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Do plants that lose their leaves (i.e., deciduous plants) do so because of external conditions (e.g., drought, cold), or because of an internal process?

Another way of looking at it: if you take a deciduous plant that loses its leaves during cold winters with long nights (e.g., Canada), and plant it in an environment where it is always warm and sunny (i.e., at the equator), would this plant continue to shed its leaves and re-grow them according to the seasons in Canada, or would it behave as an evergreen instead?

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  • $\begingroup$ I think lose of leaves depend upon both external condition and internal condition .By internal I mean cell death (Programmed Cell Death ). $\endgroup$ – user15346 Apr 15 '15 at 12:33
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    $\begingroup$ I edited the question to improve clarity. Please feel free to roll back. Nice question! +1 $\endgroup$ – AliceD Apr 15 '15 at 14:01
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The process of a deciduous plant losing its leaves seasonally is known as abscission. It occurs when a layer of cells known as the abscission zone elongate and weaken, causing the leaf to fall off. It is mediated mainly by the hormones auxin and ethylene.

The functional purpose of abscission is to remove leaves when they are no longer producing a net gain of biomass. Leaves decrease in productivity during drought, decreased day length, and when under the effect of herbivory.

In some species (according to the day-length source), "When the daylength exceeds a certain 'critical' duration, growth may be maintained continuously for at least 18 months under favourable tempera­ture conditions, e.g., in Liriodendron tulipifera, Robinia pseudacacia". So, to answer your final question, some deciduous species (but not all) may indeed retain their leaves if they are grown in favorable conditions. One reason why not all deciduous trees retain their leaves even in favorable conditions is that internal ageing can also induce abscission: "In such species, growth is determined primarily by the endogenous ageing process and is only modified by environmental factors, including daylength"

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  • $\begingroup$ So, to understand correctly, the plant produces the hormons because the growth is unsustainable. So my next question would be, why not all deciduous retain their leaves in favorable conditions? the answer stems from your answer or I make a new question? $\endgroup$ – chuse Apr 15 '15 at 16:02
  • $\begingroup$ You can edit your post to include your new question and I'll try to answer it $\endgroup$ – C_Z_ Apr 15 '15 at 16:06
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The shedding of leaves has more to do with the condition of the leaf itself. When leaves become inefficient and unable to produce food and growth regulators, a process of abscission starts.

Abscission a step in the planned senescence process within tree leaves. Senescence is a series of events that allow trees to conserve resources, prepare for a dormant period, and shed inefficient tissues. Senescence is not disruptive and not always caused by climatic factors. Senescence is a highly ordered and carefully controlled set of steps initiated in preparation for a resting period of a tree (winter).

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