Last updated on October 23rd, 2023 at 08:31 pm
As is well known, chlorophyll gives plants their green color and makes photosynthesis, which is so important for our life on this planet, possible in the first place. However, the foliage of the Japanese maple or the copper beech is bright red even in summer – there seems to be no trace of the green chlorophyll. This article explains why trees and other ornamental plants do not starve for lack of energy despite their red leaves, why plants form red instead of green leaves in the first place, and why the Japanese maple only develops the full splendor of its red hues in full sun.
Probably nowhere else in nature do we find such a wide range of green tones as in the plant world. After all, it is only through the green pigment chlorophyll that plants manage to carry out the most important biological process for life on earth – photosynthesis. Plants are therefore known to be green.
But when walking through the park and in some gardens now and then among the green trees and shrubs suddenly shine red-leaved plant species. In spring, this interesting color spectacle is at its best. The red to purple trees then form particularly great color contrasts against the young light green foliage of the other tree species. Fiery red leaves glow in the sun on the picturesque branches of the Japanese maple. Elsewhere, the deep red foliage of the imposing copper beech draws the eye. In the flower bed, the variegated nettle becomes an eye-catcher, mixing with its patterned leaves as red spots among the summer flowers.
At the sight of blood beech & Co., however, every trace of the green chlorophyll seems to be missing. Some people therefore wonder how these pretty red-leaved trees or ornamental plants actually photosynthesize. Without the green pigment, chlorophyll, how are the red plants supposed to convert sunlight into the energy they need for growth? Red-leaved plant species would basically have to starve to death if they had no chlorophyll. But red-leaved trees and shrubs thrive as magnificently as their green neighbors. The reason: under their splendid red coat of color, the Japanese maple or the copper beech are just as green as all other plants. The green chlorophyll of the Japanese maple is only covered by a reddish or blue pigment.
This is the plant pigment anthocyanin, which also gives the respective color to e.g. blue cornflowers, blackberries and raspberries, blueberries and strawberries, grapes or cherries. The foliage of Japanese maple or beech contains more anthocyanin than chlorophyll. The green color of the leaves is thus simply “hidden” under the red tones, so to speak.
The plant world normally appears green to us because plants use only the red and blue light of the sun for photosynthesis. However, light in the green wavelength range is of no use to plants, so they simply reflect this color of light, causing us to perceive it as green in our eyes. The situation is different for the pigment anthocyanin. This pigment absorbs green light very well, but red, blue and violet light quite poorly. Plants such as the copper beech, which contain an abundance of this pigment, therefore reflect the light color red better and thus appear to us in their magnificent red hues.
Are red leaves as efficient as green in photosynthesis?
Although the foliage of the Japanese maple contains less chlorophyll, on sunny days its red leaves are just as powerful as the green leaves of other trees. Therefore, its red foliage still contains enough chlorophyll so that it gains sufficient energy from sunlight through photosynthesis. In shady locations, however, the power of the smaller amount of chlorophyll is often not quite enough. The Japanese maple then endows its red leaves, which are in the shade, with more chlorophyll. The tree thus increases the photosynthetic power of its leaves and obtains more energy. However, the higher chlorophyll content makes the leaves look very dark. The bright red colors of the Japanese maple therefore usually only come into their own in full sun. But why do plants form red leaves at all if they are less efficient at photosynthesis in shady locations?
Plants protect themselves with red leaves
Plants often use the red pigment as a sunscreen. This phenomenon can sometimes be observed in houseplants. If the potted plant is moved from the shade to the sunny window sill, the leaves often turn red after some time. In this way, the plant protects and gets used to the higher light supply. This is somewhat comparable to our skin turning brown in the sun. The tender seedlings and the fresh sensitive foliage of many plants are therefore often reddish in color. Until the young plantlets and leaves are strong enough, the red pigment protects them from sun damage.
The copper beech, on the other hand, retains its sun protection for most of the summer because it lacks an enzyme that normally breaks down the red pigment in young leaves some time after they emerge. As a result, the foliage of the copper beech remains red throughout the summer and only turns a little greener in the fall.
However, red leaves protect not only from too much harmful sunlight, but probably also from predators. The red coloration could serve as a warning to insects and other herbivores that the plant is inedible. Why some plants have red leaves, however, is still not fully understood. There are therefore still many secrets to be uncovered in the plant world.