Durham, NC Researchers have found new clues to how plants evolved to withstand wintry weather. In a study to appear in the December 22 issue of the journal Nature, the team constructed an evolutionary tree of more than 32,000 species of flowering plants the largest time-scaled evolutionary tree to date. By combining their tree with freezing exposure records and leaf and stem data for thousands of species, the researchers were able to reconstruct how plants evolved to cope with cold as they spread across the globe. The results suggest 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.
Fossil evidence and reconstructions of past climatic conditions suggest that early flowering plants lived in warm tropical environments, explained co-author Jeremy Beaulieu at the National Institute for Mathematical & Biological Synthesis (NIMBioS) at the University of Tennessee.
As plants spread to higher latitudes and elevations, they evolved in ways that helped them deal with cold conditions. Plants that live in the tundra, such as Arctic cinquefoil and three-toothed saxifrage, can withstand winter temperatures below minus 15 degrees Celsius.
Unlike animals, most plants can't move to escape the cold or generate heat to keep them warm. It's not so much the cold but the ice that poses problems for plants. For instance, freezing and thawing cause air bubbles to form in the plant's internal water transport system.
"Think about the air bubbles you see suspended in the ice cubes," said co-author Amy Zanne of the George Washington University. "If enough of these air bubbles come together as water thaws they can block the flow of water from the roots to the leaves and kill the plant."
The researchers identified three traits that help plants get around these problems.
Some plants, such as hickories and oa
|Contact: Kurtis Hiatt|
National Evolutionary Synthesis Center (NESCent)