Why do sunflowers face east? Maybe it has to do with bees

sunflower

According to a study published Aug. 9 in the journal The New Botanist at the University of California, Davis, sunflowers are moving toward the rising sun in order to raise temperatures to attract more bees and thus reproduce more efficiently.

During the process of growth, the sunflower head will move with the change of the sun's position. Stacey Harmer, a professor of plant biology in the College of Biological Sciences, is the paper's corresponding author, after work in his lab showed that this tracking was controlled by a biological clock inside plants. But as the cephalic inflorescence matures, the sunflower's stem becomes woody and stiff, and the head-shaped inflorescence gradually decreases with the rotation of the sun. Eventually, they will be permanently fixed in the direction in which the sun rises.

When postdoc Nicky Creux changed the orientation of the sunflowers by rotating the pots, she noticed that flowers facing east attracted more bees than flowers facing west, especially in the morning. Subsequently, through a series of experiments, Creux, Harmer, and colleagues found that the temperature of sunflowers facing east in the morning was significantly higher than that of sunflowers facing west. Harmer says the warmth of the flowers brings energy benefits to early morning foraging bees, and bees can also detect ultraviolet markers on petals illuminated by direct sunlight.

In fact, sunflowers are a combination of hundreds, sometimes, even thousands of small flowers. These florets initially develop at the outer edge of the cephalic inflorescence, forming a distinctive spiral pattern. The orientation of sunflowers affects the development and reproduction of flowers, and sunflowers facing east tend to produce larger, heavier seeds. They also release pollen earlier in the morning, just in time for the bees to come and collect honey.

These effects appear to be controlled by the flower head temperature, and when the researchers used portable heaters to artificially raise the temperature toward the western flowers, they got similar results to the east-facing flowers.

Finally, Evan Brown, an undergraduate student at the University of Virginia in the United States, targets sterile male sunflowers (which can produce seeds but not pollen) and places normal sunflowers facing east or west around them. The results showed that sunflowers facing east produced more offspring than those facing west.

Compiler: Filament Reviewer: Seamus Editor-in-Charge: Chen Zhihan

Journal Source: The New Botanist

Issue No. 0028-646X

Original link: https://phys.org/news/2021-08-sunflowers-east.html

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