The Ice-Defying Science Behind Cherry Trees’ Supercooling Survival

In the chilly winters of British Columbia, sweet cherry trees employ a fascinating survival trick called supercooling, allowing their flower buds to stay unfrozen even in sub-zero temperatures.

But this delicate balance can be shattered by a sudden cold snap, as seen in January 2024 when extreme weather wiped out most of the region’s cherry crop. Researchers are digging deep into how these trees manage this feat and why their protection fades in early spring. These insights could be crucial as climate change threatens to make winter even more unpredictable.

Understanding How Cherry Trees Survive Winter

Researchers at The University of British Columbia, Okanagan Campus are studying how sweet cherry trees protect their flower buds from freezing during harsh winter conditions.

Dr. Elizabeth Houghton, a recent graduate from the Department of Biology in the Irving K. Barber Faculty of Science, published new research in Plant Biology exploring this natural defense. Like many fruit trees, sweet cherries use a survival strategy called supercooling, a process that allows their undeveloped flower buds to avoid freezing even in sub-zero temperatures.

This ability is essential for fruit production, as the buds must survive the winter to grow into fruit the following season.

Cold Snap Devastation in the Okanagan

In January 2024, a severe cold snap in the Okanagan saw temperatures drop to -27°C (-17°F), causing widespread damage to fruit trees. An estimated 90 percent of the expected cherry crop was lost.

While many trees have natural methods to survive harsh winters, a supercooling survival process in stone fruits still raises questions for researchers.

The Metastable Magic of Cherry Buds

“Plants like sweet cherries can survive freezing temperatures in winter using supercooling. When in a supercooled state, the liquid in plant cells can avoid freezing, even at temperatures well below 0°C —we call this a metastable liquid. However, the liquid can freeze if triggered by an impurity or ice particle,” she says.

“We don’t fully understand how this works in some plant structures, and we wanted to learn more about how sweet cherry flower buds survive cold temperatures.”

Unique Structures in Cherry Buds

While most research on stone fruit-bearing trees has focused on peaches, Dr. Houghton notes that little attention has been paid to sweet cherry flower buds containing multiple primordia. These cell structures develop into a flower and eventually produce fruit, rather than just a single one like those of a peach tree.

Dr. Houghton examined several factors to better understand supercooling, including how ice forms in the buds, how the outer layers freeze, and the internal changes buds undergo as the weather warms and spring approaches.

Vulnerability in Early Spring

Dr. Houghton notes that cherry trees are especially vulnerable in early spring because they lose their ability to supercool as the buds grow. A sudden cold snap can be disastrous, she explains.

“Cherry buds have a special way of protecting themselves from freezing in winter, but as buds grow in the spring, they lose some of that protection,” says Dr. Houghton.

Protecting Fruit Crops in a Changing Climate

“We are trying to understand better how these fruit buds survive extreme winter temperatures,” she adds. “And because there is some debate about what winters might look like in the future—we may experience more extreme cold snaps—it’s important that we learn from the cherry trees to work towards protecting fruit crops.”

Reference: “Investigating properties of sweet cherry (Prunus avium) flower buds that help promote freezing avoidance by supercooling” by E. Houghton, Y. Watanabe, D. Neilsen, L. M. Nelson and K. Hannam, 21 August 2024, Plant Biology.
DOI: 10.1111/plb.13697

The governments of Canada and British Columbia funded this project through the Canadian Agricultural Partnership, a federal-provincial-territorial initiative. The Investment Agriculture Foundation of BC delivered the program.

An anonymous private foundation, Agriculture and Agri-Food Canada, the BC Cherry Association and the Natural Sciences and Engineering Research Council of Canada provided additional funding.

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