Pine trees become sterile, at least temporarily, when they are exposed to ultraviolet radiation with intensity comparable to what our planet experienced when the worst mass extinction happened more than 250 million years ago.
Depletion Of Ozone Layer Caused By Volcanic Eruptions
Jeffrey Benca, a graduate student from the University of California, Berkeley, irradiated bonsai-like pines with UV-B dosages to simulate the effects of ozone depletion that was caused by the volcanic eruptions at the end of the Permian Period.
The trees did not die over the two months that the experiment was conducted. However, Benca noticed that all seed cones shriveled up just days after they emerged, which left the trees sterile.
"We find that pollen malformation frequencies increase fivefold under high UV-B intensities. Surprisingly, all trees survived but were sterilized under enhanced UV-B," Benca and colleagues wrote in their study. "These results support the hypothesis that heightened UV-B stress could have contributed not only to pollen malformation production but also to deforestation during Permian-Triassic crisis intervals."
Ozone Depletion And The End-Permian Extinction
One of the suggested causes of the end-Permian extinction was the eruptions of volcanoes over a period of almost one million years.
Acid rain was a local effect of these volcanic eruptions but the extinction of a large majority of land animals, plant species and marine life was a global phenomenon. More than 90 percent of the species on Earth died out during this mass extinction.
Earlier studies have suggested that the periodic volcanic eruptions may have damaged the ozone layer albeit not permanently.
Bouts With Sterility Impacted Population Of Ancient Trees
In Benca's studies, trees that were placed outside and no longer subjected to enhanced UV-B exposure were able to produce health seed cones again in later years.
If the ancient trees were able to regain fertility, their repeated bouts with sterility may still have eventually affected their population, which led to the global collapse of the biosphere.
"With pulses of volcanic eruptions happening, we would expect pulsed ozone shield weakening, which may have led to forest declines previously observed in the fossil record," Benca said.
Implications Of The Findings
The findings, which were published in the journal Science Advances on Feb. 7, supports the theory that ozone depletion had a part in the largest extinction event our planet experienced. They also highlight the dangers of using chemicals that can deplete the still-recovering ozone layer.