Summary How do daylight hours affect plants? Just like humans do, plants respond with developmental and physiological changes to short and long days. It is known as photoperiodism and can be used as a powerful tool to manipulate and improve the vigour of your crops, together with correct fertilisation. Find out how in this article. 1. What is it?
It is well known that what defines a species is the content of its genetic information. However, environmental conditions play an important role in the nature of plant communities. One of those environmental factors is the hours of sunlight, required to perform photosynthesis. The light induces in plants a variety of responses that can modify their development, physiology and growth, which in some cases can lead to serious crop management problems. The length of light time mainly affects seed dormancy and germination, asexual reproduction and flowering. This reaction to the hours of light, called photoperiods, is defined as photoperiodism. Do not confuse this concept with phototropism: when a plant leans or grows directionally in response to light (the shoots usually move towards the light; the roots tend to move away from it).
The preferred sunlight length is called “Critical Day Length” and it varies between species. According to this, we can distinguish between long-day plants and short-day plants. Similar to humans, some species are more active during the day or the night. Long-day plants present a higher activity during hen days have long periods of sunlight and struggle when the majority of the day is occupied by a period without sunlight. Short-day plants show the opposite, suggesting that long nights are favourable for their proper development. 2. How do scientists study it? The sunlight radiates ultraviolet light, visible light and infrared radiation containing a wide variety of wavelengths. Some of them produce effects in plants that can be tested under controlled conditions. To measure the photoperiod effects, light receptors located in the leaves are exposed to different wavelengths. For example, it was observed that those photoreceptors react to changes in far-red light, sending signals that regulate seed germination and flowering. The photoreceptors determine the preference for the short or long days. They are present in two reversible forms that were discovered to be switched by the far-red light. When long-day plants are treated with a flash of red light, they produce flowers. However, when if they are exposed to far-red light, flowering is prevented. The results obtained when studied short-day plants are exactly the opposite: red light prevents their flowering, whereas far-red light promotes flowering. So far, this is one of the main wavelengths defined to have a direct effect in the photoperiodism, together with the blue light that opens stomata and promotes flowering in some long-day plants. We recommend doing a brief research on what type of plant your crop belongs to, although some authors extend this classification by also defining day-neutral plants, which are insensitive to day length. 3. Take advantage of it Once you know what type of plants your crop belongs to, especially in controlled environments like a greenhouse, you can manipulate the length of the light periods to maximise your benefits. Adding flashlights in the middle of long nights periods (the absence of sunlight period) can promote certain characteristics in the plant development according to our necessities. When working with long-day plants, the addition of a flashlight in the middle of a long night will promote the flowering since this night break will make the plants behave as they would do in short night days. The opposite can be induced in short-day plants. With a flashlight interrupting the constant absence of light long nights, you can avoid or delay flowering in your crops.
If your field is in the Equator, it will constantly get 12 hours of light per day in all seasons. However, the duration at all other latitudes varies with the seasons. Find the information about the daylight hours in your specific area to choose the plants that can give you more benefits. In addition, use the i-Plant Nutrition software to find the best fertilization program and reinforce its profitability to the maximum.