Dormancy

From Free net encyclopedia

In plant physiology, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species, which enables them to survive in climates where part of the year is unsuitable for growth, such as winters and dry seasons.

Species which exhibit dormancy have a biological clock that tells them to slow activity and to prepare soft tissues for a period of freezing temperatures or water shortage. After a normal growing season, dormancy can be brought on by decreasing temperatures, shortened daylength or a reduction in rainfall.

TREES

Species that have well-developed dormancy needs can be tricked to some degree, but not fully. For instance, if a Japanese Maple (Acer palmatum) is given an eternal summer by giving it additional daylight, it will grow continuously for as long as two years. After a maximum period of sustained growth, a temperate climate plant will automatically go dormant no matter what the season or condition. Deciduous plants will lose their leaves, evergreens will curtail all new growth. This is very stressful to the plant and usually fatal. It will be 100% fatal if the plant does not receive the necessary period of cold temperatures required to break the dormancy. Most plants will require a certain number of hours of "chilling" at temperatures between about 0 °C and 10 °C to be able to break dormancy.

SEEDS

When a mature seed is placed under favorable conditions and fails to germinate, it is said to be dormant. There are two basic types of seed dormancy. The first, seed coat dormancy or external dormancy, is caused by the presence of a hard seed covering or seed coat that prevents water and oxygen from reaching and activating the embryo. The second type of dormancy, embryo dormancy or internal dormancy, is caused by a condition of the embryo which prevents germination. The oldest C-14 dated seed that was germinated into a viable plant was a ~1,300-yr-old lotus fruit, recovered from dry lakebed in northeastern China. [1]de:Dormanz