Light deprivation works by manipulating the amount and duration of light exposure that plants receive. By controlling the photoperiod, or the duration of light and darkness in a 24-hour period, growers can mimic changing seasons and trigger or suppress the flowering process in plants.
Understanding Photoperiodism
Plants possess a remarkable ability to sense and respond to environmental changes, particularly in light exposure. Photoperiodism is the physiological response of plants to the duration of light and darkness in a 24-hour period. It is through this mechanism that plants determine the appropriate timing for various stages of growth, including flowering.
Plants rely on their leaves to collect information from the environment. They are sensitive to light intensity, temperature, and the length of darkness. This sensitivity allows plants to categorize themselves as short-day plants, long-day plants, or day-neutral plants based on their reactions to changes in the photoperiod.
It’s All About the Night
It’s interesting to note that the terms “short-day plants,” “long-day plants,” and “photoperiodism” have been used for many years to describe plants that flower in response to different lengths of daylight. However, research has demonstrated that the duration of the night period is more important than the length of the day for controlling photoperiodic responses.
Short-day plants require long nights and short days to initiate flowering. They typically release their flowers or fruits in the fall when the days become shorter and the nights longer. Short-day plants will not flower if they receive more than 12 hours of light in a photoperiod. Light deprivation techniques can manipulate these plants to flower earlier by giving them shorter days.
Some common examples of short-day crops are peanuts, legumes, broccoli, cauliflower, and buckwheat.
Long-day plants require shorter nights and longer days to initiate flowering. They need more than 12 hours of light per day to bloom. These plants are often tricked into flowering earlier using supplemental lighting to extend their daylight hours, along with light-deprivation techniques to control periods of darkness.
Some familiar long-day plants include asters, hibiscus, coneflowers, lettuce, spinach, radishes, sugar beets, carrots, and certain strawberry varieties.
Some types of plants, known as day-neutral, are not influenced by the duration of night or day hours. Most can flower regardless of the day length and rely more on environmental conditions and plant development cues. Examples of day-neutral plants include cucumbers, tomatoes, corn, peas, and some strawberry varieties that can fruit all year as long as temperatures stay between 40-90°F.
The Science Behind Light Deprivation
While light is essential for photosynthesis and plant growth, periods of darkness also play a crucial role in regulating various physiological and developmental processes in plants. One of the most significant processes that occur during periods of darkness is the regulation of gene expression. In the absence of light, specific genes are activated or repressed, initiating various physiological and developmental responses.
One important process that occurs during darkness is de-etiolation, where seedlings transition from etiolated (elongated and pale) to the green, photosynthetically active stage. Their leaves become darker green, their stems become shorter and thicker, and their roots become more developed. This stage includes the activation of genes responsible for chlorophyll synthesis, leading to the development of chloroplasts and the accumulation of pigment molecules. As a result, plants acquire the ability to carry out photosynthesis efficiently, promoting robust growth.
Dark periods are also crucial for regulating flowering in many plant species. Plants use photoperiodism to determine the appropriate time for flowering based on the length of the dark period. Short-day plants require a long, uninterrupted dark period to initiate flowering, while long-day plants require a limited dark period. The duration of the dark period also influences the production of flowering hormones, such as florigen, which trigger the transition from vegetative to reproductive growth.
In addition to flowering, dark periods also help regulate other physiological processes, including the biosynthesis of secondary metabolites, root growth, circadian rhythms, and stress responses. These processes are controlled by intricate networks of molecular signaling pathways and transcriptional regulators, which are modulated during the dark period.
Light deprivation techniques take advantage of the influence of darkness on plant growth and development. By manipulating the photoperiod, growers can control the timing of flowering and redirect the plant's energy and resources towards specific activities, such as excess foliage growth or sexual reproduction. This allows growers to optimize their harvest schedules, meet market demands more effectively, and maximize their profits.
Key Benefits of Light Deprivation
The primary goal of light-deprivation techniques is to direct a plant's energy to specific activities, such as excess foliage growth or sexual reproduction, i.e., flowering and fruit production. For example, by simulating shorter day lengths, short-day plants such as chrysanthemums and poinsettias perceive that it is later in the season and rush to produce flowers and fruits as a form of self-preservation and seed dispersal. This redirection of energy and resources allows flower growers to control the timing of flowering for specific seasonal events.
This is especially important for commercial purposes, as it enables growers to optimize their harvest schedules and meet market demands more effectively and maximize their profits.
Some other important benefits enabled by light-deprivation include:
Multiple Harvests
Light deprivation allows for up to three harvests per year, including early summer, late summer, and winter. This flexibility in harvest timing enables growers to maximize production and meet market demands more efficiently.
Increased Yields
By controlling the timing of flowering, light-deprivation techniques can significantly increase yields. Plants that flower earlier and grow longer produce larger crops, resulting in higher overall productivity.
Season Extension:
Light deprivation techniques enable growers to extend the growing season and cultivate plants outside their regular seasonal schedule. This allows for continuous production and the ability to provide crops during off-season periods, increasing market competitiveness and profitability.
Controlled Cultivation Environment
Light deprivation techniques provide growers with greater control over their cultivation environment. By manipulating the photoperiod, growers can optimize plant growth and development, leading to healthier, more robust plants.
