The Color of Survival

These blackberry leaves (Rubus species) displayed multiple colors this fall.

If conditions are favorable, fall gives us a brilliant display of yellow, orange, red and almost purple leaves. As green fades and other colors appear, leaves are also revealing what makes them tick. The pigments in their blades aren’t just for show. They’re workhorses, and their tasks are critical to a plant’s survival. 

The following sequence shows a leaf of highbush cranberry photographed from September into November. As the season progresses, the blade changes from green to orange-red to dark red, each phase produced by a different set of pigments, each set with a different purpose. The leaf was photographed in 2008.

September 20

The leaf is green from the pigment chlorophyll. Two nearly identical forms of chlorophyll, called chlorophyll a and chlorophyll b, absorb mostly red and blue light and reflect green. These pigments are vital for photosynthesis, the process that converts light energy into chemical energy in the form of glucose. 

October 11

As day length shortens and temperatures fall, chlorophyll production slows. As green fades, yellows, oranges and scarlet reds appear. These colors are from carotenoids, pigments that have been there all along but have been masked by chlorophyll. Carotenoids are accessory pigments in photosynthesis; they absorb blue and green light, expanding the wavelengths available to power this process.

 

October 19

As chlorophyll continues to be degraded, more carotenoids are visible. The leaf blade is distinctly pale green with larger areas of light red. This trend continues as the days pass.

 

October 27

Nearly all chlorophyll is gone and more carotenoids are revealed. At the same time, darker red pigments called anthocyanins begin to form. These pigments need sugars to develop, so their deep red to purple hues are muted when fall months are cloudy and rainy and photosynthesis is limited. Some plant species produce only small amounts of anthocyanins. Highbush cranberry, dogwoods, red oak, red maple and sumac are among those that produce higher amounts.

November 1

Abundant anthocyanins now mask the carotenoids. Anthocyanins absorb yellow, green and ultraviolet light but are not involved in photosynthesis. At one time they were considered a useless waste of a plant's energy. Now, though, they're thought to block excess light energy from damaging leaf tissues, similar to sunscreen. Anthocyanins can also form in other stressful conditions, such as drought, high salinity, and nutrient deficiency.

Chlorophyll, carotenoids and anthocyanins may be present in other parts of plants, too. Flowers, fruits, stems and roots -- carrots, for example -- bear many kinds of pigments, and their roles in those organs may be different from those in leaves. The color of survival is complex. 

Learn more about leaf pigments and photosynthesis:

Absorption of light. LibreTexts Biology. 

Leaf Pigments. Harvard Forest.

When and why leaves change color. Minnesota DNR.