Absorption and Transport of Mineral elements in Orchid Plant

The mineral elements needed by the orchid plant are mainly obtained from the inorganic salts of the cultivation substrate. Therefore, the root system is the main absorption organ. At the same time, Chinese orchid cultivation also pays attention to extra-root fertilization, so the leaves absorb inorganic salt plants more directly. On the other hand, the inorganic salts in the cultivation substrate must be dissolved in water and become ionic before they can be absorbed by the roots. For example, the nitrogen absorbed by the plant is mainly ammonia ion (NH+4) or nitrate ion (NO3), and the phosphorus absorbed is mainly phosphate ion (H _ 2PO ~ (2 +)), potassium ion (K +) from potassium salt or calcium ion (Ca++) from calcium salt, etc.

Inorganic salt can be absorbed by roots only when dissolved in water, but the amount of nutrients absorbed is not consistent with the amount of water absorbed. In fact, only a small amount of nutrients in the cultivation substrate are absorbed and utilized by plants, some of them are nutrients dissolved in the matrix solution, and some are solid-phase nutrients in equilibrium with the nutrients in the matrix solution. However, when there are too many ions in the matrix solution, or there is only a single salt in the solution, the plant will be poisoned or die. Only when the proportion of various ions is appropriate, the plant can grow and develop well. Therefore, there is antagonism between ions to eliminate the toxicity to each other. Therefore, it is necessary to create the solution of the cultivation substrate as the equilibrium solution, so that the cultivated plants not only have appropriate mineral nutrients, but also avoid the toxic effect of ions. The substrate solution becomes acidic or alkaline due to the physiological selection of physiological acidic salt or physiological alkaline salt. Changing acid or alkali is disadvantageous to the growth of orchid plant, so it should be balanced when mineral nutrients are supplemented.

Root absorption of mineral elements is a complex physiological process, which includes passive absorption and active absorption. When the concentration of the matrix solution is higher than the intracellular concentration, the ions enter the plant in the way of diffusion and form passive absorption. This mode of absorption does not require energy supply. However, if the cell wants to absorb continuously, it must always maintain the ion concentration difference between inside and outside the cell. Only when the absorbed ion can immediately participate in the synthesis or rapid upward transport of other substances, and does not accumulate in the very cell, can such absorption be carried out actively.

Mineral elements enter the protoplast surface by ion exchange and then combine with transport enzymes to enter the protoplast. This absorption is achieved by the energy produced by breathing. This active absorption mode is the main form of mineral element absorption by plant roots. Through ion exchange adsorption, the ions adsorbed by the protoplast are transferred to the protoplasm and vacuoles, so that the mineral elements are transferred from the inner layer of the protoplast to the vessel. After entering the vessel, the mineral elements rise with the flow of transpiration and are transported to all parts of the plant to supply growth and living consumption.

There are differences in the amount of anions and cations absorbed by roots to some salts. For example, when applying (NH4) 2SO4, because the plant needs more nitrogen than sparse, it always absorbs more cations (NH+4) than anions (SO=4), which makes a lot of unabsorbed SO= remain in the cultivation medium and make the solution acidified gradually. This happens to most ammonium salts. If the plant is supplied with NaNo3, the amount of NO-3 absorbed by the plant is much more than that of Na+, so the cultivation medium solution is alkaline gradually due to the presence of too much Na+. Most nitrates produce this result. However, the cations and anions of salts such as NH4NO3 are absorbed by plants in almost the same amount, and because there is no excessive single ion, the medium solution is mostly neutral. This selectivity of ion absorption should not be used alone for a long time in the process of cultivation, so as not to make the cultivation substrate too acidic or alkali, which is disadvantageous to the growth of plants. However, in the process of Chinese orchid cultivation, a single chemical fertilizer is rarely used, because it is easy to decompose, the plant is easy to absorb, often produce fertilizer damage.

In addition to absorbing nutrient elements from the cultivation substrate through roots, many chemicals, including mineral elements, can be absorbed by the leaf surface in the form of aqueous solution. Guolan often uses this method for foliar fertilization. In this way, it can be solved that it takes a long time for fertilizer to be applied into the cultivation substrate to be absorbed and utilized by the plant, so that it can not meet the needs of the fast-growing period. Foliar fertilization can be used to solve the root injury or the difficulty of root absorption in the later stage of plant growth, or before the new report is not growing.

The amount of extra-root topdressing is less, and the effect is quick. Therefore, it has become the main method of cultivation and fertilization of national orchid. However, it can not completely replace soil fertilization, but can only be the supplement of cultivation substrate fertilization.

When topdressing outside the root, the concentration of the solution, pH, spraying amount and spraying position should be taken into account. In addition, the influence of weather should also be considered, such as wind speed, temperature, atmospheric humidity, sunny and rainy days and so on. Generally speaking, the effect is worse when it is too dry, in which case the concentration of fertilizer should be smaller and sprayed on the back of the leaves in the early morning or evening.

The absorption of mineral elements by plants is a physiological process related to respiratory metabolism. All the factors that affect root respiration can also affect the absorption of mineral elements. (Liu Zhongjian)