Trees may ‘sleep’ at night

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There are trees that “weep” and trees that “quake,” trees that are “bitter,” “brittle,” “common” and “dynamite.”

But trees that sleep?It sounds strange.

Scientists from Austria, Finland and Hungary did the research using lasers to measure the overnight movements of birch trees.Their unexpected finding: During the hours of darkness, the trees appeared to relax, or droop, their branches at the tips by as much as 4 inches.

No one has observed this effect before at the scale of whole trees, and the extent of changes.

At the center of the research were two birches, one in Finland and one in Austria. Their canopies were scanned with lasers from sunset to sunrise at regular intervals, each over the course of a single night. The conditions in each location were the same: no rain, little wind and during the solar equinox so that the length of darkness was relatively equal.“The results obtained from the measurements showed it’s  similar temporal response.Close to sunrise, the branches were hanging lower than at the time of sunset.

The team offered two hypotheses for their findings: The drooping could be because of a loss of internal water pressure, called turgor pressure, causing the branches and leaf stems to lose their rigidity. Because turgor pressure results from photosynthesis — the use of sunlight to create sugar from carbon dioxide and water, which only happens during the day — the trees would appear to relax with the darkness.

The other explanation is that trees really are resting, following the same circadian rhythms of other flora and fauna. In the daylight, leaves and branches are angled upwards to catch more sun, but during the night, this positioning is no longer necessary.

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