Seasonal change is a common phenomenon in temperate regional countries. Plants get new looks during every new season. Have you ever wondered how plants recognize and change according to these seasons? After reading this article, you will be able to find the answer to this question.
As we already know, there are four major seasons named spring, summer, autumn, and winter. Seasonal changes can be described as the differences in temperature and the hours of getting daylight during a year. Therefore, it relates to changes in day and night lengths. These changes occur due to the Earth’s movement around the sun and the tilted rotational axis of the Earth. It allows some parts of the Earth to get direct sunlight and the other parts to get less sunlight and heat. Furthermore, the parts getting most of the direct sunlight and heat will have spring and summer, while other parts have autumn and winter. In summer, daylight lasts longer, and nights are short whereas in winter, days are shorts and nights are long.
According to seasonal changes, plants change their appearance by blooming, flowering, shedding, and becoming dormant. In spring, flowers start to bloom, and trees have young leaves and flowers. They have mature leaves and flowers during summer. They get tall, bear fruits, and most of their growth happens during this season. In autumn, their leaves become brown and shed. Since winter is colder and gets less sunlight compared to the other seasons, plants tend to stay dormant without any leaves, flowers, or fruits.
Figure 1: Leaves turn brown and shed during autumn
How do they decide to change as above at the correct time? Unlike us, they do not have clocks or calendars! The main reason is that plants are composed of light-detectors called photoreceptors. There are two types of photoreceptors in plants, and they are phytochromes and cryptochromes. Phytochromes are sensitive to the red and far-red region of the visible spectrum, whereas cryptochromes are sensitive to the blue region. The amount of the receiving light can be detected by those receptors.
During shorter days (daytime is less), they identify that there is less sunlight to be obtained and change accordingly. This response, according to the length of day and night, was described by the word photoperiodism. In other words, photoperiodism is showing responses to the length of day or night by organisms. This fascinating discovery was done by W. W. Garner and H. A. Allard in 1920. Different plants have different photoperiods. Some plants prefer more daylight, while others prefer less daylight.
Figure 2: Plants remain dormant during winter
The best-described example of photoperiodism is the flowering of plants. Most plants recognize the length of the dark period which is critical for the initiation of flowering. When a plant reaches its critical photoperiod by receiving an appropriate length of night period, it acts as a stimulus and starts flowering as a response. Based on photoperiod, plants can be classified into three categories. They are long-day plants, short-day plants, and day-neutral plants. When the length of night exceeds its critical photoperiod, some plants start flowering. Those plants are called short-day plants. Plants that start flowering when the length of night is less than their critical photoperiod are called long-day plants. However, some plants do not respond to photoperiod at all. Those plants are named day-neutral plants.
Now you know how plants get new looks during every new season at the correct time. By perceiving light signals via phytochromes or cryptochromes, plants undergo this amazing phenomenon called photoperiodism. They bloom, flower, shed, and become dormant in this astonishing world based on the season! Isn’t it amazing?
References:
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/photoperiodism
https://www.happysprout.com/inspiration/seasons-plant/#:~:text=These%20amazing%20seasonal%20changes%20in,temperature%20also%20plays%20a%20role.
https://www.britannica.com/science/photoperiodism
http://www.biologyreference.com/Ph-Po/Photoperiodism.html
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