Reds and purples are caused by the presence of anthocyanins, produced after the chlorophyll is destroyed.
Yellows are due to the presence of xanthophylls, a yellow to gold pigment present in the leaf throughout the growing season but masked by the chlorophyll.
Oranges are the result of carotenes and xanthophylls.
Browns are the presence of tannins in the leaf.
Fall colors are influenced by several factors including the plant genetic makeup. Some plants naturally produce stunning fall colors: red maples, oaks, burning bushes, ashes.
Environmental conditions also affect fall colors. Cool, bright, sunny fall days increase photosynthesis production and thus sugar accumulation in the leaves. In fall, leaves develop an abscision layer at the base of the petiole (leaf stem), preventing sugars from being transported to the roots or stems for storage; the increased sugar concentration produces more intense colors.
The environmental conditions during the growing season can also cause differences in color intensity. Hot, dry weather usually reduces the chances of good fall color, as does excessive moisture in the early spring. Heavy autumn rainfalls also diminish falls colors. Frosts and freezes usually spell the end of the reds, yellows, and oranges.
See: Anthocyanin; Carotene; Chlorophyll, Tannin, Xanthophyll
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