The green coloration, caused by the pigment chlorophyll, is no longer in the leaf because it has been broken down as the leaf ages or in preparation for winter [].
The disappearance of green coloration (de-greening) is due to several factors:
Chlorophyll Breakdown: As autumn approaches, trees begin the process of senescence (aging). This process involves breaking down chlorophyll molecules into simpler compounds. This allows the tree to recover and store valuable nutrients, such as nitrogen and magnesium, from the leaves before they fall off .
Changing Pigments: The green of the chlorophyll usually masks other pigments already present in the leaf, such as yellow and orange carotenoids. Once the green fades, these other colors become visible.
New Pigment Production: In some trees, new red or purple pigments (anthocyanins) are produced in the autumn, leading to vibrant fall foliage colors