Prevention of high temperature injury of seedlings
Factors Affecting High Temperature Damage The degree of damage to trees caused by high temperatures varies according to the species, age, organ and tissue condition, and is influenced by environmental conditions and cultivation practices. Different trees or different trees of the same species have different sensitivities to high temperatures. For example, trunks of P. platyphylla, cherry, eucalyptus, paulownia, and eucalyptus are susceptible to flaring; leaves of red maple, silver alum, and camellia are susceptible to leaf char. Saplings of the same tree species are thin and young and vulnerable to high temperatures. In the same tree, new shoots are most vulnerable to high temperatures. When the climate is dry and the soil moisture is insufficient, the water absorbed by the root system cannot compensate for the loss of transpiration, which will aggravate the burn of the leaves; the trees grown near the hard paving surface are affected by the intense radiant heat and impervious paving materials. The most prone to skin coke and sunburn. For example, near the intersection of cement paved roads and streets, the plants that cause sunburn are clearly higher than the trees along the streets, lawns and country roads. Sudden changes in the growing environment of the trees and damage to the roots can also cause irritation. For example, the newly planted saplings are exposed to hot sunlight before the self-shade canopy is formed, or the northern species are moved south to high-temperature areas, or the crown plants, trunks and large branches suddenly lose their shade protection and are accustomed to dense clusters. Trees that are shaded sideways are prone to sunburn when they are transplanted to open spaces or severely exposed to intense sun exposure. When a tree is seriously attacked by aphids and other sucking insects, it can often make the coke worse. In addition, the lack of potassium in trees can accelerate the loss of water in leaves and are prone to sunburn. Prevention of high temperature hazards According to the law of high temperature damage to trees, the following measures can be taken: 1. Select strong tree species. Select high temperature resistant and resistant tree species or planting varieties. The pre-planting resistance exercise strengthens the resistance exercise before the trees are transplanted, such as gradually opening the tree canopy and shade tree to adapt to the new environment. To maintain the roots of transplanted plants with complete roots as far as possible to retain a relatively complete root system, so that the soil and the root system close, so that black pine seedlings can absorb water smoothly. 2. The trunk is painted white. Whitening the trunk can reflect sunlight and ease the dramatic changes in bark temperature, which has a significant effect on reducing sunburn and freezing injury. Tu Bai is mostly carried out in the late autumn and early winter, and some areas are also in the summer. The formulation of the whitening agent is: water 72%, quicklime 22%, lime sulfur and 3% each, and evenly mix and brush. According to the Hebei Changli Fruit Tree Institute (1975), in the late summer apple tree trunks painted white, the temperature difference between day and night at direct sunlight was 18C, and the negative surface was only 8.5C. The maximum temperatures were 23.5C and 14C, respectively, with a difference of 9.5C. After coating with white, the effect was significant. The total amount of trunk cooling was 21.6C in the south, 3.6C in the east, 13.5C in the west, and 3.8C in the north. The highest temperature in the south fell to 14.5C, and it was close to the north. This is enough to show that whitening can significantly ease the temperature changes and can prevent sunburn. In addition, trunk binding, mud coating and earthing can also prevent sunburn. 3. Strengthen the scientific management of the canopy. In plastic trimming, the height of the main trunk can be appropriately reduced, leaving more auxiliary branches and avoiding branches, dry baldness and bareness. In the case of heading or heavy shearing, it should be carried out in 2 to 3 years, avoiding too much light transmission at a time, otherwise corresponding protective measures should be taken. When there is a need to increase the height of the trunk, some weak branches should be systematically reserved for self-shadowing, and they will be repaired in batches later. If necessary, water can be sprayed on the canopy or anti-transpiration agent. 4. Strengthen comprehensive management, promote root growth, improve tree condition, and increase resistance. In the growing season, we must especially prevent drought, avoid leaf damage caused by various causes, prevent and control pests and diseases, and reasonably apply chemical fertilizers, especially potassium fertilizers. Strengthen the management of damaged trees. For trees that have already suffered damage, pruning should be carried out prudently to remove the dead foliage. The skin coke area should be trimmed, disinfected, painted, and bridged or patched if necessary. Timely irrigation and rational fertilization, especially the addition of potash fertilizer, help restore the viability of trees. 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