What is the effect of planting Alnus cremastogyne seedlings in cold weather?

Afforestation of Alnus cremastogyne seedlings in low temperature weather will cause frostbite of trees, and trees are often threatened by natural disasters such as freezing injury, freezing drought, freezing injury, sunburn, wind injury and drought injury during their growth and development. The damage of low temperature to trees is really serious. It can reduce the ornamental value and growth of trees, and it can lead to the death of trees. In Northeast China, low temperature is the greatest threat to trees, and the harm is the most common.

First, the basic types of low temperature injury

Low temperature will not only harm the above-ground or underground tissues and organs of trees, but also change the normal relationship between trees and soil, thus affecting the growth and survival of trees. The low temperature hazards in Northeast China mainly include the following.

Freeze cracking

In winter when the temperature is low and changes greatly, trees are easy to freeze and crack. When the temperature fluctuates greatly, frost cracking is most likely to occur. As the temperature drops below 0℃ and freezes, the water in the xylem cells near the surface of the trunk keeps oozing out, which leads to the drying and shrinkage of the outer xylem. At the same time, due to the poor thermal conductivity of wood, the internal cells still maintain a high temperature and humidity. Therefore, the internal and external shrinkage of wood is uneven, resulting in great tension, which eventually leads to longitudinal cracking of the trunk. The frost crack of trunk often occurs at night, and the crack may increase as the temperature drops.

Frost cracking generally does not directly lead to the death of trees, but due to bark cracking, xylem loses protection, which is easy to cause pests and diseases, especially wood rot fungi, which not only seriously weakens the vitality of trees, but also leads to trunk decay and formation of tree holes.

Generally, the frost cracking of deciduous trees is more serious than that of evergreen trees, such as willow and poplar in Harbin. Frost cracking caused by individual tree planting is more sensitive than forest tree planting. Trees in vigorous growth period are more sensitive than young trees or old trees; Trees growing on poorly drained soil are also fragile.

Frozen drawing

In the cold area of high latitude, when the soil water content is too high, the soil freezes and connects with the root system. Because of the expansion of the frozen volume of water, the root system and the soil rise at the same time. When thawing, the soil is separated from the root system. Under the action of gravity, the soil sinks and the root system of the seedling is exposed, as if it had been pulled out. The occurrence of freezing injury is closely related to the age and root depth of trees. The smaller the tree, the shallower the root system, and the more serious the damage, so the seedlings and newly planted trees are very fragile.

Freezing drought

Freezing drought is a physiological drought caused by soil freezing. In cold areas, because the soil is frozen in winter, it is difficult for the roots of trees to absorb water from the soil, while the branches, buds, leaf scars and leaves of evergreen trees on the ground are still transpiration and constantly losing water. After this situation lasted for a certain period of time, because the water balance was destroyed, cells died, branches dried up, and even the whole plant died. Evergreens are more vulnerable to freezing and drought because of their leaves. After evergreen conifers are damaged, the needles turn completely or gradually brown from the tip down, the terminal buds are fragile and the branchlets are easy to analyze.

winter injury

When the temperature drops below 0℃, the temperature of plants will also drop below zero, and the intercellular space will freeze. In severe cases, it will cause plasma-wall separation, cell membrane or cell wall rupture and death. This low temperature hazard is the biggest threat to the introduction of garden trees, and it is also the key to directly affect the success or failure of introduction. Attention should be paid to the different growth and development conditions of the same plant, and its ability to resist freezing injury is very different. The dormancy period is the strongest, the vegetative growth period is the second, and the reproductive period is the weakest. In addition, it should be noted that the frost resistance of different organs or tissues of the same plant is also different. The ovule is the weakest, carpels are the second, fruits and leaves are the second, and stems are the strongest. But as far as the specific stem position is concerned, the root neck, that is, the junction of stem and root, has the weakest cold resistance. This knowledge is very important for the cold protection and maintenance management measures of our plants.

Frost damage

As the temperature drops sharply to 0℃ or even lower, the saturated water vapor in the air contacts with the surface of the tree and condenses into ice crystals, causing damage to young tissues or organs.

According to the time of frost occurrence and its relationship with tree growth, it can be divided into early frost damage and late frost damage.

Early frost, also known as autumn frost, is harmful to early autumn frost, because cool summer is accompanied by warm autumn, which delays the growing season, and the twigs and buds of trees cannot mature in time, and the degree of lignification is low. Frost has appeared in our province in September, causing disasters.

Late frost, also known as late spring cold, is harmful because the temperature suddenly drops to 0℃ or lower after the trees germinate, which leads to the wilting, blackening and death of the branches and leaves of broad-leaved trees, and the leaves of conifers turn red and fall off. In spring, the low temperature time is delayed, and the growth of new shoots is large, which is the most serious damage.

Second, the main measures to prevent low temperature injury

The ability of trees to tolerate low temperature is affected by many non-human control factors, but we can take reasonable preventive measures within a certain range to reduce the harm of low temperature. There have been some mature empirical measures at home and abroad to prevent and control low-temperature injuries in production, but they must be comprehensively applied and improved on the basis of theoretical analysis and verification without violating genetic laws, in order to achieve practical results. Introduce the following measures for research and production.

1, select cold-resistant tree species or varieties, and implement the principle of suitable site and suitable tree.

This is the fundamental measure to reduce low temperature injury. Native tree species and domesticated exotic tree species or varieties have adapted to the local climate conditions and have strong resistance, so they should be the main tree species for garden planting. Newly introduced tree species must be tested and proved to have strong adaptability and cold resistance before they can be popularized. In areas with good microclimate conditions and no obvious cold air concentration, planting trees in marginal distribution areas can greatly reduce the workload of wintering and cold protection. Generally speaking, tree species sensitive to low temperature should be planted in soil with good ventilation and drainage performance to promote root growth and improve low temperature tolerance.

2. Strengthen cold-resistant cultivation and improve the stress resistance of trees.

Strengthening cultivation management (especially in the late growth stage) is helpful to the storage of nutrients in trees. Experience has proved that strengthening the supply of fertilizer and water in spring and rational application of irrigation and fertilization technology can promote the growth of new shoots and leaves, improve photosynthetic efficiency, increase nutrient accumulation and ensure the health of trees; Controlling irrigation in the later stage, timely drainage, proper application of phosphorus and potassium fertilizer and intensive cultivation can promote the early end of branch growth, which is beneficial to tissue enrichment, prolong nutrient accumulation time, improve lignification degree and increase cold resistance. Correct scarification and fertilization can not only increase the amount of roots, but also promote deep roots and help reduce low temperature damage.

In addition, in summer, pick the heart in time to promote the maturity of branches; Pruning, reducing transpiration area and artificial defoliation in winter have good effects on preventing low temperature injury. At the same time, the prevention and control of pests and diseases must be strengthened throughout the growth period.

3. Improve microclimate conditions and increase the stability of temperature and humidity.

By biological, physical or chemical methods, the harm of low temperature, especially late frost and freezing drought, can be alleviated by improving microclimate conditions, reducing the temperature change of trees, increasing atmospheric humidity, promoting convection between upper and lower air and avoiding the accumulation of cold air. Therefore, according to the frost forecast of the Meteorological Observatory, it is very important to take timely frost prevention measures to protect trees. The specific methods are as follows.

(1) water spraying method

Using artificial rainfall and spraying equipment, spray water on the canopy at dawn when frost will appear to prevent sharp cooling. Because the temperature of water is higher than that of the surrounding air and its heat capacity is large, water will still release heat when it freezes when it is cold. At the same time, spraying water can also improve the air humidity near the surface layer, reduce the radiation loss on the ground, and play the role of cooling and frost prevention.

(2) fumigation method

According to the weather forecast, the smoke was ignited in time in the early morning to form a smoke screen. Smoking can reduce the radiation loss of soil heat, at the same time, smoke particles absorb water, make water vapor condense into liquid to release heat, raise temperature and protect trees. But when there is wind or the temperature drops below -3℃, the effect is not good.

(3) Topdressing outside the roots

Topdressing outside the root can increase the cell concentration and has a good anti-freezing effect.

It is wrong for us to ignore the aftermath after frost and give up the management after frost. Especially for flowering shrubs and fruit trees, in order to minimize the losses caused by disasters, active measures should be taken, such as spraying fertilizer on leaves to restore the vitality of trees.

4. Strengthen tree protection and reduce low temperature hazards.

There are many measures to protect trees. Generally, trees are watered with "frozen water" and "spring water" to prevent colds. Irrigation before freezing, especially for the soil around evergreen trees, is very effective for preventing freezing drought and ensuring adequate water supply in winter. In order to protect the tree species that are easily damaged by freezing, we can also adopt measures such as whole tree (peony), root neck (30cm high), whitewashing, whitewashing, winding and wind protection. Practice has proved that spreading horse manure, humus soil or peat, sawdust and other insulation materials around the trunk to cover the root zone can increase the soil temperature, shorten the soil freezing period, thaw ahead of time, help the roots absorb water and replenish the water lost from branches in time.

In addition, when the trees have germinated and started to spread their branches or flowers, topdressing potassium dihydrogen phosphate outside the roots is beneficial to increase the concentration of cell sap and enhance the ability to resist late frost.

Three, the maintenance and management measures of frozen trees

The maintenance of frozen trees is extremely important, because the transportation organization of frozen trees is blocked by resin, which destroys the absorption and transportation of roots, transpiration of leaves, photosynthesis and tree growth. In order to revive plants damaged by low temperature, appropriate conservation and management measures should be taken.

1, reasonable pruning

It will have harmful side effects on replanting of damaged plants. Therefore, the pruning amount should be strictly controlled, the trees damaged by freezing should be cut late and lightly, and the branches should be given a certain recovery period, and the obvious frozen parts can be cut off in time to facilitate wound healing. For those who can't see the frozen parts temporarily, they should be cut after germination in spring, and the frozen wounds should be sprayed with white agent in time to prevent sunburn.

2. Rational fertilization

Trees generally show poor growth after freezing, so management should be strengthened first to ensure the supply of water and fertilizer in the early stage, or topdressing in advance to supplement nutrients outside the roots to restore the growth of trees as much as possible. However, in practical work, fertilization measures should be flexibly mastered according to tree species and degree of damage.

3. Strengthen the prevention of pests and diseases.

After suffering from low temperature, trees are weak and vulnerable to pests and diseases. Some chemicals can be used in combination with prevention and treatment of hypothermia.

4, wound protection and repair

Trees suffering from low temperature should be trimmed, disinfected and coated in time to speed up wound healing.

For all kinds of low-temperature disasters, we should implement the policy of "prevention first, comprehensive prevention", and pay full attention to it at the beginning of tree species planning and design, such as paying attention to the right place and tree, soil improvement and so on. In the process of planting and maintenance, comprehensive management and tree protection should be strengthened to promote the healthy growth of trees and enhance their resilience.

Therefore, it is the key to ensure the normal growth of trees and give full play to their comprehensive benefits to understand the laws of various low-temperature disasters and take active preventive measures to improve the resilience of trees.