Why do leaves fall in autumn? What's the short answer?

There is not enough moisture, temperature and sunshine in autumn, so leaves will fall in autumn. The main function of green leaves is to absorb sunlight for photosynthesis, produce nutrients and transpiration water.

2. In autumn and winter, the rain is scarce, the air is dry, and the moisture content in the soil is also reduced, which cannot meet the needs of tree growth. Coupled with the oblique sunlight in the northern hemisphere, the sunshine hours are getting shorter every day, which indicates the coming of winter for trees.

3. At this time, a hormone abscisic acid will be produced in the leaves. Under the action of abscisic acid, a natural fracture surface will be formed around the abscission layer. Leaves will gradually dry up because they can't get normal water supplement, and the natural fracture surface will become more and more obvious. Leaves will fly after the autumn wind blows.

Related information:

Autumn is one of the four seasons. In China, traditionally, "beginning of autumn" in the 24 solar terms is taken as the starting point of autumn. Entering autumn means that rainfall and humidity tend to decrease or decrease, and everything in nature begins to mature from lush.

According to the average climate temperature of modern scholar Zhang Baokun, there are four seasons in a year. The index is that the average temperature is lower than 10℃ in winter, higher than 22℃ in summer, and 10~22℃ in spring and autumn respectively.