Adaptations that Reduce Water Loss

Water is critical for plants to photosynthesize, metabolize, and maintain cellular structure. So, excessive water loss is a serious problem for plants. What adaptations help plants endure and resist water loss?

Most plants have a waxy cuticle that covers the leaf surface and helps prevent water from evaporating. The specific composition of the cuticle affects its water permeability, so some cuticles reduce water loss better than others.

Tiny openings on the leaf surface, called stomata, allow gas exchange and transpiration. To reduce water loss, plants adjust stomatal density and position on developing leaves in response to water and light availability.

For example, most trees have stomata located mainly on the undersides of leaves to reduce water loss. Also, stomatal density often differs between leaves near the center of the tree and those at the outer edge, helping regulate transpiration under different light conditions.

Water conservation is especially important for desert plants. The desert shrub, brittlebush, traps moisture around its leaves with tiny leaf hairs. These hairs, called trichomes, reflect sunlight and reduce the drying effect of wind.

Other desert plants, such as Opuntia, a type of cactus, store water in fleshy stems during dry periods. These cacti also have modified leaves called spines, which reduce evaporation and help dissipate heat.

Plants in arid environments can also reduce evaporation by taking in carbon dioxide mostly at night for use during the day, when stomata stay closed. This process is called crassulacean acid metabolism, or CAM.

Specific leaf architectures may also help reduce water loss. Small or narrow leaves reduce evaporative surface area. Grasses also evolved rolled or folded leaves, which lowers the exposed surface area and reduces evaporation.