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A new research has suggested that plants sleep after a long day in the sun.
Most living organisms adapt their behaviour to the rhythm of day and night. Plants are no exception: Flowers open in the morning, some tree leaves close during the night.
How the research was done?
The team of researchers from Austria, Finland and Hungary measured the movement of fully grown trees using laser scanners.
Eetu Puttonen from Finnish Geospatial Research Institute said, the results show that the whole tree droops during night, which can be seen as position change in leaves and branches.
The changes are not too large, only up to 10 cm for trees with a height of about 5 metres, but they were systematic and well within the accuracy of our instruments.
To rule out effects of weather and location, the experiment was done twice with two different trees.
The first tree was surveyed in Finland and the other in Austria. Both tests were done close to solar equinox, under calm conditions with no wind or condensation.
The leaves and branches were shown to droop gradually, with the lowest position reached a couple of hours before sunrise. In the morning, the trees returned to their original position within a few hours.
However, it is not yet clear whether they were woken up by the sun or by their own internal rhythm.