Geography – Vegetation and soils in arid environments | e-Consult

Plants in hot arid and semi-arid environments face significant challenges, primarily water scarcity and extreme temperatures. To survive, they have evolved a range of remarkable adaptations. These adaptations can be broadly categorized into those related to water conservation and those related to temperature regulation.

Water Conservation Adaptations:

• Reduced Leaf Surface Area: Many plants have small leaves, spines, or no leaves at all (e.g., cacti). This reduces the surface area exposed to the sun, minimizing transpiration.
• Thick, Waxy Cuticle: A thick, waxy cuticle on leaves and stems reduces water loss through evaporation.
• Succulence: Succulent plants (e.g., cacti, aloe) store water in their stems, leaves, or roots. This provides a reservoir of water during dry periods.
• Deep Roots: Some plants have very deep taproots that reach underground water sources. Others have shallow, widespread root systems to quickly absorb surface water after rainfall.
• Reduced Stomata: Stomata (pores for gas exchange) are often sunken or protected by hairs to reduce water loss. They may also be closed during the hottest part of the day.
• CAM Photosynthesis: Crassulacean Acid Metabolism (CAM) is a photosynthetic pathway where stomata open at night to take in CO2, reducing water loss during the day. CO2 is stored as an acid and then used for photosynthesis during the day when stomata are closed.

Temperature Regulation Adaptations:

• Light Colour: Light-coloured leaves and stems reflect sunlight, reducing heat absorption.
• Hairy Leaves: Hairs on leaves create a layer of insulation, reducing heat absorption and transpiration.
• Vertical Orientation: Some plants have a vertical orientation to minimize exposure to the intense midday sun.

Examples of plants exhibiting these adaptations include cacti (succulence, spines, CAM photosynthesis), xerophytic shrubs (reduced leaves, thick cuticle), and grasses with deep roots.