Definition of Freezing Damage Freezing damage is the phenomenon that trees and tissues are injured or even died due to cold damage. Frost damage can be divided into frost damage and winter frost damage. The damage to green trees is mainly caused by frost and frost damage. The performance of freezing injury (1) bud buds are the organs with weaker cold resistance, and flower buds freeze injury mostly occurs in the early spring period, and the top flower buds have weaker cold resistance. After the flower buds were frozen, the interior turned brown. In the initial stage, only bud scales were seen to be loose, and later buds did not germinate and dry shrinkage died. (2) The frost damage of shoots is related to their maturity. Mature branches in the dormant period to form a layer of the most cold-resistant, skin level, and xylem, pith most not resistant to cold. Therefore, after the occurrence of frost damage, the pith and the xylem first become discolored, and the phloem is severely injured. If the layers are discolored, the shoots lose their ability to recover. In the growth phase, on the contrary, the formation of the cold resistance is the worst. The saplings are greedy for long periods in the autumn when the water is long, and the branches are not full and are prone to frost damage. In particular, the mature shoots are sensitive to cold, and often cause freezing injury. The light part has discoloration in the pith part, and the severe ones are dehydrated, dried and shrunk, or even freeze to death. Perennial branches occur frost damage, which is often caused by local frostbite in the bark. The frozen part of the bark is slightly discolored and is not easy to find. If you cut with a knife, you will find that the skin becomes brown, then gradually dry and die, the skin cracking and browning off, but if the formation layer is not frozen can also be restored. (3) Branches and base corners or main branch corners enter into the dormancy phase later, and the conducting tissues are not well developed and are prone to freezing injury. The cold injury of the branches is characterized by the browning of the cortex or forming layer, followed by the dry depression, and some bark pieces are frozen and frozen, and some form vertical cracks along the trunk to form litchi. The smaller the angle between the main branch and the trunk, the more severe the freezing injury. (4) After the trunk is frozen, it forms a longitudinal crack, which is generally called “frozen crackingâ€. The bark is detached from the xylem in a blocky manner or curled to the outside along the crack. (5) The root neck and root system stopped growing at the latest in the year and entered the dormancy at the latest, but the earliest activities and the release of dormancy were the earliest. Therefore, the root neck was not subjected to very good cold resistance in the event of a sudden drop in temperature. , And near the surface temperature changes drastically, easily cause root-cold damage. After the root neck is frozen, the bark first discolors and then dries, causing great harm to the plants. There is no dormancy period in the root system, so the cold resistance of the root system is lower than that of the underground system. The fibrous root activity decreased significantly during the winter and the cold resistance was slightly stronger than in the growing season. After the roots were frozen, the cortex was separated from the xylem. In general, the coarse root system has a stronger cold-resistance than the fine root system, and the rough roots near the ground are susceptible to freezing due to low ground temperature. The newly planted tree or sapling is prone to frost damage due to its small root system, and the large tree is relatively resistant to cold. Factors Affecting Freezing Injury 1. Internal factors (1) Frost resistance is related to tree species and species. Different species or different varieties have different frost resistance. For example, the plum varieties of the Yangtze River basin that originated in the country are colder than those of Guangdong. (2) Frost resistance is related to the sugar content inside the shoots. The relationship between the dynamic changes of sugars in the branches of honeysuckle and the ability to resist overwintering over the winter shows that in the growing season, the sugar in the plants is mostly in the form of starch. At the end of the growing season, starch accumulation reached a peak. By the end of November, starch began to decompose into simpler oligosaccharide compounds. The starch in the apricot and yam branches had been decomposed at the end of the month, and the plum branches remained starch at this time. As far as the performance of cold resistance is concerned, Mei is inferior to apricot and mountain peach. The higher the content of oligosaccharides in the visible tree, the stronger the cold resistance. In addition, it was also observed that the content of nitrogen in plum branch was closely related to overwintering, and the single-necked jade butterfly with stronger wintering power had higher nitrogen content, especially protein nitrogen content, than Huangmei without wintering power. (3) It is related to the maturity of shoots. The more mature the branches, the stronger the cold resistance. The degree of lignification is high, the water content is small, the concentration of the cell fluid is increased, and the accumulation of starch is large, so the cold resistance is strong. (4) Related to the dormancy of branches. The severity of frost damage is related to the dormancy and cold-resistance of trees. Generally, plants in dormant state have strong cold resistance, deeper plant dormancy and stronger cold resistance. 2. External factors (1) The terrain and aspect are different, and the microclimate is different. For example, the plants on the south side of the mountain are more vulnerable than the plants on the north side of the mountain because of the large temperature difference on the south side of the mountain. Trees with thick soil layers are more resistant to freezing than trees with shallow soil layers. This is because the soil is deep, the roots are deep, the root system is developed, the nutrients and moisture are absorbed, and the plants are robust. (2) The water body also has a certain impact on freezing damage. The trees near the water body are not susceptible to freezing damage. Because the specific heat of the water is large, the heat absorbed during the day will be released at night and the ambient air temperature will drop slowly. (3) The level of cultivation and management is closely related to frost damage. The seedlings of the same species are more resistant to cold than grafted seedlings, because the roots of the seedlings are well developed, with deep roots and strong cold resistance. The cold resistance of different rootstock varieties is also different. Many people with the same type of results are more likely to suffer freeze damage than those with fewer results because they consume a lot of nutrients. The cold-resistance of under-fertilization is poor, because the fertilization is insufficient, the plants are not full, the material accumulation is small, and the cold resistance is reduced. When trees suffer from pests and diseases, they are also prone to frost damage. Freezing damage prevention 1. Macro-prevention (1) Carry out the principle of appropriate and suitable trees Planting cold-resistant tree species, varieties, and rootstocks in line with local conditions, and planting low-cold-tolerance edge tree species in places with better microclimate conditions can greatly reduce measures against overwintering and cold-proofing. Pay attention to planting shelterbelts and setting wind barriers to improve microclimate conditions and prevent and mitigate freezing damage. (2) Strengthen cultivation and management, improve cold resistance Strengthen cultivation management (especially paying attention to late-stage management) to help reserve nutrients in tree bodies. Experience has shown that the strengthening of fertilizer and water supply in the spring and the rational use of drainage, irrigation and fertilization techniques can promote shoot growth and leaf enlargement, increase photosynthetic efficiency, increase nutrient accumulation, and ensure robust trees. Control irrigation in the fall, timely drainage, appropriate application of phosphorus and potassium fertilizer, diligence and deep plowing, can prompt the end of the growth of branches, is conducive to tissue enrichment, prolong the accumulation of nutrients, and thus better cold resistance exercise. In addition, timely picking of hearts in the summer to promote the maturity of branches, pruning in winter to reduce the transpiration area, artificial deciduous and so have a good effect on the prevention of freezing injury. At the same time, pest control must be strengthened throughout the growing season. (3) Strengthen tree protection There are many protection measures for trees, and general trees use “frozen water†and irrigation “spring water†to prevent and control. In order to protect the species susceptible to freezing, whole plants can be used to prevent freezing, such as rose, grape and so on. Root-neck soil (30 cm in height), white coating, trunk package, wind barrier, and crescent-shaped earthworm in the north can also be used. The main prevention and control measures should be completed before the low temperature arrives in winter so as to avoid cold temperatures coming early and causing freezing damage. 2. Micro-prevention (1) Smoke-smoked method: At about 2 o'clock in the middle of the night, litters or chemicals are ignited in the upper wind, and smoke is used to prevent frost. This method is simple, economic, and effective. (2) Irrigation method: After irrigation of the soil, the temperature of the field can be increased by 2 to 3°C and maintained for 2 to 3 nights. (3) Coverage method: cover the blocks with rice straw, grass ash and nylon film to reduce heat loss on the ground. The remedial measures of frost damage are extremely important for the conservation of frozen trees, because the transported tissues of frozen trees are blocked by resinous substances, and the roots of trees are absorbed and transported, and the transpiration of leaves, photosynthesis and growth of plants are all destroyed. . To this end, the transfusion system should be resumed as soon as possible to heal wounds, alleviate water shortages, promote the germination of dormant buds and the rapid enlargement of leaves, and promote rapid recovery of frozen trees. The frozen trees generally show poor growth. Therefore, first of all, we must strengthen management to ensure the supply of water and fertilizer in the early stage. We can also top-dress fertilizers and top-dressing fertilizers in the early stages to supply nutrients to restore trees as much as possible. In terms of tree management, the frozen-damaged tree should be cut and lightly cut, and the branches should be given a certain recovery period. The frozen and dead parts can be cut off in time to facilitate wound healing. For those who cannot see the frozen part for a while, they should be cut after germination. The wounds caused by freezing should be sprayed with whitening agent in a timely manner to prevent sunburn, and at the same time, pest control and leaf protection must be done. (Zhang Xuehui)
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