Trees Sleep Like Humans In Day-Night Cycles: Study

Trees go to sleep too, reveal scientists from Austria, Finland, and Hungary. They have used laser scans to examine the day-night cycle of trees, revealing that trees sleep too.

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

Keeping the effects of weather and location in mind, the team conducted their experiment twice with two different trees. The first was examined in Finland and the second in Austria, both under the same conditions: close to solar equinox and in a calm environment with no wind or condensation.

The team found that overnight, the leaves and branches drooped slowly and reached their nadir just a few hours before sunrise. After morning, they awoke and returned to their original stature in a few hours, even though it was not clear whether the "awakening" was due to sunlight or prompted by their internal clock.

"Plant movement is always closely connected with the water balance of individual cells, which is affected by the availability of light through photosynthesis," said András Zlinszky of the Hungarian Academy of Sciences and co-author of the study. "But changes in the shape of the plant are difficult to document even for small herbs as classical photography uses visible light that interferes with the sleep movement."

With a laser scanner, the team could overcome this difficulty through minimal plant disturbance as it employed infrared light, which is reflected by the leaves. It enabled the team to map full-sized trees in just a few minutes at a high resolution.

"The next step will be collecting tree point clouds repeatedly and comparing the results to water use measurements during day and night," Puttonen said. "This will give us a better understanding of the trees' daily tree water use and their influence on the local or regional climate."

The findings were published in Feb. 29, 2016 issue of the journal Frontiers in Plant Science.