Extreme ultraviolet radiation causes plant sterility, UC Berkeley study finds

Jeff Benca/Courtesy

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Campus researchers found that high levels of ultraviolet radiation can cause plant sterility, damaging species’ capacity to reproduce and sustain their plant populations in a study published Wednesday.

The study, which was conducted by integrative biology graduate student Jeffrey Benca, exposed conifer trees to high UV radiation levels to simulate the trees’ response to extreme ozone damage. The radiation levels mimicked those of a period in Earth’s history, 252 million years ago, during which ozone layer depletion contributed to the largest mass extinction in Earth’s history.

Mass extinction studies often look at animal extinction patterns, but Benca turned his focus to plants.

“Plants don’t play by the same rules that animals do,” Benca said. “They have other tricks up their sleeves and have very different life cycles.”

The two-month study exposed several groups of “healthy” dwarf pines to radiation levels 7.5, 10 and 13 times the daily UV-B intensity of Berkeley. While the researchers observed the presence of malformed pollen grains from pines receiving the two higher radiation level treatments — similar to what had been noted in fossil records from 252 million years ago — a potentially more important finding surprised Benca.

The trees’ seed cones would shrivel and die before reaching the appropriate level of development that would enable pollen fertilization.

“The plants themselves looked really good,” Benca said. “You would not be able to see the difference, but (the high UV) messes up their reproductive cycle.”

Before long, every single cone on each tree died, regardless of whether it was exposed to 7.5, 10 or 13 times regular UV radiation. Cindy Looy, a co-author of Benca’s study and a campus assistant professor of integrative biology, said that if this UV exposure endured for hundreds of years because of ozone depletion, the species would start to dwindle.

According to the study, the trees showed positive signs of recovering reproductive capabilities. The following year, when the trees were placed back on the roof, they were able to properly form seed cones again.

The study offers a cautionary note for climate change and the potential damage to the ozone layer that has occured in recent decades and could ensue in the future. Earth’s ozone continues to recover since the banning of CFC use by the Montreal Protocol, adopted in 1987. Benca added, however, that a study by atmospheric scientists published a day before his own points to evidence that the ozone layer has seen less repair than previously predicted.

Campus professor of integrative biology David Ackerly said in an email that Benca’s study “alert(s) us to the unforeseen threats.”

“We see in this study the unexpected ways in which environmental change can impact natural ecosystems,” Ackerly said in his email.

Benca added that the caveat is that only one species was tested, and it was only tested for one growth season. He stated plans for more varied and long-term studies in the future.

“What we did is only the beginning,” Looy said. “This was a short-term study. What would happen in the long run?”

Contact Michele Meltzer at [email protected] and follow her on Twitter at @michele_meltzer.