The effect of light on plant photosynthesis
The intensity of plant photosynthesis is closely related to the intensity of light, but different plants have different requirements for light intensity. The unit of light intensity is lux, which can be represented by three values: light compensation point, light saturation point, and light sum intensity (ie, assimilation rate).
According to botany theory, different wavelengths of light have different effects on plant growth. The short-wave blue-violet light has the effect of inhibiting the growth of plants, and the inhibiting effect of ultraviolet light is more significant, which can make plants dwarf. Light blue plastic film is often used to cover seedlings. It can transmit ultraviolet light and inhibit plant growth. Compared with colorless film, seedlings grow more robustly. On the basis of natural lighting, the addition of supplementary lighting in the blue and red bands has a significant effect on the growth of plants in the entire street.
The length of illumination time is closely related to the photoperiod phenomenon of plants. The phenomenon that plants control flowering by sensing the length of day and night is called the photoperiod phenomenon, that is, the phenomenon in which plants control their physiological responses by sensing the length of day and night. The alternation of day and night light and darkness has a significant effect on plant development, especially flowering. In addition to inducing flowering, light also affects plant flower stem elongation, tuber and tuber formation, bud dormancy and leaf shedding.
The main role of light in tissue culture
Light intensity (lightintensity)
The light intensity has an important influence on the proliferation of cultured cells and the differentiation of organs. From the current research situation, the light intensity has a significant effect on the initial division of external plants and cells. Generally speaking, if the light intensity is strong, the seedlings grow stoutly, while the seedlings with weak light intensity are prone to lengthening. Under dark conditions, plants have the following characteristics: thin stems, long knots, fragility (underdeveloped mechanical tissues), small and curled leaves, underdeveloped roots, and yellowing of the whole plant. This phenomenon is called chlorosis.
Light quality (lightwave)
Light quality has obvious effects on callus induction, cultured tissue proliferation and organ differentiation. For example, lily bulbs are cultured under red light, and callus will be differentiated after 8 weeks. But when cultured under blue light, callus appeared after a few weeks. 15 days after the gladiolus seed ball was inoculated, the buds appeared first when cultured under blue light, and the formed seedlings grew vigorously, while the seedlings were thin under white light. Taking carnation as an example, the growth is highest under white light conditions, followed by red, yellow, green, and blue light which inhibit growth. Monochromatic light inhibits chlorophyll synthesis, and chlorophyll synthesis needs to be completed under compound light conditions.
Lightperiod
A certain light-dark cycle should be used for tissue culture when culturing test-tube plantlets. The most commonly used cycle is 16h of light and 8h of darkness. Studies have shown that the organs and tissues of varieties that are sensitive to short-day light are easy to differentiate under short-day light, and callus is produced under long-day light, which sometimes requires dark culture, especially the callus of some plants is better than light under dark culture. The next is better. Such as the callus of safflower and black rice tree.
Except for certain materials that require dark conditions to induce callus, general culture requires a certain amount of light.
The unit of measurement of light and its relationship
Luminous flux
Refers to the radiant power that the human eye can feel. It is equal to the product of the radiant energy of a certain band per unit time and the relative viewing rate of this band. Because human eyes have different relative viewing rates for light of different wavelengths, when the radiation power of light of different wavelengths is equal, the luminous flux is not equal.
Light intensity
Refers to the luminous flux of visible light received per unit area. It is used to indicate the intensity of the light and the amount of illumination of the surface area of the object.
lumen
It is the physical unit that describes the luminous flux, produced on a solid angle (on a unit sphere with a radius of 1 meter, the angle represented by the spherical cone corresponding to the spherical cap of 1 square meter, which corresponds to the central angle of the mid-section is about 65°) The total emitted luminous flux.
Lumen is a unit of measurement of luminous flux, and light intensity is the amount of luminous flux per unit area.
The difference between T5 tissue culture lamp and T8 tissue culture lamp
T stands for “Tube” which means tubular. The number after T means the diameter of the tube. T8 means 8 “Ts” and one “T” means 1/8 inch.
The tube diameter of the LED lamp T5 is much smaller than that of the T8 and T12 lamps. The inert gas atoms and electrons filled in the tube have a higher probability of elastic collision with electrons, and the energy loss is smaller, which is also very beneficial to the improvement of light efficiency. Because the filled inert gas is a unique inert mixed gas, it can not only better protect the cathode of the lamp tube and help the lamp to jump off, but also can appropriately reduce the inflation pressure of the lamp tube to further increase the luminous flux output of the lamp tube. Therefore, although the power of the lamp is lower, the total luminous flux has not been reduced, so the luminous efficiency of the lamp has been improved, that is to say, T5 is brighter and more energy-efficient than T8.
The influence of light on plant growth, in addition to affecting its growth through metabolism, can also directly affect plant organ differentiation and morphology by inhibiting cell growth and promoting cell differentiation. The direct influence of light on plant morphogenesis is called light paradigm effect. Light is a necessary condition for the normal growth of green plants, and the light factors that affect plant growth mainly include light intensity, light wavelength and light time.
Light has a particularly important position in the growth and development of plants, and it affects almost all growth stages of plants. The effects of light on plants are mainly manifested in two aspects:
One is to provide radiant energy for plant photosynthesis;
The second is as a signal to regulate many physiological processes throughout the life cycle of plants.
The effect of light on plant growth-photosynthesis and phytochrome
Generally, the growth and development of plants rely on sunlight, but the factory production of vegetables, flowers and other economic crops, tissue culture, and the propagation of test tube seedlings also require supplementary light from artificial light sources to promote photosynthesis.
Photosynthesis refers to the process by which green plants use light energy through chloroplasts to convert carbon dioxide and water into energy-storing organic matter and release oxygen. The key participant in this process is the chloroplast inside the plant cell. Under the action of sunlight, the chloroplast converts the carbon dioxide that enters the leaves through the stomata and the water absorbed by the roots into glucose and releases oxygen at the same time.
The photosystem that undergoes photoreaction is composed of a variety of pigments, such as chlorophyll a (Chlorophyll a), chlorophyll b (Chlorophyll b), and carotenoids (Catotenoids). The main absorption spectra of chlorophyll a, chlorophyll b and carotenoids are concentrated at 450nm and 660nm. Therefore, in order to promote photosynthesis, 450nm deep blue LED and 660nm super red LED are mainly used, and some white LEDs are added to achieve this. Efficient LED plant lighting.
In order to be able to perceive the light intensity, light quality, light direction and photoperiod of the surrounding environment and respond to its changes, plants have evolved a photoreceptive system (photoreceptor).
Photoreceptors are the key for plants to sense changes in the external environment. In the photoreaction of plants, the most important photoreceptors are phytochromes that absorb red light/far-red light.
Phytochrome is a type of pigment protein that has a reversal effect on the absorption of red light and far red light, participates in the formation of light, and regulates plant development. It is resistant to red light (R) and far red light (FR). It is extremely sensitive and plays an important role in regulating the growth and development of plants from germination to maturity.
Phytochromes in plants exist in two relatively stable states: red light absorbing type (Pr, lmax=660nm) and far-red light absorbing type (Pfr, lmax=730nm). The two light absorption types can reverse each other under the irradiation of red light and far-red light. The effects of phytochromes (Pr, Pfr) on plant morphology include seed germination, de-yellowing, stem elongation, leaf expansion, shade avoidance, and flowering induction.
Therefore, a complete LED plant lighting program not only requires 450 nm blue light and 660 nm red light, but also requires 730 nm far red light. Deep blue light (450nm) and super red light (660nm) can provide the spectrum required for photosynthesis, and far red light (730nm) can control the whole process of plants from germination to vegetative growth and flowering.
Two major effects of 730nm far-red LED on plants
Shade avoidance
If the plant is only irradiated by the deep red light of 660nm, the plant will feel that it is under direct sunlight and grow normally. And if the plant is mainly irradiated by the far-red light of 730nm, the plant will feel as if it is blocked by another taller plant from the direct light of the sun, so the plant will grow harder to break through the obscuration. Helping plants grow taller does not mean that there will be more biomass (bio mass).
Flowering induction
Another important role of 730nm far-red light in horticultural lighting applications is that the flowering cycle can be controlled by 660nm and 730nm lighting, without relying only on the influence of the season, which has important value for ornamental flowers. The conversion of the phytochrome Pr to Pfr is mainly induced by the deep red light of 660nm (representing the sunlight during the day), and the conversion of Pfr to Pr usually occurs naturally at night, and it can also be excited by the irradiation of 730nm far-red light.
Phytochrome controls the flowering of plants mainly depends on the ratio of Pfr/Pr, so we can control the Pfr/Pr value by 730 nm far-red light irradiation, so as to more accurately control the flowering cycle.
Customized light formula for LED plant lighting
LED is used for horticultural lighting, which can promote the growth of plants up to 40% or flexibly control the flowering period. Since the individual LEDs are independent of each other, the lighting performance can be easily controlled in the greenhouse.
The photosynthetic photon flux (PPF) of the LED itself is very high. The typical PPF luminous efficiency of the LED is about 2.3mol/J, and the typical PPF luminous efficiency of the super red (660nm) LED is about 3.1mol/J. In addition, the wavelength of the LED is very matched with the absorption spectrum of chlorophyll a/b, carotenoids and the photosensitive pigment Pr/Pfr, which can achieve efficient lighting and significantly reduce energy consumption.
LED will not radiate heat in the lighting direction and will not damage the plants. It is suitable for top lighting, internal lighting and multi-layer cultivation. The R/FR ratio is the ratio of the intensity of red light (660 nm) to far-red light (730 nm). The R/B ratio is the ratio of the intensity of red light (660 nm) to blue light (450 nm). Through the control of R/FR ratio and R/B ratio, the best customized light formula for various plants can be realized.
