Pakkasjäädytys

Pakkasjäädytys, also known as frost or freezing damage, refers to the cellular and tissue injury that occurs in plants when temperatures drop below a critical threshold, typically around the freezing point of water. This phenomenon is a significant factor limiting the geographic distribution of many plant species and can cause substantial damage to agricultural crops.

The primary mechanism of injury involves the formation of ice crystals. Extracellular ice formation, which occurs between plant cells, can lead to dehydration as water moves out of the cells to form ice. This dehydration stresses the cells and can disrupt cellular functions. Intracellular ice formation, where ice crystals form within the cells, is generally more damaging. The sharp ice crystals can rupture cell membranes and organelles, leading to irreversible damage.

Several factors influence a plant's susceptibility to pakkasjäädytys. These include the rate of cooling, the minimum temperature reached, the duration of freezing temperatures, and the plant's genetic makeup. Acclimation, a process where plants gradually adapt to colder temperatures, can significantly increase their freezing tolerance. This acclimation involves physiological changes such as the accumulation of solutes within cells, which lowers the freezing point of cellular water, and changes in membrane composition.

Symptoms of pakkasjäädytys can vary depending on the plant part and the severity of the damage. They may include wilting, browning or blackening of leaves and stems, and in severe cases, the death of the plant. Understanding and mitigating pakkasjäädytys is crucial for agriculture and horticulture, with strategies such as selecting cold-hardy varieties, using protective covers, and employing irrigation techniques to moderate soil temperatures.