Ottawa Citizen

Plants, bugs need set number of cold days

- TOM SPEARS tspears@postmedia.com twitter.com/TomSpears1

Today we continue our annual look at what makes this season special, a time when nature is doing much more than just hitting the Pause button for three months. Welcome to the Science of Late Winter.

Plants have been busy through the deep freeze, even though winter keeps them very still and we can’t see any activity. They are silently and invisibly preparing for the approachin­g spring.

Recharging batteries is “a good analogy,” says plant biologist Jessica Forrest of the University of Ottawa. “Basically there is some genetic reprogramm­ing that happens, that basically restarts the clock in a sense and lets organisms spring back to life in the spring. It’s a clock where — maybe the way to express it is that it (the plant) is not just responding to time. It’s responding to thermal time.”

This appears to be the flip side of a fact of life for many farmers, she said. Crops such as corn and soybeans need a certain number of “heat units” in summer to do well, meaning a certain number of days of warm weather. A sunny but cool summer won’t let them mature. In the same vein, overwinter­ing plants need “cold units,” rather than just a long pause before spring arrives. “The heating units are more familiar, but there is also a chilling process that is very widespread in organisms.

“I think at the epigenetic level … something is happening ” in the cold, Forrest said. “Gene expression is changing.”

Gene expression refers to the fact that individual genes are sometimes more active and other times less active, though the genes themselves never change.

“It is a biological­ly important time,” she said. “It’s actually relevant to plants and insects and lots of things that are dormant.

“I don’t think anyone understand­s the mechanism by which this happens but organisms do have chilling requiremen­ts in order to flower or do their thing in the spring. They seem to require a certain number of cold days — days below a certain temperatur­e.

“If you get a warm day in January, things don’t just start to bloom because they haven’t met that chilling requiremen­t yet.

“Insects do this, too. We don’t tend to think about the insects in the winter but they are around, they’re dormant, undergroun­d or some of them are under tree bark.” She studies wild bees (not honeybees) that survive the winter in isolation. Again, she said, winter is important: A bee needs a certain length of “chilling ” time and won’t wake up during a January thaw.

“The bees I study actually overwinter as adults inside cocoons inside trees. They are adults. They are basically completely ready to go, but … they need to get a certain amount of chilling in first.”

 ?? LARS HAGBERG/THE CANADIAN PRESS ?? Winter is “biological­ly important” to living things lying dormant, says scientist Jessica Forrest.
LARS HAGBERG/THE CANADIAN PRESS Winter is “biological­ly important” to living things lying dormant, says scientist Jessica Forrest.
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