For the study, George Washington University reserachers constructed an evolutionary tree of more than 32,000 species of flowering plants to understand how plants evolved to withstand cold. They found that many plants acquired unique characteristics even before they encountered freezing.
Previous studies supported by plant fossil finds established that ancient plants thrived in warmer temperatures. However, due to climatic changes and shift in habitat to higher latitudes and elevations, plants evolved in such a way that they could cope with the cold. Currently, there are some plant species like the Arctic cinquefoil and three-toothed saxifrage that can survive in temperatures below -14°Celsius.
While animals fight the cold by shifting to different locations or generating heat to keep themselves warm, plants are incapable of doing any of these. The snow on the ground poses some major problems for them. Freezing temperatures result in the formation of air bubbles that block the internal water transport system in plants.
"Think about the air bubbles you see suspended in the ice cubes," said co-author Amy Zanne of the George Washington University in the statement. "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."
After mapping a large collection of leaf and stem data onto their evolutionary tree for flowering plants, researchers found that most plants equip themselves for the winters well before the season sets in. Through the study, researchers identified three traits plants developed to cope with freezing temperatures. Some plants shed their leaves before winter sets in. This eliminates the need to transport water from the roots to the leaves, which in turn avoids any internal blocking. Other plant species have narrower water transport cells, which make the parts of the plant that deliver water less susceptible to blockage during freezing and thawing. Another trait plants have developed to withstand the cold is the technique of "dying back to the roots in winter" and growing up as new plants in warmer temperatures.
"This suggests that some other environmental pressure - possibly drought - caused these plants to evolve this way, and it happened to work really well for freezing tolerance too," said Zanne.
Researchers of the study now plan to determine how plants evolved to withstand other weather conditions like droughts and heat.