The golden October is a colorful spectacle of nature. Leaves turn from green to yellow, orange, or red. This is a process that is of great importance for some plants.
Only a few weeks a year do we see colorful foliage on otherwise mostly green trees. Have you ever wondered why that is? Or why don't all plants go through this color change? Below we have the answers to these questions.
Why the leaves change color in autumn
Plants turn their leaves in autumn because they are preparing for the cold season. Most plants with autumn colors are deciduous plants. In contrast to the evergreen plants, they pursue the strategy of taking a break during the inhospitable season. Both strategies are justified: evergreens save the energy of new growth, while deciduous ones don't bother to form particularly frost-resistant leaves.
Before deciduous plants shed their leaves, they try to recycle and store as many nutrients and reserve substances as possible from the leaves. When autumn announces itself with low temperatures and short days, plants perceive this as the starting signal for an important process.
The leaf pigment chlorophyll, which turns the leaves green in spring and summer, is slowly broken down and converted. This allows nutrients such as iron and nitrogen to be recovered. This is how chromoplasts appear, which are colored yellow by carotenoids. Many chloroplasts are converted into so-called gerontoplasts, which are also rich in yellow and orange carotenoids. Finally, anthocyanins, which are formed as sun protection and pest protection, are responsible for the red or violet parts. Because in autumn, leaves can easily get sunburned, especially when photosynthesis is inhibited by the low temperatures. Incidentally, red-colored leaves are less likely to be attacked by insects. This is useful because the red leaves usually contain a particularly large numberplant defenses.
Tip: The so-called "Indian summer" makes the autumn colors particularly strong, because strong sunshine combined with already low temperatures can damage the leaves. To protect against "sunburn", anthocyanin is formed, which colors the leaves. If the autumn is rather cloudy, the coloring is correspondingly weaker.
Which plants change their leaves in autumn?
Especially in deciduous plants, i.e. deciduous plants, the leaves change color in autumn. Gingko (Ginkgo biloba) in bright yellow, red oak (Quercus rubra), sweetgum (Liquidambar styraciflua) ensure particularly magnificent autumn colors ), Vinegar (Rhus typhina) and Birch (Betula spec.).
Some deciduous plants show only a very short or weak autumn colour. Here are mainly the ash (Fraxinus spec.), the alder (Alnus spec.) and the elder (Sambuccus spec.) as examples. Their leaves turn yellow and brown quickly.
Even some evergreen plants such as mahonia (Mahonia spec.) or cotoneaster species (Cotoneaster spec.) discolour their leaves in the Autumn to protect against sunburn. Their leaves are mainly red and not yellow, because they hardly break down green chlorophyll. Instead, they build red or purple anthocyanins.
Tip: Even conifers shed their leaves. However, this happens continuously, needle by needle, so there is always green foliage.
Why do the leaves fall off the trees in autumn?
Deciduous plants lose their leaves to protect themselves. There are many factors that make it difficult for plants to retain their foliage and photosynthesize during the winter. One reason is the ground frost: Because of this, no water can be absorbed from the soil into the roots. If a tree kept its leaves in winter, they would allow a lot of water to evaporate. However, no new water could be absorbed by the plant from the frozen ground. The lack of water would then cause a so-called frost drought, which is known, for example, fromevergreen rhododendrons.
Pausing life processes in winter is also a good way to save energy. In order for the plant to be able to keep its leaves, the soft leaf tissue would have to be made frost-hard before winter, which requires a lot of energy. To do this, it stores s alts or sugar in the cells. Soil activity also almost comes to a standstill when it is cold, so that fewer nutrients are available to the plants. In addition, there is less light during the day, which means that photosynthesis is no longer worthwhile. In any case, the effectiveness of photosynthesis is greatly reduced in cold weather - the tree could hardly generate the energy for all the complex measures to protect against frost. For more information on plant overwintering strategies, see our special article.
A bare tree also has the advantage that it can withstand a possible snow load better. Hardly any snow stays on the thin branches and twigs, making them less likely to break off.
How does leaf shedding work?
The mechanism behind the leaf drop is relatively simple and effective at the same time. A thin layer of cork forms at the base of each leaf. This serves as protection, because it closes the pathways. This layer also protects against frost and pathogens. When the layer is complete, the leaf loses its connection to the branch and falls off at the slightest gust of wind. You can also try this yourself: If you gently touch a leaf when the leaves are beginning to change colour, nothing will happen. But if the leaves have changed color for several days to weeks, it will most likely just fall off.
How do evergreen trees keep their foliage?
Evergreen plants have leaves that are better protected against frost in the first place. Building such a stable foliage is time-consuming, which is why pushing it off is not worthwhile. Although the design of the leaves results in a lower photosynthetic capacity, the plant can also use its leaves in winter if the conditions allow it for a short time.
Would you like to enjoy the wonderfully bright colors of autumn in your garden? We have in ourSpecial article Shrubs and trees with intensive autumn colors compiled for you.