Deciduous trees allow their leaves to fall to avoid the cost of preparing them for winter. But changing foliage would be too costly if the trees were losing all their valuable nutrients, which they had to extract from the soil with great difficulty. At the beginning, the trees process the leaves, dismantling the cells and the photosynthesis apparatus from the inside in order to regain the spent nitrogen and phosphorus, keeping it in the branches until the next spring. This is very difficult to do, because during processing, chlorophyll molecules continue to absorb solar energy. But photosynthesis no longer occurs and they begin to transfer energy to oxygen molecules, which is currently not used. These molecules wreak havoc by damaging parts of the leaf that collect and transport nutrients back to the tree. To minimize this damaging effect, the leaves break down their chlorophyll into less dangerous molecules that are most often clear or sometimes yellow.
After the bright green molecules disappear, the yellow and orange pigments that were in the leaf from the very beginning turn the leaves yellow and orange, respectively. Some trees choose a safer defense against the damaging effects of chlorophyll. When leaf processing begins, trees produce special pigments to shield chlorophyll from sunlight. These pigments are most often red or purple. The leaves of trees that use them in autumn turn red. Exquisite yellow and red robes allow trees to regain up to 50% of phosphorus and nitrogen from old leaves, which will help grow green in spring. Trees are the most beautiful recycling factories in the world.