Root system type
According to the source of root system, it can be divided into three categories (Figure 1): ① Root system: the root system formed by radicle after fruit tree seeds are sown, characterized by developed taproots, deep distribution and strong vitality and adaptability. ② Stem root system: the root system formed by cutting and layering propagation, such as the root system of grapes and strawberries; The roots of bananas and pineapples reproduce by sucking buds. Its characteristics are that the taproot is not obvious, the distribution is shallow and the individuals are relatively consistent. (3) Roots and tillers: Roots and tillers are formed by adventitious buds on the roots of fruit trees, and they live independently after leaving the mother plant, and their characteristics are similar to those of stem roots.
Figure 1 According to the root morphology, the primary root from the radicle to the ground is called the main root, and the branches on the main root are called the lateral roots. When the lateral roots grow to a certain length, the new branches can be divided into fibrous roots. Roots that grow vertically downward in soil are called vertical roots, and roots that grow horizontally are called horizontal roots.
According to the function and structure of roots: ① Elongated roots (growing roots). The new root of primary tissue is white, the meristem is strong, and it grows faster and longer, reaching more than 10 ~ 25 cm. The continuous extension of root system can expand the distribution range of root system, make root system enter a new soil layer and differentiate into lateral roots; Slender roots also have absorptive capacity. With the extension, their backs gradually differentiate into secondary structures, and some can become trunk roots. ② Active roots. Also known as vegetative root, it is a white root with primary structure, with a large number, and the root system can reach more than 90% of the total root when it grows most vigorously; Most active roots can't be transformed into secondary tissue, and their life span is usually 7 ~ 25 days, with a length of 0. 1 ~ 4 mm and a diameter of 0.3 ~1mm; Active roots have a large number of root hairs, which can absorb water and nutrients from soil, and can be converted into organic compounds and active substances, with high physiological activity; The number of active roots is closely related to the nutritional status and growth of fruit trees. ③ Transitional root. It is also the root of primary tissue, pale yellow to yellowish brown, transformed from elongated roots or movable roots. A few of them developed into transport roots, and most of them died of self-thinning. Generally, active roots and transitional roots are collectively referred to as absorption roots. (4) guiding roots. Developed from the transition root, it is the root of the secondary structure. If it continues to grow, it can form a trunk root. Transport roots transport water and nutrients absorbed or transformed by absorption roots to the aboveground parts, and at the same time transport organic nutrients synthesized from the aboveground parts to the whole root system, which has storage function (Figure 2).
Fig. 2 Distribution of roots
The depth and range of root distribution in soil vary with soil, tree species and rootstock. Peach, cherry and plum are shallowly distributed, pear, persimmon and walnut are deeply distributed, and citrus and apple are in between. The horizontal roots of dwarf rootstock are developed, while the vertical roots of Qiao Hua rootstock are developed. The horizontal root distribution layer of most fruit trees is 8 ~ 40 cm below the surface, and the extension range is generally 2 ~ 3 times of the crown diameter. Orchards with deep and fertile soil or frequent fertilization have small horizontal roots and many fine roots; Under the condition of arid and barren soil, the root system extends far and the fine roots are few. The depth of vertical distribution depends on soil thickness and soil physical and chemical properties. In the soil with loose soil and good aeration, the vertical roots develop vigorously and deeply; In the soil with high groundwater level and thick clay or gravel layer, the downward extension of vertical roots is limited. Generally, the root system of adult fruit trees can be more than 2 ~ 3 meters deep, and sometimes the root system can extend down to more than 10 meters along the soil pores. Ginkgo biloba, walnut and chestnut have strong vertical roots, but most drupe trees have underdeveloped vertical roots. The roots of pomelo, lime and sweet orange are deeper than those of kumquat, orange, orange and orange. Vertical roots from radicles are more developed than roots from stem roots. Vertical roots can absorb water and nutrients from deeper soil layers, but their absorption capacity is far less than that of horizontal roots.
Root growth
The roots of fruit trees are not naturally dormant. As long as there are necessary conditions for growth all year round, new roots will grow at any time. Generally, the root growth of fruit trees is periodic, and the frequency of occurrence in a year, the growth intensity in each period and the root composition are restricted by internal factors such as tree species, varieties, tree age, yield, aboveground growth and development, soil conditions and management measures.
Fig. 3 Most young deciduous fruit trees have three growth peaks a year, such as tulip rootstock "Golden Crown Apple" in Shandong and Hebei. The first growth peak is from mid-March to mid-April, and then it turns to low tide, flowering and new shoots flourish. The second peak usually appears from late June to early July, that is, from the time when the new shoots come to a halt to the flower bud differentiation. This time is the period with the largest root system in the whole year, and then it turns to low tide due to the rapid development of fruit. The third peak is from early September to mid-June165438+1October. The assimilated nutrients in the leaves flow back to the roots for accumulation, and then enter a low tide or stop growing with the decrease of soil temperature (Figure 3). In orchards with deep soil layers, sometimes a small number of new roots grow in the lower roots all year round, and new roots often grow in sunny places in winter or under cover, and when the weather gets warmer after February. Due to the influence of a large number of fruits of adult trees, the first growth climax of roots often begins when the growth of new shoots slows down; The second time is after the fruit is harvested. Although new roots grow in early spring, it is often not an obvious climax, and the climax after harvest in years with too many fruits is not obvious.
The roots of citrus fruit trees began to take root before the spring shoots appeared, but the number was very small. When a large number of spring shoots occur, the root growth weakens, and after a large number of new shoots turn green, the root growth becomes active and reaches its peak before the spring shoots occur. The second and third peaks are before the summer shoot and after the autumn shoot leaves turn green (Figure 4).
According to the observation of grapes and plum trees, the growth dynamics of roots in one day and night are that the growth amount at night and the number of hairy roots are more than during the day. Roots also have self-thinning and regeneration. In addition to the continuous death of absorbing roots in the growth process, with the deterioration of local soil physical and chemical conditions in the area where fibrous roots are located, some branch fine roots die, some growth roots die, and then branch root axes begin to die; In the process of root branch death, there will be growing roots and absorbing roots extending into the new soil behind the shaft, and so on. When the root age increases and carbohydrate accumulation decreases, the death process of peripheral roots will be accelerated, and regeneration will only occur near the root neck, and the decay process of these new roots will also be accelerated, resulting in a large number of dead branches above the ground.
Fig. 4 Factors affecting root growth
soil temperature
Because of the variety of fruit trees, the soil temperature of fruit trees originating in the north is generally lower than that of southern tree species. In spring, the surface soil temperature rises rapidly, and the upper root system activities are earlier than the lower root system. In summer, the upper soil temperature is too high, and the root growth stops, while the root system in the middle still grows more; In autumn, the surface soil temperature drops and the upper root system grows (see table).
Air and moisture
The root growth of fruit trees needs sufficient water and good ventilation. The optimum soil water content for fruit tree root growth is 60 ~ 80% of the maximum soil water capacity in the field. When the soil moisture drops to a certain limit, even if the temperature, ventilation and other factors are suitable, the root system will stop growing; Excessive soil moisture will lead to poor ventilation and produce toxic substances such as hydrogen sulfide, ferrous oxide and nitrite, which will affect the normal respiration and physiological activities of roots and is not conducive to root growth. In order to promote the occurrence and function of roots, the soil needs sufficient oxygen. Generally, apple roots stop growing when the oxygen concentration is 2 ~ 3%, 5% grow slowly, and can grow normally when the oxygen concentration is above 10%, and new roots appear above 15%. When the oxygen content of citrus root system is above 3 ~ 4%, it can grow normally, and when it is below 2%, the growth stops.
In addition, it is also related to the content of carbon dioxide. For example, if the carbon dioxide content in the soil is low, even if the oxygen content in the rhizosphere air is only 3%, the roots can still play a role. If the content of carbon dioxide rises above 10%, the function of root system will be destroyed. Root growth is also related to the accumulation of organic nutrients and the balance of endogenous hormones in the tree itself. For example, auxin produced by new buds plays an important role in stimulating the occurrence of new roots; Another example is that when the assimilates on the ground are supplied adequately, the root system is large; Therefore, the growth climax of root system is mostly after the slow growth of new shoots and the formation of a large number of leaves. When too many fruits restrict the downward transport of nutrients on the ground, it also seriously restricts the growth of root system.
Function of root
Roots can absorb water, inorganic salts and carbon dioxide from soil for plants to grow and bear fruit; Inorganic nitrogen absorbed from the soil is transformed into various organic substances, such as amino acids and cysteamine, and some enzymes, hormones and plant alkaloids can be formed and transported to the ground, or some nitrogen-containing organic substances and carbohydrates can be stored. About two-thirds of carbohydrates absorbed by deciduous fruit trees are transported to the roots for storage. These storage materials are needed to construct new organs (branches, leaves, roots, etc.). ) and the next year's life activities, which play an important role in the annual growth and development of perennial fruit trees. After many branches, the roots form a huge root system, which is closely connected with the soil, and plays a role in fixing and supporting plants, ensuring that stems, leaves, flowers and fruits extend above the ground and stand on the ground stably for normal life activities.
Root grafting
A grafting method using root segments as rootstocks. When a large number of seedlings are lacking rootstocks, they can be supplemented by root segments to accelerate the reproduction of rare rootstocks. In addition, when the root system is defective or infected, healthy roots can be inserted to repair the root system, thus restoring the tree potential.
Rootstocks collected from orchards or nurseries are cut into root segments about 10 cm long, and indoor grafting (also called digging grafting) is carried out by splitting, cutting and tongue grafting (see branch grafting). Pay attention to the connection between the base of scion and the end of root segment to avoid polarity confusion. Then cultivated with clean and moist river sand, placed at 20 5℃ to promote interface healing, and planted in nursery after soil thawing in spring. If the root segment is thinner than the scion, insert the root segment into the scion for root grafting, and insert 1 ~ 2 thin root segments according to the thickness of the scion (see figure 1, 2). Each tree species should choose the most suitable rootstock variety to ensure the quality of seedlings. (Wang) According to
Figure 1
Fig. 2 Root neck
The joint between the root and the trunk of a fruit tree. The root neck of true root fruit trees is developed from the hypocotyl of seeds, which is called true root neck, and it has been in its infancy during the development process, and the sprouting strips produced have original characteristics; The root neck of fruit trees with stem root system and tillering root system is called pseudoroot neck, and its development is in the mature stage. Root neck is a channel for nutrient and water exchange between aboveground and underground parts. Because it is located at the junction of soil and atmosphere, the temperature changes dramatically in the annual cycle and between day and night, and it is also sensitive to environmental conditions. The root neck of deciduous fruit trees in northern China entered dormancy in late autumn at the latest and was released in spring at the earliest. When the management is extensive, the root neck is often prone to freezing injury or infection on the sunny side. If the fruit trees are planted too deep or too shallow, so that the root neck is buried deep underground or exposed on the ground, it is unfavorable to the growth and development of young trees, which will cause the tree to weaken and delay the fruit bearing.
Root tiller
Adventitious buds on the roots of mother plants germinate seedlings. Under proper cultivation, it can become an independent plant for reproduction after being separated from its mother. Such as jujube, hawthorn, raspberry, China cherry, plum, pear, Vitex negundo, Catalpa bungeana, Haitang Xifu, etc. can be propagated by tillering.
Normal tillering germination is seasonal. For example, jujube trees mostly occur from May to July, and there are concentrated parts, especially around the trunk and the edge of the crown, in the soil layer 8 ~ 20 cm below the surface. In clay, the tillering area is shallow, while in sandy soil, the tillering area is deep. When the tiller (see figure) germinates, a tumor-like process is first produced on the root, which is called "root brain". After germination, the root system occurs at the base and grows in the centrifugal direction, becoming a shallow horizontal root system without main roots. Roots with tillers generally need to have a certain thickness. For example, jujube roots with a diameter of 1 cm are easy to take root and tiller, and those that are too thick and too thin are not easy to send out; The roots of apple rootstocks tend to tiller on shallow roots, and most of them are near the root neck. Usually, natural tillers are used for ramet propagation in production, but artificial methods are also used to promote germination and accelerate propagation. That is, before dormancy or germination, the periphery of the crown of the mother plant is dug out and buried with base fertilizer. After the roots and tillers are unearthed, add fertilizer and water to make the roots and tillers grow vigorously. When the root tillers are too dense, they should be sparse and strong, and the seedlings should be thinned to ensure that the root tillers have a certain nutritional area. Then, dig it out in autumn or the next spring and separate it from the mother plant to become a seedling. The occurrence of tillering consumes a lot of nutrients in the mother plant, so it should be removed in time when it is not used as propagation material in the early stage of tillering. (Shu Huairui)
Root bark rate
See early identification.