Not all trees sleep the same - High temporal resolution terrestrial laser scanning shows differences in nocturnal plant movement

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Circadian leaf movements are widely known in plants, but nocturnal movement of tree
branches were only recently discovered by using terrestrial laser scanning (TLS), a high
resolution three-dimensional surveying technique. TLS uses a pulsed laser emitted in a
regular scan pattern for rapid measurement of distances to the targets, thus producing
three dimensional point cloud models of sub-centimeter resolution and accuracy in a few
minutes. Here, we aimto gain an overview of the variability of circadianmovement of small
trees across different taxonomic groups, growth forms and leaf anatomies. We surveyed
a series of 18 full scans over a 12-h night period to measure nocturnal changes in shape
simultaneously for an experimental setup of 22 plants representing different species.
Resulting point clouds were evaluated by comparing changes in height percentiles of
laser scanning points belonging to the canopy. Changes in crown shape were observed
for all studied trees, but clearly distinguishable sleep movements are apparently rare.
Ambient light conditions were continuously dark between sunset (7:30 p.m.) and sunrise
(6:00 a.m.), but most changes in movement direction occurred during this period, thus
most of the recorded changes in crown shape were probably not controlled by ambient
light. The highest movement amplitudes, for periodic circadian movement around 2 cm
were observed for Aesculus and Acer, compared to non-periodic continuous change in
shape of 5 cm for Gleditschia and 2 cm for Fargesia. In several species we detected
2–4 h cycles of minor crown movement of 0.5–1 cm, which is close to the limit of our
measurement accuracy. We present a conceptual framework for interpreting observed
changes as a combination of circadian rhythm with a period close to 12 h, short-term
oscillation repeated every 2–4 h, aperiodic continuous movement in one direction and
measurement noise which we assume to be random. Observed movement patterns
are interpreted within this framework, and connections with morphology and taxonomy
are proposed. We confirm the existence of overnight “sleep” movement for some trees,
but conclude that circadian movement is a variable phenomenon in plants, probably
controlled by a complex combination of anatomical, physiological, and morphological
factors.
Original languageEnglish
JournalFrontiers in Plant Science
Volume8
Pages (from-to)1
Number of pages25
ISSN1664-462X
DOIs
StatePublished - 20 Oct 2017

    Research areas

  • circadian plant movement, laser scanning, tree canopy movement, 3-dimensional modelling, Tree physiology, turgor, chronobiology

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