Transport of water in plants

Cacti are typical xerophytes.

Xerophytes

Plants are put into categories according to there adaptation to water availability.

• Hydrophytic- adapted to aquatic or semi-aquatic conditions. A classic example is Potamogetum, a genus of pond weeds where the stems have large air species in order to raise the leaves as near to the surface of the water as possible. Rice is semi-aquatic.

• Mesophytic- Middle water conditions, typical temperate terrestrial conditions.

• Xerophytic- adapted to conditions of low water availability. This includes plants from a variety of conditions, including sand dunes, high alpine habitats and equatorial deserts. Sorghum is a xerophytic plant that was looked at in Module 2.

Mesophytic plants are not especially adapted to low water/high temperatures. If water is lost (by transpiration) faster than it is lost then wilting results. The cells become flaccid. The stomata close as a result of the guard cells becoming flaccid. This helps to prevent further water loss. As the leaves fold up as the plant wilts it also helps to remove some of the leaf surfaces from the direct effects of the sun.

Transpiration itself helps to keep plants cool by the evaporation of water, in a similar way to the way sweating helps to cool down the skin of mammals.

Most mesophytic plants maintain a temperature slightly higher than the air temperature if the air temperature is below 25*C and lower than the air temperature if it rises above 30*C.

Click on next to start the slide show on xerophytes.