Why do leaves fall in autumn?

Question 1: Why do plants fall in autumn? 1. Why do trees fall in autumn?

When autumn comes quietly, the air becomes dry, and the water in the leaves evaporates through many gaps on the surface of the leaves. At the same time, due to the cold weather, the role of roots is weakened, and the water absorbed from underground is reduced, making water in short supply. At this rate, the tree will die soon. In order to survive, the petiole and the branch are connected together to form a separation layer (pay attention to what a separation layer is)-the petiole originally grows rigidly on the branch. In autumn, as the temperature drops, several layers of fragile parenchyma cells form at the base of petiole. Because these cells can be easily separated from each other, it is called stratification. After the separation layer is formed, it will break when a slight breeze blows, so the leaves will fall.

-), moisture is no longer transported to the blades. After the leaves fall off, there are bare branches left, so the water consumption of trees is reduced, which makes the trees safe for the winter, so it is also beneficial to the trees to fall off their leaves.

2. Not all trees will lose their leaves in autumn.

Do all the trees fall in autumn? No, trees like pine and cypress are often described as "evergreen trees". It seems that the leaves are not yellow, but when we walk in the pine and cypress forest, we will find that there are always layers of leaves on the ground. Pine and cypress belong to evergreen plants. Their leaves are much longer than fallen leaves. The needles of pine trees can live for 3-5 years. Unlike deciduous plants, the old leaves fall off and then grow new leaves. Instead, after the new leaves are born, the old leaves fall off first and then fall off, so the tree remains green all year round and will never be bare.

Third, the characteristics of deciduous trees in autumn

Pay attention to observation. In autumn, the more leaves hang on the treetops, the more leaves fall in the end. This is because in the process of growth, trees always strive to develop into a larger space, so they always transport a lot of nutrients to the branches so that the branches can grow outward faster. Under the supply of tree nutrition, the treetops grow up step by step, and new leaves are constantly growing in the process of growing up. These new leaves have the task of making "rations" for big trees. The treetops have been enjoying nutritious treatment. When the tree no longer provides nutrition and almost all other parts have fallen leaves, the treetops can still rely on the previous "savings" to keep chlorophyll from being destroyed in a short time. The leaves of this branch are the last leaves on the big tree.

Question 2: Why do trees lose their leaves in autumn?

Because autumn means the coming of winter, trees need to sleep for self-protection, and the hibernating trees themselves need nutrients. In order to adjust their internal balance, many trees need to shed leaves, reduce the loss of water and nutrients, and conserve energy until the punishment is appropriate. And some trees, such as pine and cypress, can remain evergreen because their leaves are like needle tips, and there is little loss of water and nutrients.

People often use "autumn wind sweeping leaves" to describe autumn scenery in temperate regions. Autumn has come, and the leaves of broad-leaved trees such as poplar and locust tree are gradually aging. With the rustling autumn wind, the yellow leaves fall quietly. You may feel sorry for the fallen leaves, but have you ever thought that the fallen leaves are just the self-protection of trees?

It's cold, people put on stoves and cotton-padded clothes. But what about trees? They can only spend the winter safely by shedding all the leaves to minimize water transpiration. Otherwise, due to the freezing weather and whistling wind, it is difficult for the roots to absorb water, and the transpiration of the leaves will proceed as usual. Think about it, what is waiting for the trees besides death?

Petiole used to grow stiff on branches. In autumn, as the temperature drops, several layers of fragile parenchyma cells form at the base of petiole. Because these cells can be easily separated from each other, it is called stratification. After the separation layer is formed, it will break when a slight breeze blows, so the leaves will fall.

Leaves are broad-leaved trees in temperate regions, which is a skill to reduce transpiration and prepare for safe winter.

And it has a lot to do with abscisic acid contained in trees.

Question 3: Why are maple leaves red in autumn and why do they fall in autumn? Deciduous tree species will have some chemical reactions in autumn and winter, so that the substances or some tissues contained in the original leaves can be recovered and stored in stems or roots, and can be reused in the next spring. Chloroplast and chlorophyll are one of the objects of decomposition and recycling, so when chlorophyll in leaves is gone, the colors of other pigments are highlighted, such as red anthocyanin, yellow carotene and yellow lutein. Because of the high chlorophyll content, it covers other colors and makes the leaves green. In addition, the sugar stored in maple leaves will be decomposed into anthocyanins, making the leaves brighter. When the temperature drops, the trees stop growing and enter a "hibernation" state, and the leaves do not need photosynthesis and wither and die.

Question 4: Which trees will lose their leaves in autumn? Pear, plum, buttonwood, plum wintersweet tree, willow, poplar and peach trees. . . .

Question 5: Why do trees shed their leaves? Whether trees shed leaves depends on their long-term evolution and adaptation to different natural environments. Deciduous trees shed leaves because they have to fight against unfavorable environmental factors, such as defoliation in winter, so as to reduce water evaporation and change the cytoplasm in the body from liquid to gel to enhance its stress resistance, so as to survive the severe winter. When a plant leaves, the plant hormone abscisic acid in the body will change the separation layer between the leaf and the plant. Cells separate, so leaves fall off.

Question 6: Why do leaves fall in autumn? In autumn, the temperature drops, the trees stop growing, and the amount of leaves supplied by plants decreases, so the leaves fall.

Question 7: Why do trees lose their leaves in autumn? As soon as we enter autumn, we will see that the leaves of most trees slowly turn yellow and dry, and then fall off the trees. I'm confused about this. Why do these trees shed their leaves every autumn? Why are other trees green all year round?

I looked up some information and went to the field for an afternoon to observe, and finally understood the reason why trees fell leaves.

From the information I consulted, I know that defoliation of trees is a normal physiological phenomenon and an adaptability of trees to low temperature and dry climate.

In autumn, the temperature drops, the light time shortens, the root absorption and photosynthesis of trees decrease, which can not meet the growth and development of trees. At this time, the water in leaves evaporates quickly, but the ability of roots to absorb water is greatly reduced, so the supply of water and nutrients is insufficient. Trees choose the method of "discarding" leaves to reduce water evaporation, maintain water and nutrients, and spend the cold and dry autumn and winter safely.

So how did the leaves fall from the tree? From the data, I know that there is a plant hormone called abscisic acid in plants, which will cause a "detachment layer" at the base of petiole to make the leaves fall off. I climbed to the high stone and found that the leaves began to turn yellow. I pulled it gently with my hand and the leaves fell off. I found another camellia tree, and I had to pull it hard to pick it. Observe the fracture of the yellow petiole, it is very flat, the color of the fracture is dark, the fracture of Camellia leaves is still fresh, and there are tiny wires connected. Obviously, there is no "separation layer" at the base of the green petiole.

After observation, I also found that short trees have less leaves and tall trees have more leaves. I think it's because the roots of dwarf trees absorb water easily.

The autumn leaves of trees are related to the weather. I recall the warm Hainan Island and the cold Dalian in winter. I also found some information and pictures, and found that there are many deciduous trees in Dalian in autumn, but evergreen trees all grow in Hainan Island.

In the wild, I also saw a tea tree with withered leaves. I am surprised that it is an evergreen tree! On closer inspection, it turns out that the tree is dead. This is not the fall of leaves, by the way, in fact, evergreen trees will also lose leaves, but that is because the leaves are aging, not because of the arrival of autumn. Most of these leaves fall in spring.

There are so many mysteries in nature. I want to master more knowledge and explore more natural mysteries.

Question 8: What trees lose their leaves in autumn? What trees don't lose their leaves? In temperate forests in the northern hemisphere, trees will lose their leaves in autumn, because cold weather is coming. In tropical and subtropical forests, trees will shed their leaves at the beginning of the dry season. A tree whose leaves all fall off at a certain time of the year is called a deciduous tree, and vice versa.

Common deciduous trees in the northern hemisphere are ash, poplar, beech, birch, cherry, elm, walnut, kiwi, maple, oak and willow. In tropical and subtropical regions, deciduous trees include several species, such as Robinia pseudoacacia, baobab, white oak, kapok and tea tree.

Most deciduous trees have wide leaves, which are said to be easily damaged in cold or dry seasons. In contrast, evergreen trees often live in a warm and humid climate, or their leaves have weathering-resistant needles. However, there are exceptions in nature. For example, every autumn, all the needles of larch will fall off, while oak trees can keep their broad leaves intact all year round even in a relatively cold climate.

Typical common evergreen trees, such as pine, cypress, camphor tree, orange tree, agave tree and gladiolus tree, are evergreen because their leaves have a life span of 2 or 3 years, and they keep growing new leaves and dropping old ones all year round, so the green leaves remain on the stems all year round.