Researchers use laser scanners to study the day-night rhythm of trees

May 17, 2016, Vienna University of Technology
Trees have their own day-night rhythm too

Most living organisms adapt their behavior to the rhythm of day and night. Plants are no exception: flowers open in the morning, some tree leaves close during the night. Researchers have been studying the day and night cycle in plants for a long time: Linnaeus observed that flowers in a dark cellar continued to open and close, and Darwin recorded the overnight movement of plant leaves and stalks and called it "sleep". But even to this day, such studies have only been done with small plants grown in pots, and nobody knew whether trees sleep as well. Now, a team of researchers from Austria, Finland and Hungary measured the sleep movement of fully grown trees using a time series of laser scanning point clouds consisting of millions of points each.

Trees droop their branches at night

"Our results show that the whole tree droops during night which can be seen as position change in leaves and branches", says Eetu Puttonen (Finnish Geospatial Research Institute), "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."

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. It is not yet clear whether they were "woken up" by the sun or by their own internal rhythm.

"On molecular level, the scientific field of chronobiology is well developed, and especially the genetic background of the daily periodicity of plants has been studied extensively", explains András Zlinszky (Centre for Ecological Research, Hungarian Academy of Sciences). "Plant movement is always closely connected with the water balance of individual cells, which is affected by the availability of light through photosynthesis. 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, plant disturbance is minimal. The scanners use infrared light, which is reflected by the leaves. Individual points on a plant are only illuminated for fractions of a second. With this technique, a full-sized tree can be automatically mapped within minutes with sub-centimeter resolution.

"We believe that laser scanning point clouds will allow us to develop a deeper understanding ofplant sleep patterns and to extend our measurement scope from individual plants to larger areas, like orchards or forest plots," says Norbert Pfeifer (TU Wien).

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

Explore further: MRI imaging moves from hospitals to forests to help sick trees

More information: Eetu Puttonen et al. Quantification of Overnight Movement of Birch (Betula pendula) Branches and Foliage with Short Interval Terrestrial Laser Scanning, Frontiers in Plant Science (2016). DOI: 10.3389/fpls.2016.00222

Related Stories

Bringing nitrogen out to pasture

April 20, 2016

Cows in Brazil might start bellowing "leguuume" rather than "moo." That's because Jose Dubeux Jr. wants to plant more legume trees in cow pastures.

Trees trade carbon among each other, study reports

April 14, 2016

Forest trees use carbon not only for themselves; they also trade large quantities of it with their neighbours. Botanists from the University of Basel report this in the journal Science. The extensive carbon trade among trees ...

Treetop leaves of tall trees store extra water

November 2, 2015

A research team led by Associate Professor Ishii Roaki and Doctoral Student Azuma Wakana from the Kobe University Graduate School of Agricultural Science has discovered that the water storage tissue that they recently found ...

Can trees really change sex?

November 5, 2015

The revelation that the UK's oldest tree is showing signs of switching sex has sparked much excitement in the world of horticultural science. The Fortingall yew (main image) in Perthshire, Scotland, having apparently spent ...

Recommended for you

Study finds key to plant growth control mechanism

July 20, 2018

A Purdue University study has mapped a complex series of pathways that control the shape of plant cells. The findings are an important step toward customizing how plants grow to suit particular agronomic needs and improving ...

Mixed mRNA tails act like a shield to delay its shortening

July 20, 2018

Cells curb the amount of specific proteins at any desired time via the control of mRNA degradation. As mRNA nucleotides tail plays a role in this process, biologists at the Center for RNA Research, within the Institute for ...

Fruit fly species can learn each other's dialects

July 19, 2018

Fruit flies from different species can warn each other when parasitic wasps are near. But according to a new study led by Balint Z. Kacsoh of Geisel School of Medicine at Dartmouth, published July 19th in PLOS Genetics, they ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.