Detailed Explanation of Essential Elements for Orchid Plants and Their Physiological Functions

Apart from water content, the remaining substance in an orchid plant is dry matter. This includes organic matter and ash. Organic matter accounts for 90% of dry matter and mainly consists of four elements: carbon, hydrogen, helium, and oxygen. During measurement processing, they are released as carbon dioxide, water vapor, free nitrogen, and other substances. Ash is derived from the mineral salts absorbed by the plantcultivationsubstrate, and the elements it contains are mineral elements. Although nitrogen is not a mineral element, fororchidsit is also absorbed from thecultivationsubstrate in the form of inorganic salts, so when studying the physiology of Chineseorchidsit is also included among mineral elements. Orchidsrequire more than ten essential mineral elements, among which the major elements needed in large amounts include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. The trace elements needed in smaller amounts include iron, boron, copper, zinc, manganese, chlorine, molybdenum, and others. Hydrogen and oxygen are obtained by the plant from water, carbon is absorbed from the atmosphere, while mineral elements and nitrogen are obtained from thecultivationsubstrate. The physiological functions of essential elements are manifold. Some elements directly participate in the composition of protoplasm or other parts, such as nitrogen being one of the constituent elements of amino acids, proteins, chlorophyll, and many enzymes; phosphorus being an important constituent element of nucleic acids and phospholipids; the salt formed by calcium and pectic acid being the main component of the middle lamella of the cell wall; magnesium being a constituent element of the chlorophyll molecule, etc. Some elements are components of enzymes or regulators of enzymes, such as iron being a component of the prosthetic group of cytochrome oxidase, catalase, and peroxidase; copper being a component of the prosthetic group of ascorbic acid oxidase; potassium ions acting as activators of enzymes, etc. Phosphorus can promote the synthesis, mutual transformation, and transport of carbohydrates, proteins, and fats in the plant body, demonstrating that some elements can play a certain role in the transformation and transport of substances. Since various essential elements have specific physiological functions for the plant, when an orchid plant lacks or absorbs excessive amounts of a certain element, it will exhibit some characteristic symptoms. For example, when a plant lacks nitrogen, it will become stunted and the leaves will turn yellow, etc. Excessive nitrogen absorption will cause excessive vegetative growth with soft, drooping leaves, affecting ornamental value. Especially for variegated-leaf varieties of Chinese orchids, excessive nitrogen may cause the variegation to fade or become less distinct. This is mainly because it increases the amount of chlorophyll, which masks other pigments. Phosphorus is a constituent of nucleic acids, phospholipids, and many enzymes, and actively participates in intracellular material metabolism and energy metabolism within the plant body. It can promote flowering and fruiting, and improve the plant's cold resistance and drought resistance. Therefore, when phosphorus is deficient, the plant, including the root system, may be severely inhibited. The plant becomes relatively short and weak, the pseudobulbs are small, and the roots are underdeveloped and thin and long. Therefore, during cultivation, phosphorus supplementation should be strengthened, especially for variegated-leaf orchids and fancy-flower varieties, to promote well-developed root systems and promote pseudobulb "heading" (referring to the enlargement of pseudobulbs), making fancy-flower varieties easier to bloom. For variegated-leaf varieties, drought resistance is enhanced, which can prevent the variegated parts of the leaves from being scorched by sunlight. For other orchid varieties, because of well-developed root systems and larger pseudobulbs, it will also promote the sprouting of new shoots and increase propagation speed. Potassium is an activator of certain enzymes and actively participates in various physiological activities of cell protoplasm. It can promote protein metabolism and improve the hydration capacity of cell colloids. When potassium is adequate, the plant is robust, pseudobulbs enlarge noticeably, and leaves are thick and hard. If potassium is deficient, the plant becomes short and weak and slender, and young leaves are prone to wilting. The leaf margins of old leaves turn brown and withered, and the leaves are thin and weak. Therefore, in order to make orchid plants robust and improve leaf disease resistance, especially during the period when new shoots and new leaves are unfolding, potassium supplementation should be strengthened. This is especially true forCymbidium sinenseproduced in some areas of Guangxi and Vietnam, which, because their leaves are relatively thin and soft and prone to excessive vegetative growth, should receive enhanced potassium input to increase leaf thickness and promote compact, sturdy growth. Magnesium is a constituent element of chlorophyll and also an activator of certain enzymes. Orchids cultivated in relatively strong-light growing locations often need magnesium to promote chlorophyll formation. If magnesium is deficient, leaves are prone to aging and cannot remain connected for multiple generations, affecting market competitiveness. At the same time, flowering is also inhibited, and theflower'scolor is pale and not vivid. However, since magnesium is a main component of chlorophyll, when cultivating variegated-leaf orchids with green moss spots or "rotten base," it may make the green pigment more prominent and affect the ornamental value of the variegation. This must be noted during cultivation. What is worth trying is that for some late-manifesting or late-brightening variegated varieties, such as some varieties of "Dashimen" and the late-brightening residual-variegation varieties of the Daming orchid line, magnesium supplementation should be specially controlled to prevent the variegation from fading and to promote the variegation to change from late-manifesting to early-manifesting or to improve, making the variegation color emerge. Calcium can promote protoplasm to tend toward a gel state and is one of the constituent elements of the cell wall. In Chinese orchid cultivation, calcium can make the plant firm and upright, make the "heading" robust, increase meristematic capacity, and improve root absorption capacity. If calcium is deficient, the plant becomes weak and small, shows excessive vegetative growth, and ages prematurely. Young leaves are fragile and yellowed, the cells of the very tip meristematic tissue are prone to rotting, and pseudobulb heading is not obvious. Therefore, measures are taken in Chinese orchid cultivation to supplement calcium. Generally, bone meal or shell powder is used for topdressing, and the effect is easily achieved. Because these bone meals contain a large amount of calcium and require a corresponding process to decompose, they will not cause fertilizer burn to orchid plants, and are a commonly used method for adding calcium elements in large-scale cultivation of Chinese orchids. Especially when orchids previously cultivated with pond mud are transferred to other cultivation substrates, because the old [roots] are prone to rotting, strengthening calcium supplementation to improve the meristematic capacity of the root system and improve product quality is of great significance. Sulfur is one of the main elements composing proteins. If sulfur is deficient, the plant's later growth will be inhibited, pseudobulbs will be small, and [growth] will be sparse. In order to promote the later growth of orchid plants and make pseudobulbs head earlier, sulfur supplementation can be strengthened. However, sulfur may cause the yellow leaves of some varieties whose early new shoots have yellow and red pigments to turn green earlier, reducing ornamental value in orchid appreciation. Therefore, these varieties should be treated with caution when topdressing sulfur. Even some varieties with variegation appearing in the leaf vein areas may have their variegation color dimmed when sulfur is strengthened. Iron is a constituent element of certain enzymes, such as cytochrome oxidase, catalase, etc. If iron is deficient, the plant generally grows abnormally and appears weak and small, and pseudobulb and root growth are inhibited. Therefore, to ensure normal growth of orchid plants, promote well-developed root systems, and achieve earlier "heading," iron should be appropriately supplemented during cultivation. However, variegated-leaf orchids pursue the artistic effect of distinct yellow or white lines on the leaves. If the cultivation substrate contains excessive iron, it may cause the variegation color to revert to green, losing the value of cultivating variegated-leaf orchids. Therefore, to make some varieties with indistinct variegation quickly display distinct variegation color, one may choose a cultivation substrate low in iron or not supplement iron. Everyone might as well give it a try and see what effect it has. Manganese is an activator of certain enzymes and is closely related to the oxygen-releasing reaction in photosynthesis. Because manganese deficiency makes the plant short, thin, and weak, with weak pseudobulb growth and reduced flowering quantity, non-variegated varieties and varieties pursued for flowering effect should receive enhanced manganese supplementation. However, for variegated-leaf varieties, because manganese can make the yellow-white variegation of leaves turn green again and make the variegation color less vivid, manganese supplementation in variegated-leaf orchids should be done in moderation. Boron has corresponding significance for material transport within the plant body, biomembrane permeability, and the differentiation of conducting tissues. Boron deficiency can make the plant short, thin, and weak, with dry leaf tips, rough new leaves, brittle leaf veins, inactive meristematic tissue, dead root tips, and flowers that easily drop. For cultivating ornamentalflowerorchid varieties, boron supplementation should be strengthened. Boron deficiency can make leaves turn red. When variegated-leaf orchids are pursued for color effect, one may restrict the plant's absorption of boron to improve the ornamental value of the orchid. Copper is a component of oxidase and can improve the plant's drought resistance. But copper deficiency will cause poor development of orchid plants, with thin and slender plants prone to disease. Therefore, to improve the plant's drought resistance and promote its normal development, copper should be appropriately supplemented during cultivation. However, copper deficiency can cause chlorosis in the plant and yellowing of leaf tips, so when cultivating variegated-leaf orchids, the plant's absorption of copper should be appropriately restricted in order to maintain or even strengthen the variegation color. Zinc is both a constituent of certain enzymes and an activator of certain enzymes. Therefore, zinc deficiency affects enzyme composition and activity, causing abnormal plant growth, making it short, thin, and weak. However, zinc deficiency can cause leaves to become yellow due to nutrient deficiency. In this respect, variegated-leaf orchids should not be too eager to supplement zinc, so as not to affect the variegation effect. A plant deficient in any essential element will exhibit certain physiological symptoms. However, some external factors, such as yellowing caused by viruses among diseases, or even conditions of the cultivation substrate that affect the plant's absorption or transport of nutrient elements, can also cause symptoms of element deficiency. Symptoms caused by insect toxins produced by some pests are often similar to nutrient deficiency symptoms and must be distinguished so that measures taken in mineral nutrition management can be effective. (Liu Zhongjian)