A nutritional organ of a plant. The whole or system is also known as the root system. It mainly plays the role of absorbing water, nutrients, carbon dioxide and fixing the plant. Understanding the types, distribution, growth and function of roots and roots is important for fruit tree cultivation.

Types of root systems

By the source of the root system is divided into three categories (Figure 1): ① solid root system: the root system formed by the embryonic roots of fruit tree seeds after sowing, characterized by the main root is developed, the distribution of the deeper, the vitality and adaptability of the strong. ② Stem-derived root system: root system formed by cuttings and pressure propagation, such as the root system of grapes and strawberries; root system of banana and pineapple propagated by sucker buds. Characterized by the main root is not obvious, shallow distribution, more consistent between individuals. ③ Root tiller root system: root tiller seedlings formed by adventitious buds occurring on the roots of fruit trees, the root system that lives independently after being separated from the mother plant, characterized by similar characteristics to the stem-derived root system.

Figure 1 according to the root system form: the embryonic root to the ground from the growth of the primary root is called the main root, the main root on the occurrence of the branch is called the lateral root, the lateral root grows to a certain length and can be divided into new branches for the fibrous root. Roots that grow vertically downward in the soil are called vertical roots, while roots that grow in a horizontal direction are called horizontal roots.

According to the function of the root system, structure: ① prolongation root (growing root). With primary tissue of the new root, white, with a strong meristematic tissue, growth faster and longer, up to 10 ~ 25 cm or more; from it to continue to extend the distribution of the root system can expand the scope of the root system into a new layer of soil, and the lateral roots; extension of the root also has the ability to absorb, along with the extension of the forward part of the back of the gradual differentiation of the secondary structure, and some of them can be the backbone of the root. ② Active roots. Also known as nutrient roots, is white with primary structure of the root, the number of many, in the most vigorous root growth, up to more than 90% of the total amount of roots; most of the active roots can not be converted into secondary tissues, its life expectancy is generally 7 to 25 days, the length of 0.1 to 4 mm, 0.3 to 1 mm in diameter; the active root has a large number of root hairs, can absorb water and nutrients from the soil and can be converted into organic compounds and active substances, with a high degree of physiological activity. Substances, with a high degree of physiological activity; how many active roots on the nutritional status of fruit trees and growth and development of the relationship is extremely close. ③Transitional roots. It is also the root of primary organization, light yellow to yellow-brown, transformed from extended root or active root. Among them, a small part of the development of the transmission root, most of which is since the thinning dead. Usually, active roots and transitional roots are collectively called absorptive roots. ④ Conductive roots. From the transition root development, is the secondary structure of the root, if continue to grow can form the backbone root. Conducting roots will absorb or transform the absorption roots of water and nutrients transported to the ground, but also the ground synthesized organic nutrients transported to the entire root system, and has a storage function (Figure 2)

Figure 2 root distribution

Roots in the soil distribution of the depth and scope of the soil according to the soil, species, rootstock and so on varies. Peach, cherry, plum, etc. are shallowly distributed, pear, persimmon, walnut, etc. are y distributed, and citrus, apple, etc. are in between. Dwarfing rootstocks have well-developed horizontal roots, while arborizing rootstocks have well-developed vertical roots. Most of the horizontal root distribution layer of fruit trees in the surface between 8 ~ 40 cm, stretching range is generally 2 ~ 3 times the diameter of the crown. In the soil layer deep fertile or often fertilizer cultivation orchard, horizontal root distribution distance is small, more fine roots; in arid and thin soil conditions, the root extension far, and less fine roots. Vertical distribution depth depends on the thickness of the soil layer and the physical and chemical properties of the soil, loose soil, good aeration of the soil, vertical root development is strong and deep: high water table, sticky or gravel layer of the soil, it is to limit the vertical root downward extension. General adult fruit tree roots can be as deep as 2 to 3 meters or deeper, and sometimes the roots can extend downward along the soil pore space up to more than 10 meters. Ginkgo, walnut, chestnut, etc. have strong vertical roots, while most of the nuclear fruit fruit trees vertical roots are not developed, grapefruit, sour orange, sweet orange root system is deeper than the golden citrus, Hovenia, citrus and orange. Vertical roots extending from the radicle are more developed than those of the stem-derived root system. Vertical roots can absorb water and nutrients from deeper soil layers, but the amount of absorption is much less than the horizontal root system.

Root growth

The fruit tree root system has no natural dormancy, as long as there are conditions necessary for growth throughout the year, there is always new root growth. Usually fruit tree root growth is cyclical, the number of times in a year, the growth of each period of the strength of the composition of the root class, subject to the species, varieties, age, yield, above ground growth and development of the status of the intrinsic factors, as well as the soil conditions and management measures of the constraints.

Figure 3 most deciduous fruit trees young trees have three growth peaks a year, such as rowan anvil Golden Crown apple in Shandong, Hebei and other places, the first growth peak in mid-March to mid-April, with the flowering and new shoots of the exuberant growth and turn into a low tide; the second peak from the new shoots close to the stop to the flower buds before the differentiation of the flower buds, usually in late June to early July, this time is the most hairy roots throughout the year, and then due to the rapid development of fruit The third peak was from early September to mid-November, when leaf assimilated nutrients accumulated back to the roots, and then entered a low tide or stopped growing as the soil temperature decreased (Figure 3). In orchards with deeper soils, the lower roots sometimes have a small amount of new root growth throughout the year, and new root growth often occurs in winter in sunny locations or under mulched conditions when the weather warms up after February. Mature trees due to the impact of a large number of results, the first growth of the roots of the climax of the new growth in the new growth to slow down the beginning; the second more in the fruit after harvest. Although there is new root growth in early spring, often do not form a clear climax, in the year of too much fruit, the post-harvest climax is not obvious.

Citrus fruit tree root system in the spring before the occurrence of roots, but the amount of less, when a large number of spring, root growth turned weak, a large number of new green, root growth began to be active, in the spring before the occurrence of the peak; the second and the third peak in the summer before the occurrence of the leaves and fall after the green (Figure 4).

Observations on grapes and plum trees show that the dynamics of root growth during the day and night are such that the amount of growth and the number of roots developed during the night are more than during the day. Roots also have self-sparing and regeneration phenomenon, in addition to the absorption roots continue to die during the growth process, with the deterioration of the physical and chemical conditions of the soil where the fibrous roots are located in the scope of the local soil, part of the branched fine roots die, some of the growing roots die, followed by branching roots in the middle of the axis began to die; root branching in the process of death, the rear of their axes will appear again in the growth of the root and the absorption roots to reach out to the new soil, and so on and so on, in the root age increases, carbohydrate accumulation is reduced, peripheral root death process accelerate When the root age increases and the accumulation of carbohydrates decreases, the process of peripheral root death is accelerated, only the regeneration phenomenon near the root neck, and the decay process of these new roots is also accelerated, which causes the emergence of a large number of withered branches in the above ground.

Figure 4 Factors affecting root growth

Soil temperature

Varies depending on the type of fruit tree, generally fruit trees of northern origin require lower soil temperatures than southern species. Spring topsoil temperature rises faster, the upper root activity earlier than the lower root; summer upper soil temperature is too high, the root growth stops, while the middle root still grows more; fall topsoil temperature drops, the upper root growth and increase (see table).

Air and water

Fruit tree root growth requires adequate water and good aeration. The optimum soil moisture content for fruit tree root growth are equal to 60 to 80% of the maximum field water holding capacity of the soil. When the soil moisture drops to a certain limit, even if the temperature, aeration and other factors are suitable, the root also stops growing; too much soil moisture, poor aeration, will produce hydrogen sulfide, ferrous oxide and nitrite and other toxic substances, affecting the root's normal respiratory and physiological activities, but also not conducive to the growth of the root system. In order to promote the occurrence of roots and play the function of the root, the soil needs to have sufficient oxygen, general apple root system in oxygen concentration of 2 to 3% when the growth stops, 5% growth is slow, more than 10% to normal growth, new roots occur to be more than 15%; Wenzhou mandarin orange root system oxygen content of 3 to 4% or more can be normal growth, 2% of the following growth stops.

In addition, also related to the content of carbon dioxide, such as low carbon dioxide content in the soil, even if the inter-root air oxygen content of only 3%, the root system can still exercise the function, such as carbon dioxide content increased to 10% or more, the root function is damaged. Root growth is also related to the tree itself, the accumulation of organic nutrients, endogenous hormone balance and other endogenous factors, such as new shoots of growth hormones produced by the new roots have an important role in stimulating the occurrence of new roots; another example of the aboveground assimilates the supply is sufficient, the amount of root occurrence; so the root of the growth of the culmination of the new growth in the new shoots of slow growth, the formation of large numbers of leaves after the formation of the culmination of the new shoots. When the result is too much to limit the downward transportation of nutrients from the ground, it also severely limits the growth of roots.

Root function

Roots can absorb water, inorganic salts and carbon dioxide from the soil for plant growth and fruiting; the use of carbohydrates will be absorbed from the soil inorganic nitrogen into a variety of organic substances, such as amino acids and cystamine, etc., but also the formation of certain enzymes, hormones and plant bases, transported to the ground, or part of the nitrogen-containing organic matter and carbohydrates stored. Deciduous fruit trees in the second half of the growth of leaf assimilation of carbohydrates about 2 / 3 is transported to the root storage, these storage materials for the second year of the new organs (branches, leaves, roots, etc.) of the construction and life activities required for perennial fruit trees throughout the year play an important role in growth and development. Roots through many branches to form a huge root system, and the soil is closely linked to the plant plays a solid and supportive role to ensure that the above ground stems, leaves, flowers, fruits of the extension, stable on the ground for normal life activities.

Root grafting

A grafting method using rootstock as rootstock. When there is a lack of rootstocks in a large number of seedlings, the rootstock can be used to make up for the lack of rootstocks, and it can also speed up the propagation of rare rootstocks. In addition, when the root system is missing or the root system is infected, the healthy roots can be inserted to replenish the roots, so as to restore the strength of the tree.

The rootstock from the orchard or nursery collection of roots, cut to about 10 cm long root section, with split, cut, tongue and other methods (see branching), in the dormant period in the indoor grafting (also known as digging), pay attention to the base of the scion and the end of the root section connected to avoid confusion of polarity. Cultivate the clean moist river sand after connection, set at 20 ± 5 ℃ to promote the healing of the interface, to be planted in the nursery after the soil thawed in the spring. If the root section is finer than the scion, to insert the root section into the scion for root grafting, depending on the thickness of the scion inserted 1 to 2 fine root sections (see Figure 1, 2). Root grafting seedlings, should utilize the most suitable rootstock species for each tree species to ensure the quality of seedlings. (Wang Fengcai)

Figure 1

Figure 2 Root neck

Fruit trees from the root transition to the above-ground trunk of the intersection site. The root neck of fruit trees with a solid root system is developed from the hypocotyl of the seed, called the true root neck, in the process of development has been in the stage of childhood, the birth of the cork with the primitive traits; and the root neck of the stem source root system and root cork root system of fruit trees is called the pseudo-root neck, the development of the maturity of the stage. Root neck is the aboveground and underground nutrition and water exchange channel, because in the soil and the atmosphere at the junction, in the annual cycle and between day and night, subjected to drastic temperature changes, the response to environmental conditions is also more sensitive. The root-neck portion of northern deciduous fruit trees enters dormancy in late fall at the latest, and lifts dormancy in spring at the earliest. Sloppy management, the sunny side of the root neck is often prone to frost damage, or thus infected with disease. Fruit trees planted too deep or too shallow, so that the root neck deep underground or bare ground, are unfavorable to the growth and development of young trees, will cause tree weakness, delayed results.

Root tiller

Sprouting from the mother plant's roots of indeterminate buds into seedlings. Under proper cultivation, after separating from the mother, it can become an independent plant for reproduction. Such as jujube, hawthorn, raspberry, Chinese cherry, plum, juniper, zinnia, rowan and Xifu begonia can be propagated by root tillers.

Normal root tiller germination has seasonality, such as jujube more in May to July, and there is a concentrated part of the occurrence of the trunk around the tree and the edge of the tree crown, the surface of the soil layer of 8 to 20 centimeters below the depth of the occurrence of the most. On clayey soils the rooting zone is shallow, whereas in sandy soils the rooting zone is deeper. When a root tiller (see photo) sprouts, it first produces a tumor-like protrusion on the root, called the "root brain". After sprouting, a root system develops at its base, growing in a centrifugal direction and becoming a shallow horizontal root system without a main root. Root tiller root, generally need to have a certain thickness, such as jujube with a diameter of up to 1 cm thick root easy to root tiller, too thick and too fine are less issued; apple rootstock root system, often in the shallow root root tiller, and to the most near the root neck. Usually in the production of natural root tillers, planting propagation, but there are also artificial methods to promote sprouting tillers, accelerated reproduction. That is, in the dormant period or sprouting before the mother plant crown periphery dug a trench to break the roots, applied to the base fertilizer buried, to be the root tiller out of the ground, increase the fertilizer and water, so that the root tiller seedling vigorous growth, the root tiller is too dense, should be thinning the weak to retain the strong, inter-seedling to ensure that the root tiller has a certain amount of nutrient area, and then dug out in the fall or the following spring and the separation of the mother plant, to become the young plant planting. The root tillers consume a lot of nutrients from the mother plant, so they should be removed at the beginning of the season when they are not utilized as propagation material. (Shuanghuairui)

Root bark rate

See Early Identification.