Why do sunflowers chase the sun during the growing period, but persist in the East when they are mature?

Stacey Harmer, a professor of plant biology at the University of California, Davis, said: "This is the first example of plants using clocks to regulate their growth in the natural environment, which has a practical impact on themselves."

According to research, researchers planted sunflowers in flowerpots in the wild, some of which were facing west. Using infrared photography to measure flowers, they found that the flowers facing east warmed up faster in the morning, attracting more than five times as many pollinators. Using portable heaters to heat flowers facing west can also bring more pollinators back to the flowers. Sunflowers facing the sun may also be the result of natural selection, which is beneficial to the reproduction of sunflowers.

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In fact, when plants track the sun, the east side of the stem grows faster than the west side. At night, as the stems move in the opposite direction, the west grows faster. This situation shows that there seem to be two growth mechanisms at work in sunflower stems. The first mechanism is based on available light sources and sets the basic growth rate of plants. The second mechanism is controlled by biological clock and influenced by the direction of light source. This mechanism makes one side of the stem grow faster than the other, so it swings from east to west during the day.

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With the maturity of sunflower, the disk unfolds and the overall growth slows down. Plants no longer move towards the sun during the day, but always face the east. This may be because, as the overall growth slows down, the biological clock ensures that plants respond more strongly to morning light than in the afternoon or evening, so they gradually stop moving westward during the day. In fact, these sunflowers go out at night like people, and plants also rely on daily circadian rhythm activities.