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This is a strategy used by plants to protect themselves from the cold, reducing their energy expenditure as much as possible. “When autumn arrives and the days start to get shorter, nature is signaling to the trees that the time has come to change some of their characteristics”, says biologist Gilberto Kerdauy, from USP.
With less sunlight, the first change is to stop producing chlorophyll, the substance responsible for absorbing carbon dioxide and transforming it into carbohydrates, used to generate energy for the plant. With the decrease of chlorophyll, the leaves of the trees become yellowish or reddish.
The plant then begins to produce a hormone called abscisic acid. It accumulates at the base of the leaf stem, the petiole, killing the cells in that region. The petiole ends up breaking and the leaf falls, no longer needing to be fed by the tree, which can then use this energy for its own heating.