On August 21, 2017, about 215 million American adults watched one of nature’s most dramatic events: a total solar eclipse. However, most of the country could only see a partial eclipse. The path of the total eclipse was a strip just 70 miles wide, arcing across the country from Oregon to South Carolina.
The University of Missouri-Columbia lies directly on that path of totality. Scientists there knew they had a once-in-a-generation opportunity to study how a total eclipse affects plants. During the event, there would be 45 minutes of gradually decreasing light. Temperatures would also fall. Next would be two minutes and 36 seconds of total eclipse: a span as dark as night and noticeably cooler. Light and warmth would then gradually return.
Tim Reinbott and colleagues at the university’s South Farm Research Center were curious to see how plants would react when night conditions interrupted the day. Would leaves fold up for the night? Would plants respond more to the change in light or the change in temperature? Would different kinds of plants respond differently?
“We were wondering if plants had a circadian rhythm—meaning that they have sensed when sunup and sundown are and have developed an internal clock, separate from sensing changes in light,“ Reinbott said. “So when we have totality of the eclipse in the middle of the day, would they even react?”
The team chose to observe four types of plants with different habits:
- Mimosa close their leaves at night and when they are touched.
- Oxalis (purple clover) close their leaves and fold their flowers at night.
- Drought-stressed soybeans fold up their leaves during the day and open them at night.
- Drought-stressed corn curls during the day and uncurls at night.
The research team prepared two mimosa plants in advance by exposing them to either 72 hours of light or 72 hours of darkness. One mimosa was exposed to a normal light/dark cycle.
The varied results have left the researchers with interesting questions.
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