Factors affecting photosynthesis

Photosynthesis, like other physiological processes, is affected by a series of internal and external factors. The age of orchid plants and the content of chlorophyll in organs and their bodies have a direct impact on photosynthesis.

Light intensity is the energy source of photosynthesis. Without light, photosynthesis cannot be carried out. There is a close relationship between photosynthetic intensity and light intensity.

The commonly used unit of light intensity is lx. The actual light intensity can be measured directly by illuminance meter. At noon on a sunny day in summer, the light intensity in the open field is about 100000lx. The light intensity of sunny day and open field in winter is about 25000lx, while that of rainy day and sunny day is only 5.

Generally speaking, orchid plants can carry out photosynthesis in very weak light. The weaker the light, the weaker the photosynthesis. if the light intensity increases, the photosynthesis will be enhanced. However, when the light intensity reaches a certain degree, when the light intensity increases to the light saturation point, the photosynthesis will no longer increase. At this time, if we continue to increase the light intensity, the photosynthesis of the orchid plant will decrease. This is due to the passivation of photosynthetic pigments and important enzymes caused by strong light, while strong light often leads to high temperature, water deficit, stomatal closure and insufficient supply of CO2.

Most varieties of Chinese orchids belong to pre-tolerant plants, that is, they can carry out photosynthesis normally under the condition of 1 + 10 light intensity, and when the light intensity is too high, it will lead to the weakening of photosynthesis, which is the main reason why shading is needed in the cultivation of Chinese orchids.

The orchid plant is still breathing during photosynthesis. In the range of light intensity required by orchid plants, when the light intensity is high, the photosynthetic intensity is often several times higher than the respiration intensity; when the light intensity decreases, the photosynthetic intensity also decreases, and the light intensity decreases to a certain extent, the CO2 absorbed by photosynthesis is equal to the CO2 released by respiration and reaches the light compensation point. Orchids are pre-tolerant plants whose light compensation point does not exceed 1% of the total light intensity. The orchid plant can not accumulate in the matter at the light compensation point, and the sub-material is consumed at night, which is very disadvantageous to the growth of the orchid plant. Therefore, when considering the establishment of cultivation sites for Chinese orchids, the minimum requirement for light intensity must be higher than the light compensation point.

Light saturation point and light compensation point represent the utilization ability of plant leaves to strong and weak light, and can be used to measure the light requirement of plants. The orchid plants cultivated in a controllable greenhouse usually maintain an optimal temperature condition, and the position of the compensation point can be appropriately reduced, which is of great significance for effectively using weak light to maintain normal photosynthesis.

The concentration of CO2 CO2 is the main raw material of photosynthesis, and its content directly affects the progress of photosynthesis. When the content of CO2 in the air was lower than that of 60mg/m2 (PPm), photosynthesis decreased significantly, or even stopped completely, reaching the CO2 compensation point. Increasing the concentration of CO2 can improve the photosynthetic rate in a certain range. In general, the optimum CO2 concentration for photosynthesis is about 0.1%, while the content of CO2 in the air is usually 0.02%-0.03%. Therefore, if the concentration of CO2 in the air can be increased appropriately, photosynthesis can be significantly increased. The method of CO2 fertilization can be used to increase the content of air CO2 in cultivated greenhouse or plastic film greenhouse. It can also be fermented with saccharified feed, or fermented with stable manure, peanut money and other organic manure in a water tank to increase indoor CO2 concentration.

Under outdoor cultivation conditions, there are still considerable difficulties in applying CO2 fertilizer, mainly relying on natural wind or

The air blowing equipment causes the air flow and makes the air containing CO2 close to the leaf surface to ensure the normal photosynthesis. In addition, bicarbonate fertilizer and organic fertilizer were applied to increase the CO2 content of the culture medium. The application of organic fertilizer can increase the humus in the cultivation substrate, increase the number of microorganisms in the substrate and improve the microbial community in the substrate, so as to achieve the purpose of CO2 fertilization. Part of the CO2 in the culture medium was diffused into the air and absorbed by the leaves of the orchid plant, while the other part was directly absorbed by the leaves of the orchid plant.

Under normal circumstances, too high CO2 content in the air is also disadvantageous to photosynthesis. when the concentration is more than 1%, it will cause protoplast poisoning and stomatal closure of orchid plants, thus inhibiting photosynthesis, but if the light intensity is increased at the same time, the utilization concentration of CO2 can be relatively increased, so the orchid chamber must be equipped with ventilation and ventilation and lighting equipment.

The temperature range of photosynthesis varies with different varieties of orchids. At 0: 4 degrees, the interaction is inhibited. Starting from the low limit of temperature, the photosynthetic rate increases with the increase of temperature. Beyond the optimum point, photosynthesis decreases. Generally speaking, Chinese orchids undergo normal photosynthesis at 5-36 degrees, but the optimum temperature is 18-28 degrees. The time combination of more than 36 degrees is weak or even stops.

The effect of temperature on photosynthesis was related to light intensity and CO2 concentration. Under the conditions of higher light intensity and higher CO2 concentration, the optimum temperature of photosynthesis also increased. At low light intensity and low CO2 concentration, the increase of temperature was disadvantageous to the growth of orchid plants. Therefore, the heating equipment should be equipped with lighting equipment to achieve results, and in night or rainy days with insufficient light, the temperature in the orchid room should be appropriately reduced to increase the temperature difference and promote the accumulation of matter to increase the speed of "knot".

As the microclimate is different in different places, and Chinese orchids originally grow in deep mountains and old forests, in order to transfer from the wild environment to artificial cultivation, the optimum temperature is a problem that must be solved. The change of air temperature is often beyond the range of photosynthesis, which is one of the main measures in addition to choosing the microclimate environment suitable for its growth. When the cold spell or frost comes, it often causes damage to the orchid plant. At this time, the thermal insulation should be covered with plastic film, the light transmittance of the orchid chamber should be increased, the heating and lighting equipment should be turned on, and the constant heating equipment can be arranged in the high-grade orchid chamber to keep the room temperature within the range suitable for photosynthesis.

In fact, it is easier to raise the temperature than to lower the temperature in cultivating Chinese orchids. In the hot summer, the temperature is often as high as 35 degrees, at this time, we should increase the shading rate, turn on automatic humidification equipment to humidify and cool down, or set up water curtains around the orchid room, and find ways to promote air flow, such as turning on the electric fan. Set up air-conditioning equipment in the orchid room to cool down, if this equipment must be dehumidified before the temperature can be lowered, so cooling and maintaining a certain humidity will become a contradiction, or even excessive dehumidification to make the orchid plant dehydrated, this method is not desirable.

Water and mineral element water are the raw materials of 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 in other physiological processes and lost through transpiration. Therefore, the effect of water on photosynthesis is not direct, but mainly affects other physiological activities, thus indirectly affecting the progress of photosynthesis. When the water metabolism of the plant was destroyed, the leaf water content decreased, resulting in 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 ammonia are the constituent elements of chlorophyll, iron and manganese are involved in the formation of chlorophyll, boron, potassium and phosphorus can promote the transport and transformation of organic matter. Therefore, rational fertilization is very important to ensure the smooth progress of photosynthesis. (Liu Zhongjian)