The earliest person who discovered the plant sleep movement was Darwin, a famous British biologist. 100 years ago, in the process of studying the growth behavior of plants, he observed the nocturnal activities of 69 species of plants, and found that some leaves covered with dew were not easy to move because of the weight of water droplets, and they were often more likely to be injured than other leaves that could move freely. Later, he repaired the leaves manually and got similar results. Although Darwin could not directly measure the temperature of leaves, he concluded that the sleeping movement of leaves was very beneficial to plant growth, probably mainly to protect leaves from the cold at night.

Moonlight theory

At first, the most extensive theory to explain plant sleep movement was "moonlight theory". Scientists who put forward this argument believe that the sleeping movement of leaves can make plants suffer from moonlight as little as possible. Because too much moonlight exposure may interfere with the normal photoperiod sensing mechanism of plants and damage the adaptation of plants to diurnal changes. However, it is puzzling why many tropical plants without photoperiod are also "sleepy". This point can't be explained clearly by the theory of moonlight.

It is caused by the swelling and pressure changes of some cells at the base of petiole.

Later, scientists found that the sleep movement of some plants is not controlled by temperature and light intensity, but caused by the expansion and pressure change of some cells at the base of petiole. Such as acacia, sorrel, red clover and so on. By closing the blades at night, the heat loss and water evaporation are reduced. Especially Albizia Albizia, the leaves not only close to sleep at night, but also gradually close in case of strong wind and heavy rain to prevent the young leaves from being destroyed. This protective response is an adaptation to the environment.

Enright

Scientists put forward one viewpoint after another, but failed to have a satisfactory explanation. Just when they were confused, American scientist Enright put forward a new explanation after a series of interesting experiments. He uses a sensitive temperature detector to measure the temperature of many plant leaves at night. The results show that the leaf temperature in horizontal direction (without sleep exercise) is always about 65438 0℃ lower than that in vertical direction (with sleep exercise). Enright thinks that it is the slight difference of 1℃ that becomes an important factor to prevent or slow down the growth of leaves. Therefore, in the same environment, plants that can sleep exercise grow faster and have stronger survival competitiveness than other plants that can't sleep exercise.

Plant villi

With the deepening of research, scientists also found an interesting phenomenon about plant sleep: plants have the habit of taking a nap just like people. The time for plants to take a nap is about 1 1 until 2 pm. At this time, the stomata of leaves are closed and photosynthesis is obviously reduced. Why is this happening? Scientists believe that plant siesta is mainly caused by the dryness and heat of the atmospheric environment. Napping is an instinct of plants to resist drought in the long-term evolution process, in order to reduce water loss and survive in harsh environment.