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News Article

Trees that move in the night


Study shows water pressure induced movement can occur in sub-circadian cycles

Whilst trees may appear to be the most sedentary of organisms, the study of short-term plant movement has existed since Darwin and discoveries are still being made today about the driving forces behind the many different types of movement displayed by plants. For instance; nastic movements are those evoked in response to a non-directional stimuli e.g. temperature and caused by changes in turgor -cell pressure- or growth. Conversely, tropic movements are a growth response to a directional stimulus. Picture a flower opening and closing compared to a seedling growing towards the light. Over a period of several hours numerous dynamic changes can occur within plants that result in this movement, many of them relying on changes in water pressure creating turgid or flaccid cells. These changes can occur even in the absence of environmental changes e.g. light which display similar dynamics. In trees the most notable form of movement is that of leaves however, more recently, branch movement has also been proven.

The occurrence of ‘sleep’ motion, which occurs as part of a 12hr circadian cycle in response to light, has previously been demonstrated in trees, most famously Legumes, whereby branches and leaves may droop overnight before returning to their original position by morning. These movements were attributed to changes in water pressure within the plant, varying in response to the stimuli of light.

But a study carried out by Danish and Hungarian researchers has shown that trees are also capable of smaller, more regular movement on the timescale of 2-6 hours. As the majority of tree movement is at such a slow speed as to be imperceptible to the human eye, the authors used high-resolution terrestrial scanning to visualise variation in the level of movement shown by 22 trees in their branches and leaves. The technique was originally designed for architectural purposes and allowed the researchers to detect changes as little as 1cm over the study period, outputting a sub-centimetre resolution point cloud model that records in three dimensions how the tree canopy has moved over time.

The results of the study showed large variation between species and different anatomies: Aesculu and Acer both demonstrated periodic circadian movement of 2cm whilst Gleditschia and Fargesia both showed continuous non-periodic change or 5 and 2cm respectively. Not all species showed what the authors termed ‘sleep’ motion whereby movement which returned back to the starting position was detected in line with a 12 hr cycle. Most interestingly, some species were shown to move distances of 1cm in 2-6 hour cycles, with Magnolia exhibiting the largest movements of this type. The movements displayed in this study were attributed to three different vertical movement types: sleep, drift and oscillation. These phenomena correspond to circadian, non-cyclic and short term cycles. 

The researchers go on to suggest a reason for these shorter cycles; Water pressure was already known to vary on the scale of day to night however the discovery that tree movement could be detected over the course of 2-6hrs led the authors to propose that water pressure acts an oscillating force rather than the constant stream it has previously been assumed to be. As remote monitoring of crops becomes an accepted part of future agriculture, a more accurate understanding of plant movement may allow scientists to better predict abnormal movement and therefore pre-empt stress or disease and allow early intervention.

 

To read the original articles, follow the citations below:

  • Zlinszky, A. and Barfod, A., 2018. Short interval overnight laser scanning suggest sub-circadian periodicity of tree turgor. Plant signaling & behavior, 13(2), p.e1439655. https://doi.org/10.1080/15592324.2018.1439655

  • Zlinszky, A., Molnár, B. and Barfod, A.S., 2017. Not All Trees Sleep the Same—High Temporal Resolution Terrestrial Laser Scanning Shows Differences in Nocturnal Plant Movement. Frontiers in plant science, 8, p.1814. https://doi.org/10.3389/fpls.2017.01814

 

To find over 1000 similar papers use the search string below in the Forest Science Database:

("turgor" OR "osmotic pressure" OR "circadian rhythm") AND ("tree*")

Article details

  • Author(s)
  • Ellen Baker
  • Date
  • 01 October 2018
  • Subject(s)
  • Forest trees