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The effect of light on plant growth

Time: 2018-12-01  View: 876  Author: Paul
Light has a particularly important position on the growth and development of plants, which affects almost all stages of growth of plants.

The effect of light on plants is mainly manifested in two aspects:

One is to provide radiant energy for plant photosynthesis;

The second is to regulate many physiological processes throughout the life cycle of plants.

No.1

Effects of light on plant growth - photosynthesis and phytochrome

Usually, the growth and development of plants depends on sunlight, but the industrial production, tissue culture and propagation of test-tube seedlings of other economic crops such as vegetables and flowers require artificial light sources to supplement the illumination to promote photosynthesis.

Photosynthesis refers to the process by which green plants use light energy to convert carbon dioxide and water into organic matter that stores energy and release oxygen through the chloroplast. A key player in this process is the chloroplast inside the plant cell. Under the action of sunlight, the chloroplast transforms the carbon dioxide that enters the interior of the leaf through the stomata and the water absorbed by the root into glucose, while releasing oxygen.

The photoreaction photosystem consists of a variety of pigments, such as Chlorophyll a, Chlorophyll b, Carotenoids, and the like. The main absorption spectra of chlorophyll a, chlorophyll b and carotenoids are concentrated at 450 nm and 660 nm. Therefore, in order to promote photosynthesis, 450 nm deep blue LEDs and 660 nm ultra red LEDs are added, and some white LEDs are combined. Efficient LED plant fill light illumination, as shown in Figure 1:



In order to be able to sense the light intensity, light quality, light direction and photoperiod of the surrounding environment and respond to changes in it, plants have developed a photoreceptor system (photoreceptor).

Photoreceptors are the key to the perception of changes in the environment. In plant photoreaction, the most important photoreceptor is the phytochrome that absorbs red/far red light.

Photosensitive pigments are a class of pigment proteins that have a reversal effect on the absorption of red and far red light, participate in photomorphogenesis, and regulate plant development. They are red light (R) and far red light (FR). Extremely sensitive, it plays an important regulatory role in the whole growth and development of plants from germination to maturity.

The phytochrome in plants is present in two more stable states: red light absorption (Pr, lmax = 660 nm) and far red light absorption (Pfr, lmax = 730 nm). The two light absorption types can reverse each other under the illumination of red light and far red light.

Studies on phytochrome have shown that the effects of phytochrome (Pr, Pfr) on plant morphology include seed germination, de-yellowing, stem elongation, leaf expansion, shading and flowering induction.

Therefore, the complete LED plant lighting solution requires not only 450 nm of blue light and 660 nm of red light, but also 730 nm of far red light. Deep blue (450nm) and ultra-red (660nm) provide the spectrum needed for photosynthesis, and far-red light (730nm) controls the whole process from planting to vegetative growth to flowering.

As shown in Figure 2, the appropriate combination of dark blue (450 nm), super red (660 nm) and far red light (730 nm) provides better chromatographic coverage and optimal growth mode.



No.2

Two major effects of 730nm far red LED on plants

1, 730nm far red light to avoid the shade

One of the most important effects of 730 nm far red illumination on plants is the shading effect (Figure 3).



If the plant is only illuminated by 660 nm deep red light, the plant will feel under normal sunlight and grow normally. And if the plant is mainly illuminated by the far red light of 730 nm, the plant will feel like it is blocked by the other taller plant, so the plant will grow harder to break through the occlusion, that is, Helping plants grow taller, but does not mean that there will be more biomass.

2. Flowering induction of 730 nm far red light

Another important role of 730nm far red light in horticultural lighting applications is the ability to control the flowering cycle through 660nm and 730nm illumination, without the need to rely solely on seasonal effects, which is of great value for ornamental flowers.

The conversion of phytochrome Pr to Pfr is mainly induced by 660 nm deep red light (representing daytime sunlight), while the conversion of Pfr to Pr usually occurs naturally at night time, and can also be excited by 730 nm far red light. 4 is shown.



It is generally believed that phytochrome control plant flowering 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 control the flowering cycle more precisely.

3, LED plant lighting customized light formula

LEDs are used in horticultural lighting to increase plant growth by up to 40% or to control flowering time. 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 has high light efficiency, and the typical PPF light efficiency of the deep blue (450 nm) and far red (730 nm) light LED is about 2.3?mol/J, and the super red (660 nm) The typical PPF efficacy of LEDs is around 3.1?mol/J, and the wavelengths of these LEDs match the chlorophyll a/b, carotenoids and phytochrome Pr/Pfr absorption spectra to achieve efficient illumination and significantly reduce Energy consumption.

LEDs do not dissipate heat in the direction of illumination and do not damage plants. They are suitable for top lighting, interior 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). By controlling the R/FR ratio and the R/B ratio, the optimal customized light formulation for a variety of plants can be achieved.
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