The Japanese maple, or Acer palmatum, is an ornamental tree with a unique and recognizable silhouette. The leaves are characteristic of all Acer species, but are in varying tones of red, orange or purple. Japanese maple produces its best color in full sun -- but raises the question of how the plant photosynthesizes without green leaves. Chlorophyll is an important component of photosynthesis and makes leaves green. Chlorophyll and light together make a process that absorbs carbon dioxide and water, which is turned into carbohydrates or plant energy. Red leaves would appear not to have chlorophyll, but it is contained in the leaf.
Colors in Leaves
Color is comprised of a variety of hues reflected through a prism of light. Tree leaves contain a variety of pigments that create those hues. They are chlorophyll, carotenoids and anthocyanins. Chlorophyll absorbs the red and blue tones in the light, leaving behind green, which is what we see. Carotenoids absorb blue and blue-green and anthocyanins absorb green, blue and blue-green. Carotenoids appear orange or yellow to our eyes, and anthocyanins look red or purple.
Photosynthesis cannot occur without sunlight and oxygen. The two combined form carbon dioxide which is processed by chlorophyll. The resulting chemicals from the process are oxygen which is released from the plant and carbohydrates or sugars. These are stored in the plant's vascular system for food. Chloroplasts are small organs contained in each cell of a plant leaf. They are where the process of photosynthesis takes place. These small organelles are where the carbon dioxide and water combine with the sun's energy and minerals to create sugar.
Japanese Red Maple Photosynthesis
Red leaves contain the anthocyanin that makes the characteristic color. The leaves also contain chlorophyll, but the anthocyanin levels are much greater. In shady areas, the leaves tend to darken and look muddy because the plant has to produce more chlorophyll to drive the photosynthesis process. This is why most Japanese maples produce their best color in full sun where excess chlorophyll is not needed to gather the sun's energy. The lower levels of chlorophyll are still enough for the Japanese maple to form energy.
Maple Leaves and Anthocyanins
The Japanese red maple comes in a wide variety of red and plum colors and even a variegated green and pink to red variety. The fall color is stunning and may last for several weeks. Anthocyanins may act as a sun screen so when the plant's leaves turn colors in fall the anthocyanins help protect the leaf to the last second so it can continue to provide energy to the plant. Anthocyanins are also water soluble, which changes the freezing point of the leaves and may help the maple hold on to leaves longer to gather more energy.
- Backyard Nature: Why Does Foliage Change Colors in the Fall?
- FT Exploring Zoo; Photosynthesis Pages -- The Busy Leaf; David Watson; 2010
- North Dakota State University: Photosynthesis
- Clemson Cooperative Extension; Maple; Debbie Shaughnessey, Bob Polomski; May, 1999
- Oregon State University Extension Service; Colored Leaves Have Chlorophyll Too; Carol Savonen
- Liquidlibrary/liquidlibrary/Getty Images