Why fall leaves in autumn

Because autumn means the coming of winter, trees need to sleep in order to protect themselves, and the dormant trees themselves need nutrients. In order to regulate their internal balance, many trees need to leave leaves, reduce the loss of water and nutrients, save energy, and then sprout again when the conditions are suitable; And some pine and cypress trees, because the leaves are like needle tips, the loss of water and nutrients is particularly small, so they can keep evergreen. Trees only take off the leaves of the whole body, to reduce the transpiration of water as far as possible, in order to survive the winter safely. Otherwise, it will be very difficult for the roots to absorb water, but the transpiration of leaves will continue as usual. Think about it, what else can wait for the trees to die? The petioles were originally grown on the branches. In autumn, with the decrease of temperature, several layers of thin-walled cells formed at the base of petiole. Because these cells are easy to separate from each other, they are called dissociation layers. After the separation layer is formed, if there is a slight breeze, it will break, and the leaves will fall down. Leaves are broad-leaved trees in temperate regions, which can reduce transpiration and prepare for safe winter. And it has a lot to do with abscisic acid in trees.