviour is replicated in other species. “I’m confident it will apply to other trees,” said Zlinszky. If you want to go full Bruce Banner mode, you can find the original research article at the Frontiers in Plant Science site.