In the process of growth and development, plants not only need a certain amount of light, water, air and heat, but also must constantly absorb various necessary nutrients from the outside and assimilate them to maintain their normal life activities. So what chemical elements do plants contain? Through analysis, it is found that there are about 70 kinds of chemical elements absorbed by plants from the environment, and 16 kinds of essential nutrient elements for plants. They are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, molybdenum, boron and chlorine.

(2) The main physiological functions of essential nutrients

① Carbon, hydrogen and oxygen: The contents of carbon, hydrogen and oxygen are the highest in plants, and the sum of their contents accounts for more than 90% of the total dry matter. Among them, the content of carbon is the highest, accounting for about 45%. Various organic compounds in plants, such as carbohydrates, cellulose, hemicellulose and pectin, are mainly composed of these elements. Sugar is the initial product of photosynthesis, the raw material for plants to synthesize many important organic compounds, and the energy source for plant respiration and a series of metabolism. In addition, hydrogen and oxygen also play an important role in the biological redox process of plants.

② Nitrogen: Nitrogen has an important physiological function in vegetables, which has a greater impact on the growth and development of vegetables than other major elements. Known as the "life element" of organisms.

First, nitrogen can promote the formation of chlorophyll.

Second, nitrogen can promote the synthesis of protein and nucleic acid, and accelerate the growth and development of vegetables.

Third, nitrogen is a component of various enzymes and vitamins. Enzyme itself is a kind of protein, which is a biocatalyst for metabolism in plants. Nitrogen affects various biochemical reactions in organisms through the catalysis of enzymes. In addition, there are many vitamins, phytohormones, alkaloids, phospholipids and so on. , is an active substance in plants, which has a great influence on the life activities of plants. They are all nitrogen-containing substances.

③ Phosphorus: Phosphorus is also an important element, and its content in plants is second only to nitrogen and potassium. It has a great influence on the growth, yield and quality of vegetables. As I said just now, nucleic acids, nucleoproteins, phospholipids, plant hormones, enzymes and adenosine phosphate all participate in important metabolic processes in plants. These are phosphorus-containing organics.

In addition, phosphorus plays a very important role in improving the drought resistance, cold resistance and salt tolerance of vegetables.

④ Potassium: Potassium is not a component of plants, but mainly exists in the juice of plants or adsorbed on the surface of protoplasm in a water-soluble inorganic state. The most important function of potassium is as an activator of enzyme, that is to say, with potassium, the activity of enzyme is strong and its function can be fully exerted.

1. Potassium can promote photosynthesis of plants, promote nitrogen metabolism, improve the ability of plants to absorb and utilize nitrogen, and increase the content of protein. Potassium participates in the metabolism and transportation of carbohydrates and the opening and closing of stomata in leaves.

Second, potassium can enhance the stress resistance of vegetables and enhance the cold resistance of vegetables.

Third, potassium can improve the quality of vegetables.

⑤ Calcium: Calcium is mainly distributed in leaves, which is an important factor to ensure the healthy growth and improve the quality of vegetables.

First of all, calcium is an important element in plasma membrane and cell wall. The intercellular layer of cell wall is composed of calcium, which is of great significance to the formation and stability of intercellular layer. Calcium deficiency will affect the formation and development of cells and hinder cell division and the formation of new cells. Calcium can also stabilize the structure of biofilm and maintain the integrity of cells.

Secondly, calcium can increase the content of cytokinin, keep the activity of leaves and prevent vegetables from aging.

Third, calcium can enhance the disease resistance of vegetables. The high calcium content in intercellular layer can inhibit the destruction of cell wall and plasma membrane when fungi invade and enhance the disease resistance of vegetables.

⑥ Magnesium: Magnesium is the only component of chlorophyll, which directly participates in photosynthesis by synthesizing chlorophyll. Magnesium ion is also an activator of many enzymes, which regulates substance metabolism and energy conversion.

⑦ Sulfur: Sulfur is a component of protein. Sulfur deficiency, protein synthesis is blocked, and non-protein nitrogen accumulation leads to fertility disorder. Sulfur can promote the formation of root nodules in leguminous plants, participate in the formation of nitrogenase and enhance nitrogen fixation activity.

8 Iron: The synthesis of chlorophyll must be catalyzed by iron-containing enzymes. Otherwise, chlorophyll can't be formed, and the leaves lose their green color, which directly affects photosynthesis. Iron is a component of some enzymes related to respiration, which affects the respiration of plants.