Three particular coping mechanisms help plants deal with cold weather, according to a study on over 32,000 species of flowering plants. (Photo: Bruce Guenter, CC BY 2.0)

Most of us know that nature has endowed organisms with skills and traits to survive harsh weather. However, scientists involved with a new study have claimed to identify the exact evolutionary mechanisms in some plants that let them survive freezing temperatures well below negative fifteen degrees.

The project was based on the construction of the largest evolutionary tree to date. That is, over 32,000 species of flowering plants were studied. The researchers were able to study the evolutionary coping mechanisms in each of the plants based on freezing exposure records and leaf and stem data. One of the most important findings was that many plants acquired a unique characteristic - dying back to the roots in winter - to help them cope with the harsh climate.

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The research team studied fossil evidence and reconstructed past climatic conditions to suggest that early flowering plants lived in warm tropical environments. They evolved ways to survive the cold conditions as they spread out to higher elevations. Those in the tundra region, such as the Arctic cinquefoil and the three toothed saxifrage, have developed abilities to survive in freezing temperatures below negative 15 degrees Celsius, according to coauthor Jeremy Beaulieu, of the National Institute for Mathematical & Biological Synthesis (NIMBioS) at the University of Tennessee.

Plants, unlike animals, are unable to move or generate heat in order to escape the cold. Therefore, their coping mechanism involves structural and functional changes. It's not actually the cold, but the ice that plants need to resist. Freezing and thawing, for instance, can block internal water transport mechanisms by causing air bubbles to form within. These can block the flow of water from the roots to the leaves, and end up killing the plant, co-author Amy Zanne, of George Washington University, said in a press release.  

Plants have, however, developed traits to overcome these problems, three of which the researchers identified.

There are plants - hickories and oaks, for example - that drop their leaves before the winter sets in, thereby shutting off the flow of water between roots and leaves. They grow new leaves, specifically water transport leaves, when weather gets warmer. Another category of plants - including birches and poplars - constricts water transport cells to prevent blockage during freezing and thawing. Finally, there are some plants that die back into the ground during the winter, and miraculously re-emerge under a congenial climate. They either re-sprout from their roots or begin growing from new seeds. 

The researchers found that many plant species, with the exception of the plants that shed and replace their leaves, equipped themselves with these coping strategies well before the onset of icy winters. This led the researchers to speculate that drought-like environmental pressures could have caused the plants to evolve this way.

The study team is currently planning to further their study on the evolutionary tree to account for coping mechanisms in plants against other stressors, such as drought and heat.