Salt, Water and Gas Regulation
What is a xerophyte?
A xerophyte is a plant which is adapted to live in dry, arid conditions. The different types of adaptations which xerophytes have are categorised as being structural (physical) or physiological (functional processes).
What are the structural adaptations of xerophytes?
Thick, waxy cuticle
By being impermeable to water, this prevents evaporation and water loss from occurring. It also stops uncontrolled evaporation through leaf cells (epidermal cells, specifically).
Small leaf surface area
Fewer stomata are present due to smaller leaf surface area, leading to reduced water loss; there is less surface area for evaporation to occur. The smaller surface area of the leaf is exposed to the drying effects of wind, reducing evaporation and reducing water loss.
Sunken stomata, rolled leaves with stomata on the inside
Having stomata in sunken pits within rolled leaves prevents water loss by increasing the relative humidity in the vicinity of each stoma, decreasing the concentration gradient and reducing evaporation/diffusion. This creates a moist micro-climate.
Reduced number of leaves
Having a reduced number of leaves reduces the total surface area available for water loss to occur, for example cacti and conifers.
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What are the physiological adaptations of xerophytes?
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Stomata opening at night (reverse stomatal rhythm)
This assists in reducing water loss as the stomata are closed during the hottest part of the day which acts to reduce water loss by transpiration and evaporation. Carbon dioxide intake occurs at night and then it is stored for use in photosynthesis during the day.
Storage of water in succulent tissues
Plants store water in cells in fleshy stems or leaves instead of transpiring it out of the plant. This is usually for use during dry periods, and it acts to reduce water loss from occurring.