Plant cultivation method, plant cultivation apparatus, and photosynthetic organism production method
Irradiation with main light for photosynthesis and irradiation with additional light with which irradiation can be performed in addition to the main light are performed in at least a part of a cultivation period from sowing to harvesting, and the additional light includes at least additional signal light among the additional signal light of which a light intensity periodically fluctuates and additional moderate light of which a light intensity gently changes as compared with the additional signal light.
1 . A plant cultivation method comprising:
performing irradiation with main light for photosynthesis and irradiation with additional light for promoting the photosynthesis of photosynthetic organism by the main light, in at least a part of a cultivation period from sowing to harvesting, wherein
a light intensity of the main light is consistent, smaller than a photosynthesis saturated light intensity of the photosynthetic organism, and larger than a light intensity of the additional light,
the additional light includes
additional signal light of which a light intensity periodically fluctuates in a predetermined signal fluctuation period (T) such that a pulse of the light intensity in the signal fluctuation period is in a trapezoidal shape, and the pulse is composed with a rising period (ΔT 1 ) during with the light intensity increases, a peak period (ΔT 2 ) during which the light intensity is maintained with a maximum value, and a declining time (ΔT 3 ) during which the light intensity decreases, and
additional wave light of which a light intensity periodically changes in a predetermined wave fluctuation period (TM) such that the light intensity of the additional wave light continues to gradually changes to form a wave shape, and
a gradient of the light intensity of the additional wave light is smaller than a gradient of the light intensity either at the rising period (ΔT 1 ) or at the declining period (ΔT 3 ) of the additional signal light.
2 . The plant cultivation method according to claim 1 , wherein
the gradient of the light intensity of the additional wave light is smaller than the gradients of the light intensity at both the rising period (ΔT 1 ) and at the declining period (ΔT 3 ) of the additional signal light.
3 . The plant cultivation method according to claim 1 , wherein
a light intensity of the main light is 1000 times or more than a light intensity of the additional light.
4 . The plant cultivation method according to claim 1 , wherein
the light intensity of the additional light is smaller than a light compensation point wherein the light compensation point is defined as the light intensity at which a carbon dioxide absorption rate in photosynthesis of the photosynthetic organism is equal to or more than a carbon dioxide release rate in respiration of the photosynthetic organism.
5 . The plant cultivation method according to claim 1 , wherein
the light intensity of the additional signal light and the light intensity of the additional wave light are both measured by a photosynthesis effective photon flux density (or PPFD) which is defined as an amount of light radiation with which a leaf surface of the photosynthetic organism is irradiated per unit area per second, and
the PPFD of the additional moderate light is equal to or more than the PPFD of the additional signal light.
6 . The plant cultivation method according to claim 5 , wherein
the PPFD of the additional signal light is ranged from 0.001 to 0.01.
7 . The plant cultivation method according to claim 6 , wherein
the PPFD of the additional moderate light is ranged from 0.002 to 0.05.
8 . The plant cultivation method according to claim 1 , wherein
the light intensity of the additional light is determined depending on the photosynthetic organism.
9 . The plant cultivation method according to claim 8 , wherein
the photosynthetic organism is classified as one of types following: a seedling, a plankton, and algae, and
fluctuation period of the light intensity related to the additional signal light is determined depending on the type of the photosynthetic organism.
10 . The plant cultivation method according to claim 9 , wherein
the signal fluctuation period (T) of the light intensity related to the additional signal light is 8 μs or more and 200 μs or less.
11 . The plant cultivation method according to claim 10 , wherein
the signal fluctuation period (T) of the light intensity related to the additional signal light is 100 μs or less.
12 . The plant cultivation method according to claim 10 , wherein
the wave fluctuation period (TM) of the light intensity related to the additional wave light is 1 ms or more, and
the signal fluctuation period (T) of the light intensity related to the additional signal light is shorter than the wave fluctuation period (TM) of the light intensity related to the additional wave light.
13 . The plant cultivation method according to claim 9 ,
the wave fluctuation period (TM) of the additional moderate wave light is 125 to 2 times longer than the signal fluctuation period (TS) (T) of the additional signal light.
14 . The plant cultivation method according to claim 9 , wherein
a ratio of the rising period (ΔT 1 ) with respect to the signal fluctuation period (T) of the light intensity related to the additional signal light is ranged from 1/40 to ⅝, wherein the rising period (ΔT 1 ) is determined from a lowest point to a peak point of the light intensity.
15 . The plant cultivation method according to claim 1 , wherein
a rising period (ΔTM) of the light intensity related to the additional wave light is longer than 10 μs, and is more than four times as longer as the rising period (ΔT 1 ) of the additional signal light, wherein the rising period (ΔTM) of the additional wave light is determined from a lowest point to a peak point of the light intensity in their fluctuations.
16 . The plant cultivation method according to claim 1 , wherein
the cultivation period is divided into two periods that are a seedling growing period, which is defined from sowing to planting, and a growth period, which is defined from planting to harvesting,
a portion of the cultivation period during which the irradiation of the additional light is performed is longer than half the seedling growing period.
17 . The plant cultivation method according to claim 1 , wherein
the cultivation period is divided into two periods that are a seedling growing period, which is defined from sowing to planting, and a growth period, which is defined from planting to harvesting,
a portion of the cultivation period during which the irradiation of the additional light is performed is longer than half the growth period.
18 . A plant cultivation apparatus which performs irradiation with main light for photosynthesis of a target plant, which is a cultivation target, wherein a light intensity of the main light is consistent, and smaller than a photosynthesis saturated light intensity of the photosynthetic organism, the plant cultivation apparatus comprising:
an additional light source that performs irradiation with additional light which promotes the photosynthesis of the target plant by the main light, wherein the light intensity of the main light is larger than a light intensity of the additional light; and
an irradiation light control unit capable of driving and controlling the additional light source, wherein
the additional light source includes
an additional signal light source that performs irradiation with additional signal light of which a light intensity periodically fluctuates in a predetermined signal fluctuation period (T) such that a pulse of the light intensity in the signal fluctuation period is in a trapezoidal shape, and the pulse is composed with a rising period (ΔT 1 ) during with the light intensity increases, a peak period (ΔT 2 ) during which the light intensity is maintained with a maximum value, and a declining time (ΔT 3 ) during which the light intensity decreases, and
an additional wave light source that performs irradiation with additional wave light of which a light intensity periodically changes in a predetermined wave fluctuation period (TM) such that the light intensity of the additional wave light continues to gradually changes to form a wave shape,
the plant cultivation apparatus performs irradiation with the additional wave light together with the additional signal light, and
a gradient of the light intensity of the additional wave light is smaller than a gradient of the light intensity either at the rising period (ΔT 1 ) or at the declining period (ΔT 3 ) of the additional signal light.