Chapter 2 Plant Adaptations to Aridity, Heat, and Salinity

Chapter Outline

Introduction
Enduring Drought
   Water: the essence of life
   Water movement through plants
   Xerophytes
   Ephemerals
   Efficient water uptake
   Minimizing water loss
   Morphological traits
   CAM Photosynthesis
   C4 Photosynthesis
   Developmental adjustments
   Physiological response to dehydration
   Dehydration tolerance
Enduring Excessive Heat
   The thermal environment
   Adaptations that reduce heat gain
   Physiological consequences of high temperatures
   High temperature tolerance
Enduring Saline Soils
   Halophytes defined
   Adaptations that limit ion toxicity
   Water uptake in saline soils

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Study Questions

1. Water moves through plants on its journey from soil to atmosphere. a) Describe the movement of water through a plant. Include the mechanisms by which the water moves. b) Describe hydraulic lift and the circumstances under which it occurs. What are the benefits and costs of hydraulic lift to the plant?

2. Ephemerals are particularly common in the desert. a) Explain how the ephemeral way of life may be of particular value in the desert. b) How is drought deciduousness analogous to emphemeralness?

3. McAuliffe and Burgess categorized the modes of water use by desert plants as intensive exploitation and extensive exploitation. Explain what is meant by these two phrases.

4. Certain morphological characteristics of desert perennials have traditionally been interpreted as adaptive in limiting water loss. However, these specific traits are actually somewhat rare. a) Describe three characteristics of desert perennials that are traditionally interpreted as adaptations to limit water loss. b) Gibson and others have argued that there may be good reason such traits are actually rare. Explain their reasoning.

5. Excessive heating of plants can accelerate dehydration and result in direct tissue damage. a) Describe desert plant characteristics that help encourage heat loss and reduced heat gain. b) How is it that tissue heating accelerates water loss? c) Describe how high temperatures can injure plants and how the most heat resistant plants may prevent injury.

6. Cacti are well adapted to the desert environment with a host of adaptations that allow efficient water uptake and limited water loss. a) Describe the adaptations, both morphological and physiological, that allow cacti to survive the desert environment. Do not just list the adaptations, describe how each benefits the cactus. b) Would you consider cacti as drought escapers, avoiders, or tolerators? You may want to begin your explanation by defining the three categories.

7. Some desert plants such as the saltbushes and many desert grasses utilize the C₄ pathway. a) Describe the C₄ pathway and explain how it benefits plants. b) Explain why C₄ plants are particularly common in the Chihuahuan Desert.

8. Even though they may be moist, saline soils can be a problem for plants. a) Describe how excessive soil salts can harm a plant. b) How do halophytes physiologically survive in highly saline soils? c) Moist, highly-saline soils and dry soils impose similar physiologically stresses on plants. How so?

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