As the crispness of fall in the air refreshed my senses, I couldn’t help but think of the even cooler temperatures to come and their effects on plants.
My curiosity led me to ask questions like “What is happening inside a plant during the winter?” and “What mechanisms allow a plant to make it through freezing temperatures?” So, I did my research. After digging through science-based resources to learn more about winter’s influence on plants, the topic of dormancy came up again and again.
As leaves filled with chlorophyll die in the fall, plants store carbohydrates and other nutrients in their roots to survive the winter and spur spring growth. In Pennsylvania and other temperate regions, winter is a time of reduced metabolic activity called dormancy. It’s when the freezing temperatures and limited liquid water prevent plants from growing. This ability to stop growing when conditions are unfavorable is crucial to a plant’s survival and provides a time of rest.
When I explored facts about dormancy, I learned two different types occur in plants: ecodormancy and endodormancy.
Ecodormancy is when a plant’s environment puts it into a resting state. Cooling temperatures, shorter days, changes in the sun’s angle and the availability of moisture initiate ecodormancy. Once temperatures get warmer and conditions are favorable, plants start to grow again.
Endodormancy, sometimes called deep dormancy, involves complex physiological changes that result in the plant not growing, even when conditions are favorable. Shorter day length and freezing temperatures result in an internal suppression of growth. Scientists have discovered that endodormant plants contain an increased amount of abscisic acid, or ABA. ABA’s primary purpose is to decrease the plant’s growth and prevent the germination
Dormant plants also contain cryoprotectants, which allow plants to control when and where water freezes within their tissues. Stored sugars, salts, and other materials are concentrated within the plant’s cells, decreasing their freezing point. Water moves out of each plant cell and forms ice crystals in the intercellular spaces, protecting the plant’s cells from freezing.
Once a plant enters endodormancy, a combination of time and cold temperatures known as “chilling hours” are needed to eliminate the internal mechanism that stops a plant from growing.
Seeds have a system of protection that prevents them from premature germination in cold temperatures. Many seeds need to be stratified or held for periods at low temperatures before they will germinate. Cold stratification begins the process of breaking down seed coats through exposure to both cold and moist conditions. As the warming trends that accompany spring slowly rise, the latent energy stored within seeds will germinate. The freezing and thawing of winter help break the tough seed coat, which is necessary for some plants to germinate, but not for all.
Nature truly does seem to think of everything.
Penn State Extension is dedicated to delivering science-based information to people, businesses and communities. They partner with and are funded by federal, state and county governments. For more information on what they’re doing in Lackawanna County, visit extension.psu.edu/lackawanna-county.