The influence of light on plants mainly has two aspects: one is the necessary condition for the photosynthesis of green plants; the other is that light regulates the whole growth and development of plants. Plants absorb light energy, assimilate carbon dioxide and water, make organic matter and release oxygen. The growth and development of medicinal plants depend on photosynthesis to provide the necessary organic matter. In addition, light can inhibit the longitudinal elongation of plant cells, making plants grow strong and depend on light to control the growth, development and differentiation of plants, which is called light morphogenesis. Light quality, illumination and photoperiod are closely related to the growth and development of medicinal plants, and affect the quality and yield of medicinal materials.
(1) Effect of illumination intensity on growth and development of medicinal plants
The photosynthetic rate of plants increases with the increase of illumination. In a certain range, they are almost positively correlated, but when they exceed a certain range, the increase of photosynthetic rate slows down. When they reach a certain illumination, the photosynthetic rate no longer increases. This phenomenon is called light saturation phenomenon, and the illumination at this time is called light saturation point. When the illumination is strong, the photosynthetic rate is several times higher than the respiratory rate, but with the decrease of illumination, the photosynthetic rate gradually approaches the respiratory rate, and finally reaches a point, that is, the photosynthetic rate is equal to the respiratory rate, at this time the illumination is called the light compensation point. Different plants have different light saturation points and light compensation points. According to the different needs of different plants for illumination, they are usually divided into sun plants, shade plants and intermediate plants.
Under natural conditions, when medicinal plants grow and develop, the more light they receive around the light saturation point (or slightly higher than the light saturation point), the longer time they spend, the more photosynthetic accumulation they have, and the best growth and development they have. Generally, the illumination is lower than the light saturation point. Even if the illumination is insufficient and the illumination is slightly higher than the compensation point, the plant can grow and develop, but the yield is low and the quality is poor. If the illumination is lower than the light compensation point, the plant can not produce nutrients, but also consume nutrients. Therefore, attention should be paid to rational close planting in production to ensure good light transmission.
The illumination requirement of the same plant is different at different growth stages. For example, Magnolia officinalis should avoid intense sunshine at seedling stage or early transplanting stage, and try to shade for a short time, while growing up, it is not afraid of intense sunshine. Although Coptis chinensis is a shady plant, it has different shade tolerance in different growth stages and is the most shade-tolerant in seedling stage. But shade shelter can be removed in the fourth year after planting, so that it can grow under strong light, so as to benefit root growth. Generally speaking, plants need more nutrients and higher light requirements during flowering and fruiting stage or tuber storage organ formation stage.
Although light is necessary for photosynthesis, photosynthesis is inhibited and photosynthetic rate decreases when light is too strong, especially in hot summer. If the time of intense light is too long, even photooxidation will occur, that is, photosynthetic system and photosynthetic pigments will be destroyed. Low temperature, high temperature, drought and other adverse environmental conditions will aggravate the harm of photoinhibition. Therefore, in the cultivation of medicinal plants, special attention should be paid to preventing the simultaneous occurrence of several stress factors and minimizing photoinhibition.
(2) Effects of Light Quality on the Growth and Development of Medicinal Plants
By studying the different demands of medicinal plants for quality and choosing suitable plastic film according to the different kinds of medicinal plants, the growth needs of medicinal plants can be met. For example, in the cultivation of ginseng and American ginseng, light color is the best color film. Among them, light intensity is insufficient for dark color, resulting in poor plant growth, light yellow and light green film is the best. In the film mulching cultivation of Angelica sinensis, the effect of film color on yield was black film > blue film > silver grey film > red film > white film > yellow film > green film.
In addition, medicinal plants are always cultivated in groups. Sunlight irradiates the population, and through the selective absorption of upper leaves, the radiation transmitted to the lower part is more far-infrared and green. Therefore, in the composite population of high-dwarf medicinal plant intercropping, the light spectrum received by dwarf crops is different from that received by high-dwarf crops. If the crop density is moderate, the light quality of each layer of leaves is comparatively similar.
(3) The Role of Photoperiod
The relative length of day and night in a day is called the photoperiod. The so-called "relative length" refers to the theoretical sunshine hours from sunrise to sunset, rather than the actual sunshine hours. Photoperiod is an important factor in plant growth and development, affecting flower bud differentiation, flowering, fruiting, branching habits and the formation of some underground organs (tubers, tubers, corms, bulbs, etc.). The response of plants to the relative length of day and night is called photoperiodic phenomenon. The length of sunshine hours is an important factor for the development of various medicinal plants in different growing seasons, especially before the transfer from vegetative growth to reproductive growth.
Understanding and understanding the photoperiodic response of medicinal plants plays an important role in the cultivation of medicinal plants. In the process of introduction, we must first consider whether the introduced medicinal plants can grow, develop, blossom and bear fruits in time under the local photoperiod induction; in cultivation, we should determine the appropriate sowing date according to the response of plants to photoperiod; through artificial control of photoperiod, we can promote or delay flowering, which is in the breeding of medicinal plants. Work can play a role.