Evolutionary Timeline Of Cold Weather Adaptation In Plants
December 23, 2013

Researchers Analyze How Plants Evolved To Deal With Cold Weather

redOrbit Staff & Wire Reports - Your Universe Online

A team of researchers have compiled the largest-ever dated evolutionary tree of angiosperms, and their efforts have led to new insights into how these flowering plants changed in order to withstand winter weather.

The study, which currently appears online in the journal Nature, features evolutionary information on more than 32,000 angiosperm species, including leaf and stem data. They combined that information with freezing exposure records in order to recreate how plants altered their characteristics over time in order to cope with cold temperatures as they spread globally.

“Freezing is a challenge for plants. Their living tissues can be damaged. It's like a plant's equivalent to frostbite. Their water-conducting pipes can also be blocked by air bubbles as water freezes and thaws,” lead author Amy Zanne, an assistant professor of biology in the George Washington University's Columbian College of Arts and Sciences, said in a statement Sunday.

“Until now, we haven't had a compelling narrative about how leaf and stem traits have evolved to tolerate cold temperatures,” she added. “Our research gives us this insight, showing us the whens, hows and whys behind plant species' trait evolution and movements around the globe.”

According to Zanne and her co-authors, their findings indicate that plants most likely acquired the majority of their adaptive traits before moving into colder regions. Furthermore, the study also suggests that most modern flowering plants, trees and agricultural crops might not have the characteristics required to respond to climate change.

“Only some plants were able to make the adjustments to survive in cold climates,” explained co-author Pam Soltis of the University of Florida (UF) Department of Biology. “In fact, some had traits used for other purposes that they co-opted for cold tolerance. The results have implications for plant response to climate change – some plant lineages, including many crops, will not have the underlying genetic attributes that will allow for rapid responses to climate change.”

The investigators identified three frequently repeated evolutionary shifts that they believed flowing plants made in order to combat cold temperatures. Those adaptations include seasonal dropping of the leaves in order to shut down the pathways that carry water between roots and leaves, creating thinner water-conducting pathways to allow them to maintain their leaves while reducing the risk of air bubbles during the freezing/thawing process, or dying into the ground either re-sprouting from their roots or growing new plants from seeds when conditions improve.

Furthermore, they identified the order of evolutionary events. Typically, woody plants became herbs or developed skinnier water-conducing pathways prior to entering freezing climates, while other plants usually began dropping their leaves after they reached the lower-temperature regions. Compiling the data required hundreds of hours of work combing multiple plant databases including tens of thousands of plant species, the researchers said.

"Some of these changes were probably not as simple as we once thought. Adjusting to big shifts in their environments is probably not easy for plants to do,” Soltis said. She and her colleagues plan to use their findings in order to analyze other aspects of the evolutionary history of plants, including their responses to environmental factors other than cold weather.

“The onset of freezing temperatures did not affect the entire world, but only certain habitats became colder,” the UF professor added. “Certain lineages could not move into the cold, but were able to persist unaffected by the cold in warmer areas. With climate change that is human-induced, all habitats will be affected over a short period of time, and plants and other organisms will have to adapt quickly if they are to survive.”