Plant response to high temperatures
Evaporative cooling: exposure to heat and light causes the stomata of the plant to open; this allows the water inside to evaporate. By evaporating this water the plants internal temperature is reduced – however the plant runs the risk of dehydration.
Turgor response: (wilting) some plants respond by altering the turgor pressure, causing the leaves to wilt, which allows them to reduce the surface area of the leaves exposed to the sun.
Leaf orientation: to overcome the problems of overheating and excessive water loss some plants are able to orientate their leaves such that they hang vertically, reducing the surface area exposed to the hot sun during the midday. Eucalypts can also regulate the times of the stomata opening and closing.
Leaf fall: many trees lose their leaves during the cold winter months, however eucalypts are evergreen and drop leaves during hot summer months in order to reduce water loss and reduce the risk of excessive transpiration.
Re-seeding in fire: some plants have developed a system in which, if they are exposed to extreme heat – they will resprout or reseed. Eucalypts have buds underneath their bark, which protects them from the fire, which will then resprout. Some plants have lignotubers, which are underground and sprout new growth after a fire. Some plants release large amounts of seeds when exposed to extreme heat (banksias rely on this in order to survive)
Thermogenic plants: some plants are able to heat up by increasing their metabolic rate when the ambient temperature drops (the bud of a sacred lotus)
Plant responses to cold temperatures
Organic anti-freeze: often the water between cells that freezes and poses the greatest risk of damage to the plant. Some plants produce an organic compound that acts as antifreeze, which reduces the temperature at which the cytoplasm freezes. (arctic environments)
Dormancy: deciduous trees lose their leaves in winter and enter a stage of dormancy which allows them to survive extremely low temperatures, water shortages and lower availability of sunlight. To survive long periods of low temperatures some plans may produce seeds or spores, or the above ground section of the plant may die off, whilst the below ground remains dormant ready to grow again in warmer weather.
Vernalisation: some plants flower in response to cold temperatures (tulips)
Many responses of plants to temperature change are the result of chemical concentrations changing within the plant – due to temperature or light changes. Responding to temperature change and the regulation of internal temperature is important not only for the individual plant, but for the continuation of the species.