How do plants minimize water loss? How do they handle soils with high solute potentials?
Plants have adapted to minimize water loss in different ways:
- Some have developed annual life cycles. This means that the plants avoid the times of year when the environment is harsh, and water loss would be the greatest. Organisms may only grow and reproduce in rain seasons, when conditions are good.
- Drought-deciduous plants become dormant in hot seasons by simply dropping their leaves. Because leaves are the source of transpiration, less water is lost when the plant gets rid of them. The plant becomes sealed, and water evaporation slows.
- Some plants have simply developed more efficient leaves. Sclerophyllous leaves are smaller and have thicker cuticles which limit water loss through transpiration. Stomata may also be located inside protected pits. Epidermal hairs at the opening to these pits limit water molecules from being released into the environment.
- Actual leaf shape can reduce water loss. Leaf hairs can collect atmospheric water (fog) and also provide shade. Shade decreases the temperature of the leaf and decreases transpiration. Some leaves may also be shaped to direct rain droplets directly to the roots. This ensures that all the water coming into contact with the leaves will be available for absorption at the roots.
- Root structures are also important to combating water stress. For biennials and perennials, it is adventitious to have tap roots that utilize stable water sources deep within the earth. For annuals, shallower roots allows the plant to access rain water closer to the surface without using up energy toward root growth.
- Plants may also perform different photosynthetic pathways to limit water loss. C4 plants photosynthesize more efficiently. CAM plants have the ability to divide the photosynthetic process into light and dark reactions, allowing stomata to be closed during the day. When they open at night, the temperature is cooler and less water is lost.
Plants in areas with high solute potentials, or halophytes, actively absorb the solute so that the concentrations within the cells are greater than external concentration. Water concentration (reverse of solute concentration) therefore becomes lower inside the cells, and this gradient causes water molecules to flow to the plant.