What external factors affect respiration in orchids

Within a certain limit, as temperature rises, respiration intensity also increases. Temperature has three cardinal points for respiration: the minimum, optimum and maximum points. Compared with photosynthesis, the minimum temperature for respiration is much lower, because as long as life continues, respiration goes on. However, if suddenly affected by low temperature in midsummer, respiration may stop. The optimum temperature for respiration only indicates that the respiration intensity of the orchid plant reaches its highest point at that time, but for its entire life cycle it is not necessarily beneficial. Because an increase in respiration intensity sometimes causes unnecessary consumption of substances and damages the plant; for example, when temperature is high and light is insufficient, respiration exceeds photosynthesis, which affects the plant's accumulation of organic matter and growth. Oxygen Oxygen is a necessary condition for the oxidative decomposition of organic matter in respiration. Under normal conditions, the oxygen content in air is about 21 percent; if the oxygen content changes little, it has no great effect on respiration, and only when the oxygen content in air drops to 1 percent to 2 percent does respiration decrease significantly. The aboveground part of the plant is in contact with air, so under normal conditions it will not experience oxygen deficiency affecting respiration. But the underground part of the plant is prone to oxygen deficiency, ifcultivationthe substrate is poorly aerated and air exchange is difficult, oxygen cannot easily enter thecultivationsubstrate, and oxygen deficiency readily occurs. At the same time, in thecultivationsubstrate, microbial activity and the root's absorption of water and inorganic salts both consume oxygen, which affects root growth and normal respiration and affects the normal growth of the orchid plant. Carbon dioxide concentration Carbon dioxide is a product of respiration, and at a certain content it can increase the progress of photosynthesis, thus benefiting plant growth. But if the carbon dioxide content is too high, it will reduce or inhibit respiration. Under normal weather conditions, the carbon dioxide content is very low (about 0.03 percent), and does not affect respiration. When the carbon dioxide concentration rises above 1 percent to 10 percent, respiration is clearly inhibited. In the cultivation substrate, due to root activity and microbial respiration, a large amount of carbon dioxide is released; especially in the high-temperature seasons of summer and autumn, if the cultivation substrate is poorly ventilated or compacted, accumulated carbon dioxide may reach as high as 4 percent to 10 percent or even higher. Therefore, the cultivation container must have air exchange holes, and the cultivation substrate must have a large number of pores to facilitate exchange with the atmosphere, so as to ensure normal respiration of the root system. Water How much water is in the environment can affect the water content of the plant's cells. The water content of cells has a great influence on respiration, because only when the protoplasm is saturated with water can various life activities proceed vigorously. But roots, leaves and so on sometimes show the opposite result. When leaves wilt, their respiration becomes strongly active; this is because the cells lack water, the hydrolytic activity of enzymes strengthens, starch is hydrolysed into soluble sugar, which raises the cell osmotic pressure and increases water absorption capacity to adapt to the dry environment. However, soluble sugar is the substrate of respiration, and its increase causes respiration to strengthen. Respiration is the centre of the plant's metabolism, and it is linked with the entire process of the plant's life activities. Respiration releases energy to supply the plant's needs for growth and life, and promoting respiration can enhance the plant's growth and development. But respiration consumes organic matter, and excessively strong respiration is unfavourable to the accumulation of organic matter. During long-distance transport of orchid plants or when they are being sorted and kept for dispatch, respiration should be reduced as much as possible in order to reduce the consumption of organic matter. Respiration can both release energy for the plant's various physiological processes, and its intermediate products are also raw materials for synthesising many important organic substances. Respiration is the centre of metabolism; it helps the plant absorb nutrients and also helps the transformation and transport of substances within the orchid plant. The formation of new cells and organs and the growth of the plant are all closely related to respiration. The cultivation and management measures for orchid plants are all intended to ensure that the plant's respiration proceeds normally, such as keeping the cultivation substrate loose, easy to drain and well aerated to facilitate root respiration. Sometimes respiration must also be inhibited, because excessively vigorous respiration sometimes causes unnecessary consumption of organic matter. orchid90 percent to 95 percent of the plant's dry weight is organic matter synthesised by photosynthesis after subtracting what is consumed by respiration. The respiration intensity of leaves is equivalent to 5 percent to 10 percent of the photosynthesis intensity, but because photosynthesis is limited to the leaves and takes place during the day, while respiration is a process carried out by all living cells day and night, the plant may in one day and night consume 15 percent to 25 percent of the total organic matter produced by one day's photosynthesis, and under extreme conditions 30 percent to 50 percent. In winter the rate of photosynthesis decreases or even stops, while respiration, because its minimum temperature is lower than the temperature for photosynthesis, can still continue. When new buds sprout and new leaves emerge, photosynthesis is negligible for respiration. Therefore, in theorchidcultivation process, in addition to increasing photosynthesis by improving light conditions, respiration should also be controlled to reduce the consumption of photosynthetic products, so as to facilitate the accumulation of dry matter and promote the growth and development of the orchid plant. In the hot summer, because the water content of the leaves decreases, photosynthesis is hindered and respiration is strengthened, and at times other than morning and evening the photosynthesis intensity weakens somewhat while respiration remains fairly strong, so the growth of the orchid plant is inhibited. Therefore, in midsummer the shading level should be appropriately increased, and measures should be taken to increase humidity and lower leaf surface temperature so as to weaken respiration. An appropriate water supply is beneficial to the formation and transport of photosynthetic products and to the growth of the plant. In the orchid room in winter, because the light is weak, the photosynthesis of the orchid plant is weakened. At this time, if the indoor temperature is too high, respiration will exceed photosynthesis, and this is even more serious on cloudy and rainy days, causing excessive consumption of organic matter. Therefore, in winter the greenhouse, affected by the climate, easily rises in temperature, which is unfavourable to the growth of the orchid plant. Measures to increase light intensity must be taken, such as turning on sun lamps and so on; when the light intensity increases, the temperature may be appropriately raised, but generally it should not exceed 25 degrees during the day and should not exceed 20 degrees at night. Therefore, in the equipment provided for the orchid room, an artificial light source must be included. (Liu Zhongjian)