Plants, as living organisms, are subjected to numerous stimuli that help them “know” what to do and how to act at all times. For example, when it begins to cool, deciduous trees stop feeding their leaves, since they would not survive frost.
But the thing goes beyond knowing when it is time to rest or resume activity. In fact, the number of hours of daylight will determine, to a large extent, when the plants must perform each of their functions. This process is known as photoperiodand is vital for all plant beings.
What is the photoperiod?
The photoperiod is the set of functions that plants perform depending on whether it is day or night, the season of the year and even the solar cycle. In other words, the variation in the number of hours of light, as well as its duration and periodicity, are factors that influence the regulation of plant germination and growth.
For this reason, in the humid tropical forests the vast majority of plants are evergreen, since temperatures remain stable all year round, and it rains frequently.
On the other hand, in regions where frosts and / or droughts are registered, there are many that are deciduous: some because they have leaves that would die if they were covered with ice or snow; others to avoid dehydration (the maintenance of the leaves entails a significant cost of water, which, if heat and drought are combined, it is to be expected that the plant goes thirsty, since the precious element will be lost quickly. the fewer leaves they have, the less water they will need, and the less they will lose too).
How do you recognize the photoperiod?
The plants have photoreceptors that are light-sensitive cells, which convert optical energy into electrical energy. There are two types: phytochromes, which are proteins that act as photoreceptors for both red light and far red light; and cryptochromes, which are those that detect blue light.
When they do, trigger a whole series of activitiesdepending on the type of light they detect. Thus, while phytochromes trigger the production or inhibition of flowers, cryptochromes regulate seed germination and growth, in addition to the circadian rhythm, that is, the variation over time of the biological processes that occur in the plants (and also in animals).
Thanks to this, we can classify them based on how they respond to the photoperiod. For example, we know that there are plants with short days, long days and others that simply do not respond to the photoperiod and are known as neutral. The characteristics of each of them are:
- Short-day plants: these are the ones that need the nights to be longer than the days to be able to bloom. Some examples are corn, coffee, the poinsettia or the strawberry.
- Long-day plants: these are the ones that need more hours of light than darkness so that they can bloom, such as carnation, oats or campanula.
- Neutral day plants: these are the ones that bloom at some point in their development, or after being exposed to, for example, a period of low temperatures. Some examples are rose bushes, tomatoes or pumpkins.
All plants, since they are only seeds, are subjected to numerous stimuli that will determine their life. Depending on whether they are short, long or neutral days, and the type of light that their photoreceptors detect, they will perform some functions or others.
Therefore, When a photoreceptor of a short-day plant detects, let’s say, red light, what will happen inside them is that they will not produce flowers; On the other hand, if the light is far red, the effect will be reversed. In those that are of long days, those that are in charge of regulating the production of the flowers are the photoreceptors of blue light, but the effect is the same.
Can you control the photoperiod?
In nature, plants know what to do at all times. They have been doing it since they began their evolution, more than 300 million years ago, and it is hoped that it will continue to be that way forever. But humans have domesticated many plants; that is, we have learned to cultivate them to benefit from them. Since the invention of greenhouses, and later of bulbs that stimulate growth and / or flowering, we are also learning to control the photoperiod of plants.
Although at first it was done to have food all year round, now it is also done to accelerate a process that we likefor example so that they are beautiful in a specific month (like the poinsettia, which is a shrub that we force to flower, that is, to remove its red bracts, at Christmas).
The most interesting thing is that we don’t need much to control the photoperiod. Continuing with the example of the poinsettia, in winter you will only have to put it in an area where the sun does not shine directly for twelve hours, and where it is at a temperature of about 20ºC, until you see it bloom.
How to redden the leaves of the Poinsettia
And if what you want is to advance the season of a crop, you can sow its seeds in a germinator electric. In this way, you can harvest lettuces, for example, much earlier than expected.
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