Trees Do Slumber, New Study Shows

For decades, scientist observed some physical changes in plant that corresponds to sleep. Some flowers close at night, and blooms majestically at day. Other small plants exhibit similar behavior in their leaves and stalk. Now, a first-of-its-kind study revealed that large trees may also adapt their behavior in the rhythm of day and night.

The study, published in the journal Frontiers in Plant Science, suggests that trees droop during the night, which researchers believed to be their sleeping position.

For the study, researchers scanned two silver birch (Petula Bendula) geographically separated in Finland and in Austria using terrestrial laser scanning (TLS). The experiment was conducted at the same time of the year and in similar outdoor conditions.

Researchers then analyzed 14 (Finland) and 77 (Austria) individual laser scans taken between sunset and sunrise. They found out from the resulting point clouds that both trees gradually droop throughout the night, reaching its lowest position a couple of hour before sunrise. The trees both came back to their original height within a few hours in the morning.

"Our results show that the whole tree droops during night which can be seen as position change in leaves and branches", said Eetu Puttonen of Finnish Geospatial Research Institute and lead author of the study, in a statement. "The changes are not too large, only up to 10 cm for trees with a height of about 5 meters, but they were systematic and well within the accuracy of our instruments."

In a report from New Scientist, András Zlinszky of the Centre for Ecological Research believes that the drooping effect is more likely to be caused by the loss of internal water pressure within the plant cell, a phenomena known as turgor pressure.

"It means branches and leaf stems are less rigid, and more prone to drooping under their own weight," Zlinsky explained.

Turgor pressure is somewhat affected by photosynthesis, a process which plants utilize sunlight to create sugar from carbon dioxide and water. No sunlight can be used during the night time.