Study Offers Clues to How Plants Evolved to Cope with Cold
Researchers at UT have found new clues to how plants evolved to withstand wintry weather.
The study suggests that many plants acquired characteristics that helped them thrive in colder climates—such as dying back to the roots in winter—long before they first encountered freezing.
The research, published the journal Nature, was conducted by Jeremy Beaulieu, postdoctoral researcher at the National Institute for Mathematical and Biological Synthesis at UT, and Brian O’Meara, assistant professor in the Department of Ecology and Evolutionary Biology. It was led by Amy Zanne at George Washington University in collaboration with the National Evolutionary Synthesis Center in North Carolina and Macquarie University in Australia.
Unlike animals, most plants can’t move to escape the cold or generate heat to keep them warm. For example, freezing and thawing causes air bubbles in plants’ internal water transport systems, which can fatally block the flow of water from the roots to the leaves.
The researchers discovered three traits that help deal with cold conditions as plants spread to higher latitudes and elevations:
- Some plants, such as hickories and oaks, avoid freezing damage by dropping their leaves before the winter chill sets in—effectively shutting off the flow of water between roots and leaves—and growing new leaves and water transport cells when warmer weather returns.
- Other plants, such as birches and poplars, protect themselves by having narrower water transport cells, which makes the parts of the plant that deliver water less susceptible to blockage during freezing and thawing.
- Other plants die back to the ground in winter and then resprout from their roots or start growing as new plants from seeds when conditions are right.
To compile the plant trait data for their study, the researchers spent hundreds of hours scouring and merging multiple plant databases containing tens of thousands of species. They mapped their collected leaf and stem data onto an evolutionary tree consisting of 32,000 species of flowering plants—the largest time-scaled evolutionary tree to date.
They found that many plants were well equipped for icy climates even before cold conditions hit.
“For example, plants that die back to the ground in winter acquired the ability to die and come back when conditions improve long before they first experienced freezing,” said Beaulieu. “Similarly, species with narrow water transport cells acquired a finer circulatory system well before they confronted cold climates.”
This suggests that some other environmental pressure such as drought caused plants to evolve this way, according to the researchers.
The only exceptions were plants that shed and replace their leaves seasonally.
The researchers plan to expand their study to look at how plants evolved to withstand other environmental stresses, such as drought and heat.
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