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Diel changes in leaf growth activity of chrysanthemums in response to light
intensity and abrupt changes in the onset of day
Katrine Kjær and Carl Otto Ottosen
Department of Horticulture
Aarhus University
Kirstinebjergvej 10
5792 Aarslev
Denmark
[email protected]
Richard Poire and Achim Walter
Institut of chemistry and geosphere
Jülich Forschungszentrum
Germany,
Keywords: leaf growth, light fluctuations, photosynthesis, carbohydrate dynamics
Abstract
In a new energy-saving strategy for climate control in greenhouses, the use of
additional light is controlled in relation to the weather forecast and the energy
prices of the coming day. The light is only turned on when needed and only when
the energy prices are low. This often result in long days (LD) with low light
followed by extended nights and short days (SD) with high light.
To understand how plants respond to such changes, Chrysanthemums were
grown in climate chamber under LD conditions with fluctuating light (18 h light,
6 h dark). After three days, the night was extended to 12 h followed by SD (12 h)
with constant high light (1000 µmol m-2 s-1). Non-invasive measurements of leaf
growth were monitored throughout the experiment, together with leaf
photosynthesis and carbohydrate turnover.
Chrysanthemums had maximum leaf growth activity in the beginning of the day.
Furthermore, leaf growth activity and photosynthesis fluctuated in relation to
the fluctuating light, showing that chrysanthemums are highly responsive to
dynamic changes in light.
When the night was extended, the plants maintained their diel pattern in leaf
growth, but when the high light was turned on, leaf growth activity declined to
zero, although the photosynthesis rate and carbohydrate turnover increased
normally. After 24 h, the leaf growth pattern started to show adaptive changes to
the 12 h day/12 h night conditions.
The results demonstrate that chrysanthemum plants have a diel pattern in
growth activity which is interrupted when the night is extended and followed by
high light. However, the changes does not influence significantly on plant
photosynthesis and carbohydrate turnover. The results indicate that day-to-day
changes in night length may increase the production time of horticultural crops.
However, this needs to be evaluated in relation to the energy savings of the
climate strategy.