desert plant adaptations

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powerpoint presentation 10/24/07 * environment growing deserts 10/24/07 * desert plant adaptations environmental stresses for desert plants: 1. long periods of drought; unpredictable precipitation 2. high soil and leaf temperatures 3. saline soils plants use anatomical, physiological and life history mechanisms for coping with harsh desert environments 10/24/07 * 1. drought tolerators 1a. evergreen shrubs  “true xerophytes”  high root-to-shoot ratio: take up a lot of water, transpire less. cost: low maximum growth rates  creosote bush is prime example extensive rooting system helps collect moisture from large soil volume withstands very low water potentials high rates of photosynthesis at high temperatures sheds some leaves in extreme drought flowers opportunistically 10/24/07 * jojoba is another drought tolerator can alter leaf size and color (pubescence) depending on season of growth leaf angle can respond to diurnal changes in sun angle 10/24/07 * plants cool by evapotranspiration when water is available …

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agave basal rosette of succulent leaves flowers once, then dies (monocarpic, semelparous) cam photosynthesis 10/24/07 * cam-idling: when conditions are extremely arid, cam plants leave their stomata closed night and day. oxygen given off in photosynthesis is used for respiration and co2 given off in respiration is used for photosynthesis. cam photosynthesis used by many succulent species 10/24/07 * 2. drought avoiders 2a. drought deciduous shrubs  leaves not drought tolerant but inexpensive to produce  high maximum photosynthetic rates  limited photosynthetic period  may have carbohydrate storage for rapid manufacture of new leaves when conditions become favorable 10/24/07 * ocotillo is drought-deciduous 4-5 leaf crops/year leaf-out after rain stems photosynthesize very shallow roots 10/24/07 * blue paloverde is drought-deciduous photosynthetic stems microphyllous leaves one crop of leaves/year thorns 10/24/07 * 2. drought avoiders 2b. phreatophytes  deep root systems tap into capillary fringe above water table seeds of …

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ts rosettes initially for warmth; elongate later solar tracking of leaves (heliotropism) to maximize light collection during the short wet period, which is the only growing season summer annuals seeds germinate after heavier rains in summer may be c4 plants grow rapidly away from soil surface high photosynthetic rates on bright days seeds must withstand herbivory; high diversity of annuals correlates with rodent diversity! 10/24/07 * 3. halophytes  salt tolerant plants: saltbush, greasewood, saltgrass, and many others salt secreting glands on leaves of some species  osmoregulation: organic acids and soluble carbohydrates create a high solute concentration in their cells. why?  some think that cam evolved first in response to salinity palisade tissue hypodermis thick-walled fibers protect midvein four-wing saltbush salt-secreting glands

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powerpoint presentation 10/24/07 * environment growing deserts 10/24/07 * desert plant adaptations environmental stresses for desert plants: 1. long periods of drought; unpredictable precipitation 2. high soil and leaf temperatures 3. saline soils plants use anatomical, physiological and life history mechanisms for coping with harsh desert environments 10/24/07 * 1. drought tolerators 1a. evergreen shrubs  “true xerophytes”  high root-to-shoot ratio: take up a lot of water, transpire less. cost: low maximum growth rates  creosote bush is prime example extensive rooting system helps collect moisture from large soil volume withstands very low water potentials high rates of photosynthesis at high temperatures sheds some leaves in extreme drought flowers opportunistically 10/24/07 * jojoba ...

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