What should watermelon seedlings do at night when the temperature drops?

Watermelon seedlings in the open field when the temperature drops:

There are several key periods to control and adjust the temperature of watermelon seedbed: from the germination of seeds to the emergence of cotyledons (9% cotyledons, the same below), the bed temperature is required to be higher, and generally it is required to be 28~3℃ in sunny days and 25℃ in cloudy days. At this time, if the bed temperature is low, the unearthed time will be prolonged, the seeds will consume more nutrients, and the seedlings will be thin and yellow after emergence. After the cotyledons are unearthed, the temperature should be appropriately reduced, with sunny days of 22~25℃ and cloudy days of 18~2℃ to prevent the hypocotyls from being too long. When the first true leaf of 9% plants is displayed, the bed temperature is gradually increased to 25~27℃. One week before planting, the temperature should be gradually lowered to make the bed temperature drop from 27℃ to about 2℃ until it is consistent with the outside temperature. The control and adjustment of seedbed temperature varies with different seedling facilities. Seedling raising in sunny beds or hotbeds is mainly carried out by uncovering grass curtains and opening and closing vents. The size of the vent is adjusted by uncovering the plastic film covering the seedbed (it can be supported by two bricks or stones, forming a vent in the middle), and the larger the uncovered part, the greater the ventilation volume. Vents in sloping sunny beds and hotbeds are generally located on the south side and at both ends; Vents in arched sunny beds and hotbeds can be located on the side of temporary film pressing that is not fixed when the bed is covered with plastic film. After the cotyledons are unearthed, in order to strengthen the illumination and prolong the illumination time, the straw curtain can be uncovered from 1 am to 4 pm every day, and then covered after 4 pm. As the weather gets warmer, after the real leaves are displayed, they should be ventilated in time to cool down. As the temperature rises, the ventilation openings will be from small to large, and the ventilation time will be from short to long, until all the covers are removed for exercise. In addition, the position of the vent should also be changed in time. Generally, it is changed every 5 days or so to keep the temperature, humidity and gas conditions in the seedbed relatively consistent. Promote melon seedlings to be strong and tidy. The control and adjustment of seedbed temperature in greenhouse and plastic shed mainly depends on the opening and closing of skylight and the uncovering of straw curtain. If it is a heated greenhouse or shed, it can be adjusted by increasing or decreasing the heating temperature. The temperature of the electrothermal hotbed can be controlled by the power of the electrothermal wire and the line spacing during wiring. The higher the power of the heating wire, the faster the temperature rise and the higher the bed temperature; The smaller the line spacing, the faster the temperature rise and the higher the bed temperature. On the contrary, the lower the power of the heating wire, the slower the temperature rise and the lower the bed temperature; The larger the line spacing, the slower the temperature rise and the lower the bed temperature. Adjusting the temperature of the electrothermal hotbed can also be carried out by a temperature controller. Turning the adjusting knob of the temperature controller can change the current intensity to the electric heating wire, thus changing the power of the electric heating wire, so as to achieve the purpose of adjusting the bed temperature.