Photosynthetic plant cultivation method and photosynthetic plant cultivation apparatus

Abstract

To provide a plant cultivation method capable of effectively adjusting growth of plants.SOLUTION: Growth of a plant to be cultivated is adjusted by performing irradiation of main light for photosynthesis of the plant, and irradiation of additional signal light whose light intensity is lower than a light compensation point of the plant, which periodically fluctuates, and is capable of causing the plant to perceive a daytime condition in a non-daytime situation. A time period of irradiation of the additional signal light includes a time period during which a light intensity of the main light for photosynthesis is lower than the light compensation point. A wavelength band of the additional signal light is from 350 nm to 750 nm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a plant cultivation method and a photosynthetic plant cultivation device that are capable of adjusting the flowering time of photosynthetic plants, for example. [Background technology]

[0002] For example, photosynthetic plants (short-day plants) such as chrysanthemums and shiso (perilla) begin to flower and fruit when the daylight hours shorten from a certain length. Also, photosynthetic plants (long-day plants) such as radishes, spinach, and wheat begin to flower and fruit when the daylight hours extend beyond a certain length. For this reason, cultivation methods are used to expose short-day and long-day plants to artificial light before flower buds form, delaying or hastening the flowering and fruiting periods. These methods are called electric lighting or long-day treatment.

[0003] Long-day treatment allows plants (photosynthetic plants) to be harvested in time for demand. Conventional long-day treatment involves using incandescent or LED bulbs to irradiate light with a brightness above the light compensation point. This extends the daylight hours beyond a certain length. However, using incandescent or LED bulbs for a fixed amount of time every day poses problems such as increased electricity costs and the cost of replacing bulbs that have exceeded their lifespan. Therefore, there is a demand for long-day treatment methods and devices that consume less power and have a longer lifespan. Patent Document 1 (paragraph 0012, etc.) discloses a long-day treatment technology using LED bulbs. Patent Document 2 (paragraph 0009, etc.) discloses the use of light of a specific wavelength to regulate the flowering of short-day plants. Patent Document 3 (paragraph 0186, etc.) also discloses the effect of suppressing the growth of specific photosynthetic organisms. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-212011 [Patent Document 2] Japanese Patent Application Publication No. 8-228599 [Patent Document 3] International Publication No. 2023 / 105939 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 (Claim 1, etc.) discloses a method for suppressing flower bud formation in short-day plants by simultaneously irradiating the short-day plants with red light and far-red light at predetermined time intervals. However, Patent Document 1 does not disclose periodically varying the light intensity. Furthermore, Patent Document 2 does not disclose a growth regulation method that acts on genes by irradiating additional signal light. Furthermore, Patent Document 3 only discloses a method for combining accelerated growth with slowed growth in a multi-stage growth process (paragraph 0193, etc.).

[0006] An object of the present invention is to provide a photosynthetic plant cultivation method and a photosynthetic plant cultivation device that can effectively regulate the growth of photosynthetic plants. [Means for solving the problem]

[0007] The photosynthetic plant cultivation method according to the present invention comprises: Irradiation of primary light for photosynthesis of the photosynthetic plants to be cultivated; The growth of the photosynthetic plant is adjusted by irradiating it with additional signal light whose light intensity is smaller than the light compensation point of the photosynthetic plant, fluctuates periodically, and can make the photosynthetic plant feel that it is daytime even when it is not daytime. The photosynthetic plant cultivation device according to the present invention comprises: A photosynthetic plant cultivation device that irradiates a main light for photosynthesis of a photosynthetic plant to be cultivated, an additional light source that emits additional signal light in addition to the main light; an irradiation light control unit capable of driving and controlling the additional light source, the light intensity of the additional signal light is smaller than the light compensation point of the photosynthetic plant and fluctuates periodically to make the photosynthetic plant perceive it as daytime even when it is not daytime; The growth of the photosynthetic plant is adjusted by irradiating the additional signal light. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a photosynthetic plant cultivation method and a photosynthetic plant cultivation device that can effectively regulate the growth of photosynthetic plants. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing an example of a light-photosynthesis curve. [Figure 2] FIG. 10 is an explanatory diagram showing an irradiation profile of additional signal light. [Figure 3] FIG. 10 is an explanatory diagram showing the time spectrum of additional signal light. [Figure 4] FIG. 10 is an explanatory diagram showing an example of the time spectrum of additional signal light. [Figure 5] FIG. 1 is an explanatory diagram showing survival crisis response protocols for humans and plants. [Figure 6] FIG. 10 is an explanatory diagram showing the mechanism by which a plant senses sunlight by irradiation with additional signal light. [Figure 7] FIG. 1 is a schematic diagram of a plant cultivation device. [Figure 8] FIG. 1(a) is an explanatory diagram showing a photographic image of a control according to Example 1, and FIG. 1(b) is an explanatory diagram showing a photographic image of a test plot according to Example 1. [Figure 9] FIG. 1(a) is an explanatory diagram showing a photographic image of a control according to Example 2, and FIG. 1(b) is an explanatory diagram showing a photographic image of a test plot according to Example 2. [Figure 10] 10(a) is an explanatory diagram showing the waveform of additional signal light according to the third embodiment, and FIG. 10(b) is an explanatory diagram showing the waveform of another additional signal light according to the third embodiment. [Figure 11]FIG. 1(a) is an explanatory diagram showing a photographic image of a control according to Example 4, and FIG. 1(b) is an explanatory diagram showing a photographic image of a test plot according to Example 4. [Figure 12] FIG. 10 is an explanatory diagram showing the state of cultivation according to Example 4. [Figure 13] FIG. 1 is an explanatory diagram showing the relationship between light wavelength bands and flowering regulation. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail.

[0011] <Photosynthetic plant cultivation method> <<Outline of the photosynthetic plant cultivation method according to this embodiment>> As disclosed in the aforementioned Patent Document 3, photosynthetic plants (hereinafter referred to as "plants") produce carbohydrates necessary for life and growth through photosynthesis. In photosynthesis, the carbohydrate glucose (CH) is produced from the raw materials water (H2O) and carbon dioxide (CO2). 12 O6) is produced. Light energy is essential for the reaction to proceed. Light energy is absorbed by pigment aggregates called light antennas.

[0012] This embodiment provides a plant cultivation method in which light whose intensity is periodically changed is additionally irradiated to a plant in an environment where the plant is grown using sunlight (natural light) or artificial light such as LED. The additional light stimulates the viability of the plant's DNA, thereby indirectly promoting photosynthesis. The additional light is also referred to as "additional light" below. Additional light will be described later.

[0013] <<Plant growth with primary light>> Plants carry out photosynthesis and respiration simultaneously. Photosynthesis absorbs carbon dioxide and releases oxygen. Respiration absorbs oxygen and releases carbon dioxide. The rate of carbon dioxide absorption during photosynthesis (unit: μmol CO2 m -2 s -1) depends on light intensity (see Figure 1), but the amount of carbon dioxide absorbed during respiration does not depend on light intensity.

[0014] Carbon dioxide absorption rate during photosynthesis (μmol CO2 m -2 s -1 ) and the rate of carbon dioxide release in breathing (μmol CO2 m -2 s -1 ) is the rate of photosynthesis (μmol CO2 m -2 s -1 ) The PPFD (Photosynthetic Quantum Flux Density, described below) at which the photosynthetic rate becomes zero is the light compensation point (Figure 1). The value of the light compensation point varies depending on the type of plant.

[0015] Light intensity in photosynthesis is defined as the number of rays of light irradiating a leaf surface per unit area per second, which is called the photosynthesis photon flux density (PPFD).

[0016] When there is a sufficient supply of water and carbon dioxide, glucose production increases in proportion to PPFD up to a certain saturation value. The light intensity at which glucose production saturates is defined as the photosynthetic saturation light intensity. To promote plant growth, light at a level equivalent to the photosynthetic saturation light intensity is required. The "light saturation point" in Figure 1 corresponds to the photosynthetic saturation light intensity.

[0017] When the irradiated light falls below the photosynthetic saturation intensity, artificial light such as LED light may be irradiated to compensate for the lack of light. Compensating for a lack of light in this way is called "supplemental lighting." Supplemental lighting is a method of directly increasing photosynthesis. Artificial light that directly increases photosynthesis can also be called "supplemental lighting."

[0018] In this embodiment, sunlight (natural light) and artificial supplemental light are referred to as "main light" for photosynthesis. This main light is light that directly initiates or enhances photosynthesis. Main light is light emitted from sunlight or LEDs, etc., and is the light that is primarily responsible for photosynthesis.

[0019] <<Growth Promotion by Additional Light>> In this embodiment, auxiliary light different from the main light is artificially created and irradiated to plants. This auxiliary light is referred to as "additional light". The irradiation of this additional light is carried out at a predetermined time or period, details of which will be described later. The additional light is light for indirectly promoting photosynthesis.

[0020] For example, in the plant cultivation method of this embodiment, during the process of irradiating sunlight or artificial light as the main light (main light) for photosynthesis, additional light is irradiated during an arbitrary cultivation period from sowing to harvesting. The additional light is only light whose light intensity varies periodically (additional signal light), or a combination of the additional signal light and light whose light intensity changes gently (additional relaxation light).

[0021] As disclosed in Patent Document 3, the additional relaxation light has a sine-wave-like waveform and a basic period of 1 ms or more. When the period of the additional signal light is 8 μs < T < 200 μs, the basic period of the additional relaxation light is 125 to 2 times or more the period T of the additional signal light. The additional relaxation light can also be described as light showing a waveform with a smaller change rate (light intensity change rate) related to the intensity gradient compared to the additional signal light. Also, regarding the additional relaxation light, when comparing with the additional signal light using the waveform of one period, it can also be described as light having a gentler overall light intensity change rate compared to the additional signal light. The additional relaxation light is light for mitigating the side effects (such as the growth of plants being suppressed by strong light stimulation) of the additional signal light whose intensity changes relatively rapidly. Therefore, the time change of the additional relaxation light must be gentler than the time change of the light intensity of the additional signal light.

[0022] By irradiating plants with the additional light obtained by combining the additional signal light and the additional relaxation light in this way, the light stress felt by the plants can be further mitigated compared to the case of irradiating the additional signal light alone. That is, the additional light of this embodiment is light that can combine the additional signal light and the additional relaxation light to improve the light stress reduction effect by the additional light as much as possible.

[0023] In this embodiment, plant growth can be regulated solely by the additional signal light. The inventors have newly discovered that irradiation of the additional signal light can induce plants to perceive daytime conditions even when they are not daytime, thereby promoting gene expression. In this embodiment, this new discovery by the inventors is utilized to enable growth regulation according to plant classification (short-day plants, long-day plants, and day-neutral plants). Irradiation of the additional signal light (hereinafter also referred to as "gene expression light") does not necessarily have to be stopped during irradiation of the main light, for example, but it is preferable to irradiate the additional signal light so that it includes at least a portion of the time period during which the light intensity of the main light for photosynthesis is lower than the light compensation point. The wavelength band of the additional signal light is preferably 350 nm to 750 nm.

[0024] First, the mechanism by which additional light with periodically changing light intensity (PPFD) promotes photosynthesis will be described below. The mechanism by which additional light promotes photosynthesis is also explained in the aforementioned Patent Document 3.

[0025] It is known that plants have a light integration function, accumulating the intensity and duration of sunlight daily. When a decrease in PPFD (PPFD decrease) in the main light is detected by this integration function, the DNA in the plant's chloroplasts issues a command to increase the production of chlorophyll in the light antenna. This increases the amount of light absorbed and promotes photosynthesis.

[0026] In this embodiment, a differentiation function that is potentially present in plants is utilized to detect the rate of change in light intensity. The most efficient way to stimulate a plant's differentiation function is pulsed light (signal light) that repeatedly turns on and off at regular time intervals. This pulsed light (signal light) is hereinafter referred to as "additional signal light." The additional signal light is light that is included in the additional light. In this embodiment, the additional signal light is irradiated onto the plant alone or together with the additional mitigating light.

[0027] The additional signal light is insufficient compared to the main light to trigger photosynthesis. Therefore, the plant recognizes that it is temporarily in a state of photosynthesis starvation. When DNA detects this state of photosynthesis starvation, it issues a command to increase chlorophyll production in order to absorb more light necessary for photosynthesis. Furthermore, the additional signal light causes DNA to issue a command to control the opening and closing of stomata, which are the entrances and exits for outside air, so as to increase the amount of carbon dioxide absorbed. As a result, the irradiation of the additional pulsed light increases the light energy necessary for photosynthesis and the amount of carbon dioxide absorbed. In other words, the additional signal light in this embodiment functions as a trigger signal to cause DNA to issue a command to increase chlorophyll production and a command to open and close stomata. The effect of the additional signal light in this way is defined as the DNA trigger effect of the additional signal light.

[0028] The DNA trigger effect increases in proportion to the number of triggers per unit time, but does not depend on the strength of the trigger signal. If the time interval between trigger signals becomes too short, the DNA trigger effect decreases. Furthermore, the photosynthesis-promoting effect of additional light, including additional signal light, can be obtained regardless of the PPFD value of the main light.

[0029] The above mechanism is also explained in Patent Document 3, but the inventors, through further research, have discovered that it is also effective in suppressing flowering in short-day plants. As shown in Figure 2, when a plant is exposed to additional signal light, it detects sunlight (perceives it as daytime). This function is achieved by the plant having a light-related differential circuit function. As a result, the length of the dark period is shortened, and the effective day length (effective day length), which is the combination of sunlight and additional signal light, increases. This allows the suppression of flowering and flower bud formation in short-day plants, and the promotion of flowering and flower bud formation in long-day plants.

[0030] In Figure 2, additional signal light is irradiated in the evening from the time when sunset approaches and the main light (here, sunlight) weakens (for example, after 4:00 p.m., two to three hours before sunset) until a specified period until sunrise. Furthermore, inhibiting flower bud formation can prevent excessive consumption of nutrients for flower bud formation, promoting the growth of individual leaves and encouraging stem growth to increase the number of leaves. More specifically, inhibiting flowering extends the cultivation period during which harvesting is possible. Regarding harvest timing, extending the harvest period until the cooler months of autumn improves the quality of plants targeted by inhibited flowering. Furthermore, extending the harvest period is expected to increase yields.

[0031] Fig. 3 shows a basic waveform of the additional signal light. In the example of Fig. 3, the additional signal light has a periodic mountain-shaped (also called "sawtooth") waveform. One cycle (ΔT) of the waveform of the additional signal light has a waveform of a period (ΔTa) in which the light intensity increases and a waveform of a period (ΔTb) in which the light intensity decreases. The sum of the period (ΔTa) in which the light intensity increases and the period (ΔTb) in which the light intensity decreases is one cycle (ΔT). Note that in Fig. 3, the unit of light intensity on the vertical axis is arbitrary units (AU), and the unit of time on the horizontal axis is μs.

[0032] Figure 4 shows an example of the time spectrum of an actual additional signal light. As in Figure 3, the horizontal axis of the graph represents time (μs) and the vertical axis represents optical intensity (AU). In the example of Figure 4, the period from when a rising edge of the waveform occurs to when the next rising edge occurs is one cycle (ΔT1 to ΔTn, where n is an integer equal to or greater than 1). Here, ΔT1 = ΔT2 = ΔT3 = ··· = ΔTn-1 = ΔTn = ΔT. The output of the additional signal light is controlled so that the optical intensity does not become 0 (zero) and the duty is 100% in each cycle (ΔT).

[0033] Figure 5 shows the results of a study comparing the plant's response to the irradiation of additional signal light with the human response to high-altitude training. First, when humans engage in high-altitude training, blood oxygen starvation occurs. In this situation, the human body increases the blood oxygen concentration through the action of hemoglobin, improving cardiopulmonary function.

[0034] In the case of plants, irradiation with extremely weak light (EDL irradiation), such as additional signal light, causes photosynthesis starvation. In such a situation, plants increase their light harvesting efficiency through the action of chlorophyll, thereby increasing the photosynthetic rate. Here, "EDL" stands for "Extremely Dark Light."

[0035] When such a plant survival threat response is applied to short-day plants, flowering can be suppressed, as shown at the right end of Figure 5. In other words, if weak photosynthesis due to the additional signal light continues, a state of photosynthetic starvation occurs, and the plant perceives it as daytime, even in an environment that is darker than daytime. This increases the effective hours of sunlight in the plant, suppressing flowering in short-day plants. Because the additional signal light is extremely weak light that induces weak photosynthesis, the plant cultivation method of this embodiment and the plant cultivation device 10 described below can regulate plant growth with low power consumption.

[0036] The growth slowdown (growth deceleration) disclosed in Patent Document 3 (paragraphs 0186-0195) involves increasing the wavelength of irradiated light as harvest approaches (the end of growth) compared to the early stage, when growth promotion is prioritized, thereby prioritizing the promotion of secondary carbohydrate metabolism. In other words, Patent Document 3 (paragraphs 0186-0195) describes accelerating growth and maintaining and / or converting carbohydrates into metabolic substances. In contrast, the irradiation of additional signal light in this embodiment is intended to regulate flowering and is carried out at any time between sunset and sunrise. The inventors discovered that plants have the ability to recognize the light period when irradiated with additional signal light at a regular interval, and utilized this function. This plant perception function increases the effective day length. As a result, flowering can be suppressed in short-day plants and promoted in long-day plants.

[0037] It is possible to say that such a sunshine perception mechanism (sunshine perception mechanism) involves the following steps occurring in chronological order: First, a weak oscillating light (additional signal light) is irradiated while being buried in a strong light (main light). Next, the plant performs signal processing while changing the frequency of the reference wave. Furthermore, the plant detects only the oscillating light (additional signal light) and performs a differential operation on the detected signal. As a result, sunshine perception is achieved. Furthermore, it can be inferred that such a sunshine perception mechanism is one in which the plant has a function similar to that of a lock-in amplifier in the technical field of signal processing, as shown in Figure 6, for example. In the technical field of signal processing, a lock-in amplifier detects a weak repetitive signal (AC) buried in noise.

[0038] The top row of Figure 6 shows, from left to right, the mechanism by which plants perceive sunlight. The box in the bottom row of Figure 6 shows, from left to right, the functions of a lock-in amplifier. Here, as shown in the top left row of Figure 6, we consider the case in which a relatively strong light (here, the main light) and a weak oscillating light (additional signal light, light with a constant period) are simultaneously irradiated onto the plant. Furthermore, we consider that the plant behaves in the same way as if a reference wave had been input into the lock-in amplifier.

[0039] As shown in the lower part of Figure 6, the lock-in amplifier circuit multiplies the input signal (f(t) = Asin(ωt)) by the reference signal (sin(ωt)). Using the trigonometric multiplication formula (Asin(ωt) x sin(ωt) = (A / 2){cos(ω-ω0) - cos(ω+ω0)t}), a signal (A / 2){cos(ω-ω0) - cos(ω+ω0)t} is generated. When the angular frequency condition is ω = ω0, this signal becomes (A / 2){cos(0) - cos(2ω0)t}. The (2ω0) component is then removed by a low-pass filter (LPF), and only the signal synchronized with the reference signal is detected. The detected signal is f(t) = (A / 2) sin(ωt).

[0040] As shown in the upper left of Figure 6, when a plant is irradiated with strong light (main light) and weak light (additional signal light), only the weak signal (additional signal light) is detected by the detection function (lock-in detection function) of the lock-in amplifier, as shown in the adjacent right. Furthermore, as shown in the adjacent right, a differential calculation function is performed and the signal is converted into light of a constant intensity. Then, as shown from top to bottom in the lower right of the figure, sunlight perception is performed based on the obtained signal, and the effective daylight hours in the plant are extended. As a result, flowering can be suppressed in short-day plants and promoted in long-day plants.

[0041] According to the findings of the inventors, when non-periodic random pulsed light was irradiated instead of the additional signal light (Figure 4), the lock amplifier detection function was not observed, and no growth-promoting effect was observed. The random pulsed light referred to here is pulsed light with a waveform such that T1 ≠ ΔT2 ≠ ΔT3 ≠ ··· ≠ ΔTn-1 ≠ ΔTn in Figure 4, for example. It is presumed that plants cannot detect random pulsed light in principle and therefore cannot sense a state of photosynthetic starvation. In other words, it is presumed that plants can detect weak light with a constant period that is buried in strong light. This function can be called, for example, the "cocktail party effect associated with additional signal light."

[0042] Regarding the reference wave in plants, the inventors presume that the plants themselves emit a signal equivalent to the reference wave of a lock-in amplifier. In other words, it is thought that plants have a lock-in amplifier function. In other words, plants have a function (organ) that generates a reference wave and a pathway that transmits the periodic signal detected by the lock-in amplifier to genes. As for the location where lock-in detection occurs, the inventors believe that it is either photosynthetic pigments, pigments, or photoreceptor proteins. Future experiments are needed to prove these hypotheses.

[0043] <Plant cultivation equipment 10> 7 shows a schematic configuration of a plant cultivation device 10 of this embodiment. Similar to the plant cultivation device disclosed in Patent Document 3, the plant cultivation device 10 includes a cultivation bed 12 for hydroponic or soil cultivation, a light irradiating unit 14 that irradiates light toward the cultivation bed 12, and an irradiation light control unit 16 that drives and turns on the light irradiating unit 14. The plant cultivation device 10 includes a protective member 18 that covers the cultivation bed 12 to form a cultivation chamber. The protective member 18 may be omitted.

[0044] The light irradiation unit 14 has a main light source 20 that irradiates main light and an additional light source 22 that irradiates additional light. The main light source 20 and the additional light source 22 are individually driven and controlled by the irradiation light control unit 16 (current control in this case). In FIG. 7, the main light source 20 and the additional light source 22 are shown side by side, but the light from the main light source 20 and the light from the additional light source 22 are irradiated toward the cultivation bed 12 along the same path via a diffuser plate (which may be a diffuser lens) not shown. The light from the additional light source 22 may be irradiated toward the cultivation bed 12 via an optical fiber (not shown). An end-emitting or side-emitting optical fiber can be used as appropriate.

[0045] The main light source 20 is continuously lit for a predetermined period of time and continuously emits main light (also referred to as "continuous irradiation light"). The main light source 20 may be an artificial light source such as an LED, fluorescent lamp, plasma lamp, mercury lamp, incandescent lamp, metal halide lamp, sodium lamp, electrodeless lamp, pulsed laser, or the like.

[0046] Sunlight can also be used as another type of primary light. When using sunlight, it is possible not to use the primary light source 20 or to omit the primary light source 20. It is also possible to use both sunlight and the light from the primary light source 20 in combination. In this case, the light from the sunlight and the light from the primary light source 20 may be used differently depending on conditions such as the time of day. Furthermore, there may be cases where sunlight and the light from the primary light source 20 are emitted simultaneously.

[0047] The additional light source 22 has an additional signal light source 24 and an additional mitigating light source 26. The additional signal light source 24 can emit additional signal light, and the additional mitigating light source 26 can emit additional mitigating light. Additional light can be obtained by using only the additional signal light source 24, or by combining the additional signal light and the additional mitigating light. In this embodiment, flowering is regulated by irradiating only the additional signal light source 24. However, as in the example of FIG. 7, the additional mitigating light source 26 may be added to enable irradiation of additional mitigating light. Therefore, the following description will explain not only the configuration related to the additional signal light source 24, but also the configuration related to the additional mitigating light source 26. In addition, in experiments conducted by the inventors, when plants showed poor growth in terms of growth regulation with only irradiation of additional signal light, the growth conditions of the plants improved when they were subsequently irradiated with additional mitigating light.

[0048] 7, the additional signal light source 24 and the additional mitigating light source 26 are shown side by side, but the additional signal light and the additional mitigating light are irradiated toward the cultivation bed 12 along the same path via a diffusion plate (which may be a diffusion lens) not shown. The additional light source 22 may be an integrated unit formed by integrating the additional signal light source 24 and the additional mitigating light source 26.

[0049] The additional light source 22 can emit light in a wavelength range of 220 nm to 2000 nm by the additional signal light source 24. The additional signal light source 24 can be any light source, such as an LED, an EL (electroluminescence), a laser, an ultraviolet light, or an infrared light, as long as it can emit light of a wavelength suitable for the growth of the target plant. It is also desirable to use a light source that can easily be pulsed for the additional signal light source 24. The additional relaxation light source 26 can be any light source, such as a cold cathode fluorescent lamp, a monochromatic LED lamp, or an LED fluorescent lamp, all of which are driven by a lamp line (50 Hz or 60 Hz).

[0050] Although not shown, the additional light source 22 may be equipped with a light source that emits continuous light and a shutter disposed midway along the light path. In this case, the shutter intermittently blocks the light path to form signal light. It is also possible to form light of the required wavelength by attaching a wavelength limiting filter to the white light source. A shutter and a filter may be provided for each of the additional signal light source 24 and the additional relaxation light source 26.

[0051] The light irradiation unit 14 is installed above the ceiling surface or side wall of the protective member 18, or above a pillar installed on the cultivation bed 12. The light irradiation unit 14 illuminates the cultivation bed 12 in response to a command from the irradiation light control unit 16.

[0052] The light irradiation unit 14 may include a plurality of main light sources 20 and a plurality of additional light sources 22. In this case, the plurality of main light sources 20 and the plurality of additional light sources 22 may be arranged at different positions and with different irradiation angles. For example, the plurality of main light sources 20 and the plurality of additional light sources 22 may be arranged alternately. It is also possible to include a plurality of main light sources 20 and a single additional light source 22 (or a single main light source 20 and a plurality of additional light sources 22). The additional light source 22 may also be installed so that light is irradiated onto the cultivation bed 12 from a plurality of directions. In this way, a more stable growth regulation effect can be obtained.

[0053] In this way, more precise light irradiation can be performed by providing multiple main light sources 20 and / or multiple additional light sources 22. Furthermore, by varying the arrangement and irradiation angle of the multiple light sources, the plants in the cultivation bed 12 can be uniformly irradiated with light, and uneven growth due to location can be suppressed.

[0054] The irradiation light control unit 16 drives and turns on the light irradiation unit 14 based on the plant cultivation method of this embodiment. The irradiation light control unit 16 can drive and turn on only the main light source 20, drive and turn on only the additional light source 22, or drive and turn on both the main light source 20 and the additional light source 22 simultaneously.

[0055] When the light irradiation unit 14 is equipped with a plurality of main light sources 20 and / or a plurality of additional light sources 22, the irradiation light control unit 16 can turn on the light sources of the same type in synchronization. Furthermore, when the cultivation bed 12 is divided into a plurality of blocks (test plots), the irradiation light control unit 16 can individually control the main light source 20 and the additional light source 22 in each block.

[0056] The irradiation light control unit 16 may synchronize the main light source 20 and the additional light source 22 on a block basis, or may synchronize the main light source 20 and the additional light source 22 for multiple blocks or for all blocks. By synchronizing the additional signal light in the additional light source 22, the duty ratio (duty) of the additional signal light irradiated to the plant can be accurately maintained.

[0057] Such a plant cultivation device 10 can be widely applied to small cultivation kits for easy indoor cultivation in ordinary households, agricultural greenhouses, large-scale plant factories with constructed cultivation rooms, etc.

[0058] Here, agricultural greenhouses can refer to agricultural vinyl greenhouses in which a translucent film is stretched over the entire surface of the greenhouse, as well as agricultural glass greenhouses in which a film is stretched over the entire inside of the glass windows. In agricultural glass greenhouses, moisture-laden air in the cultivation space inside the greenhouse passes through the film and escapes to the outside through the gaps between the glass windows and the frame of the glass window. Therefore, even in agricultural glass greenhouses, high temperatures and humidity inside the greenhouse can be prevented. Note that the above-mentioned "translucency" refers to the property of transmitting light necessary for growing plants during the daytime.

[0059] When a light source of additional light (here, additional light source 22) is installed inside an agricultural greenhouse, there is an advantage that the irradiation efficiency of the additional light is increased because part of the additional light is reflected and diffused (reflected and diffused) by glass plates, resin plates, resin films, etc. A similar effect of improving irradiation efficiency can be obtained in small cultivation kits, plant factories, etc.

[0060] We can also consider the effective irradiation direction of the additional light (additional signal light and / or additional mitigation light). The growth-promoting effect can be obtained whether the additional light is irradiated from the same direction as the main light or from a different direction from the main light. Furthermore, if the additional light is irradiated to areas where the main light does not reach sufficiently (for example, the upper and lower surfaces of leaves in shaded areas or the undersides of leaves in sunny areas), a greater growth-promoting effect can be obtained.

[0061] Specifically, for example, for a plant whose branches grow horizontally, such as grapes, supplemental light is irradiated upward (including diagonally upward) from the ground. In this case, the amount of light that reaches the underside of the leaves in the shade (the surface facing the ground) increases. Compared to when supplemental light is not irradiated, photosynthesis occurs more actively, resulting in sweeter grapes. In this way, by setting the irradiation direction of the supplemental light according to the environment in which the plants are grown and the characteristics of the plants, plant growth can be promoted more effectively. For example, in tomato cultivation, it is also effective to install a side-emitting optical fiber among the bushes to irradiate supplemental light.

[0062] <Application of this embodiment> It should be noted that the present embodiment is merely an example of a specific embodiment of the present invention, and should not be construed as limiting the technical scope of the present invention. In other words, the present invention can be embodied in various forms without departing from the gist or main characteristics thereof.

[0063] The plant cultivation method according to this embodiment is effective for regulating the growth of a wide variety of plants. Therefore, it can be applied to promoting the growth of leafy vegetables, root vegetables, ornamental plants, fruit trees, seaweed, algae, and microalgae. Furthermore, it is effective for plant cultivation in farms, greenhouses, plant factories, smart cells (smart cell industry, biological material production), land-based aquaculture, sea surface, underwater, surface water, and mountainous areas.

[0064] The plant cultivation method according to this embodiment can be applied to both inhibiting flowering in short-day plants and promoting flowering in long-day plants. Furthermore, this embodiment can also be applied to promoting the growth of day-neutral plants. Typical examples of short-day plants include mitsuba (Japanese laurel wort), watercress, mioga (ginger), mizuna (Japanese mustard greens), chrysanthemum (chrysanthemum), morning glory, cocklebur, and shiso (perilla). Typical examples of long-day plants include iris (iris), radish (radish), spinach, rice, wheat, corn, soybean, tomato, watermelon, pumpkin, sweet potato, cabbage, and Chinese cabbage. Typical examples of day-neutral plants include strawberry, spinach, lettuce, taro, tomato, cucumber, pea, and lettuce.

[0065] <Effects of different plant uses> Supplemental light has the effect of promoting photosynthesis and promoting the movement of products of photosynthesis (photosynthetic products) into primary metabolic pathways (primary metabolic circuits, pathways for primary metabolism) and secondary metabolic pathways (secondary metabolic circuits, pathways for primary metabolism).

[0066] Plants are often used as food, medicine, aromatic components, etc. According to the various photosynthetic organism production methods described above, the production of food, specific medicinal components, aromatic components, etc. can be increased by irradiating additional light in addition to primary light such as sunlight.

[0067] For example, vegetables such as lettuce generally have a bitter taste that children dislike. In experiments conducted by the inventors, when additional signal light with a wavelength of 500 nm to 600 nm or more was irradiated, the bitter taste of the lettuce was reduced to an unnoticeable level. This is thought to be because the nitrogenous components contained in the vegetables were converted into amino acids, glutamic acid, etc. This can reduce the number of consumers who dislike vegetables and increase vegetable consumption.

[0068] The same was true for coriander. Japanese coriander is sometimes considered to have a stronger gustatory stimulant than, for example, Thai coriander. However, by irradiating it with additional light, the stimulant stimulant can be reduced, increasing the number of consumers and consumption. As mentioned above, irradiation with additional light increases the sweetness of grapes. In experiments conducted by the inventors, the sweetness of grapes was also significantly increased by irradiating it with additional signal light of a wavelength of 500 nm to 600 nm or more.

[0069] Based on these findings, it is believed that irradiation with additional light may enhance the aroma and sweetness of green tea, for example.

[0070] Seedlings that have been irradiated with additional light for at least part of the seedling raising period (seedlings grown in an additional light environment during the seedling raising period) show a sustained effect of promoting growth and metabolic product production compared to seedlings that have not been irradiated with additional light. This is true whether the seedlings are grown using only primary light, such as sunlight or white LED light, after the additional light irradiation, or whether the primary light and additional light are used. For example, by simply irradiating the seedlings with additional light a few days before the harvest period and completing the irradiation, it is possible to harvest vegetables with less bitterness or fruits with a strong sweetness at a later date.

[0071] Supplemental light also has the effect of increasing the germination rate and yield of seeds. When plants are grown in a supplemental light environment from germination to seedling raising, the effect of promoting growth and metabolic product production is sustained compared to when the supplemental light is not applied thereafter. This is true whether the plants are cultivated under main light alone after the supplemental light irradiation or whether the plants are irradiated with main light and supplemental light.

[0072] The additional signal light can control the weight of rice, wheat, and barley seeds, as well as the production of umami components such as glutamic acid, medicinal components such as beta-glucan, and pungent and aromatic components in herbs and spices such as coriander.

[0073] Therefore, using the various photosynthetic organism production methods described so far, it is possible to cultivate annual herbs (annual plants) such as lettuce, tomato, and rice seedlings, which grow faster than conventional methods; fruits such as grapes and peaches, which have high sugar content; medicinal herbs with many medicinal ingredients; aromatic herbs with reduced spiciness; aromatic herbs with many aromatic ingredients; and indigo plants and red shiso, which are rich in pigments. For example, in the case of shiso (red shiso, etc.), specific metabolic components such as anthocyanins and rosmarinic acid increase.

[0074] To selectively increase the production of secondary metabolic components contained in plants, such as ascorbic acid (vitamin C), beta-carotene (a precursor to vitamin A), polyphenols, and s-allylcysteine, it is effective to selectively excite the photoreceptor protein phytochrome.

[0075] There are two types of phytochromes, Pr and Pfr, depending on the protein assembly form. The Pr form transitions to the Pfr form upon light excitation. Conversely, the Pfr form transitions to the Pr form upon light excitation.

[0076] Pr-type phytochromes have the effect of promoting the production of secondary metabolites, particularly ascorbic acid. On the other hand, Pfr-type phytochromes have the effect of promoting the production of secondary metabolites other than ascorbic acid, such as polyphenols, β-carotene, and s-allylcysteine, a medicinal component of garlic. Utilizing these properties makes it possible to control the production of secondary metabolites while promoting growth.

[0077] In addition to phytochromes, photoreceptor proteins found in photosynthetic organisms such as plants include phototropins, which are involved in chlorophyll movement, phototropism, and stomatal opening and closing, and cryptochromes, which are involved in flowering time and photoavoidance responses. By selectively exciting these photoreceptor proteins with additional signal light, it is possible to more precisely control growth rate and secondary metabolite production.

[0078] Furthermore, with regard to flowering regulation, if the wavelength of the additional signal light is in the visible range (380nm to 750nm), the flowering regulation function can be achieved. This is because when the additional signal light is irradiated onto the plant, sunlight perception occurs through the mechanism already explained, and the effective daylight hours for the plant are lengthened.

[0079] Photoreceptor proteins called cryptochromes, phytochromes, and phototropins are distributed throughout plants. Cryptochromes and phytochromes are involved in flower bud formation. As shown in Figure 13, cryptochromes are known to promote flower bud formation by absorbing light with wavelengths between 400 and 500 nm. As mentioned above, there are two types of phytochromes: Pr and Pfr. Phytochromes undergo tissue transformation between the Pr and Pfr forms when they absorb light with wavelengths between 600 and 700 nm and between 800 and 600 nm. Pr-type phytochromes promote flower bud formation, while Pfr-type phytochromes suppress it. Phototropins absorb light with wavelengths between 400 and 500 nm and are involved in light refraction, stomatal opening and closing, and chloroplast movement.

[0080] As already explained, in this embodiment, the effective daylight hours are extended by irradiating additional signal light, thereby suppressing flower bud formation in short-day plants and promoting flower bud formation in long-day plants. According to this embodiment, even if the wavelength of the additional signal light overlaps with the absorption wavelength band of cryptochrome or phytochrome, the effect of suppressing flowering in short-day plants is obtained.

[0081] These results indicate that the suppressive effect of the additional signal light exceeds the promoting effect of the photoreceptor protein on flower bud formation, suggesting that photoperiod is more important than the physiological response of the photoreceptor protein in flower bud formation.

[0082] In this way, the additional signal light can be irradiated immediately after sunset or continuously or intermittently for a certain period of time during the dark period, and the effect of suppressing or promoting flower bud formation can be obtained.

[0083] <Various Examples of Plant Cultivation Methods> Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following description.

[0084] Example 1 Figures 8(a) and (b) show an example (Example 1) related to the flowering suppression effect. Figures 8(a) and (b) show photographs of the cultivation conditions of Polygonum indigo during the same period. Figure 8(a) is a photograph of the control exposed to sunlight only. Figure 8(b) is a photograph of the test plot exposed to additional signal light.

[0085] As shown in Figure 8(a), in the control, many flower buds appear as small white areas (light-colored areas). In contrast, in the test plot shown in Figure 8(b), irradiation with additional signal light (gene expression light) creates a period that feels like daytime even when the main light is not irradiated, and almost no flower buds appear. In this way, growth is suppressed by irradiation with additional signal light, and as a result, flowering (and growth) is suppressed.

[0086] <Example 2> Figures 9(a) and (b) show an example (Example 2) related to the flowering suppression effect. Similar to Figures 8(a) and (b) related to Example 1, Figures 9(a) and (b) show photographs of the cultivation conditions of Polygonum indigo during the same period. Figure 9(a) is a photograph of the control exposed to sunlight only. Figure 9(b) is a photograph of the test plot exposed to additional signal light.

[0087] In Example 2, as in Example 1, many flower buds appear as small white areas in the control plot in Figure 9(a). In contrast, in the test plot in Figure 9(b), irradiation with additional signal light (gene expression light) creates a period that feels like daytime even when no main light is irradiated, and almost no flower buds appear. In this way, growth is suppressed by irradiation with additional signal light, and as a result, flowering (and growth) is suppressed.

[0088] Example 3 Figures 10(a) and (b) show waveforms of two types of additional signal light according to Example 3. In Example 3, the growth state of plants (short-day plants and long-day plants) was observed when additional signal light with different waveforms was irradiated. In Example 3, additional signal light with a peak width (peak retention time ΔTp) of 1 μs (Figure 10(a)) and additional signal light with a peak retention time ΔTp of 5 μs (Figure 10(b)) were used. The horizontal axis of Figures 10(a) and (b) represents time, and the vertical axis represents light intensity.

[0089] 10(a) and 10(b) have the same period, but different peak holding times ΔTp. In addition, the duty cycle of both the waveforms in FIG. 10(a) and 10(b) is 100%.

[0090] In Example 3, for both waveforms of additional signal light, flowering suppression (and increased metabolic components) was observed in short-day plants, while growth promotion was observed in long-day plants. Thus, additional signal light suppresses flowering in short-day plants and promotes photosynthesis in long-day plants.

[0091] Example 4 Figures 11(a) and (b) show an example (Example 4) related to the antifungal effect. Figures 11(a) and (b) show photographs of the cultivation conditions of Polygonum indigo during the same period. Figure 11(a) is a photograph of the control exposed to sunlight only. Figure 11(b) is a photograph of the test plot exposed to additional signal light.

[0092] As shown in Figure 11(a), in the control, white mold (light-colored areas) appeared on some stems (areas surrounded by oval A). In contrast, in the test plot shown in Figure 11(b), no white mold appeared due to irradiation with additional signal light (gene expression light).

[0093] Figure 12 shows a schematic diagram of the experimental environment for Example 4. As shown in Figure 12, some Polygonum indigo plants were irradiated with additional signal light from a pulsed light source, while the remaining Polygonum indigo plants were not irradiated with additional signal light. White mold developed in the Polygonum indigo plants that were not irradiated with the additional signal light (corresponding to Figure 11(a)), while no white mold developed in the Polygonum indigo plants that were irradiated with the additional signal light (corresponding to Figure 11(b)).

[0094] The leaves of Polygonum indigo contain specific metabolic components such as tryptanthrin, 6-methoxykaempferol, kaempferol, and 3,5,4'-trihydroxy-6,7-methylenedioxyflavone, all of which have been shown to have high antibacterial activity. From Example 4, it can be seen that irradiation with additional signal light results in the production of a large amount of these specific metabolic components, resulting in a significant antifungal effect.

[0095] <Other forms of growth regulation of photosynthetic plants> When additional signal light is applied, sunlight perception occurs through the aforementioned mechanism, and flowering is regulated. In addition, similar additional signal light can be used to control the production of specific metabolites.

[0096] Regardless of whether the plant is a short-day plant or a long-day plant, the concentration and total weight of specific metabolic components contained in the plant can be controlled by changing the intensity of the additional signal light (PPFD). The concentration and total weight of specific metabolic components are defined as the weight of specific metabolic components per unit plant weight and the weight of the whole plant, respectively. When the growth environment, such as temperature and light, deviates significantly from normal values, the amount of reactive oxygen species increases in plants. This is called the plant's light stress response. When plants detect light stress, they increase the production of antioxidants specific to that plant by preferentially channeling the glucose obtained through photosynthesis into specific metabolic pathways. Antioxidants are one type of a large group of specific metabolic substances.

[0097] The raw material for antioxidant production is glucose obtained through photosynthesis. During periods when plants are under light stress, the amount of glucose used for plant growth decreases in proportion to the increase in antioxidant production. One of the characteristics of the additional signal light is that its light intensity is lower than the value of the light compensation point. However, because the light intensity changes relatively rapidly over time, it is a light stress factor for plants. Adding the aforementioned additional mitigation light to the additional signal light is one way to mitigate light stress.

[0098] The degree to which sunlight perception and antioxidant production are promoted varies depending on the intensity (PPFD value) of the additional signal light. Light that primarily promotes sunlight perception (light intended for sunlight perception) is defined as additional signal light under low light conditions, and light that causes both sunlight perception and light stress (light intended for both sunlight perception and light stress) is defined as additional signal light under high light conditions. The degree of light stress depends on the wavelength and irradiation time of the additional signal light, temperature, humidity, etc., so there is no clear boundary between the PPFD values ​​of additional signal light under low light and high light conditions. The additional mitigating light that has the effect of mitigating light stress may or may not be irradiated.

[0099] When plants are exposed to additional signal light under high light conditions, in addition to adjusting flowering through light perception, they also increase the production of antioxidants to alleviate light stress. The raw material for antioxidant production is synthetic glucose. During periods when plants are under light stress, the production of leaves, stems, roots, and fruits decreases.

[0100] In order to extract as many antioxidants as possible from plants, it is necessary to efficiently convert the remaining carbohydrates into antioxidants. Therefore, by irradiating the plant with additional signal light under weak light conditions until harvest and then switching to additional signal light under strong light conditions just before harvest, it is possible to promote the influx of carbohydrates into the specific metabolic pathway and maximize the yield of specific metabolites. In this way, by increasing the intensity of the additional signal light after the flowering adjustment process, it is possible to cultivate the plant in a chronological order, with the flowering adjustment process and the specific metabolite (here, antioxidant) production increase process. It is not necessary to perform the flowering adjustment process and the specific metabolite production increase process in chronological order; for example, it is also possible to perform only the specific metabolite production increase process.

[0101] <Inventions that can be extracted from the embodiments and examples> (1) Irradiation of primary light for photosynthesis of the photosynthetic plants to be cultivated; and irradiating the photosynthetic plant with additional signal light whose light intensity is smaller than the light compensation point of the photosynthetic plant, fluctuates periodically, and makes the photosynthetic plant feel that it is daytime even when it is not daytime. (2) The photosynthetic plant cultivation method according to (1) above, wherein the time period during which the additional signal light is irradiated includes a time period during which the light intensity of the main light for photosynthesis is lower than a light compensation point. (3) The photosynthetic plant cultivation method according to (1) or (2) above, wherein the wavelength band of the additional signal light is 350 nm to 750 nm. (4) A photosynthetic plant cultivation device (such as the plant cultivation device 10) that irradiates a main light for photosynthesis of a target photosynthetic plant, an additional light source (such as the additional light source 22) that emits additional signal light in addition to the main light; an irradiation light control unit (such as the irradiation light control unit 16) capable of driving and controlling the additional light source; the light intensity of the additional signal light is smaller than the light compensation point of the photosynthetic plant and fluctuates periodically to make the photosynthetic plant perceive it as daytime even when it is not daytime; A plant cultivation device that adjusts the growth of the photosynthetic plant by irradiating the additional signal light. (5) The plant cultivation device according to (4) above, comprising a main light source (such as the main light source 20) that irradiates the main light. (6) Irradiation of primary light for photosynthesis of the photosynthetic plants to be cultivated; and irradiating the photosynthetic plants with additional signal light whose light intensity is smaller than the light compensation point of the photosynthetic plants and fluctuates periodically, so that the photosynthetic plants perceive it as daytime even when it is not daytime. and increasing the intensity of the additional signal light to increase production of specific metabolic substances (antioxidants, etc.). [Industrial Applicability]

[0102] The plant cultivation method and plant cultivation device of the present invention are effective for outdoor cultivation, greenhouse cultivation, and plant factory cultivation. [Explanation of symbols]

[0103] 10:Plant cultivation equipment 12:Cultivation bed 14: Light irradiation unit 16: Irradiation light control unit 18: Protective material 20: Main light source 22:Additional light source 24: Additional signal light source 26: Additional relaxation light source

Claims

1. Irradiation of primary light for photosynthesis of the photosynthetic plants to be cultivated; and irradiating the photosynthetic plant with additional signal light whose light intensity is smaller than the light compensation point of the photosynthetic plant, fluctuates periodically, and makes the photosynthetic plant feel that it is daytime even when it is not daytime.

2. The plant cultivation method according to claim 1 , wherein the time period during which the additional signal light is irradiated includes a time period during which the light intensity of the main light for photosynthesis is lower than a light compensation point.

3. 3. The plant cultivation method according to claim 1, wherein the wavelength band of the additional signal light is from 350 nm to 750 nm.

4. A photosynthetic plant cultivation device that irradiates a main light for photosynthesis of a photosynthetic plant to be cultivated, an additional light source that emits additional signal light in addition to the main light; an irradiation light control unit capable of driving and controlling the additional light source, the light intensity of the additional signal light is smaller than the light compensation point of the photosynthetic plant and fluctuates periodically to make the photosynthetic plant perceive it as daytime even when it is not daytime; A photosynthetic plant cultivation device that adjusts the growth of the photosynthetic plant by irradiating the additional signal light.

5. 5. The photosynthetic plant cultivation device according to claim 4, further comprising a main light source for irradiating the main light.

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