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Plant Science: Why Do Leaves Change Color?

The changing colors of autumn leaves invites reflection on the nature of life. The changing colors of autumn leaves invites reflection on the nature of life.


As the greenish hue of summer turns to yellow and the branches of trees and shrubs soon find themselves bare, you might see the skeletal remains of a leaf. It is intricate in design, knit in webs, and the veins of a leaf appear to remind us of their place among all other living things.

A leaf falls because plants are programmed to go through a seasonal senescence. No divine intervention, only plant hormones and environmental change. Life is mysterious and botanists are perplexed – how does a plant use hormones to induce itself to die?

This we know: the shortening of days and lengthening of nights plus fluctuations in temperature gradually prevent and shut down a leaf’s ability to photosynthesize. If a plant is unable to photosynthesize, it is no longer able to produce the energy needed to propel its existence. As this inevitable seasonal process continues, the level of chlorophyll within the leaf's chloroplast diminishes and its tissue weakens. The same hormone responsible for both phototropism and apical dominance, the hormone auxin, will also cease production.

The skeletal remains of leaves decompose, return to the earth, and fertilize their surroundings. Soon the reflective tone of autumn is replaced with the pregnant ecstasy of spring.

The leaf's delicate webbing of veins is used to slowly drain any useful elements to its root system and then is closed through an abscission layer at the base of the leaf. This is made possible due to the absence of auxin, which during the growing season keeps these arteries open. Soon after, the leaf drops in a beautiful spiral down to earth.

Plants of every kind will drop their leaves at some point, but they don't always do it at the same time nor all at once. Evergreens and needled-plants are no exception. They drop their needles and leaves throughout the course of a season instead of altogether, making their seasonal transition a little less noticeable.

As the chlorophyll in a leaf becomes less and less, other colors will soon show through. Depending on temperatures, leaf composition, light levels, and sugar production, chemical pigments in leaves called anthocyanins, tannins, and carotenoids will create the red, orange, yellow, and brown shades we know to decorate fall trees so well.

Walking through the trees in autumn is one of life's simple pleasures. But while the spectacular change of color is a charming process of nature, it is also a reminder of our shared life force.

Green spaces, in their constant cycle of renewal, likely give the illusion of ageless perpetuity. But a seasonal senescence, most grandly illustrated in autumn, is also part of a plant’s biological aging. It is when they pause, shed, and start anew, one season older, aging and wheeling towards the inevitability of death just like us.

But what Mother Nature leaves for death, she also gives new life. The skeletal remains of leaves decompose, return to the earth, and fertilize their surroundings. Soon the reflective tone of autumn is replaced with the pregnant ecstasy of spring.

Take this time to reflect and, most of all, appreciate fall…it’s really one of the most dramatic times of the year!


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The great artists have often used the change from summer to fall as fodder for creative expression.
Last modified on Thursday, 10 October 2013 19:21

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