Table 6- 1 Essential elements of plant nutrition, beneficial elements and its main sources
* For leguminous crops, it can be supplied by air.
* * The so-called beneficial elements refers to the supply of these elements to some plants, which can improve growth and development or increase yield, but it is not necessary.
(Excerpted from Handbook of Agricultural Chemistry)
I. Physiological Functions of Essential Nutrients in Medicinal Plants
It is known that the physiological functions of plant essential nutrients can be summarized in three aspects: first, they are components of cell structure and metabolically active compounds; The second is to maintain the function of cells and tissues; There is also energy conversion, which is involved in promoting enzymatic reactions. However, the function of these elements can not explain all physiological changes, and many aspects are still unclear. Table 6-2 only briefly describes some physiological functions of various essential nutrients.
Table 6-2 Absorption Forms and Physiological Functions of Plant Nutrients
Table 6-2 Absorption Forms and Physiological Functions of Plant Nutrients (Continued)-1
(Excerpted from Handbook of Agricultural Chemistry)
According to the different contents of essential nutrients in plants, they can be divided into macronutrients and trace elements. Carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are the main elements. Iron, boron, manganese, copper, zinc, molybdenum and chlorine are trace elements. Among them, nitrogen, phosphorus and potassium are elements in great demand for plants, but the available nutrients in soil are often in short supply and need to be supplemented by fertilization, so they are called "three elements of nitrogen, phosphorus and potassium" or "three elements of fertilizer". This paper focuses on the physiological effects of nitrogen, phosphorus and potassium on medicinal plants.
(1) nitrogen
Nitrogen generally only accounts for 65,438+0-3% of the dry weight of plants (referring to the whole plant), but it is the main component of many important organic substances in plants, such as amino acids, protein, nucleic acids, enzymes, chlorophyll, most biofilm and plant hormones. Therefore, nitrogen directly or indirectly affects the metabolic activities and growth and development of plants in many aspects. So nitrogen is called "life element". Therefore, when the nitrogen nutrition of plants is insufficient, many kinds of metabolism of plants will be affected, the most significant of which is the decrease of chlorophyll synthesis rate and content, thus affecting the formation of carbohydrates, the product of photosynthesis; At the same time, protein synthesis is inhibited, which leads to the reduction of cell division, and the plant morphology is reflected as short plants with light green or yellow leaves, especially the lower leaves will die and fall off. For example, if Salvia miltiorrhiza lacks N, it will yellow in half a month, then the plant will stop growing and finally the growing point will die. American ginseng lacks nitrogen, its plants are short, its leaves are light green and thin, and it returns to seedlings 1-2 months earlier than normal American ginseng. However, too much nitrogen can also make plants grow abnormally, because the photosynthetic products-carbohydrates are widely used to synthesize nitrogen-containing compounds such as protein and chlorophyll, which makes plant tissues soft and forms wild stems and leaves, leading to lodging and prolonging maturity. At the same time, due to the abundance of cell sap, the plants are fresh and tender, which is easy to produce pests and diseases. Especially serious, for medicinal plants such as roots and rhizomes, as well as medicinal plants such as seeds and fruits, because of excessive nitrogen content, the transportation and storage of carbohydrates are affected, and their output is greatly reduced. Moreover, the disharmony of nitrogen nutrition seriously affects the accumulation of effective components in some medicinal plants, most obviously affecting the contents of alkaloids and volatile oil. Because alkaloid is an intermediate product of plant nitrogen metabolism, its synthetic predecessor is amino acid. Ephedrine is an alkaloid contained in Herba Ephedrae, which may be a metabolite of tyrosine. The N- methyl group in the molecule comes from methionine. Proper nitrogen nutrition can increase the alkaloid content in plants, and too much or too little will reduce the alkaloid content. Another example is that the content of peppermint oil decreases when nitrogen fertilizer is used too much.
The nitrogen sources used by plants are mainly inorganic nitrogen compounds, including nitrate nitrogen (NO-3) and ammonium nitrogen (NH+4). Nitrous nitrogen (NO-2) is low in soil, which is of little significance to plant nutrition, but harmful to plants at high concentration. In addition, plants can also use small molecules of organic nitrogen, such as amino acids, asparagine and urea, but this is secondary. Most medicinal plants can make good use of these two forms of inorganic nitrogen, but some medicinal plants prefer one of them, which will be introduced in detail in "selective absorption"
(2) Phosphorus
The nutritional effects of phosphorus on plants are as follows: firstly, phosphorus is a component of many important organic compounds in plants, such as nucleic acids, phospholipids, phytochemicals, high-phosphorus compounds and enzymes, which are extremely important substances in plant growth, reproduction, genetic variation, energy transfer and communication with external substances. Secondly, phosphorus actively participates in various metabolic activities in plants, such as carbohydrate metabolism, nitrogen metabolism, fat synthesis and decomposition. Therefore, phosphorus can be called "energy" element for plants, and it is very important in the whole growth period of plants, especially in seedling stage and reproductive stage. For example, Fu Jianguo and others sprayed 2.0% calcium superphosphate at different growth stages of Coix lacryma-jobi, but the spraying effect was the most obvious at the "three-leaf" stage and "filling stage", the former could increase the yield of Coix lacryma-jobi by 18.40%, and the latter by 9.77%. In addition, phosphorus is also important for roots, rhizomes and medicinal plants such as seeds, flowers and fruits. Adding phosphorus to these medicinal plants can often achieve high yield, because phosphorus can promote root development and promote carbohydrate transportation. Therefore, it can promote the growth of roots, rhizomes and fruits, the fullness of seeds and the improvement of quality. Phosphorus can also improve the stress resistance of plants, such as drought resistance, cold resistance and saline-alkali resistance, which undoubtedly makes medicinal plants more adaptable to harsh living environment.
When medicinal plants are short of phosphorus, their growth and development will be hindered, mainly manifested as slow growth, short stature, emaciation, erect, few branches, delayed maturity and small fruits. For example, when three-year-old American ginseng is short of phosphorus, there are few flowers and fruits, and sometimes the buds are sterile.
Phosphorus absorbed by plants is mainly inorganic phosphate ion, among which H2PO-4 is the most easily absorbed, followed by HPO2-4, while PO8-4 is difficult to be absorbed by ordinary plants.
(3) Potassium
Unlike nitrogen and phosphorus, potassium is not a component of any organic compounds in plant cells. It mainly exists in the cytoplasm and vacuoles of all living cells in ionic state (K+), and a small amount exists in the nucleus or adsorbed on the surface of protoplasm colloid. In recent years, potassium, as a coenzyme or activator of many enzymes, plays an important role in the physiological functions of plants. It is known that the activation of more than 60 enzymes requires monovalent cations, and potassium is the most effective ion to promote activation. Therefore, potassium has a great influence on plant metabolism. For example, potassium can promote photosynthesis, increase chlorophyll content and net photosynthetic efficiency, and accelerate the transportation of assimilation products to storage organs, so rhizome medicinal plants often like potassium, which has a good effect on their yield increase. For example, Yu Derong and others pointed out in the "Diagnostic Study on Three Elements of Ginseng" that the ratio of potassium to nitrogen of ginseng in high-yield fields is higher than that in low-yield fields, while the ratio of potassium to phosphorus in high-yield fields is often higher than that in low-yield fields. Not only that, because potassium can obviously improve the absorption and utilization of nitrogen by plants, so that it can be quickly transformed into protein, so potassium can obviously improve the quality of medicinal plants. If ginseng is planted in northeast albic soil, the content of 17 amino acid in ginseng can be obviously increased after applying potassium fertilizer, and the yield can also be increased accordingly. In addition, potassium can also eliminate the adverse effects caused by excessive application of nitrogen and phosphorus fertilizers. Like phosphorus, increasing potassium application can also improve the resistance of plants to adverse environment.
Potassium deficiency in plants will cause growth retardation. In severe cases, the leaf edge will turn yellow, then brown and scorching. For example, Salvia miltiorrhiza lacks potassium, and there is a big brown spot on the edge of the old leaves, with light green veins and light green mesophyll. Three-year-old American ginseng is short of potassium, the tip of which begins to turn yellow, then scorches, and the root has low disease resistance, which is prone to root rot.
These are the physiological effects of the three nutrients on crop nutrition, but in fact, these 16 nutrients are very important to crops. Even trace elements with minimum requirements have their unique and specific functions, which cannot be replaced by other elements. At present, people pay more and more attention to the role of trace elements in increasing yield and improving quality of medicinal plants. For example, copper can increase mint yield and oil yield, boron can increase Amomum tsaoko yield by 22.3%, and applying compound fertilizer (containing trace elements) outside roots can increase ginseng yield by 9.7 1-62.9%, ginsenoside content by 26% and total amino acid content by 33.82%. In addition, some trace elements, such as iron, copper and zinc, are listed as effective components of medicinal plants as essential nutrients for human body. In this way, the research on the nutrition of medicinal plants is not limited to the medicinal plants themselves, but closely combined with human beings, so the research on the nutrition of medicinal plants is more important and meaningful.
With the passage of time, in addition to the 16 nutritional elements that have been recognized as essential for plants, people will continue to find that new elements have beneficial physiological effects on medicinal plants. The research on the effect of germanium on the growth and development of medicinal plants has been paid attention to at home and abroad. For example, under hydroponic conditions, 0.05ppm germanium oxide can significantly promote the root growth of American ginseng seedlings (annual).
When studying the nutritional problems of medicinal plants, we should pay special attention to the problem of nutritional balance, that is, pay attention to the relationship between nutritional elements. As far as nitrogen, phosphorus and potassium are concerned, the application of nitrogen fertilizer is beneficial to the absorption of phosphorus, and conversely, the application of phosphorus fertilizer is also beneficial to the absorption, transformation and utilization of nitrogen. The relationship between nitrogen and potassium also shows mutual promotion. Therefore, in actual production, the combined application of nitrogen, phosphorus and potassium often has the greatest effect on increasing the yield of medicinal plants, but the ratio of nitrogen, phosphorus and potassium required by different medicinal plants is different.
Second, the main characteristics of medicinal plants to absorb nutrients
(1) selective absorption
The so-called selective absorption means that the nutrients needed by plants are not arbitrary, that is, the utilization of nutrient elements in soil solution is selective, which is the first meaning. Secondly, the selective absorption of plants shows that the absorption of nutrients by plants is not a mechanically passive process, but an active process. The above-mentioned 16 essential nutrients are selectively absorbed by plants. Therefore, the selective absorption characteristics of plants reflect the nutritional characteristics of plants themselves. Medicinal plants also have this characteristic, for example, different medicinal plants use different forms of nitrogen differently. When Marco and others studied the nitrogen absorption and utilization of foxglove and American ginseng by soilless culture, they found that cultivating foxglove with nitrate nitrogen or nitrate nitrogen plus a small amount of ammonium nitrogen as nitrogen source could make the plants grow vigorously, increase leaves and increase yield. When only ammonium nitrogen was used as nitrogen source, the root poisoning of foxglove turned black and finally died. On the contrary, American ginseng uses nitrate nitrogen as nitrogen source, its leaves turn yellow to light green, and its plants are short, which looks like nitrogen deficiency treatment from the outside. American ginseng plants with ammonium nitrogen as nitrogen source have dark green leaves and grow healthily. At the same time, the root weight of annual American ginseng with ammonium nitrogen as nitrogen source increased by 35. 1% compared with that with nitrate nitrogen as nitrogen source, which also had the same effect on two-year American ginseng plants. This may be due to the influence of nitrate nitrogen and ammonium nitrogen compounds on the pH value of the culture medium.
Generally speaking, medicinal plants such as roots and rhizomes need more potassium; Seed and fruit medicinal plants need more phosphorus; Medicinal plants with leaves or whole grass need more nitrogen. In addition, fertilizer-tolerant medicinal plants can be fertilized more, such as Fritillaria thunbergii. In the case of a large amount of fertilization, there will be no phenomenon such as virtual long lodging, and a large amount of organic fertilizer must be applied to obtain high yield. However, Coix lachryma-jobi is barren-tolerant, and a certain yield can be obtained with less fertilization. If a large number of fertilizers are applied, it is easy to grow in vain and greatly reduce the yield. Another example is the underground rhizome of Amomum villosum. The content of potassium in aboveground stems, leaves and seeds is the highest, followed by nitrogen and less phosphorus. Therefore, according to this nutritional characteristic of Amomum villosum, on the basis of applying nitrogen and phosphorus fertilizer, high yield can be obtained by 5- 10t fumigation soil per mu in autumn and winter. It can be seen that according to the characteristics of selective absorption of medicinal plants, supplementing corresponding nutrient elements is one of the principles of fertilization for medicinal plants.
(2) phased absorption
During the whole life cycle from seed germination to seed formation, plants go through several growth and development stages. In different growth stages, plants have different characteristics of nutritional needs, which is the stage of plant nutrition. For example, the growth period of Coix lachryma-jobi can be divided into seedling stage, jointing stage, booting stage, heading and filling stage and maturity stage. Another example is that ginseng is a perennial herb, and the annual growth period of ginseng is more than two years, which can be divided into green turning period, leaf unfolding period, flowering and fruiting period, root swelling period and defoliation period. Rehmannia glutinosa can be divided into seedling stage, vegetative growth stage, rhizome expansion stage and harvest stage from planting to harvesting.
It is very important to define the division of nutritional periods of medicinal plants in fertilization technology, because only by defining the nutritional characteristics of medicinal plants in each nutritional period can we determine the fertilization period, fertilization type and fertilization amount. Taking Chuanxiong as an example, it is described as follows:
Chuanxiong is a perennial herb, and its propagation material is aerial stem nodes with internodes (commonly known as "Zi Ling"). The growing period from planting to harvest is 280-290 days. Because it has to go through the wintering period, the aboveground part will germinate twice and the underground part will swell twice. The whole growth period (referring to yield) can be divided into five periods, namely the first overground growth period; The first expansion stage of the underground part; Overwintering period; The second growth period of new shoots; The second expansion stage of the underground part. See Chapter 14, Chuanxiong Diagram 14-24 for the changes of dry matter accumulation and tuber volume expansion. Variation characteristics of dry matter accumulation and tuber volume expansion of Ligusticum chuanxiong hort. During the whole growth period, the aerial parts of Ligusticum chuanxiong hort. The growth after overwintering is larger than that before overwintering, and there are two growth peaks in the whole growth period, that is, the growth peak of aboveground parts before overwintering is from mid-June to mid-February, and from mid-March to harvest after overwintering. The first growth peak of underground tuber is from mid-October to early October of 165438+. During the wintering period, the growth is slow, but the volume increases, but the dry matter accumulation has a downward trend. At the end of March and the beginning of April, the dry matter accumulation of underground stems increased rapidly again. The growth and decline trend of nitrogen and phosphorus nutrient contents (aboveground and underground) of corresponding Ligusticum chuanxiong plants is consistent (Figure 6- 1). Before overwintering, the total nitrogen content in the aboveground stems, leaves and underground parts of Ligusticum chuanxiong increased with the growth of Ligusticum chuanxiong, reaching the highest at the beginning of 1 1, and then gradually decreasing to the lowest before overwintering. After overwintering, the contents of nitrogen and phosphorus in plants gradually increased, reaching the highest in mid-March, and then gradually decreased until harvest. The total nitrogen content of Ligusticum chuanxiong Hort. was higher than that of total phosphorus. Therefore, Chuanxiong needs more nitrogen nutrition than phosphorus nutrition. Chuanxiong has two peak periods of fertilizer absorption, namely, the middle of 10 before overwintering and the middle of March after overwintering. According to the nutrition and growth characteristics of Ligusticum chuanxiong, the fertilization measures should be as follows: 1. In addition to the base fertilizer, Ligusticum chuanxiong must be topdressing, and the topdressing period is within two months after planting and early spring after wintering. The former can be divided into three topdressing times, each time 20 days apart. The latter can be topdressing 1-2 times. Secondly, the nitrogen supply of Ligusticum chuanxiong should be greater than that of phosphorus and potassium, and nitrogen fertilizer can be used as the main topdressing before wintering. Phosphorus and potassium fertilizer should be applied in combination after wintering, and phosphorus fertilizer should be applied in early spring than before wintering because underground tubers need more phosphorus after wintering.
Fig. 6— Changes of nitrogen and phosphorus contents in aerial parts and tubers of Ligusticum chuanxiong Hort.
When studying the stage nutrition of medicinal plants, the critical period and the maximum efficacy period of plant nutrition are put forward. The former means that in the process of plant growth and development, there is often a period when the demand for a certain nutrient is not much in absolute quantity, but the degree of demand is very urgent. At this time, if this nutrition is lacking, the growth and development of plants will be affected, and the resulting impact and loss will be irreparable even if this nutrition is supplemented later. The critical period of the same plant is not exactly the same for different kinds of nutrients. In most plants, the key period of phosphorus is at seedling stage, such as the key period of coix lachryma-jobi phosphorus is at trilobal stage. The critical period of nitrogen is often in the period when vegetative growth turns to reproductive growth.
The so-called maximum efficiency period of plant nutrition refers to the maximum absorption rate and absolute amount of nutrients needed by plants during this period, so the fertilization effect is the most obvious and the yield increase effect is the best. The maximum efficiency period of plant nutrition is often the middle period of plant growth. However, the maximum efficacy period of various nutrient elements is different. For Rehmannia glutinosa, the effect of nitrogen nutrition is better in the middle growth stage, but the effect of phosphorus and potassium nutrition, especially potassium, is better in the root swelling stage.
It should also be pointed out that although plant nutrition is staged, it is necessary to ensure adequate nutrient supply in the critical period, but the continuity of nutrient absorption by plants should also be considered. Therefore, in production practice, it is often necessary to apply sufficient base fertilizer to lay a good foundation, and at the same time pay attention to the coordinated application of seed fertilizer and topdressing.
The characteristics of medicinal plants absorbing nutrients are also influenced by external environment, such as climate conditions, soil conditions, people's farming measures, etc., especially soil conditions are more direct and important. Because the nutrients needed by plants are basically supplied by soil, it is necessary to study the soil nutrition of medicinal plants when studying their nutritional characteristics.