What’s puzzling is that anthocyanins are actually newly minted, made in the leaves at the same time as the tree is preparing to drop them. They belong to a class of sugar-based chemical compounds also known as flavonoids.
This unmasking explains the autumn colours of yellow and orange, but not the brilliant reds and purples of trees such as the maple or sumac.Ĭ The source of the red is widely known: it is created by anthocyanins, water-soluble plant pigments reflecting the red to blue range of the visible spectrum. As chlorophyll is depleted, other colours that have been dominated by it throughout the summer begin to be revealed. But before letting its leaves go, the tree dismantles their chlorophyll molecules and ships their valuable nitrogen back into the twigs. So rather than maintaining the now redundant leaves throughout the winter, the tree saves its precious resources and discards them. For many trees – evergreen conifers being an exception – the best strategy is to abandon photosynthesis* until the spring. As fall approaches in the northern hemisphere, the amount of solar energy available declines considerably.
SUNLIGHT THROUGH AUTUMN TREES FULL
The colours are magnificent, but the question of exactly why some trees turn yellow or orange, and others red or purple, is something which has long puzzled scientists.ī Summer leaves are green because they are full of chlorophyll, the molecule that captures sunlight converts that energy into new building materials for the tree.
SUNLIGHT THROUGH AUTUMN TREES LICENSE
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