Dicotyledon plant cultivation method and dicotyledon plant cultivation device

Abstract

The present invention provides a plant cultivation method that makes it possible to increase plant growth speed by irradiation with high-illuminance light while suppressing the occurrence of a photoinhibition or photoprotection reaction in the plant.　Provided is a dicotyledon plant cultivation method in which light 3 of a wavelength in a red region that is included in the wavelength band for the absorption peak of chlorophyll a is radiated toward a dicotyledon plant 4. The light 3 is emitted from a laser light source 1, does not include light of a wavelength outside the wavelength band for the absorption peak of the chlorophyll a, and, at the point of arrival at the dicotyledon plant 4, has a photon flux density (PPFD) which is a predetermined value or greater.

Description

Method for growing dicotyledonous plants and device for growing dicotyledonous plants

[0001] The present invention relates to a plant cultivation method.

[0002] Plant leaves contain several types of chlorophyll, and it is known that chlorophyll a is the one that is primarily used in photosynthesis. Chlorophyll a has a light absorption spectrum peak in the red around 660 nm.

[0003] In order to improve the efficiency of photosynthesis in plants using light sources for plant cultivation, for example, Patent Document 1 proposes a light source having emission peaks in a first wavelength range of 600 nm to 700 nm and a second wavelength range of 720 nm to 800 nm. This light source is designed so that the ratio (d2 / d1) of the photon flux density (d2) in the second wavelength range to the photon flux density (d1) in the first wavelength range is 0.1 or greater. Patent Document 1 discloses that, in addition to light-emitting diodes (LEDs), laser diodes (LDs) can also be used as light-emitting elements constituting the light source (see paragraph 0050 of Patent Document 1).

[0004] On the other hand, Patent Document 2 proposes cultivating plants by combining a white light source with a narrow bandpass filter and irradiating the plants with light of a specific wavelength band, where the wavelength showing the maximum transmittance is 400 nm to 500 nm or 630 nm to 700 nm.

[0005] JP 2021-52671 A International Publication No. 2013 / 105374

[0006] As described above, the technology of Patent Document 1 proposes a light source having an emission peak in each of a first wavelength range of 600 nm or more and 700 nm or less and a second wavelength range of 720 nm or more and 800 nm or less, while the technology of Patent Document 2 proposes irradiating light having a wavelength of 400 nm or more and 500 nm or less, or 630 nm or more and 700 nm or less.

[0007] The peak bands of the light absorption spectrum of chlorophyll a are the bands from around 600 nm to around 700 nm and the bands from around 300 nm to around 450 nm, so the light bands in Patent Documents 1 and 2 almost match the peak bands of the absorption spectrum of chlorophyll a.

[0008] On the other hand, research by the inventors has suggested that even when light with a wavelength matching the peak band of the absorption spectrum of chlorophyll a is irradiated, if the irradiance is increased to increase the growth rate of the plant, the relative growth rate (RGR) will saturate once a certain irradiance is reached, and irradiation with light above the saturation irradiance can cause leaf color to change depending on the plant species. These phenomena are thought to be caused by a decrease in photosynthetic function known as "photoinhibition" and a "photoprotection response," a mechanism by which plants process excess light energy.

[0009] An object of the present invention is to provide a method for growing plants that can increase the growth rate of plants by irradiating them with high-intensity light while suppressing the occurrence of photoinhibition and photoprotective reactions in plants.

[0010] To achieve the above object, the present invention provides a method for growing dicotyledonous plants, which comprises irradiating the dicotyledonous plants with light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a. This light is emitted from a laser light source, does not contain light of wavelengths outside the wavelength band of the absorption peak of chlorophyll a, and has a photon flux density (PPFD) at the time of reaching the dicotyledonous plants equal to or greater than a predetermined value.

[0011] According to the present invention, the light irradiated onto the plants is light emitted from a laser light source, and therefore, even if high-intensity light is irradiated, the occurrence of photoinhibition and photoprotection reactions in the plants can be suppressed, thereby increasing the plant growth rate.

[0012] 1 is a diagram illustrating the configuration of a dicotyledonous plant growing apparatus 100 according to an embodiment of the present invention; 2 is a graph showing the absorption spectrum of chlorophyll a; 3 is a graph showing the emission spectrum of a laser light source 1 of the dicotyledonous plant growing apparatus 100 according to an embodiment; 4 is a diagram illustrating the configuration of a dicotyledonous plant growing apparatus 100 according to a first modified embodiment; 5 is a diagram illustrating the configuration of a dicotyledonous plant growing apparatus 100 according to a second modified embodiment; 6 is a diagram illustrating the configuration of an optical element 2 of a dicotyledonous plant growing apparatus 100 according to a third modified embodiment; 7 is a diagram illustrating the configuration of an optical element 2 of a dicotyledonous plant growing apparatus 100 according to a fourth modified embodiment; 8 is an image and graph showing measurement results of the appearance, photosynthetic activity, light irradiation stress, dry weight, and leaf area of ​​dicotyledonous plants grown in Examples 1 and 2 of the present invention and Comparative Examples 1 and 2; 9 is an image showing the appearance of dicotyledonous plants grown in Example 3 and Comparative Example 3 of the present invention; 10 is a graph showing measurement results of the photosynthetic rate when tobacco is irradiated with laser light 3 from four types of laser light sources 1 with center wavelengths of 637 nm, 659 nm, 675 nm, and 690 nm in the examples of the present invention. 1 is a graph showing the relationship between normalized photosynthetic rate and wavelength obtained in an example of the present invention.

[0013] An embodiment of the present invention will be described below.

[0014] In this embodiment, dicotyledonous plants are grown by irradiating them with light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a.

[0015] For example, as shown in FIG. 1, a dicotyledonous plant growing device 100 is used, which combines a laser light source 1 of a predetermined wavelength band with an optical element 2 that irradiates the entire dicotyledonous plant with laser light 3 emitted from the laser light source 1.

[0016] The laser light 3 emitted from the laser light source 1 is light with a wavelength in the red region. When this laser light 3 passes through the optical element 2 and is irradiated onto the plant 4, it does not contain light with wavelengths outside a predetermined wavelength band (specifically, 640 nm to 675 nm) that includes the absorption peak of chlorophyll a (see FIG. 2 ). Furthermore, the photon flux density (PPFD) of the laser light 3 at the time of reaching the dicotyledonous plant is equal to or greater than a predetermined value at which light with a wavelength outside the predetermined wavelength band causes physiological disorders in the dicotyledonous plant.

[0017] As shown in Fig. 3, the wavelength band of the emission spectrum of the laser light 3 preferably includes the absorption peak of chlorophyll a (specifically, 660 nm). Furthermore, the spectrum of the laser light 3 preferably has a steep half-width of 5 nm or less. To achieve these, it is preferable that the laser light source 1 is of one type, and that the center wavelength is around 660 nm.

[0018] The dicotyledonous plant growing device 100 may irradiate the dicotyledonous plant 4 with two types of laser light having different central wavelengths, as long as the laser light is within the wavelength band of the absorption peak of chlorophyll a.

[0019] As described above, the laser light 3 does not include light outside the wavelength band of 640 nm or more and 675 nm or less, and it is particularly preferable that the laser light 3 does not include light outside the wavelength band of 645 nm or more and 670 nm or less.

[0020] The photon flux density (PPFD) at the time of reaching the dicotyledonous plant 4 is 150 μmol m －２ s －１ It is preferable that this is equal to or greater than this.

[0021] For example, a diffusion plate can be used as the optical element 2. Since the laser light 3 does not need to be in phase when it reaches the dicotyledonous plant 4, the optical element 2 that does not make the laser light 3 in phase may be used.

[0022] As described above, in this embodiment, by growing the dicotyledonous plant 4 by irradiating the entire dicotyledonous plant 4 with laser light 3 having a predetermined wavelength characteristic, the dicotyledonous plant 4 can suppress "photoinhibition," in which chlorophyll a is inactivated under high illuminance, and "photoprotective responses," such as the expression of pigments that protect the plant from high illuminance, even if the photon flux density (PPFD) at the time of reaching the dicotyledonous plant 4 is high. As a result, the growing method of this embodiment makes it possible to grow the dicotyledonous plant 4 under high illuminance light, and is expected to improve the yield through forced cultivation.

[0023] <Modification 1> In the plant growing method of the above-described embodiment, a dicotyledonous plant is grown by irradiating it with light having a wavelength in the red region. However, in addition to light in the red region, light in the blue region other than the red region may also be irradiated. For example, as shown in Figure 4, a dicotyledonous plant growing device 100 is configured to further include a light source 5 that emits light 7 in the blue region in addition to a laser light source 1 that emits laser light 3 having a wavelength in the red region. An optical element 6 that irradiates the entire dicotyledonous plant 4 with light 7 from the light source 5 may be disposed between the light source 5 and the dicotyledonous plant 4.

[0024] The wavelength of the light 7 in the blue region may be a narrow-band laser light. Furthermore, the light 7 is not limited to laser light, but may be light with a wider band than laser light emitted from a light-emitting element such as an LED. <Variation 2> In the above-described embodiment, the optical element 2 of the dicotyledonous plant growing device 100 may be configured to irradiate the entire dicotyledonous plant 4 with the laser light 3, and is not limited to a diffuser plate; an element such as a polygon mirror that scans the laser light may also be used (see FIG. 5). Furthermore, a mechanism that moves the light source 1 relative to the plant may also be used as the optical element 3.

[0025] <Variation 3> In the above-described embodiment, it is also possible to use a combination of a light guide plate 22 equipped with a scatterer and a reflective film and a polygon mirror 21 as the optical element 2 of the dicotyledonous plant growing device 100 (see FIG. 6). The laser light emitted from the laser light source 1 is reflected by the polygon mirror 21 to form a line beam, which is incident on the end face of the light guide plate 22, is scattered while being guided within the light guide plate 22, and is irradiated from below by the reflective film toward the dicotyledonous plant 4.

[0026] <Modification 4> In the above-described embodiment, it is also possible to use, as the optical element 2, a plurality of optical fibers 24 whose emitting ends are arranged in a two-dimensional array (see FIG. 7).

[0027] Light emitted from the laser light source 1 is made incident on a plurality of arranged optical fibers 24 using a branching element or the like (not shown), and is emitted from the emission ends of the plurality of optical fibers 24 to irradiate the dicotyledonous plant 4. In this way, the laser light 3 emitted from the laser light source 1 can be emitted from the emission ends of the plurality of optical fibers 24 arranged two-dimensionally, so that the entire dicotyledonous plant can be irradiated with the laser light 3.

[0028] Examples 1, 2, and 3 of the present invention will be described. In Examples 1, 2, and 3, a laser diode (LD) with a wavelength peak of 660 nm and a half-width of 1.6 nm was used as the laser light source 1, and a diffuser plate capable of expanding the irradiation range of the laser light was used as the optical element 2. The laser light 3 was irradiated for 12 consecutive days according to the cultivation method of the embodiment, and a dicotyledonous plant 4 was cultivated. The optical element 2 may be built into the laser light source 1 device. The cultivated dicotyledonous plants 4 were tobacco and lettuce (Red Fire), as shown in Table 1. The photon flux density (PPFD) of the laser light 3 at the time of reaching the dicotyledonous plant 4 was 150 μmol m －２ s －１ and 300 μmol m －２ s －１ There are two types:

[0029] In Comparative Examples 1, 2, and 3, a dicotyledonous plant 4 was grown under the same conditions as in Examples 1, 2, and 3, except that an LED with a wavelength peak of 660 nm and a half-width of 17 nm was used as the light source.

[0030] Figure 8 shows photographs of the appearance of dicotyledonous plants grown in Examples 1 and 2 and Comparative Examples 1 and 2, as well as the measurement results of photosynthetic activity, light irradiation stress, leaf dry weight, and leaf area. The photosynthetic activity and light irradiation stress shown in Figure 8 were measured using an IMAGING-PAM M-series from WALZ Corporation. Dry weight was measured after placing sampled plants in a dryer to remove moisture from the plant body and returning them to room temperature. Leaf area was measured by extracting only the leaf from the photographed image and processing it.

[0031] As is clear from the external appearance photograph in Figure 8, the tobacco grown in Example 1 had a larger leaf area than the tobacco grown in Comparative Example 1. Furthermore, the tobacco grown in Example 1 did not show leaf discoloration, whereas the tobacco grown in Comparative Example 1 did show leaf discoloration.

[0032] Similarly, the lettuce (Red Fire) grown in Example 2 had a larger leaf area than the lettuce grown in Comparative Example 2. Furthermore, the lettuce grown in Example 2 did not show any discoloration of the leaves, but the leaves of the lettuce grown in Comparative Example 2 had turned reddish purple.

[0033] Furthermore, as is clear from the chlorophyll a fluorescence imaging image obtained by the IMAGING-PAM method shown in Figure 8, it was confirmed that the photosynthetic activity value of the grown dicotyledonous plants was higher in the tobacco grown in Example 1 than in the tobacco grown in Comparative Example 1. Furthermore, the photosynthetic activity value of the lettuce grown in Example 2 was equivalent to that of the lettuce grown in Comparative Example 2.

[0034] The dry weight of the tobacco leaves grown in Example 1 was about twice that of Comparative Example 1. The dry weight of the lettuce leaves grown in Example 2 was about 1.5 times that of Comparative Example 2.

[0035] The leaf area of ​​the tobacco grown in Example 1 was about twice that of Comparative Example 1. The leaf area of ​​the lettuce grown in Example 2 was about 1.5 times that of Comparative Example 2.

[0036] In Comparative Example 2, the leaves turned reddish purple due to a photoprotective reaction in which anthocyanins accumulated. Lettuce (Red Fire) is known to accumulate anthocyanins in response to light stress.

[0037] Photographs of the appearance of the lettuce grown in Example 3 and Comparative Example 3 are shown in Figure 9. －２ s －１ Even in the case of －２ s －１As in Example 2 and Comparative Example 2, the leaf area of ​​the lettuce in Example 3 was larger than that of the lettuce grown in Comparative Example 3. Furthermore, the lettuce grown in Example 3 did not show any leaf discoloration, whereas the lettuce grown in Comparative Example 3 showed leaf discoloration to reddish purple.

[0038] These results show that photoinhibition, in which photosynthetic activity is reduced due to the decomposition of chlorophyll, occurred in Comparative Examples 1, 2, and 3, and furthermore, a photoprotective reaction occurred in lettuce in Comparative Example 2, but photoinhibition and photoprotective reactions did not occur in Examples 1, 2, and 3. This phenomenon can be presumed to be due to the fact that in Comparative Examples 1, 2, and 3, the half-width of the LED used as the light source was wide, so that wavelength components outside the absorption peak of chlorophyll a caused photoinhibition and photoprotective reactions in the dicotyledonous plant 4, but in Examples 1, 2, and 3, the use of the laser light source 1 resulted in a narrow half-width and very few wavelength components outside the absorption peak of chlorophyll a, so photoinhibition and photoprotective reactions did not occur.

[0039] From these findings, it can be inferred that when light with a wavelength that is shifted from the absorption peak of chlorophyll is irradiated, there are excess light components that cannot be absorbed by chlorophyll, resulting in a photoinhibitory or photoprotective reaction.

[0040] Even if the wavelength of light is shifted from the chlorophyll absorption peak, the wavelength range within which the photosynthetic rate does not decrease is considered to be the wavelength range that does not induce photoinhibition or photoprotection. To determine this wavelength range, we measured the photosynthetic rate when tobacco was irradiated with laser light 3 from four laser light sources 1 (LD) with center wavelengths of 637 nm, 659 nm, 675 nm, and 690 nm using a photosynthetic transpiration measurement device (Licor LI-6400XT). Figure 10 shows a graph plotting the photosynthetic rate for each wavelength.

[0041] The photosynthetic rate in FIG. 10 was normalized and fitted as a quadratic equation of wavelength λ by the least squares method to obtain an approximate formula for the photosynthetic rate shown in the following formula (1).

[0042] Normalized photosynthetic rate = -0.00149λ ２ +1.96046λ-639.37411...(1)

[0043] Figure 11 shows a plot of the above formula (1). It can also be seen from Figure 11 that the wavelength at which the photosynthetic rate peaks is very close to 660 nm, the absorption peak of chlorophyll a. Figure 11 also shows the wavelengths (645 nm, 670 nm) at which 95% of the photosynthetic rate is reached and the wavelengths (640 nm, 675 nm) at which 90% of the photosynthetic rate is reached, relative to the peak photosynthetic rate.

[0044] 11, it was confirmed that when the wavelength range of the laser light 3 irradiated onto the dicotyledonous plant 4 is a wavelength band (640 to 674 nm) that shows a photosynthetic rate of up to 90% of the peak value, the decrease in the photosynthetic rate from the peak value is small. In particular, it was confirmed that the wavelength band (644 to 671 nm) that shows a photosynthetic rate of up to 95% shows an even smaller decrease in the photosynthetic rate from the peak value. By irradiating the plant with laser light 3 in this wavelength band of 640 to 674 nm (particularly 644 to 671 nm), photoinhibition or photoprotection reactions are hardly observed in the plant even at high illuminance, and improved yields can be expected from forced cultivation.

[0045] The techniques of the present embodiment and examples can be used for growing plants used in horticulture and vegetable cultivation, for example, in a plant growth light source device (for use in a plant factory, etc.) or a light source device for greenhouse horticulture (including a light source for supplemental lighting).

[0046] 2 Optical element 3 Laser light 4 Dicotyledonous plant 5 Light source 6 Optical element 21 Polygon mirror 22 Light guide plate 24 Optical fiber 100 Dicotyledonous plant growing device

Claims

1. A method for growing dicotyledonous plants by irradiating light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a toward the dicotyledonous plants, wherein the light is light emitted from a laser light source, does not include light having a wavelength outside a predetermined wavelength band including the absorption peak of chlorophyll a, and the photosynthetic photon flux density (PPFD) at the time when the light reaches the dicotyledonous plants is equal to or greater than a predetermined value.

2. The method for growing dicotyledonous plants according to claim 1, wherein the wavelength band of the laser light includes the absorption peak of the chlorophyll a.

3. The method for growing dicotyledonous plants according to claim 1, wherein the predetermined wavelength band is a band of 640 nm or more and 675 nm or less.

4. The method for growing dicotyledonous plants according to claim 3, wherein the predetermined wavelength band is a band of 645 nm or more and 670 nm or less.

5. The method for growing dicotyledonous plants according to claim 1, wherein the full width at half maximum of the spectrum of the laser light is 5 nm or less.

6. The method for growing dicotyledonous plants according to claim 1, wherein the laser light source is of one type.

7. A method for growing a dicotyledonous plant according to claim 1, wherein the predetermined photosynthetic photon flux density (PPFD) is 150 μmol m －２ s －１ or more, characterized by the method for growing a dicotyledonous plant.

8. A dicotyledonous plant growing apparatus having a laser light source that emits laser light having a wavelength in the red region included in the wavelength band of the absorption peak of chlorophyll a, and an optical element that irradiates the entire dicotyledonous plant with the laser light, wherein the laser light emitted from the laser light source does not include light having a wavelength outside a predetermined wavelength band including the absorption peak of chlorophyll a, and when the entire dicotyledonous plant is irradiated with the laser light by the optical element, the intensity is equal to or greater than a predetermined photosynthetic photon flux density (PPFD) at which a physiological disorder occurs in the dicotyledonous plant.

9. The dicotyledonous plant growing apparatus according to claim 8, wherein the optical element is any one of a diffuser that diffuses laser light, an element that scans laser light, a light guide plate that diffuses while guiding laser light, and a plurality of optical fibers whose emission ends are arranged two-dimensionally.

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