Why do tree leaves turn color in the fall?
Tree leaves assume fall colors due to the presence of carotenoids, which are pigments in the photosynthesizing cells. (Photosynthesis is the process by which green plants use the energy of the sunlight to convert water and carbon dioxide into carbohydrates and oxygen.) Carotenoids are present in the leaves year-round. However, during the growing season their colors are masked by another pigment present in photosynthesizing cells—green chlorophyll. Toward the end of summer, when chlorophyll production ceases, the colors of the carotenoids (such as yellow, orange, red, or purple) become visible. Listed below are the autumn leaf colors of some common trees.
