Why do leaves change color with the seasons

  We know that most of the leaves will change color. In spring, the leaves just emerging from the branches are tender green; in summer, the leaves turn dark green; in autumn, the leaves turn golden yellow; in winter, they return to the soil and wait The next spring, the cycle goes back and forth, this is the life of the leaf. Why are the leaves mostly green? Why do the leaves change color with the change of seasons?
Why are the leaves mostly green

  The vitality of life on earth comes from the blessings of the sun. The sun drives the photosynthesis of plants. Through photosynthesis, plants can synthesize carbohydrates with the help of the sun’s radiant energy and carbon dioxide in the air. The sun’s rays are composed of seven visible spectra, namely red, orange, yellow, green, blue, indigo, and purple, which are the same colors as the rainbow, and are also called the seven-color rainbow spectrum. Green is the most common color in plants on earth, which is related to the spectrum of sunlight absorbed by plant leaves during photosynthesis. When a substance absorbs one or more kinds of light in the seven-color rainbow spectrum and reflects or transmits the rest of the light, it takes on the color of the rest of the light. The color and temperature of the sun and the distance between it and the earth determine that plants on the earth can absorb most wavelengths of light, but not green light, so this wavelength of light is reflected back and enters our eyes, so we You will see the plants appear green.
Why the leaves turn yellow in autumn

  Autumn is here, and the leaves in the mountains turn into beautiful yellow or red in an instant. Why is that? It turns out that when autumn arrives, the day shortens and the night stretches, and the trees begin to shed their leaves. In the cold season, plants still need a lot of energy and water to keep their leaves healthy. We know that sunlight provides energy to plants, but winter is cold and dry, and there is usually not enough sunlight. In order to reduce nutrient consumption, most plants have to abandon their leaves. Before the leaves fall, the trees no longer produce a lot of chlorophyll like in spring and summer, and chlorophyll begins to decompose gradually. In this way, as the chlorophyll content gradually decreases, the colors of other pigments will gradually appear on the leaf surface, and the leaves will show yellow, red and other colors.
  In autumn, as the weather turns cooler, about 10% of tree species in temperate regions will show their leaves changing color within a few weeks. Many types of leaves will turn yellow, such as poplar, ginkgo, etc. This is because the main chemical substance involved in photosynthesis in the leaves chlorophyll is degraded and transported back to the trunk and roots for storage; while the chemical substances that usually play an auxiliary role in photosynthesis The color of lutein and carotene appears. The leaves of some types of trees, such as maple, chrysanthemum, and cocklebur turn red. This is because when the temperature reaches 0°C to 7°C, a chemical substance called anthocyanin is produced in the leaves of these plants. As autumn approaches, the temperature gradually decreases. In order to resist the cold, maple trees and other trees increase the sugar content in their bodies. Together with dry weather and daytime sunshine, it is very conducive to the production of anthocyanins.
Why do some plants stay green all year round

  The leaves of most trees turn yellow and withered in autumn, but the pine and cypress trees stand vigorously in green clothes even in the cold winter.
  The pine and cypress trees were originally trees that grew in the cold zone and high mountains. Due to long-term living in the cold environment, they have formed a unique cold-proof structure. The leaves of pine and cypress trees are generally needle-shaped, linear or scale-shaped. Due to the small leaf area, water is not easy to evaporate and lose. At the same time, the leaves of pine and cypress trees contain less water and contain rosin. When the temperature drops, it can quickly increase the concentration of cell sap and increase sugar and fat to prevent freezing. Therefore, even in winter, the pine and cypress trees will not dry out due to lack of water, ensuring the survival of the trees.
  The leaves have a certain life cycle, and each leaf will fall off when it reaches a certain age, and pine and cypress trees are no exception. Their leaves are also declining, but the leaves of pine and cypress have a long life cycle, which can grow for 3 to 5 years. When they are removed, they alternate with each other. Generally, the old leaves will wither after the emergence of new leaves. It doesn’t seem to fall leaves, so it feels like evergreen in winter and summer.

▲ Pine and Cypress

  Although the leaves of cypress trees are still green in winter, their colors are much worse than those in spring, summer, and autumn. This is because the temperature in winter is low, and the production of chlorophyll in the leaves is restricted. This color change can weaken the photosynthesis in the leaves and slow down the physiological activities of the trees. This is very beneficial to ensure that the pine and cypress trees can survive the winter safely.
Why are there few green flowers in nature

  Why are the flowers colorful but rarely green? The emergence of this phenomenon is related to the evolution of plants. When angiosperms bloom their first flowers on the earth, the “fertility policy” of the plant world is changed. As a unique sexual reproductive organ of angiosperms, flowers play an extremely important position in the reproduction of offspring. It can form male and female reproductive cells as well as pollination and fertilization. But we know that plants do not move, so if we want to pollinate we must rely on external forces, such as wind, insects and other different media. Take insect-pollinated flowers as an example. If they want to attract insects, they must have enough charm. Therefore, they need a variety of bright colors to attract the attention of insects. If the flower and the leaves are the same color, it is not easy to be found by insects, which is not conducive to reproduction and evolution, so there are fewer green flowers. For example, wind-pollinated flowers that do not need insects to help pollinate, they will not pay so much attention to their “appearance”. Flowers such as willows, jujubes, and rice are all green. Just because their colors are not conspicuous, many people will mistake the world for them. There are no green flowers on it.
What color are plants on extraterrestrial planets

  If there were plants on extraterrestrial planets, what color would it be? We already know that most plants on the earth are green, because plants on the earth absorb the least green light. The color of plants on extraterrestrial planets depends on how the photosynthesis of plants on that planet adapts to the light emitted by their stars. The light from other stars may be different from the sun’s spectrum. The most common stars in the Milky Way are red dwarfs. Therefore, astrobiologists believe that if plants growing on planets orbiting such stars also develop photosynthesis, they will evolve different wavelength absorption patterns, which may appear red, yellow, purple, or even gray-black. And so on, in order to more effectively absorb the limited light resources. For example, if the leaves of plants on an alien planet absorb the least red light, then the forests and grasslands on this planet are likely to be red.