Section II Nutritional Requirements of Edible Fungi Most edible fungi are saprophytes. They can't directly use inorganic substances and the energy of sunlight to grow like green plants, but only rely on decomposing and oxidizing organic substances to absorb the nutrients and energy needed for their own growth. The growth of edible fungi can be roughly divided into vegetative growth stage (spawning) and reproductive growth stage (fruiting). Inoculating the mycelium on a suitable culture medium, at a suitable temperature, it began to secrete a series of enzymes, which decomposed some macromolecular organic substances into simple water-soluble small molecular substances and absorbed them into cells for their growth and development. Different growth stages have different requirements for nutritional conditions. Generally speaking, the nitrogen content in the culture medium of mycelium growth stage is relatively high, and the nitrogen content in the culture medium of fruiting body development stage is relatively low. Therefore, as far as scientific research and production are concerned, the nutrients added to the culture medium at different stages should be different. For example, during the preservation and production of strains, more nitrogen sources should be added to the culture medium, which is beneficial to the growth and development of mycelium on the one hand and can effectively prevent the premature growth of mushrooms on the other; However, nitrogen sources should be relatively reduced in the formula of cultivation materials for mushroom production, which is beneficial to mushroom production. 1. Carbon source: Different from green plants, fungi can't directly use CO2 as carbon source to synthesize organic matter, but can only use organic matter as carbon source, such as monosaccharides and disaccharides such as glucose, sucrose and maltose, and polysaccharides such as starch, cellulose, hemicellulose and lignin. Except glucose can be directly absorbed and utilized by hyphal cells, other enzymes secreted by hyphae must be hydrolyzed into monosaccharides before they can be absorbed and utilized. Nitrogen source: Organic nitrogen is the best nitrogen source for edible fungi, such as peptone, yeast extract, bran and rice bran. Natural cultivation substrates such as cottonseed hull, sawdust and plant straw also contain some nitrogen sources that can be absorbed and utilized by edible fungi, but the content is not enough, so it is necessary to add materials with high nitrogen content such as bran and rice bran, and some special varieties also need to add industrial preparations such as peptone and yeast extract. Inorganic nitrogen and small molecular organic nitrogen, such as various nitrogenous fertilizers, are easy to produce ammonia under the action of microorganisms to inhibit the growth of hyphae, so they should not be added to the culture medium unless there is special need, and can be used as topdressing if necessary. Carbon-nitrogen ratio: refers to the ratio of carbon source to nitrogen source in culture medium and culture solution. Taking Pleurotus ostreatus as an example, the ratio of carbon to nitrogen in mycelium growth stage is 20/ 1, and that in fruiting body development stage is 40/ 1. 3. Other nutrients: In addition to carbon and nitrogen sources, the growth and development of edible fungi also need some other nutrients, such as mineral elements such as calcium, phosphorus, magnesium, zinc, iron, copper, sulfur, potassium and manganese, as well as various vitamins and growth factors.