Research conducted during the Great American Eclipse of 2017 suggests the sun’s midday disappearance shocks some plants.
As the total solar eclipse crosses South America on Tuesday, it won’t just be people oohing and ahhing as the sun is blotted out.
Other living things will have their own responses, too — some of which we are just beginning to understand. As some scientists used the Great American Eclipse in August 2017 to watch how bees and birds dealt with sudden midday darkness, researchers in Wyoming investigated big sagebrush, a shaggy, aromatic desert shrub that grows throughout the western United States.
Tracking its reactions at the leaf level, scientists saw it experience a slowdown in activity as darkness fell, followed by shock at the sun’s surprise return. The study, published in June in Scientific Reports, adds to a small clump of botanical eclipse research, all produced by people with the ability to wonder, even as a celestial event occurs: What are the plants getting up to?
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“Plants haven’t really been well-documented during the eclipse,” said Daniel Beverly, a Ph.D. student in botany and hydrology at the University of Wyoming and the paper’s lead author. When he heard an eclipse was coming, he saw the chance for “a once-in-a-lifetime data set.”
Big sagebrush spends much of its life in the sun, and “it covers such a large portion of the country,” from Oregon down to New Mexico, Mr. Beverly said, making it a good subject for study. He and his colleagues chose a patch close to Yellowstone National Park. They set up instruments that could measure photosynthetic rate, as well as the speed of transpiration — how quickly its leaves lose water.
As the light faded and the temperature dropped during the 80 or so minutes before totality, Mr. Beverly and his team saw a corresponding decrease in photosynthesis and transpiration. “The plant responded as if it was dusk,” he said.
During the two minutes and 18 seconds of complete darkness, both rates fell further. Although they did not quite reach the slowdown level of an average nighttime, it was a much more precipitous drop than would have occurred for a passing cloud.
But when the sun appeared again, the shrubs were blindsided.
“That’s when we saw the most evident signals of stress,” said Mr. Beverly. “It caused a disruption in the photosynthetic pathways.”
Although they could not test this directly, he guesses that the shock of sudden sunlight messed with each plant’s circadian rhythm — the internal clock that determines an organism’s daily cycle of activity.
Over the course of the eclipse day, the team estimated, your average big sagebrush managed about 14 percent less photosynthesis than it would have if the sun hadn’t been blocked. If a plant is already drought-stressed, an eclipse might be bad news, like “losing 14 percent of a day’s income when you’re already broke,” Mr. Beverly said.
Their findings follow a few other studies, including one done during an eclipse over Europe in 1999 that showed changes in sap flow and transpiration in a beech tree near Ghent, Belgium. The tree “‘held its breath’ during the solar eclipse,” said Kathy Steppe, now a professor of plant ecology at Ghent University — meaning it stopped releasing water, even as its sap kept flowing.
Mr. Beverly looks forward to the 2024 eclipse, which will sweep from Mexico through to the Eastern United States, when he plans to take a closer look at crop and tree responses.
He’ll do one thing differently: “I would try to use as much automation as possible so I could actually enjoy the eclipse,” he said. “That’s a big thing I missed.”