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This is because when the weather gets cold, the ground becomes dry, and the ability of the leaves to make "food" decreases, and gradually becomes a burden on the trees, and they silently wither, fall around the trunks, and turn into dirt. The leaves on the treetops have always been well nourished, and when the leaves begin to wither, they can survive on their previous "savings" for a while, until the other leaves have fallen, and then fall in the autumn wind.
Because there is chlorophyll and lutein in the leaves, chlorophyll is very unstable under temperature changes, while flavin is relatively stable. The same is true for other colors of leaves, and some of them are evergreen because some of the leaves have evolved and changed their leaf structure with the change of region, which can retain water and not be afraid of temperature changes, such as pine trees.
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In winter, not only is the temperature low and the sun is less, but the rainfall will also be greatly reduced, and the ability of the tree's roots to absorb water will be greatly weakened, and the leaves will be dropped so as not to threaten the survival of the tree.
In the dry winter, the water and inorganic salts obtained by the trees will be greatly reduced, which will affect the respiration and transpiration of the trees, and if there are too many leaves, it will affect the survival of the whole tree. In order to reduce the evaporation of water, the physiological cycle of leaves is one year, and they will die in winter, so as to ensure that the trees have enough water to survive the winter.
Winters are dry and cold, and trees need to take certain measures to conserve energy. Reducing water evaporation reduces energy loss. The main transpiration route of trees is carried out by the stomata of leaves. Therefore, the amount of transpiration can be reduced when the leaves fall.
Leaf litter and photosynthesis are reduced, and the energy of the body's memory is also used to survive the winter. Therefore, in winter, the leaves begin to fall in autumn, and it is a kind of living strategy for trees. In autumn, a kind of abscisin is produced in the petiole area, which causes the leaves to break away from the branches and wither.
Extended Materials. How to prevent leaves from falling.
1. Long-term lack of light, poor plant growth. It should be gradually moved to a bright place for a certain period of time.
2. If it is not managed by a special person, it may be underwatered or overwatered, which may make the plant grow poorly or even die. Only professionals can do it without doing it or watering it, and pouring it thoroughly.
3. Corresponding methods are needed for fertilization, soil, and pests and diseases.
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Whether a tree loses its leaves or not depends on its long-term evolution and adaptation to different natural environments. The defoliation of deciduous tree species is to resist adverse environmental factors such as winter defoliation, so as to reduce water evaporation, so that the cytoplasm in the body changes from liquid to colloidal, and enhances its resistance to stress, so as to survive the cold winter. During defoliation, the action of plant kininoacids in the body is alteredThe layer of separation between the leaf and the plant.
There is separation between cells, which is called leaf detachment.
In fact, pines and cypresses do not lose their leaves. They only change the leaves every three or five years, and the leaves are not all changed together, but the plasm of the pine trees that are changed in batches are microscopically tightly arranged, and the moisture content is much lower than that of deciduous trees, which is one of the reasons for its cold resistance. In addition, the leaves of pine trees are mostly needle-shaped, and the leaf surface has a waxy surface, which reduces the evaporation of water, so the xylem of pine trees does not need to store too much water, so it is not afraid of frostbite in winter, so it is not necessary to form a series of reaction mechanisms caused by the drop in environmental temperature of deciduous trees, such as reducing the total water evaporation of deciduous trees.
It is a well-known evergreen tree.
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Because the leaves of these trees do not consume much water, and the surface of the leaves has a very thick waxy layer, so that the leaves are not afraid of cold at all, and they cannot evaporate much water, so they will not fall leaves.
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The leaves of an evergreen tree do not fall off, but they fall off and grow partially, so they always look green, like human hair.
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The reason why it does not fall defoliation is because the lifespan of the leaves is relatively long, and they can last up to 2 to 3 years.
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<> "Why Evergreen Leaves Survive Winter."
Evergreen trees have a set of skills to resist drought and cold. For example, needle-like pine leaves have a small surface area and are not easy to cause a large amount of water to evaporate. The leaves of camphor and holly, although flattened, are covered with a layer of wax on the surface of the leaves, which keeps them warm and prevents water from evaporating.
<> "Why Evergreen Leaves Survive Winter."
Deciduous trees generally have thin leaves, which evaporate water easily and also need more nutrients. In order to survive the cold winter, the leaves of the trees die and fall, in order to prevent the loss of water and nutrients. So in winter, the deciduous trees become bare.
The next year, when the weather is warmer, new foliage grows.
Evergreen trees have thicker leaves and secrete a wax that prevents the leaves from losing water, resists the cold, and safely survives the winter. Evergreen trees shed some of their leaves every year, but some of them still grow new. Because of the constant renewal, the evergreen tree stays green all year round, so this tree has a long lifespan.
What are the evergreen trees?
Evergreen trees: Pinus tabuliformis, Pinus sinensis, Pinus nigra (Pinus nigra nigra), Pinus sinensis, Pinus sinensis, Picea sinensis, Picea chinensis, Pinus sylvestris, Pinus sylvestris, Juniper, Pinus orientalis, Pinus alba, Larch, Weeping Juniper, etc. Evergreen shrubs:
Boxwood, paving cypress, antler juniper (Wanfeng juniper), Xing'an juniper, etc.
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Trees lose their leaves in winter for the following reasons:
In autumn, the temperature drops and the light time is shortened, which affects the absorption capacity of the root system and the photosynthesis of leaves, so it cannot meet the growth and development of trees. Broad-leaved trees have many pores on the leaf surface, with more than 10,000 per leaf, and these pores are the gateway for water vapor and other gases to enter and exit. When the temperature drops and the air is dry, the water in the leaves evaporates quickly, but the ability of the roots to absorb water has been greatly reduced, and the water and nutrients are insufficient.
In order to survive the tree, the connection between the petiole and the leaf stem forms an isolation layer, and the leaves are cut off from the water **, coupled with the low temperature, the chlorophyll is destroyed, and lutein and so on begin to become active, so the leaves will turn from green to yellow and fall off, and return to the earth with the autumn wind.
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