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How Did the August Eclipse Affect Plants?
The Answer Depends on the Plant...


During the eclipse, (L-R) Mimosa previously exposed to 72 hours of dark showed no response to totality. Mimosa exposed to 72 hours of light was partially closed during totality. Mimosa with prior normal light exposure closed completely during totality. Oxalis leaves opened up, but the flowers did not fold. Credit: University of Missouri Academic Support / Stephanie L. Sidoti

On August 21, 2017, a band of the United States from Oregon to South Carolina was in the path of a total solar eclipse. While most people looked to the skies in wonder, researchers at the University of Missouri-Columbia, which was in the path of totality, looked at plants to see how they reacted to the decreased light and temperature.

Four plants with different night and day habits were chosen for the experiment: mimosa, a creeping perennial that closes its leaves at night and when they are touched; oxalis, or purple clover, that closes its leaves and folds its flowers at night; drought-stressed soybeans that fold up their leaves during the day and open them at night; and drought-stressed corn that curls during the day and uncurls at night.

In the 72 hours prior to the eclipse, one mimosa was exposed to constant light, another to constant darkness, and a third to a normal light/dark cycle.

The mimosa left alone closed its leaves during the eclipse, while the other two of the same species did not react. The researchers suspect that the two plants exposed to constant light or darkness may have lost some photoreceptors during that time.

During the heat of the day, the oxalis leaves folded to reduce sun exposure and retain water. While the leaves opened during the eclipse and closed again after totality had passed, the flowers did not fold as they do at dusk. The researchers concluded that the plant only responded to the temperature change, indicating that oxalis has a circadian rhythm.

The drought-stressed corn did not visibly change during the eclipse. The drought-stressed soybeans unfolded during the totality and folded back up after it was over, but the researchers were unsure if this was a response to the changing light or the decreased temperature.

The team plans to continue their research during the next total solar eclipse in the same area, which will be in 2024.

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August 21, 2019, 5:44 am PDT

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