The principle of leaves turning yellow in autumn

The principle that leaves turn yellow in autumn is as follows:

When the leaves are green, they are full of chlorophyll. In autumn, plants will secrete lutein. After autumn comes, trees feel the climate change from autumn, which makes a lot of phytochrome cover the green chlorophyll, and people naturally see the leaves turn red or yellow.

In autumn, deciduous trees stop growing and only need a small amount of nutrients to survive. Before the leaves fall, the trunk decomposes chlorophyll, and the substances produced by decomposition are transported from the leaves to the treetops as nutrients for winter. After chlorophyll is decomposed, lycopene is left in the leaves, so you can see that the leaves turn from green to yellow.

The new leaves contain eight times as much chlorophyll as lutein. Yellow is covered with green in spring and summer. With the aging of the leaves, although the pigments contained in the leaves will be decomposed, the decomposition speed of lutein is slow, so the leaves gradually turn yellow.

Autumn solar terms:

The temperature will gradually drop in autumn, but it is generally slower than in winter. Due to the difference of dry and wet conditions, there will be cold and rainy weather conditions or dry and cool weather conditions in different regions. In the cold late autumn, due to the large temperature difference between day and night, the water vapor transpiration during the day will condense at night, either dew or frost.

In autumn, the direct point of the sun gradually moves south from the northern hemisphere, passes through the equator after the autumnal equinox, and the sun directly shines in the southern hemisphere. Seen from the northern hemisphere, the angle of the sun gradually becomes lower, and the gap between day and night becomes smaller. At the autumnal equinox, the length of day and night is equal. In autumn, the distance between the earth and the sun is from far to near. Seen from the ecliptic plane, the sun is on the background of Leo, Virgo and Libra.

The standard for dividing seasons according to the average temperature in autumn must be that the average temperature for five days is below 22℃. According to this standard, the Jianghuai area generally enters autumn in the middle and late September. After beginning of autumn, although the summer heat is hard to disappear for a while, there is still the afterglow of "autumn tiger", but the general trend is that the weather is getting colder and colder. The daily temperature range is gradually obvious, which is often very hot during the day and very cold at night.