Definition - What does Photoperiodism mean?

Photoperiodism refers to the response of plants to the lengths of dark and light periods. Many angiosperms, or flowering plants, have a protein that can sense seasonal changes in light. A plant will flower depending on these changes in light levels.

Each plant has a different photoperiod that it requires to flower and propagate. Plants generally fall into three photoperiod categories: long-day plants, short-day plants, and day-neutral plants.

MaximumYield explains Photoperiodism

The effect of photoperiodism in plants is not limited to when they will flower. Photoperiodism can also effect the growth of roots and stems. Additionally, photoperiodism affects the loss of leaves in some plants during different seasons.

Although the three photoperiod categories seem to suggest that plants depend on the amount of daylight they receive, modern biologists believe the amount of darkness that plants receive is what causes them to flower.

Long-day plants generally flower during the summer months when nights are short and days go longer. Examples of long-day plants are carnations and oats. On the other hand, short-day plants flower during seasons that have longer periods of night. They require a continuous amount of darkness before flower development can begin. Some examples of short-day plants are cotton, soybeans, and rice. However, some plants referred to as day-neutral plants do not flower based on a particular photoperiod.

Gardeners can take advantage of the knowledge of a plant’s photoperiod by manipulating a plant into flowering before it would naturally do so. Manipulating a plant into a flowering stage can provide several benefits, particularly to commercial growers. For example, plants can be forced to flower by exposing or restricting its access to light. Plants can then be manipulated to produce fruit or seeds outside of their usual season.

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