November 28, 2021
Autumn leaves (Kouyo) and maple (autumn leaves, yellow leaves) are mainly deciduous broad-leaved trees whose leaves change color before they fall. However, simply turning red may be called autumn leaves.
Generally, deciduous trees are famous, and the appearance of autumn leaves all at once is also a target for sightseeing. Some species of Aceraceae are often called maples in particular, but they are actually representative species of trees with bright autumn leaves. In autumn, the leaves of grass and shrubs also turn red, and they are sometimes collectively called "Kusamomiji".
In a narrow sense, turning red is called "autumn leaves", turning yellow is called "yellow leaves", and turning brown is called "brown leaves". It is often difficult to distinguish these strictly, and all of them are often treated as "autumn leaves". Even trees of the same type may turn red or yellow depending on the growing conditions and individual differences. The reason why the leaves are colored is botanically considered to be part of the leaf aging reaction.
Some evergreen trees also turn red, but they are not noticeable because they are at the same time as the green leaves or the times are not the same. The guideline for distinguishing Holtonoki is that a small number of leaves are always colored red. The evergreen coniferous Sugi and Oriental Arbor-vitae turn brown in winter.
Autumn leaves in Japan begin around September at Daisetsuzan in Hokkaido and gradually move southward. The transition of the best time to see the autumn leaves is called the "autumn leaves front" in contrast to the cherry blossom front. It takes about a month from the beginning of the autumn leaves to the completion. The best time to see is about 20 to 25 days after the start, from October in Hokkaido and Tohoku, and from November to early December in Kanto to Kyushu.
However, it is usually earlier than this because it tends to get cold in the morning and evening in the mountains and inland.
Mechanism of autumn leaves
The leaves usually look green because they contain chlorophyll. Chlorophyll is decomposed in autumn when the daylight hours are shortened. This is botanically considered to be a leaf aging reaction.
During the summer, chlorophyll absorbs light in the leaves and actively photosynthesizes. Deciduous tree leaves undergo an aging reaction before winter, when weather conditions are unsuitable for photosynthesis. In this process, photosynthetic devices and the like are decomposed, and the nutrients stored in the leaves are recovered to the trunk. This nutrition will be reused in the spring of the following year.
In leaves with sufficient nutrient recovery, ethylene, one of the plant hormones, forms a delamination at the base of the petiole and is separated from the branches. This prevents wasteful water and energy from being consumed during the winter.
The leaves of plants have a mechanism to protect themselves from the harmful effects of light by using "carotenoid" pigments, but various molecules including carotenoids are decomposed during the leaf aging process, so during this process It is necessary to protect the leaves from the harm caused by light. The myth that "a delamination is formed at the base of the petiole, sugars and amino acids made from the leaves are accumulated in the leaves, and new pigments are made from the sugars" is incorrect.
The difference between autumn leaves, yellow leaves, and brown leaves is a phenomenon that occurs due to the complex entanglement of the difference in the ability of each plant to produce pigments and the difference in the expression of enzyme action due to the action of natural conditions such as temperature, water and humidity, and ultraviolet rays. NS.
Principle of autumn leaves
The red color of the leaves is derived from the pigment "anthocyan". Anthocyans do not exist in the leaves from spring to summer,