减少水分流失的适应作用

Water is critical for plants to photosynthesize, metabolize, and maintain cellular structure. Hence, excessive loss of water is problematic for plants. What adaptations have evolved to allow plants to endure and resist water loss?

Most plants have a waxy cuticle that covers the leaf surface, preventing the evaporation of water. The specific composition of the cuticle influences its water 

Tiny openings on the surface, called stomata, facilitate gas exchange and transpiration. To minimize water loss, plants adjust the density and location of stomata on developing leaves in response to water and light availability. 

In most deciduous trees, for instance, stomata are located on the undersides of leaves. Additionally, the density of stomata is higher on leaves near the center of the tree and lower on leaves at its periphery.

Conservation of water is especially critical for desert-dwelling plants. The desert shrub brittlebush traps water around its leaves with tiny leaf hairs. These hairs, called trichomes, deflect the sun and diminish the drying effect of wind.

Other desert plants, such as Opuntia, store water in their fleshy stems to protect against drought. In addition, cacti have modified leaves, called spines, that reduce evaporation and dissipate heat.

Plants in arid environments can also reduce evaporation by only taking in carbon dioxide at night. During the day, the stomata remain closed. This process is called crassulacean acid metabolism, or CAM.

Specific leaf architectures may also help reduce water loss. Small or fine leaves reduce evaporation. Grasses acquired rolled or folded leaf structures that likewise reduce surface area and, therefore, evaporation.