What Are the Factors Affecting Photosynthesis

Photosynthesis, like other physiological processes, is affected by a range of internal and external factors. The age of the orchid plant, its organs, and the chlorophyll content within its body all have a direct influence on photosynthesis. Light Intensity Light is the energy source for photosynthesis; without light, photosynthesis cannot proceed. Photosynthetic intensity is closely related to light intensity. The commonly used unit of light intensity is lx. Actual light intensity can be measured directly with a light meter. At noon on a sunny summer day, the light intensity in the open is about 100000 lx. On a sunny winter day, the light intensity in the open is about 25000 lx, while on cloudy and rainy days it is only 1/4 to 1/5 of that on sunny days. Generally speaking, orchid plants can carry out photosynthesis under very weak light. The weaker the light, the weaker the photosynthesis; if light intensity increases, photosynthesis also strengthens. However, when light intensity reaches a certain level, and then increases further to the light saturation point, photosynthesis no longer increases accordingly. At this point, if light intensity continues to increase, the photosynthesis of the orchid plant will decline. This is because strong light causes the inactivation of photosynthetic pigments and important enzymes, and strong light often leads to high temperatures, which easily causes water deficit, stomatal closure and insufficient CO2 supply, etc. ChinaorchidsMost varieties belong to shade-tolerant plants. Under light conditions of 1/10 of full light intensity, they can carry out photosynthesis normally. When light intensity is too high, photosynthesis is instead weakened. This is the main reason whycultivatingChineseorchidsrequires shading. While carrying out photosynthesis, orchid plants are also carrying out respiration. Within the range of light intensity required by orchid plants, when light intensity is relatively high, photosynthetic intensity is often several times higher than respiratory intensity; when light intensity decreases, photosynthetic intensity also decreases. When light intensity drops to a certain level, the CO2 absorbed by photosynthesis equals the CO2 released by respiration, thus reaching the light compensation point.Orchidsare shade-tolerant plants, and their light compensation point does not exceed 1% of full light intensity. At the light compensation point, orchid plants cannot accumulate dry matter, and at night they still consume dry matter, which is extremely unfavorable to the growth of orchid plants. Therefore, when considering the installation of Chinese orchidflowercultivationsites, the minimum requirement for light intensity must be higher than the light compensation point. The light saturation point and light compensation point represent the ability of a plant's leaves to utilize strong light and weak light, and can be used to measure a plant's light requirement.Cultivatingorchid plants in a controlled greenhouse usually maintains an optimal temperature condition, and the position of the compensation point can be appropriately lowered. This is of great significance for effectively using weaker light to maintain normal photosynthesis. CO2 Concentration CO2 is the main raw material for photosynthesis, and its content directly affects the progress of photosynthesis. When the CO2 content in the air is lower than 60mg/m2 (PPm), photosynthesis decreases significantly, or even stops completely, reaching the CO2 compensation point. Increasing CO2 concentration can, within a certain range, increase photosynthetic intensity. Under normal circumstances, the optimal CO2 concentration for photosynthesis is about 01%, while the CO2 content in the air is usually 0.02%-0.03%. Therefore, if the CO2 concentration in the air can be appropriately increased, photosynthesis can increase significantly. In cultivation greenhouses or plastic film sheds, the method of CO2 fertilization can be applied to increase the CO2 content in the air. It is also possible to combine saccharified feed fermentation, or use water vats filled with manure, peanut meal and other organic fertilizers for fermentation, which can achieve the purpose of increasing the indoor CO2 concentration. Under outdoor cultivation conditions, applying CO2 fertilizer still presents considerable difficulties. It mainly relies on natural wind or blowing equipment to cause air movement, so that CO2-containing air approaches the leaf surface, ensuring the normal progress of photosynthesis. In addition, carbonate fertilizers and organic fertilizers are applied to increase the CO2 content of the cultivation substrate. Applying organic fertilizers can increase the humus in the cultivation substrate, increase the number of microorganisms in the substrate and improve the microbial community in the substrate, thereby achieving the purpose of CO2 fertilization. Part of the CO2 in the cultivation substrate diffuses into the air and is absorbed by the leaves of the orchid plant, while another part is directly absorbed by the roots. Under normal circumstances, too high a CO2 content in the air is also unfavorable to photosynthesis. When the concentration exceeds 1%, it will cause poisoning of the orchid plant's protoplasm and stomatal closure, thereby inhibiting photosynthesis. However, if light intensity is increased at the same time, the usable CO2 concentration can be relatively increased. Therefore, the installation of an orchid room must have equipment for adding wind and exhaust ventilation as well as supplementary lighting. Temperature Orchidflowervarieties differ, and the temperature range for carrying out photosynthesis also differs. At 0-4 degrees, photosynthesis is inhibited. Starting from the lower temperature limit, photosynthetic intensity strengthens as temperature rises. After exceeding the optimum point, photosynthesis declines. Generally speaking, Chinese orchids carry out normal photosynthesis at 5-36 degrees, but the optimum temperature is 18-28 degrees. Above 36 degrees, photosynthesis is very weak, or even stops. The effect of temperature on photosynthesis is related to both light intensity and CO2 concentration. Under conditions of higher light intensity and higher CO2 concentration, the optimum temperature for photosynthesis also rises accordingly. When light intensity is low and CO2 concentration is low, raising the temperature is instead unfavorable to the growth of orchid plants. Therefore, heating equipment should be equipped with supplementary lighting equipment to achieve results, and at night or on cloudy and rainy days with insufficient light, the temperature in the orchid room should be appropriately lowered to increase the temperature difference, promote the accumulation of dry matter and increase the speed of "forming pseudobulbs." Because the microclimates of different places vary, and Chinese orchids originally grow in deep mountains and old forests, and must be transferred from the wild environment to artificial cultivation, the optimum temperature is a problem that must be solved. Air temperature changes often exceed their photosynthetic range. In addition to selecting a microclimate environment suitable for their growth, heating and cooling are among the main measures. When a cold wave arrives or there is snow and frost, orchid plants are often harmed. At this time, plastic film should be added for insulation, the light transmittance of the orchid room should be increased, and heating and supplementary lighting equipment should be turned on. In high-grade orchid rooms, constant heating equipment can be arranged to keep the room temperature within the range suitable for photosynthesis. In fact, when cultivating Chinese orchids, raising the temperature is easier than lowering it. In hot summer, the air temperature often reaches above 35 degrees. At this time, the shading rate should be increased, automatic humidification equipment should be turned on for humidification and cooling, or water curtains should be added around the orchid room, and ways should be found to promote air movement, such as turning on electric fans. Installing air-conditioning equipment in the orchid room to lower the temperature, if such equipment must dehumidify before it can lower the temperature, then cooling and maintaining a certain humidity will become contradictory, and even excessive dehumidification will dehydrate the orchid plants. This method is not advisable. Water and Mineral Elements Water is a raw material for photosynthesis, but less than 1% of the water absorbed by orchid plants is used for photosynthesis, while a large part of the water is used for other physiological processes and lost through transpiration. Therefore, the influence of water on photosynthesis is not direct; it mainly affects various other physiological activities, thereby indirectly affecting the progress of photosynthesis. When the plant's water metabolism is disrupted, the water content of the leaves decreases, causing stomatal closure, preventing CO2 from entering the leaves, and reducing photosynthesis. The mineral elements required by orchid plants also have direct or indirect effects on photosynthesis. For example, magnesium and nitrogen are constituent elements of chlorophyll, iron and manganese participate in the process of chlorophyll formation, and boron, potassium, phosphorus, etc. can promote the transport and transformation of organic matter. Therefore, rational fertilization is very important for ensuring the smooth progress of photosynthesis. (Liu Zhongjian)