Xerophytes & Transpiration Factors

xerophytes A plant adapted to live in dry conditions They have a range of adaptations to reduce the loss of water vapour by transpiration. A plant adapted for survival in soil with a limited supply of water. Capillary water is absent from the surface horizons of the soil for extended periods of time. Some xerophytes, such as cacti and succulents, store water in their stems to survive extended periods of extreme drought. Cactus spines are modified leaves which provide protection against browsing animals. Because photosynthetic leaves are absent from most mature cactus plants, photosynthesis occurs within chloroplasts in the stems. In addition, cactus plants typically inhabit well-drained alluvial slopes and have shallow, surface roots to absorb the scant rainfall.

xerophytes Leaves Small to reduce the surface area Thick to reduce surface area: volumes ratio

xerophytes Sunken Stomata

xerophytes Stomata Set deep inside the leaf so that they are at the base of a depression full of water vapour Some plants open their stomata at night to store and absorb CO2

xerophyte Thick waxy cuticles reduce water loss through the epidermis

Xerophytes Rolling up of leaves Lower surface faces inside and traps humid air next to the stomata Varies with conditions

Xerophytes Leaf hairs Trap damp air Reduces air movement Cut down transpiration

Factors Affecting Transpiration

Potometer Measures the water absorption Estimate the rate of transpiration Air/water tight Water transpired Water entering to xylem

Factors affecting rate of transpiration Light intensity: Affects the opening and closing of the stomata ROT Indirect effect

Factors affecting rate of transpiration Humidity: Humid atmosphere Contains a lot of H2O molecules Reduction of the water potential gradient between the air spaces and atmosphere ROT decreases Low humidity increases ROT

Factors affecting rate of transpiration Temperature: Temperature kinetic energy Rate of diffusion through the stomata pores Air is able to hold more water molecules at higher temperatures ROT

Factors affecting rate of transpiration Wind speed: Still air makes the H2O molecules to accumulate around the stomata pores (leaves) Reduces the H2O potential gradient and slows the ROT Wind disperse H2O molecules gradient in H2O potential ROT