What is Dormancy for Plants?
In nature, plants must adapt to environmental conditions in order to survive. Cold weather in winter, extreme drought in summer, or other adverse environmental factors may require plants to slow down or stop their growth processes completely. This process is called dormancy. Dormancy is a natural mechanism that allows plants to survive in adverse environmental conditions.
What Are The Types Of Dormancy?
Dormancy can occur in different ways depending on the genetic structure of the plant and environmental conditions. It is generally divided into two main groups: obligatory dormancy and environmental (facultative) dormancy:
Obligatory Dormancy: It is a biological necessity that requires the plant to stop growing for a certain period of time. For example, some fruit trees, such as apples and peaches, enter a period of rest for a certain period during the cold winter months. They cannot start growing again without completing this process.
Environmental (Facultative) Dormancy: The plant stops growing due to unsuitable environmental conditions, but can quickly start growing again when suitable conditions are provided. For example, some plants growing in arid regions enter dormancy when there is no water and start growing again when the first rains come.
Factors Causing Dormancy
Sleep in plants is a state in which growth and development are temporarily supported. This helps plants adapt to adverse environmental conditions. The factors that cause dormancy are examined under two headings.
1. Environmental Factors
- Temperature Changes
Low temperatures: Especially in the winter months, many plants enter dormancy to protect themselves against cold stress.
High temperatures: Extreme heat and drought conditions can stop growth to prevent water loss. - Day Length (Photoperiod)
The emergence of daylight, especially in the fall months, can cause dormancy in plants.
Long-day flowers can enter dormancy with short days, and short-day flowers can enter dormancy with long days. - Water and Humidity Deficiency (Drought Dormancy)
A lack of water causes plants to slow down their metabolism and enter dormancy.
Some plants living in arid regions remain in dormancy until it rains. - Nutrient Deficiency
Deficiency of basic nutrients such as nitrogen, phosphorus and nutrients in the soil can lead to dormancy. - Oxygen Deficiency (Hypoxia)
When there is a lack of oxygen in the roots due to flooding or heavy soil structure, plants can enter dormancy.
2. Physiological (Internal) Factors
- Hormone Balance
Plant hormones play a major role in the onset and termination of dormancy:
Abscisic Acid (ABA): The main hormone that causes dormancy, suppresses growth.
Gibberellin
(GA): The hormone that breaks dormancy and promotes growth.
Cytokinin and Auxin: Exit from dormancy.
- Genetic Structure
Some plants are genetically programmed to enter dormancy at certain periods. - Protection of Growing Points
Dormancy is an important part of the dormancy process, especially in perennial plants. In this process, the development of buds is suppressed by certain hormones, growth is temporarily stopped and the plants are protected against adverse climatic conditions.
End of Dormancy and the Awakening Process
When environmental signals become favorable, plants gradually exit dormancy and resume active growth. This process, known as the awakening of plants, involves several key factors and physiological changes.
- Environmental Triggers for Dormancy Break
Plants rely on external cues to determine when to exit dormancy. The most important factors include: - Increasing Temperature: Warmer weather signals the end of winter dormancy in temperate plants.
Longer Daylight Hours: Many plants respond to increasing photoperiods in spring, triggering growth.
Increased Moisture: For drought-dormant plants, rainfall or higher humidity can stimulate awakening.
Chilling Requirement Completion: Some plants require a period of cold exposure before they can resume growth, ensuring they do not break dormancy too early.
Hormonal Changes Stimulating Growth
As dormancy ends, the plant’s internal hormone balance shifts:Gibberellins (GA) Increase: These hormones promote cell elongation, bud break, and seed germination.
Abscisic Acid (ABA) Decreases: Since ABA suppresses growth, its decline allows dormancy to end.
Cytokinins and Auxins Rise: These hormones stimulate root and shoot growth, encouraging new tissue development. - Bud Swelling and Leaf Emergence
Dormant buds start to swell as internal activity resumes.
Protective bud scales open, and new leaves begin to unfurl.
In trees, sap flow increases, providing nutrients to developing tissues. - Root System Reactivation
Roots resume water and nutrient uptake to support new growth.
In perennial plants, stored energy (carbohydrates) is mobilized to fuel early shoot development.