What damage can flowers suffer from high and low temperatures?
Although suitably high temperatures promote the growth of flowers, once the temperature exceeds the maximum that a given flower can tolerate, it will harm that flower, hindering its growth and development, stunting the plant, causing localized scorching of leaves and stems, reducing the number of flowers, and shortening the flowering period. Leaves are the most sensitive to high temperatures; under strong light, leaf temperature can be more than 10°C higher than air temperature, so leaves are most easily damaged when temperatures are high. Flowers are also prone to high-temperature damage during the flowering and fruiting stage.
High temperatures mainly disrupt the balance between photosynthesis and respiration in flowers, making respiration greater than photosynthesis, which leads to weakened plant growth and affects flowering and fruiting. High temperatures can also strengthen transpiration, disrupting the water balance and causing flowers to wilt, dry up and die.
In addition, high temperatures are usually associated with strong light and drought, producing complex physiological disorders.
Low-temperature damage to flowers can be broadly divided into three types: chilling injury, frost injury and freezing injury.
Chilling injury, also called cold damage, refers to the harm caused by low temperatures above 0°C to flowers that prefer warmth. The flowers affected are mainly those native to tropical or subtropical regions. The most common symptoms of chilling injury are discoloration, necrosis and spots on the surface; woody flowers may also show bud blight, tip blight, bark cracking with gum exudation and leaf drop.
When the air temperature or ground surface temperature drops to 0°C, water vapor in the air condenses into white ice crystals - frost. Damage to flowers caused by the appearance of frost is called frost injury. After flowers suffer frost injury, the affected leaves become water-soaked, soften and wilt after the ice thaws, and soon fall off. After the young buds of woody flowers are damaged, they turn black; the floral organs become water-soaked, and the petals discolor and drop.
When the temperature drops further, causing the temperature of the body fluids of certain flowers to fall below freezing point, ice forms in the intercellular spaces and causes freezing injury. Freezing injury often kills herbaceous flowers outright and causes the bark of some woody flowers to split from freezing, branches to die back, or roots to be damaged.
Low-temperature damage to flowers depends not only on external air temperature factors, but also on the ability of the flower variety to resist low temperatures; the same variety has different low-temperature resistance at different developmental stages. Resistance is strongest during the dormant period, intermediate during the vegetative growth period, and weakest during the reproductive stage.