Plant adaptations to freezing

The Big Horn Basin has an incredible temperature range. In the last six months, I saw 104 degrees in the summer and 36 degrees BELOW zero last week!

Humans are lucky to spend most of their time in nice, temperature-controlled buildings but plants aren’t that lucky. It is really quite amazing that plants can survive these temperature extremes. How do they do it? I’ll focus on plant adaptations to freezing and will write another article this summer on heat adaptations.

Freezing causes major issues for plant cells which is why tomato plants get droopy and black after one light frost. Liquid within the cell freezes, expands and bursts the cell walls. If this happens to enough cells, plant function stops and it dies. Plants avoid this through a variety of strategies.

The first option is to avoid freezing temperatures all together – snowbirds of the plant world. Annual plants complete their entire life cycle in nice summer growing conditions. The only thing that has to survive cold conditions is the seed.

The second option is to mostly avoid winter by having aboveground plant parts die back while roots survive underground. Perennial grasses and flowers take this approach. Essential nutrients and energy are pulled from leaves and stored in the roots for the winter. The ground has a more even temperature and provides nicer living conditions.

Some plants, like trees and shrubs, have woody structures that have to survive bitter cold conditions. Evergreen trees don’t even lose their leaves so continue photosynthesizing all year, although this process is greatly reduced over winter.

Plants that have permanent aboveground structures must prevent intercellular freezing. They start acclimating to cold conditions in the fall. Some plants pull water from inside the cell so it can freeze outside the cell where it doesn’t do as much damage. The liquid remaining inside the cell is concentrated and has a much lower freezing point, called “deep supercooling.” Other plants even produce antifreeze proteins to prevent ice formation.

Forty degrees below zero is a cutoff point where even adapted plants have a hard time preventing freezing. This explains why there is a tree-line in the high mountains.

Adapted plants can be damaged by cold when 1) temperatures are lower than their tolerance, 2) low temperatures occur early in the season before plants have acclimated, or 3) after the plants have deacclimated in the spring, or 4) if there are temperature swings in the winter causing plants to deacclimate.

I don’t know if I say this enough but, Plants are so COOL! Keep warm out there.