There are many reasons for the freezing damage of seedlings. We need to determine the causes of freezing injury of seedlings based on different tree species.
1 Relationship between Frost Resistance and Tree Species and Variety
Its frost resistance is not the same. Such as cedar than frost resistance, the same species or different varieties. Pinus massoniana than frost resistance. The same pear plant Qiuzi Pear than white pear and sand pear antifreeze. The plum varieties originating in the Yangtze River Valley are colder than those of Huangmei in Guangdong.
2 Relationship between Frost Resistance and Dynamic Changes of Sugars in Shoots
Plum blossoms belong to the northern cold-resistant trees of the same genus, apricots and mountain peaches, throughout the growing season. The sugars mainly exist in the form of starch. Before the end of the growth period, the accumulation of starch is the highest. The ring medullary and myelinated ray cells in the shoots are filled with starch grains.
The plum varieties originating in the Yangtze River Valley are the same as those of apricot and mountain peach, and they were at the end of the first half of November. Starch granules began to dissolve and decompose, and starch granules were completely decomposed in the branches of apricot and carya in the first month, while the starch granules remained in the twigs of plum blossoms, and were not completely decomposed. However, the phenomenon of starch decomposition has not been observed in Huangmei after winter.
The speed and extent of starch transformation in shoots during wintering is closely related to the ability of the tree species to resist overwintering overwintering. From the conversion of starch can be seen. The cold resistance of Mei varieties in the Yangtze River Valley is not as good as that of apricot or peach, but it has a certain physiological function of cold resistance. Guangzhou Huangmei does not have such internal conditions at all.
In particular, protein nitrogen also observed that the dynamics of nitrogen metabolism in the twigs of plum blossoms was closely related to the overwintering force. The single-suppressed jade butterfly with stronger wintering power had higher nitrogen content than Huangmei with no overwintering ability.
The decrease in water content, the more mature the branches, the stronger the antifreeze. The sign of full childishness of branches is mainly the high level of lignification. The concentration of cell fluid increases and more starch accumulates. Before the onset of cooling, if trees that can't stop growing but do cold resistance exercise, they are vulnerable to freezing injury.
4 Relationship with dormancy of shoots
The occurrence of cold-resistance and cold-resistance in plants that are generally dormant is related to the dormancy and cold-resistance of trees. The deeper the plant is dormant, the stronger the cold resistance. The cold resistance of plants is a process that gradually develops during autumn and early winter. This process is called "cold-resistance exercise." In general, plants acquire cold resistance through their ability to resist cold. In the spring, the antifreeze capacity gradually loses its value. This loss process is called “relaxationâ€.
In the spring and early evening of trees, it is closely related to the occurrence of frost damage. The early release of dormancy is threatened by the low temperature of early spring; late release of dormancy can avoid the threat of early spring low temperature.
The occurrence of frost damage is usually not in the dormancy period with the lowest absolute temperature, therefore. It often happens in late autumn or early spring. Therefore, overwintering not only manifests itself in resistance to low temperatures, but also adapts to comprehensive environmental conditions after appearing in dormant periods and releasing dormant periods.
5 Relationship with Low Temperature
Plants have not been cold-adapted for a period of time when the low temperatures arrive early and suddenly. When people do not use cold protection measures, they are prone to frost damage. The lower the extreme minimum temperature, the greater the damage to the plants will be. The longer the temperature is low, the greater the damage to the plants, the faster the cooling rate, and the heavier the plants will be. For example, the eucalyptus planted by you is not well protected when the low temperature comes. After the trees are affected by low temperatures, in addition. If the temperature rises sharply, it will be worse than a slow recovery.
6 Relationship with other factors
The microclimate is different. For example, in the Jiangsu and Zhejiang provinces, the citrus grown on the south side of the mountain was more severe than the citrus on the northern side under the same conditions. Because of the large temperature difference between day and night in Shannan, there is a small temperature difference between day and night. For example, in the citrus of Dongshan, Taihu, Jiangsu, the number of oranges on the south side of the mountain each year will cause freezing injury, but the oranges on the north side of the mountain will not suffer freezing injury.
The soil in the shallow orange groves was more severe than the soil in the orange groves. Because the soil is thick, the roots are deep, the roots are developed, and the nutrients and moisture are absorbed. The plants are robust.
Because of the large heat capacity of water, 2 water bodies also have a certain impact on the occurrence of frost damage. The orange juice in the same area where the water source is close is less damaging than the orangery that is far from the water. The body of water absorbs a lot of heat in the daytime. When the temperature of the surrounding air is lower than the temperature of the water at night, the body of water releases heat again, thus increasing the ambient air temperature.
Because the seedling root system is well developed, the level of cultivation and management has a certain relationship with the occurrence of frost damage. The same variety of seedlings is harder than grafted seedlings. Deep roots have strong cold resistance, while seedlings have strong plasticity and strong adaptability. The cold resistance of rootstocks varies greatly. Peach trees are used as rootstocks in the north and nectarines are used as rootstocks in the south, because they are harder than peaches. If the result of the same species is less than the result, it will be prone to frost damage. Because the result will consume a large amount of nutrients, it is susceptible to freezing.
Because there is more than enough fertilization, fertilizing more than the fertiliser applied is very poor cold resistance. Plants are not full, they have less nutrition and their cold resistance is low. When trees are affected by diseases or insects, they are prone to frost damage. The more serious the pests are, the more serious the damage is.
What are the major aspects of frozen tree damage?
1 bud
Flower bud freezing injury occurred in the spring warmer period, flower buds are weak cold resistance organs. Sap buds are stronger than the top flower buds in their cold resistance. After the flower buds are frozen, the interior turns brown, and only the bud scales are loosely seen on the surface from the initial stage, and it is difficult to identify the buds. In later stages, the buds do not germinate, and the stems shrink and die.
2 sticks
In the dormant period, the formation layer is the most resistant to cold, and the frost damage of the shoots is related to its childishness. Childish branches. The level of the skin, while the xylem, pith is the least cold. Therefore, as the degree of freezing increases, the pith and xylem become discolored. In severe freezing injury, the phloem is injured. If the layer changes color, the branches lose their ability to recover. However, in the growing season, the cold resistance of the forming layer is the worst.
The growth of branches is not substantial, and the young trees are greedy and prolonged in the autumn due to excessive rainfall. It is easy to aggravate the cold injury, especially the innocent and bad apex is sensitive to the cold, and often the first cold injury occurs. The light part of the pith discoloration, heavier when the branches dehydrated shrinkage, severe branches may be frozen to death.
The bark often suffers from frostbite, and perennial branches freeze damage. The frozen sector is initially slightly discolored and is not easy to find. If it is hard to open, it can be found that the skin has turned brown; then it gradually dies and the skin is split and falls off, but if the layer is not frozen, it can gradually recover.
3 branches and base twigs
The position is more secretive than the twig or the main branch of the base corner into the dormancy later. The development of the transport tissue is not good, and it is delayed by cold-resistance exercise. Therefore, when the low temperature or temperature difference between day and night changes, it is easy to cause freezing injury.
Some of the frozen cortex and forming layer turned brown, and there are various manifestations of cold damage to the branches. Then, dry branches fell into place. Some bark was frozen and frozen, and some trunks were cracked vertically to form litchi. The smaller the base angle between the main branch and the trunk, the more severe the freezing damage is. The level of frost damage that occurs depends on the species and species of the tree.
4 Main trunk
It is generally called the phenomenon of “cold crackingâ€. After the trunk is frozen, it forms some longitudinal cracks. The bark detaches from the xylem in blocks or curls outward along the crack. The trunks of saplings, which are generally overgrown, are prone to frost damage. These wounds are very prone to rot.
The rapid cooling and contraction of the bark and the formation of frost cracks are due to sudden and sudden temperature drops to zero. As a result, the internal and external tensions of the main tissue are uneven, so that they crack from the outside to the inside, or the bark leaves the xylem. The “cold cracking†of the trunk often occurs at night. As the temperature gets warmer, the frozen cracks can gradually heal.
5 neck and root system
At the latest into the dormant period, the growth of the root neck is the latest in one year. The beginning of activities and the release of dormancy earlier, so in the case of a sudden drop in temperature, the root neck did not pass through the cold-resistant exercise, and near the surface temperature changes are severe, it is easy to cause root-cold damage. After the root neck is frozen, the bark first discolors and then becomes dry, which can take place locally or it may form a ring. The frost damage of the root and neck is very harmful to the plants.
So the root system is less cold-tolerant than the above-ground parts. However, the activity of the root system was significantly decreased during the winter and the root system had no dormancy period. Therefore, cold tolerance is slightly stronger than growth period. Roots became brown after freezing, and the skin was easily separated from the xylem. In general, coarse roots are more resistant to cold and fine roots, and coarse roots near the ground are colder than the lower layer, and are more susceptible to freezing than lower root systems. Newly planted trees or saplings are small and shallow due to their weak roots and are prone to freezing damage, while large trees are quite resistant to cold. .
How to prevent the occurrence of frost damage?
However, due to the wide variety of trees, the country’s climate conditions are superior. Widely distributed, and often cold currents, so the occurrence of frost damage is still relatively common. Freezing damage poses a great threat to the trees, and severe tree deaths often occur for decades.
It often causes parasitic diseases of ulcerative parasites, and the trees are partially frozen. The tree vigor is greatly weakened, resulting in a vicious circle of such diseases and freezing damage. For example, the occurrence of apple rot disease, persimmon patch disease and angular spot disease in persimmon gardens are related to the occurrence of frost damage.
However, the flowering period is prone to frost damage. Some trees have strong cold resistance. Affect the viewing effect in the park. Therefore, the prevention of freezing injury has important significance for the function of trees. At the same time, the prevention of freezing damage is of great significance for introducing and enriching the species of garden trees.
Some species require cold measures within 1-3 years of planting. Such as Magnolia, Cedar, Sakura, Bamboo, Metasequoia, Parasol, Ling Xiao, Hongye Li, Japanese Fir, Spring Festival, etc., a few tree species need to shelter wintering each year, such as grapes, rose, peony, thousand cypress, and green in Beijing gardens. Bai et al. Winter measures to prevent cold are:
1 The principle of implementing suitable land
Planting marginal tree species in areas with better microclimate conditions and planting cold-resistant tree species, varieties, and rootstocks according to local conditions. This can greatly reduce the amount of wintering and cold-proof work, and at the same time pay attention to planting shelterbelts and setting up windbreaks to improve the small weather conditions and prevent and mitigate freezing damage.
Improve cold resistance
2 Strengthen cultivation management.
Enhancing the supply of fertilizers and water in the spring, and strengthening the management of cultivation (especially with regard to late-stage management) will help the stocking of nutrients in the tree. Experience proved. Rational application of irrigation and fertilization techniques can promote shoot growth and leaf enlargement, increase photosynthetic efficiency, increase nutrient accumulation, and ensure robust trees.
Timely drainage, late irrigation control. Appropriate application of phosphorus and potassium fertilizer, diligence and deep plowing, can prompt the end of growth of the shoots, is conducive to the organization fully, to extend the accumulation of nutrients, and thus better to carry out cold-resistant exercise.
The summer season is topping, and in addition. The promotion of shoots is childish, winter pruning reduces the evapotranspiration area in winter, and artificial defoliation etc. have a good effect on preventing freezing damage. It is necessary to strengthen the prevention and control of pests and diseases throughout the growing season.
Reduce frost damage
3 Strengthen tree protection.
General trees use "frozen water" and irrigation "spring water" to prevent cold. In order to shelter vulnerable species, there are many ways to protect the tree. The whole plant soil, such as rose, grape, hoop tree, root and neck soil (30 cm high) painted white, the main package grass, wind barriers, north Crescent Crescent and so on.
In order to avoid the cold temperatures coming early, the above prevention measures should be prepared before the winter cold weather arrives. Causes freezing injury. The most fundamental method is still to introduce domestication and breeding work. Such as plum blossoms, black locusts, etc. can be cultivated in open field in Beijing, and multi-branch ash, gray ash, Daphnia magna, white pine, red peony root and large leaf alfalfa, etc., have been grown in Wuhan, Changsha, Hangzhou, Hefei and other open fields for many years, and some It has been flowered.
Because frosted trees are blocked by resinous substances, care for the frozen trees is extremely important. As a result, root absorption, transduction, leaf transpiration, photosynthesis and plant growth are all destroyed. Therefore, when the growth of frozen trees is resumed, the transduction system should be resumed as soon as possible to heal wounds, alleviate water shortages, and increase germination of dormant buds and rapid increase of leaves.
In general, they all showed poor growth and were re-growth trees after freezing. Therefore, we must first strengthen management to ensure the supply of water and fertilizer in the early stages. We can also top-dress fertilizers and top-dressing fertilizers to supplement nutrients.
The tree that is subject to freezing damage should be cut later and lightly cut, and the tree body should be managed. Give the branches a certain period of recovery, the department can be cut off in order to facilitate the healing of wounds. Do not rush to prune when you don't see the frozen area for a while. The timely treatment of wounds caused by freezing should be sprayed with white paint to prevent and control
After the bark is frozen, it will be nailed off or bridging remedy. Pest and leaf protection work. The rooted and frozen trees should be bridged or rooted in time.
What are the main reasons for dry trees?
Called dry tips. Dry shoots are actually full of frozen and dehydrated shoots when they are dead. Dry shoots are called burns, burns, draws, etc. in some places. Young trees are dehydrated, shrivelled, and dried off due to poor wintering. Although the light can send branches, but it is easy to cause tree disorder, can not better expand the crown.
The branches are fully resistant to growth, and the shoots are related to the childlikeness of the shoots. On the contrary, it is easy to dry shoots. There are a variety of reasons for dry shoots, but tests have shown that the dry shoots of young trees after winter are cold and dry, that is, the temperature in winter is low, and the soil temperature decreases for a long time, until the early spring, due to low soil temperature caused Root water absorption is difficult.
Transpiration increased, while the upper part of the ground was higher in temperature and more dry and windy. The water supply is imbalanced, and the branches gradually lose water, the epidermis shrinks, and when it is severe, it finally dries. Therefore, the drawing is actually the result of winter physiological drought and freezing injury. Only by meticulous care of your own nursery stock can bring security to your seedlings.
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