Photosynthetic plant cultivation method and photosynthetic plant cultivation apparatus

Abstract

Provided is a plant cultivation method capable of effectively regulating the growth of plants. 【Solution means】Irradiation of main light for photosynthesis of the plant to be cultivated and irradiation of additional signal light whose light intensity is smaller than the light compensation point of the plant, periodically fluctuates, and can make the plant feel like it is daytime even in a situation that is not daytime are performed to regulate the growth of the plant. The time zone of irradiation of the additional signal light includes the time zone when the light intensity of the main light for photosynthesis is smaller than the light compensation point. The wavelength band of the additional signal light is from 350 nm to 750 nm.

Description

Technical Field

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

Background Art

[0002] For example, photosynthetic plants (short-day plants) such as chrysanthemums and perilla start to flower and bear fruit when the sunshine duration becomes shorter than a certain length. Also, photosynthetic plants (long-day plants) such as radishes, spinach, and wheat start to flower and bear fruit when the sunshine duration becomes longer than a certain time. For this reason, cultivation methods have been carried out in which artificial light is irradiated on short-day plants and long-day plants before flower buds are formed to delay or advance the flowering time and the fruiting time. These are called electric lighting or long-day treatment.

[0003] By performing long-day treatment, plants (photosynthetic plants) can be harvested according to the demand period. Conventional long-day treatment irradiates light with brightness above the light compensation point using incandescent bulbs or LED bulbs. Thereby, the sunshine duration is made longer than a certain length. However, when irradiating with incandescent bulbs or LED bulbs for a certain time every day, the problem is that the power cost and the replacement cost of bulbs that have passed their lifespan increase. For this reason, a long-day treatment method and a long-day treatment apparatus with low power consumption and long lifespan are desired. Patent Document 1 (paragraph 0012, etc.) discloses a long-day treatment technique using LED bulbs. Also, Patent Document 2 (paragraph 0009, etc.) discloses adjusting the flowering of short-day plants using light of a specific wavelength. Furthermore, Patent Document 3 (paragraph 0186, etc.) discloses that it has an effect of suppressing the growth of specific photosynthetic organisms.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 (Claim 1, etc.) discloses a method of suppressing flower bud formation in short-day plants by irradiating the short-day plants with red light and far-red light simultaneously at a predetermined time interval. However, Patent Document 1 does not disclose the point of periodically varying the light intensity. Further, Patent Document 2 does not disclose a growth regulation method that acts on genes by irradiating additional signal light. Furthermore, what is disclosed in Patent Document 3 only remains at the point of combining growth deceleration after growth acceleration in multi-stage growth (paragraph 0193, etc.).

[0006] An object of the present invention is to provide a photosynthetic plant cultivation method and a photosynthetic plant cultivation apparatus capable of effectively regulating the growth of photosynthetic plants.

Means for Solving the Problems

[0007] The photosynthetic plant cultivation method according to the present invention for photosynthesis of the photosynthetic plant to be cultivated Relatively strong light irradiation of main light, and the light intensity is smaller than the light compensation point of the photosynthetic plant, Relatively weak light, and the light intensity is periodically varies performed irradiation of additional signal light, and performed simultaneously, The waveform of the additional signal light is formed to have a peak time shorter than the time of one cycle, and the change in light intensity in each cycle is common, and is a waveform that causes filtering and detection from the main light and sunlight perception in the photosynthetic plant, With the additional signal light, flowering is suppressed for the photosynthetic plant that is a short-day plant, and flowering is promoted for the photosynthetic plant that is a long-day plant, regulate the growth of the photosynthetic plant. The photosynthetic plant cultivation apparatus according to the present invention is a photosynthetic plant cultivation apparatus in which main light for photosynthesis of the photosynthetic plant to be cultivated is irradiated, Relatively strong light and an additional light source for irradiating additional signal light for the main light At the same time, relatively weak light is provided, 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 varies periodically, light and is the intensity, The waveform of the additional signal light is formed to have a peak time shorter than the time of one cycle, and the change in light intensity in each cycle is common, and is a waveform that causes filtering and detection from the main light and sunlight perception in the photosynthetic plant, With the additional signal light, flowering is suppressed for the photosynthetic plant that is a short-day plant, and flowering is promoted for the photosynthetic plant that is a long-day plant, adjusts the growth of the photosynthetic plant.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a photosynthetic plant cultivation method and a photosynthetic plant cultivation apparatus capable of effectively adjusting the growth of photosynthetic plants.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out 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 in the Present Embodiment>> As also disclosed in the aforementioned Patent Document 3, photosynthetic plants (hereinafter referred to as "plants") self-produce carbohydrates necessary for maintaining life and growth through photosynthesis. In photosynthesis, water (H 2 0) and carbon dioxide (CO 2 ) are used to produce glucose (C 6 H 12 O 6 ), which is a carbohydrate. Light energy is essential for the reaction for production to proceed. Light energy is absorbed by a pigment aggregate tissue called a light antenna.

[0012] This embodiment provides a plant cultivation method in which light with a periodically changing light intensity is additionally irradiated in an environment where plants are grown by sunlight (natural light) or artificial light such as LEDs. By stimulating the viability of the plant's DNA with the additional light, photosynthesis can be indirectly promoted. The additional light is also referred to as "additional light" hereinafter. The additional light will be described later.

[0013] <<Growth of Plants by Main 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 in photosynthesis (unit: μmolCO 2 m -2 s -1 ) depends on light intensity (see Figure 1), but the amount of carbon dioxide absorbed in respiration does not depend on light intensity.

[0014] The difference between the rate of carbon dioxide absorption in photosynthesis (μmolCO 2 m -2 s -1 ) and the rate of carbon dioxide release in respiration (μmolCO 2 m -2 s -1 ) is the photosynthesis rate (μmolCO 2 m -2 s -1 ). The PPFD (Photosynthetic Photon Flux Density, described later) at which the photosynthesis 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] The light intensity in photosynthesis is defined as the number of photons of light irradiated on the leaf surface per second per unit area. This is called Photosynthetic Photon Flux Density (hereinafter abbreviated as PPFD).

[0016] When water and carbon dioxide are sufficiently supplied, the glucose production amount increases proportionally to the PPFD up to a certain saturation value. The light intensity at which the glucose production amount saturates is defined as the photosynthetic saturation light intensity. In order to promote plant growth, light of about 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 is below the photosynthetic saturation intensity, artificial light such as LED light may be irradiated to compensate for the lack of light. Compensating for light deficiency in this way is called "supplemental lighting". Supplemental lighting is a method of directly increasing photosynthesis. It is also possible to call the artificial light that directly increases photosynthesis "supplemental lighting".

[0018] In this embodiment, sunlight (natural light) and artificial supplementary light are referred to as "main light" for photosynthesis. This main light is light for directly causing or increasing photosynthesis. The main light is light emitted from sunlight, LEDs, etc., and is light mainly responsible for photosynthesis.

[0019] <<Growth Promotion by Additional Light>> In this embodiment, auxiliary light different from the main light is artificially created and irradiated onto plants. This auxiliary light is referred to as "additional light". The irradiation of this additional light is performed at a predetermined time or period, although details 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 periodically varies (additional signal light), or a combination of the additional signal light and light whose light intensity gradually changes (additional relaxation light).

[0021] As disclosed in Patent Document 3, the additional relaxation light has a sine-wave-like waveform, and the basic period is 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 explained 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 explained that the additional relaxation light has a gentler overall light intensity change rate compared to the additional signal light. The additional relaxation light is light for mitigating the influence of 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] Thus, by irradiating a plant with additional light obtained by combining additional relaxation light with additional signal light, it is possible to further alleviate the light stress felt by the plant compared to the case where only the additional signal light is irradiated. That is, the additional light of the present embodiment is light that combines 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 the present embodiment, it is possible to adjust the growth of plants by using only additional signal light. The inventors newly obtained the knowledge that by irradiating additional signal light, it is possible to make a plant feel like it is in the daytime even in a situation that is not daytime, and to promote gene expression. In the present embodiment, by utilizing such new knowledge of the inventors, it is possible to adjust the growth according to the classification of plants (classification into short-day plants, long-day plants, and neutral plants). The irradiation of the additional signal light (hereinafter also referred to as "gene expression light") does not necessarily have to be stopped during the irradiation of the main light, but it is preferably performed so as to include at least a part of the time zone in 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 from 350 nm to 750 nm.

[0024] Hereinafter, first, the mechanism by which additional light whose light intensity (PPFD) changes periodically promotes photosynthesis will be described. The mechanism by which additional light promotes photosynthesis is also described in Patent Document 3 mentioned above.

[0025] It is known that plants have a light integration function, and plants integrate the intensity and irradiation time of sunlight every day. When a decrease in PPFD (PPFD decrease) in the main light is detected by the integration function, the DNA in the chloroplasts of the plant issues an instruction to increase the production of chlorophyll in the light antenna. As a result, the light absorption amount increases and photosynthesis is promoted.

[0026] In this embodiment, a differentiation function for detecting the rate of change in light intensity potentially possessed by plants is utilized. The pulse light (signal light) that repeatedly turns on and off at regular time intervals can most efficiently stimulate the differentiation function of plants. This pulse light (signal light) is hereinafter referred to as "additional signal light". The additional signal light is the light included in the additional light. In this embodiment, this additional signal light is irradiated on plants alone or together with additional relaxation light.

[0027] Compared with the main light, the additional signal light is insufficient for photosynthesis. Therefore, plants recognize that they are in a temporary state of photosynthetic starvation. When DNA detects the state of photosynthetic starvation, in order to absorb more light necessary for photosynthesis, DNA issues an order to increase the production of chlorophyll. Furthermore, due to the additional signal light, DNA issues an order to control the opening and closing of stomata, which are the entrances and exits to the outside air, so that the amount of carbon dioxide absorbed increases. As a result, the light energy necessary for photosynthesis and the amount of carbon dioxide absorbed increase by irradiating the additional pulse light. That is, the additional signal light in this embodiment functions as a trigger signal for causing DNA to issue an order to increase chlorophyll production and an order to control the opening and closing of stomata. The effect of the additional signal light in such a concept 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 of the trigger signal becomes too short, the DNA trigger effect decreases. Also, the photosynthesis promotion effect by the additional light including the additional signal light can be obtained regardless of the value of the PPFD of the main light.

[0029] The above is the mechanism also described in Patent Document 3. However, as a result of intensive research by the inventors and others, it has been found that it is effective in suppressing the flowering of short-day plants. As shown in FIG. 2, when additional signal light hits the plant, the plant detects sunlight (feels it as daytime). Such a function is realized by the plant having the function of a differential circuit related to light. As a result, the length of the dark period is shortened, and the effective day length (actual execution day length) combining sunlight and additional signal light increases. And for short-day plants, flowering and flower bud formation can be suppressed, and for long-day plants, flowering and flower bud formation can be promoted.

[0030] In FIG. 2, irradiation with additional signal light is performed in the evening from the stage when sunset approaches and the main light (here, sunlight) weakens (for example, after 16:00, which is 2 to 3 hours before sunset) until a predetermined period until sunrise. Also, when suppressing flower bud formation, it is possible to prevent a large amount of nutrients from being consumed for flower bud formation, promote the growth of individual leaves, grow the stem and increase the number of leaves, etc. More specifically, by suppressing flowering, the harvestable period is extended for the cultivation period. Also, regarding the harvest timing, by extending the harvest period until the cool season in autumn, the quality of the plants targeted for flowering suppression is improved. Furthermore, regarding the harvest, an increase in yield can be expected due to the extension of the harvest period.

[0031] FIG. 3 shows the basic waveform of the additional signal light. In the example of FIG. 3, the additional signal light shows a periodic sawtooth (also called "sawtooth shape", etc.) waveform. The waveform of one cycle (ΔT) in 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). In FIG. 3, the unit related to the light intensity on the vertical axis is an arbitrary unit (A.U.), and the unit related to the time on the horizontal axis is μs.

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

[0033] Figure 5 shows the content of the consideration comparing the reaction of plants by the irradiation of additional signal light with the reaction of humans by high-altitude training. First, when a human (Human) undergoes high-altitude training, blood oxygen starvation occurs. In such a situation, the human body increases the blood oxygen concentration through the function of hemoglobin and improves the cardiopulmonary function.

[0034] In the case of a plant (Plant), when irradiated with extremely weak light such as additional signal light (EDL irradiation), photosynthesis starvation occurs. In such a situation, the plant increases the light harvesting efficiency and the photosynthesis rate through the function of chlorophyll. Here, "EDL" is an abbreviation of "Extremely Dark Light".

[0035] When such a plant survival crisis response is applied to short-day plants, as shown on the right end of Fig. 5, flowering can be suppressed. That is, when weak photosynthesis by additional signal light continues, a state of starvation in photosynthesis occurs, and the plant feels as if it is daytime even in an environment darker than daytime. Then, in the plant, the effective sunlight duration increases, and the flowering of short-day plants is suppressed. Since the additional signal light is extremely weak light that causes weak photosynthesis, according to the plant cultivation method of the present embodiment and the plant cultivation apparatus 10 described later, it is possible to adjust the growth of plants with low power consumption.

[0036] The growth deceleration (growth deceleration) disclosed in Patent Document 3 (paragraphs 0186 to 0195) gives a longer wavelength of irradiation light than in the initial stage that prioritizes growth promotion when the harvest is approaching (the end stage of growth), and prioritizes the promotion of secondary metabolism of carbohydrates. In other words, what is described in Patent Document 3 (paragraphs 0186 to 0195) is the point of accelerating growth and maintaining (and) converting carbohydrates into metabolites. On the other hand, the additional signal light irradiation of the present embodiment is for the purpose of flowering adjustment and is performed at an arbitrary time zone between near sunset and sunrise. This is because the inventors have discovered that plants have a function of perceiving a certain cycle of additional signal light irradiation as a light period, and this function is utilized. Due to such a perception function of plants, the effective day length time becomes longer. As a result, it becomes possible to suppress flowering in short-day plants and promote flowering in long-day plants.

[0037] Regarding such a sunlight detection mechanism (sunlight detection mechanism), it is possible to say that the following processes are carried out in chronological order. First, a weak vibration light (additional signal light) is irradiated in a state buried in strong light (main light). Subsequently, in plants, signal processing is performed while changing the frequency of the reference wave. Further, the plant detects only the vibration light (additional signal light) and differentiates the detected signal. As a result, sunlight detection is performed. Also, such a sunlight detection mechanism can be presumed to have a function similar to that of a lock-in amplifier in the technical field of signal processing, for example, as shown in FIG. 6. In the technical field of signal processing, a lock-in amplifier detects a minute repetitive signal (alternating current) buried in noise.

[0038] The upper part of FIG. 6 shows the sunlight detection mechanism by plants in order from the left. The frame in the lower part of FIG. 6 shows the functions of the lock-in amplifier in order from the left. Here, as shown in the upper left part of FIG. 6, consider the case where a relatively strong light (here, the main light) and a weak vibration light (additional signal light, light of a certain period) are simultaneously irradiated on the plant. Further, it is considered that the same function as when the reference wave in the lock-in amplifier is input occurs in the plant.

[0039] As shown in the lower part of FIG. 6, in the lock-in amplifier circuit, the input signal (f(t)=Asin(ωt)) and the reference signal (sin(ω 0 t)) are multiplied (multiplied), and according to the multiplication formula of trigonometric functions (Asin(ωt)xsin(ω 0 t)=(A / 2){cos(ω-ω 0 )-cos(ω+ω 0 )t}), a signal of (A / 2){cos(ω-ω 0 )-cos(ω+ω 0 )t} is generated. This signal becomes (A / 2){cos(0)-cos(2ω 0 )t} when the condition of the angular frequency is ω=ω 0 . Then, by a low-pass filter (LPF) (2ω 0) The components of are removed, and only the signal synchronized with the reference signal is detected. The detected signal (detection signal) becomes f(t) = (A / 2)sin(ωt).

[0040] As shown on the upper left side of FIG. 6, in a plant irradiated with strong light (main light) and weak light (additional signal light), as shown on the right adjacent side, only the signal of the weak signal (additional signal light) is detected by the detection function (lock-in detection function) of the above lock-in amplifier. Further, as shown on the right adjacent side, the differential operation function is exerted and converted into light of a certain intensity. Then, as shown from top to bottom on the lower right side of the figure, sunlight detection based on the obtained signal is performed, and the effective sunlight time in the plant becomes longer. As a result, flowering can be suppressed in short-day plants, and flowering can be promoted in long-day plants.

[0041] In the findings of the inventors, when random pulse light without periodicity is irradiated instead of the additional signal light (FIG. 4), the function of lock-in amplifier detection is not observed, and no growth promotion effect is observed. The random pulse light here is, for example, pulse light having a waveform such that T1≠ΔT2≠ΔT3≠···≠ΔTn-1≠ΔTn in FIG. 4. It is presumed that plants cannot detect random pulse light in principle and cannot feel a state of photosynthetic starvation. That is, it is presumed that plants can detect weak light of a certain period buried in strong light. Such a function can be referred to as, for example, the "cocktail party effect related to additional signal light".

[0042] Regarding the reference wave in plants, the inventors presume that the plant itself emits a signal corresponding to the reference wave of the lock-in amplifier. That is, it is considered that plants have a lock-in amplifier function. In other words, it means that plants have a function (organ) for generating a reference wave and a path for transmitting a signal of a certain period detected by the lock-in amplifier to genes. Regarding the location where lock-in detection is performed, the inventors consider that it is any one of photosynthetic pigments, pigments, and photoreceptor proteins. In the future, experiments to prove these hypotheses are necessary.

[0043] <Plant cultivation device 10> FIG. 7 shows a schematic configuration of the plant cultivation device 10 according to the present embodiment. Similar to the plant cultivation device disclosed in Patent Document 3, the plant cultivation device 10 includes a cultivation bed 12 for hydroponics or soil cultivation, a light irradiation unit 14 that irradiates light toward the cultivation bed 12, and an irradiation light control unit 16 that drives the light irradiation unit 14 to light up. The plant cultivation device 10 has a protection member 18 that covers the cultivation bed 12 to form a cultivation chamber. It is also possible to omit the protection member 18.

[0044] The light irradiation unit 14 includes 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 control (here, current control) of the irradiation light control unit 16. In FIG. 7, the main light source 20 and the additional light source 22 are shown side by side. However, the light of the main light source 20 and the light of the additional light source 22 are irradiated toward the cultivation bed 12 through a diffusion plate (which may be a diffusion lens) whose illustration is omitted, along the same path. The light of the additional light source 22 may be irradiated toward the cultivation bed 12 through an optical fiber whose illustration is omitted. As the optical fiber, one that emits light from the end face or the side face can be appropriately used.

[0045] The main light source 20 lights up continuously within a predetermined time and continuously emits main light (also referred to as "continuous irradiation light"). As the main light source 20, for example, artificial light sources such as LEDs, fluorescent lamps, plasma lamps, mercury lamps, incandescent bulbs, metal halide lamps, sodium lamps, or electrodeless lamps, pulsed oscillation lasers, etc. are used.

[0046] As another main light, it is also possible to use sunlight. When using sunlight, it is possible not to use the main light source 20 or to omit the main light source 20. It is also possible to use sunlight and the light of the main light source 20 in combination. In this case, sunlight and the light of the main light source 20 may be used separately according to conditions such as time zones. Furthermore, sunlight and the light of the main light source 20 may be emitted simultaneously.

[0047] The additional light source 22 includes an additional signal light source 24 and an additional relaxation light source 26. The additional signal light source 24 can irradiate additional signal light, and the additional relaxation light source 26 can irradiate additional relaxation light. Only the additional signal light, or a combination of the additional signal light and the additional relaxation light, constitutes the additional light. In this embodiment, flowering adjustment is performed only by the irradiation of the additional signal light source 24. However, as in the example of FIG. 7, an additional relaxation light source 26 may be added to enable the irradiation of additional relaxation light. For this reason, hereinafter, not only the configuration related to the additional signal light source 24 but also the configuration related to the additional relaxation light source 26 will be described. In the experiments of the inventors, for plants in which good growth was not observed in terms of growth adjustment only by the irradiation of the additional signal light, the subsequent irradiation of the additional relaxation light improved the growth status of the plants.

[0048] In FIG. 7, the additional signal light source 24 and the additional relaxation light source 26 are shown side by side left and right. However, the additional signal light and the additional relaxation light are irradiated toward the cultivation floor 12 through a diffusion plate (which may be a diffusion lens) whose illustration is omitted, along the same path. The additional light source 22 may integrate and incorporate the additional signal light source 24 and the additional relaxation light source 26.

[0049] The additional light source 22 can emit light in the wavelength range of 220 nm to 2000 nm by the additional signal light source 24. For the additional signal light source 24, various light sources such as LEDs, ELs (electroluminescence), lasers, ultraviolet light, and infrared light can be adopted as long as they can emit light with a wavelength suitable for the growth of the plants to be cultivated. Also, it is desirable to use a light source for the additional signal light source 24 that enables easy pulse lighting control. As the additional relaxation light source 26, various light sources such as cold cathode fluorescent lamps driven by electric light wires (50 Hz or 60 Hz), LED single-color lamps, and LED fluorescent lamps can be adopted.

[0050] Although illustration is omitted, the additional light source 22 may be a continuously emitting light source provided with a shutter disposed in the optical path. In this case, the optical path is intermittently blocked by the shutter to form signal light. Also, it is possible to attach a wavelength limiting filter to the white light source to form light of a required wavelength. The shutter and the 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 floor 12. The light irradiation unit 14 illuminates the cultivation floor 12 in response to a command from the irradiation light control unit 16.

[0052] The light irradiation unit 14 can be configured to include a plurality of main light sources 20 and a plurality of additional light sources 22, respectively. In this case, the plurality of main light sources 20 and the plurality of additional light sources 22 can be arranged at different positions and with different irradiation angles. For example, it is also possible to arrange the plurality of main light sources 20 and the plurality of additional light sources 22 alternately. Also, it is 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). It is also possible to install the additional light source 22 so that light is irradiated onto the cultivation floor 12 from a plurality of directions. By doing so, a more stable growth adjustment effect can be obtained.

[0053] In this way, by providing a plurality of main light sources 20 and / or a plurality of additional light sources 22, it becomes possible to perform more precise light irradiation. And by varying the arrangement and irradiation angles of the plurality of light sources, the plants on the cultivation floor 12 can be uniformly irradiated with light, and uneven growth due to location can be suppressed.

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

[0055] When the light irradiation unit 14 includes a plurality of main light sources 20 and / or a plurality of additional light sources 22, the irradiation light control unit 16 can synchronize and turn on the light sources of the same type. Also, when the cultivation floor 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 in units of blocks, or may synchronize the main light sources 20 and the additional light sources 22 of a plurality of blocks or 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 plants can be accurately maintained.

[0057] Such a plant cultivation device 10 can be widely applied to a small cultivation kit for easy indoor cultivation in ordinary households, a large-scale one such as an agricultural greenhouse, a plant factory having a constructed cultivation room, etc.

[0058] Here, the agricultural greenhouse refers to not only an agricultural vinyl greenhouse in which a film having light transmittance is extended over the entire surface of the greenhouse, but also an agricultural glass greenhouse in which a film is stretched and expanded over the entire inner surface of the glass window. In the agricultural glass greenhouse, the air containing moisture in the cultivation space inside the greenhouse passes through the film and exits the greenhouse through the gap between the glass window and the framework portion of the glass window. Therefore, even in the agricultural glass greenhouse, it is possible to suppress the inside of the greenhouse from becoming hot and humid. Note that the above-mentioned "light transmittance" means the property of passing the light necessary for growing plants during the day.

[0059] When the light source of the additional light (here, the additional light source 22) is installed inside the agricultural greenhouse, a part of the additional light is reflected and diffused (reflection diffusion) by a glass plate, a resin plate, a resin film, etc., so there is an advantage that the irradiation efficiency of the additional light is increased. The same effect of improving the irradiation efficiency can also be obtained in a small cultivation kit, a plant factory, etc.

[0060] Moreover, the effective irradiation direction of additional light (additional signal light and / or additional relaxation light) can also be considered. Whether the additional light is irradiated from the same direction as the main light or from a different direction from the main light, a growth promotion effect can be obtained in either case. Furthermore, if additional light is irradiated to a place where the main light does not reach sufficiently (for example, the front and back leaf surfaces of leaves located in the shade or the back surface of leaves in the sunlight), a greater growth promotion effect can be obtained.

[0061] Specifically, for example, for a plant such as a grapevine whose branches extend in the horizontal direction, additional light is irradiated upward from the ground (including an obliquely upward direction). In this case, the light hitting the back surface (the surface on the ground side) of the leaves in the shade increases. And compared with the case where no additional light is irradiated, photosynthesis is actively carried out and the sweetness of the grapes increases. Thus, by setting the irradiation direction of the additional light according to the environment in which the plant is cultivated and the characteristics of the plant, etc., the growth of the plant can be promoted more effectively. For example, in tomato cultivation, it is also effective to install a side-emitting optical fiber in the foliage and irradiate additional light.

[0062] <Use of this Embodiment> It should be noted that this embodiment only shows an example of the concretization in implementing the present invention, and the technical scope of the present invention should not be construed in a limited manner thereby. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

[0063] The plant cultivation method according to this embodiment is effective for the growth regulation of various types of plants. Therefore, it can be applied to the growth promotion of leafy vegetables, root vegetables, flowers, fruit trees, seaweeds, algae, and microalgae. Furthermore, it is effective for plant cultivation in fields, greenhouses, plant factories, smart cells (smart cell industry, substance production by organisms), land aquaculture, the sea surface, the sea, the water surface, the water, and mountainous areas.

[0064] Moreover, the plant cultivation method according to this embodiment can be applied to both suppressing the flowering of short-day plants and promoting the flowering of long-day plants. Furthermore, this embodiment can also be applied to promoting the growth of neutral plants. Representative short-day plants include clover, watercress, ginger, mizuna, chrysanthemum, morning glory, eggplant, perilla, etc. Representative long-day plants include iris, radish, spinach, rice, wheat, corn, soybean, tomato, watermelon, pumpkin, sweet potato, cabbage, Chinese cabbage, etc. Representative neutral plants include strawberry, spinach, lettuce, taro, tomato, cucumber, pea, lettuce, etc.

[0065] <Effects of plants according to their uses> Additional light has the effects of promoting photosynthesis and promoting the transfer of products (photosynthetic products) by photosynthesis to the primary metabolic pathway (primary metabolic circuit, pathway for primary metabolism) and the secondary metabolic pathway (secondary metabolic circuit, pathway for secondary metabolism).

[0066] Plants are often used as food, medicine, fragrance components, etc. According to the various photosynthetic biomanufacturing methods described so far, in addition to main light such as sunlight, by irradiating additional light, it is possible to increase the production of food, specific medicinal components, fragrance components, etc.

[0067] For example, generally, the taste of vegetables such as lettuce has a pungency that children dislike. In the experiments of the inventors, when irradiated with additional signal light having a wavelength of 500 nm to 600 nm or more, the pungency of lettuce could be suppressed to the extent that it was not felt. This is presumably because the nitrogen components contained in the vegetables were converted into amino acids, glutamic acid, etc. From this, it is possible to reduce consumers who dislike vegetables and expand the consumption volume of vegetables.

[0068] The same is true for pak choi. Japanese domestic pak choi is sometimes evaluated as having a stronger taste stimulus compared to those produced in Thailand. However, by irradiating additional light, the stimulus can be suppressed and the number of consumers and the consumption volume can be increased. As described above, irradiating additional light increases the sweetness of grapes. In the experiments conducted by the inventors and others, the sweetness of grapes can also be increased more significantly by irradiating additional signal light with a wavelength of 500 nm to 600 nm or more.

[0069] Based on these findings, it is considered possible to increase, for example, the aroma and sweetness of green tea by irradiating additional light.

[0070] Seedlings irradiated with additional light during at least a part of the seedling raising period (seedlings grown in an additional light environment during the seedling raising period) will continue to have a promoting effect on growth and metabolite production compared to seedlings not irradiated with additional light thereafter. This is the same whether cultivation is carried out only with main light such as sunlight or white LED light, or with both main light and additional light, after the irradiation of additional light. For example, by irradiating additional light a few days before the harvest period and simply completing the irradiation, it is possible to harvest vegetables with fewer thorns and fruits with strong sweetness at a later date.

[0071] In addition, additional light also has the effect of increasing the germination rate and the percentage of good seeds of seeds. When plants are grown in an additional light environment from germination to seedling raising, the promoting effect on growth and metabolite production will continue compared to the case where no additional light is irradiated thereafter. This is the same whether cultivation is carried out only with main light or with both main light and additional light after the irradiation of additional light.

[0072] Additional signal light can control the production of the weight of seeds of rice, wheat, and barley, umami components such as glutamic acid, medicinal components such as β-glucan, and pungent and aromatic components of herbs and pak choi.

[0073] Therefore, according to the various photosynthetic biomanufacturing methods described so far, seedlings such as lettuce, tomato, and rice with a faster growth rate than before, fruits such as grapes and peaches with a high sugar content, herbs with many medicinal components, herbs with reduced pungency, herbs with many aroma components, and knotweed and shiso containing many pigment components can be cultivated as annual herbs (annual plants). For example, in the case of perilla (such as red perilla), the content of specific metabolic components such as anthocyanin and rosmarinic acid increases.

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

[0075] Phytochrome exists in two types, Pr type and Pfr type, depending on the aggregated form of the protein. The Pr type transitions to the Pfr type upon photoexcitation. Conversely, the Pfr type transitions to the Pr type upon photoexcitation.

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

[0077] In addition to phytochrome, photoreceptor proteins contained in photosynthetic organisms such as plants include phototropin, which is involved in the movement of photosynthetic chlorophyll, phototropism, and stomatal opening and closing, and cryptochrome, which is involved in the flowering time and shade avoidance response. By selectively exciting these photoreceptor proteins with additional signal light, it is possible to further precisely control the growth rate and the production of secondary metabolites.

[0078] Furthermore, regarding flowering regulation, if the wavelength of the additional signal light is in the visible range (380 nm to 750 nm), the flowering regulation function (flowering regulation function) can be obtained. This is because when the additional signal light irradiates the plant, sunlight perception occurs by the mechanism already described, and the effective sunlight duration for the plant becomes longer.

[0079] In plants, photoreceptor proteins such as cryptochrome, phytochrome, and phototropin are distributed. Cryptochrome and phytochrome are involved in flower bud formation. As shown in FIG. 13, cryptochrome is known to promote flower bud formation by absorbing light with a wavelength of 400 nm to 500 nm. Phytochrome has two types, Pr type and Pfr type, as described above. When mainly absorbing light with a wavelength of 600 nm to 700 nm and light up to 800 nm, tissue changes occur between the Pr type and the Pfr type. Pr-type phytochrome promotes flower bud formation, and Pfr-type phytochrome inhibits flower bud formation. Phototropin is involved in phototropism, stomatal opening and closing, and chloroplast movement by absorbing light with a wavelength of 400 nm to 500 nm.

[0080] As already described, in this embodiment, by irradiating the additional signal light, the effective sunlight duration is extended to suppress flower bud formation in short-day plants and promote 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 flowering inhibition effect on short-day plants is obtained.

[0081] The above shows that the inhibitory effect on flower bud formation by the additional signal light exceeds the promoting effect on flower bud formation of the photoreceptor protein. That is, it can be said that in flower bud formation, the sunlight duration is more important than the physiological reaction of the photoreceptor protein.

[0082] Thus, the additional signal light can obtain the effect of suppressing or promoting flower bud formation by irradiating immediately after sunset or by continuously or intermittently irradiating for a certain period during the dark period.

[0083] <Various Examples of Plant Cultivation Methods> Hereinafter, embodiments of the present invention will be described in detail by way of examples. However, 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 inhibition effect. Photographic images of the cultivation status of the same period related to Sagittaria pygmaea are shown in Figures 8(a) and (b). Figure 8(a) is a photographic image of the control irradiated with only sunlight. Figure 8(b) is a photographic image of the test plot irradiated with additional signal light.

[0085] As shown in Figure 8(a), in the control, many flower buds appear as fine white parts (light-colored parts). In contrast, in the test plot of Figure 8(b), due to the irradiation of additional signal light (gene expression light), a period that feels like daytime occurs even without the main light irradiation, and almost no flower buds appear. Thus, the growth is suppressed by the irradiation of 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 inhibition effect. Similar to Figures 8(a) and (b) related to Example 1, photographic images of the cultivation status of the same period related to Sagittaria pygmaea are shown in Figures 9(a) and (b). Figure 9(a) is a photographic image of the control irradiated with only sunlight. Figure 9(b) is a photographic image of the test plot irradiated with additional signal light.

[0087] Also in Example 2, as in Example 1, in the control of Figure 9(a), many flower buds appear as fine white parts. In contrast, in the test plot of Figure 9(b), due to the irradiation of additional signal light (gene expression light), a period that feels like daytime occurs even without the main light irradiation, and almost no flower buds appear. Thus, the growth is suppressed by the irradiation of additional signal light, and as a result, flowering (and growth) is suppressed.

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

[0089] In the waveforms of Figures 10(a) and (b), the periods are the same, but the peak holding times ΔTp are different from each other. Also, the duty of both waveforms in Figures 10(a) and (b) is 100%.

[0090] In Example 3, for the additional signal light of any waveform, flowering inhibition (and increase in metabolic components) was observed in short-day plants, and growth promotion was observed in long-day plants. Thus, the additional signal light enables both flowering inhibition in short-day plants and 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 photographic images of the cultivation status of knotweed at the same time. Figure 11(a) is a photographic image of the control irradiated with only sunlight. Figure 11(b) is a photographic image of the test plot irradiated with additional signal light.

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

[0093] Figure 12 schematically shows the experimental environment according to Example 4. As shown in Figure 12, for some of the water shield plants, additional signal light is irradiated from the pulse light source, while for the other water shield plants, no additional signal light is irradiated. White mold has occurred on the water shield plants without irradiation of the additional signal light (corresponding to Figure 11(a)), and no white mold has occurred on the water shield plants irradiated with the additional signal light (corresponding to Figure 11(b)).

[0094] The leaves of the water shield plants contain specific metabolic components such as triptanthrin, 6-methoxykaempferol, kaempferol, and 3,5,4'-trihydroxy-6,7-methylenedioxyflavone, and all of them have been found to have high antibacterial activity. From this Example 4, it can be seen that by irradiating additional signal light, these specific metabolic components are produced in large quantities, and the anti-mold effect becomes remarkable.

[0095] <Other forms related to the growth regulation of photosynthetic plants> When additional signal light is irradiated, sunlight perception occurs by the above-described mechanism, and flowering regulation is performed. In addition to this, by irradiating the same additional signal light, it is also possible 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 the specific metabolic components contained in the plant can be controlled by changing the intensity (PPFD) of the additional signal light. The concentration and total weight of the specific metabolic components are defined as the weight of the specific metabolic components per unit weight of the plant and the weight of the whole plant, respectively. When the growth environment such as temperature and light deviates greatly from the normal values, the amount of reactive oxygen species increases in the plant. This is called the light stress response of the plant. When the plant detects light stress, it preferentially diverts the glucose obtained by photosynthesis to the specific metabolic pathway, thereby increasing the production of antioxidants specific to that plant. The antioxidants are part (one kind) of several specific metabolite groups.

[0097] The raw material for the production of antioxidant substances is glucose obtained through photosynthesis. During the period when the plant is in a light stress state, the amount of glucose used for plant growth decreases by the amount by which the production of antioxidant substances increases. One of the characteristics of the additional signal light is that its light intensity is smaller than the value of the light compensation point. However, since its light intensity changes relatively steeply over time, it is one of the light stress factors for plants. Adding the above-described additional relaxation light to the additional signal light is one of the relaxation measures for light stress.

[0098] The promotion of daylength perception and antioxidant production varies depending on the intensity (PPFD value) of the additional signal light. Light that mainly promotes daylength perception (light for the purpose of daylength perception) is defined as the additional signal light under weak light conditions, and furthermore, light that causes both daylength perception and light stress (light for the purpose of both daylength perception and light stress) is defined as the additional signal light under strong light conditions. Since the degree of light stress also depends on the wavelength and irradiation time of the additional signal light, temperature, humidity, etc., there is no clear boundary for the PPFD values of the additional signal light under weak light conditions and strong light conditions. The additional relaxation light that has the effect of alleviating light stress may or may not be irradiated.

[0099] When the plant is irradiated with the additional signal light under strong light conditions, in addition to the flowering regulation by daylength perception, the production of antioxidant substances becomes active to alleviate light stress. The raw material for the production of antioxidant substances is glucose obtained through synthesis. During the period when the plant is in a light stress state, the production amounts of leaves, stems, roots, and fruits decrease.

[0100] In order to extract as much antioxidant as possible from plants, it is necessary to efficiently convert the remaining carbohydrates into antioxidants. Therefore, until harvest, by irradiating additional signal light under low light conditions and switching to additional signal light under high light conditions immediately before harvest, it is possible to promote the influx of carbohydrates into specific metabolic pathways and maximize the yield of specific metabolites. Thus, by increasing the intensity of the additional signal light after the flowering regulation step, it becomes possible to cultivate the plant in a time series by continuously performing the flowering regulation step and the step of increasing the production of specific metabolites (here, antioxidants). Note that it is not limited to performing the flowering regulation step and the step of increasing the production of specific metabolites in a time series. For example, it is also possible to perform only the step of increasing the production of specific metabolites.

[0101] <Inventions extractable from the embodiments and examples> (1) Irradiating main light for photosynthesis of the photosynthetic plant to be cultivated, and irradiating additional signal light whose light intensity is lower than the light compensation point of the photosynthetic plant, periodically fluctuates, and can make the photosynthetic plant feel like daytime in a situation other than daytime, to adjust the growth of the photosynthetic plant. A method for cultivating a photosynthetic plant. (2) The method for cultivating a photosynthetic plant according to (1) above, wherein the time zone of the irradiation of the additional signal light includes a time zone in which the light intensity of the main light for photosynthesis is lower than the light compensation point. (3) The method for cultivating a photosynthetic plant according to (1) or (2) above, wherein the wavelength band of the additional signal light is from 350 nm to 750 nm. (4) A photosynthetic plant cultivation device (such as the plant cultivation device 10) in which main light for photosynthesis of the photosynthetic plant to be cultivated is irradiated, an additional light source (such as the additional light source 22) that irradiates additional signal light in addition to the main light, and an irradiation light control unit (such as the irradiation light control unit 16) capable of driving and controlling the additional light source, and the light intensity of the additional signal light is lower than the light compensation point of the photosynthetic plant and can make the photosynthetic plant feel like daytime in a situation other than daytime by periodically fluctuating, A plant cultivation apparatus that irradiates the additional signal light to adjust the growth of the photosynthetic plant. (5) The plant cultivation apparatus according to (4) above, comprising a main light source (such as main light source 20) that irradiates the main light. (6) Irradiation of main light for photosynthesis of the photosynthetic plant to be cultivated, irradiation of additional signal light whose light intensity is lower than the light compensation point of the photosynthetic plant, periodically fluctuates, and can make the photosynthetic plant feel like it is in the daytime in a situation other than daytime, and adjusting the growth of the photosynthetic plant by performing the above, increasing the intensity of the additional signal light to increase the production of specific metabolites (such as antioxidants), and performing a photosynthetic plant cultivation method.

Industrial Applicability

[0102] The plant cultivation method and plant cultivation apparatus of the present invention are effective for open-field cultivation, greenhouse cultivation, and plant factory cultivation.

Explanation of Signs

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

Claims

1. Irradiation of the main light, which is a relatively strong light for photosynthesis of the photosynthetic plant to be cultivated; and simultaneously irradiating the plant with additional signal light, the light intensity of which is relatively weak, being lower than the light compensation point of the plant, and the light intensity of which fluctuates periodically; The waveform of the additional signal light is A waveform having a peak time shorter than the time of one period, and formed so that the change in light intensity in each period is common, causing the photosynthetic plant to filter and detect the main light and sense sunlight; The plant cultivation method includes using the additional signal light to suppress flowering of the photosynthetic plant that is a short-day plant and to promote flowering of the photosynthetic plant that is a long-day plant, thereby regulating the growth of the photosynthetic plant.

2. The plant cultivation method according to claim 1 , wherein a 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 additional signal light has a wavelength band of 350 nm to 750 nm.

4. A photosynthetic plant cultivation device that irradiates a relatively strong main light for photosynthesis of a photosynthetic plant to be cultivated, an additional light source that irradiates additional signal light, which is a relatively weak light, simultaneously with 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 varies periodically; The waveform of the additional signal light is A waveform having a peak time shorter than the time of one period, and formed so that the change in light intensity in each period is common, causing the photosynthetic plant to filter and detect the main light and sense sunlight; The photosynthetic plant cultivation device uses the additional signal light to suppress flowering of the photosynthetic plants that are short-day plants and to promote flowering of the photosynthetic plants that are long-day plants, thereby adjusting the growth of the photosynthetic plants.

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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