Why do autumn leaves change color? - Stockdales

Why do autumn leaves change color?

Each year, leaves change colors and create beautiful scenery, but why and what exactly gives them their bright hues?

Numerous factors, including geography, growth habits, exposure to light, plant pigments, and weather conditions play important ro

les in this fascinating process. During the spring and summer, leaves are the principal site for the photosynthetic process that transforms carbon dioxide and water into the carbohydrates that fuel tree growth. This food-making process takes place in numerous cells containing chlorophyll, the pigment that gives leaves their green color.

As days shorten and temperatures cool in the autumn, the synthesis of new chlorophyll drops off, green color disappears, and the rate of photosynthesis declines. Trees become frugal and more efficient, pulling nutrients such as nitrogen and phosphorus into twigs and branches for winter storage, further enhancing the loss of chlorophyll.

Along with chlorophyll, leaves contain yellow or orange carotenoid, the same pigment that gives carrots their familiar color. Masked for much of the year by green chlorophyll, the carotenoids reveal themselves in autumn as yellow and golds. The vivid pink, red, and purple leaves are formed by reactions between various sugars and complex compounds called anthocyanins.

Fertile soil enhances the intensity of reds in leaves and the more light a leaf is exposed to, the more likely it is to turn red.  Weather conditions most favorable to brilliant color are warm, sunny days followed by cool nights with temperatures below 45 degrees but not to freezing levels. Freezing temperatures and heavy frost can kill the brilliance of autumn leaves by severely injuring leaves before pigment is fully developed.