Physical dormancy

Definition

Physical dormancy refers to a condition in seeds where their outer seed coat is impermeable to water and gases, preventing germination even when conditions are favorable. This type of dormancy acts as a survival mechanism, allowing seeds to withstand adverse environmental conditions until they can emerge and grow successfully. The physical barriers presented by the seed coat play a crucial role in determining the timing and success of germination, which is essential for the plant's lifecycle.

5 Must Know Facts For Your Next Test

1. Physical dormancy is primarily caused by a hard seed coat that prevents water and gas exchange, crucial for germination.
2. Seeds with physical dormancy often require specific environmental cues, like temperature changes or abrasion, to break their dormancy.
3. Certain plants, such as some legumes and many desert species, exhibit physical dormancy as an adaptation to their natural environments.
4. The duration of physical dormancy can vary widely among species, sometimes lasting for several years before conditions are right for germination.
5. Seeds can be stratified to help overcome physical dormancy by exposing them to cold and moist conditions, simulating natural winter conditions.

Review Questions

• How does the structure of the seed coat contribute to the phenomenon of physical dormancy?
  • The seed coat plays a vital role in physical dormancy by acting as a barrier that prevents water and gas exchange. This impermeable outer layer protects the seed from environmental stresses but also inhibits germination under favorable conditions. The hardness and thickness of the seed coat vary among species, which affects the duration of dormancy and the strategies needed to overcome it.
• What are some common methods used to break physical dormancy in seeds, and why are they effective?
  • Common methods to break physical dormancy include scarification, which involves mechanically or chemically weakening the seed coat, and stratification, which exposes seeds to cold moist conditions. These methods are effective because they mimic natural processes that seeds would experience in their native environments. For instance, scarification can replicate the wear and tear that occurs through animal digestion or weathering, while stratification simulates winter conditions that signal seeds that it is time to germinate.
• Evaluate the ecological significance of physical dormancy in relation to plant survival strategies in varying environments.
  • Physical dormancy is ecologically significant as it allows seeds to survive harsh conditions and wait for optimal growth circumstances. In environments where resources may be limited or unpredictable, this strategy ensures that seeds do not germinate until conditions improve. This adaptability increases plant survival rates across diverse habitats, contributing to biodiversity and ecosystem resilience. Additionally, understanding these mechanisms can aid in conservation efforts for endangered species that rely on specific environmental cues for successful reproduction.

Related terms

Seed coat: The protective outer layer of a seed that can influence its dormancy and germination processes.

Scarification: The process of physically or chemically altering the seed coat to promote water absorption and break dormancy.

Germination: The process by which a seed develops into a new plant, requiring specific environmental conditions and often overcoming dormancy.