Plants That Survived Earth’s Worst Mass Extinction May Reveal How Life Adapts to Extreme Heat
About 252 million years ago, life on Earth nearly collapsed. Global temperatures soared, carbon dioxide levels rose sharply, and ecosystems collapsed so severely that up to 81 percent of marine species and 89 percent of land vertebrates disappeared. Forests have disappeared, leaving much of the planet devoid of vegetation. But one group of plants not only survived, but took over.
New research from the University of Leeds reveals that primitive plants called lycophytes survived this period and spread across the landscape left behind. The study, published in Nature ecology and evolutionshows that these plants likely used a different strategy by absorbing carbon dioxide at night rather than during the day.
“Our results suggest that under future warming, plants with CAM photosynthesis characteristics may become much more important,” lead author Zhen Xu said in a press release. “If the world experiences extreme, sustained heat, plant communities could shift to species more able to tolerate high temperatures and water stress.”
Extreme heat after the Permian-Triassic mass extinction
The extinction event, often called “the Great Dying”, was followed by a prolonged period of extreme heat. For about five million years, carbon dioxide levels remained high, reaching more than four times modern levels, pushing temperatures beyond what most plants can survive.
Lycophytes.
(Image courtesy of Dr. Zhen Xu)
Under these conditions, many factories could no longer operate as they normally would. Water loss became harder to control and the process that powers photosynthesis began to fail.
The fossil record shows that dense forests gave way to low, sparse vegetation cover dominated by small, fast-growing species that could tolerate heat and drought.
Learn more: How index fossils help reconstruct Earth’s ancient and mysterious past
How Plants Survived Using Nocturnal Photosynthesis
To piece it all together, researchers combined fossil evidence, climate modeling and chemical data preserved in ancient plant remains.
Carbon isotope signatures, which show how plants processed carbon, showed that lycophytes behaved differently from other plants of the time. Their signatures closely match those of modern plants that use CAM photosynthesis, a way of absorbing carbon dioxide at night to conserve water.
Instead of following the usual diurnal cycle, these plants likely stored carbon dioxide and used it later, reducing water loss and avoiding heat stress.
Climate simulations confirm this, as many fossil sites were located in regions where average daily temperatures exceeded 104 degrees Fahrenheit (40 degrees Celsius), with peaks reaching 149 degrees Fahrenheit (65 degrees Celsius). These are the kinds of conditions these plants could handle.
“The analysis brought together many distinct scientific disciplines to test how this group of enigmatic plants not only survived the Great Dying, but also how they were able to thrive in a highly stressed environment,” co-author Barry Lomax said in the press release.
How lycophytes took over after the mass extinction
As other plants disappeared, lycophytes quickly spread across continents, becoming what scientists call “disaster taxa,” species that take hold quickly after environmental collapse.
Lycophytes.
(Image courtesy of Dr. Zhen Xu)
These smaller, less productive plants likely removed less carbon from the atmosphere than the forests they replaced and recycled fewer nutrients back into ecosystems, determining how the planet recovered over millions of years.
“Understanding how the various physiological strategies of plants have shaped ecosystems in the past helps us anticipate how vegetation might reorganize in the future, and because plants are the basis of terrestrial food webs, changes in dominant plant strategies can alter the functioning of the entire Earth system,” added co-author Benjamin Mills.
What followed was not a return to previous ecosystems, but a shift to something new, shaped by plants built for extreme conditions. If temperatures continue to rise, similar changes may not remain a thing of the past.
Learn more: Animals of the Cambrian period experienced a great evolutionary surge, shaping life today
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