In the dead of night, even trees need their sleep.
Published in Frontiers in Plant Science, researchers from Finland, Austria, and Hungary have observed characteristics akin to sleep in wild-silver birch trees (Petula Bendula).
The study focused on two trees, one in Finland and the other in Austria. Overnight, the researchers used terrestrial laser scanning to observe changes in the branches and foliage. The tree in Finland was scanned 14 times, once about every hour, while the tree in Austria was scanned 77 times, about every 10 minutes.
“The resulting point clouds were used in creating a time series of branch movements,” the researchers wrote. “The movements were monitored from dusk until morning hours in order to avoid daytime wind effects.”
The researchers witnessed the trees vertically drooping their branches by as much as 10 cm. The movement patterns between the trees were similar, with the biggest movements occurring right around sunrise.
According to New Scientist, the effects are likely caused by turgor pressure, which is driven by internal plant water balance. Study author András Zlinsky told New Scientist the process is influenced by photosynthesis, which stops once the sun sets.
“There has been some studies on circadian rhythm in trees, mostly studying gene expression, but this latest research is a beautiful way to watch it happen in individual trees,” said Dartmouth College’s C. Robertson McClung to the media outlet. McClung was not involved in the study.
However, Zlinsky said it still unknown whether the dropping effect is influenced by circadian rhythm or light and water availability.
To understand further, the researchers said they need to combine terrestrial laser scanning with physiological measurements such as trunk diameter, water potential, and photosynthetic activity.
Terrestrial laser scanning still has “significant potential to provide additional geometrical information that can be correlated with the physiological measurements, and then possibly extended to cover whole plants in their natural environment and over wider areas,” the researchers wrote.
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