Drought tolerance with high water potential OVERHEAD 1 maintenance of water uptake Increase rooting depth or extent mesquite 2 reduction of water loss i close stomata most all plants do this ii hairs sunken stomata waxy cuticle iii reduce absorbed ID: 76616
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DROUGHT RESISTANCE MECHANISMS Balance uptake with loss or tolerate dessication Drought Avoidance Rapid phenological development and plasticity Desert winter & summer annuals - population survives as seed High mortality and high natality of survivors. Drought tolerance with high water potential ( OVERHEAD) 1) maintenance of water uptake Increase rooting depth or extent (mesquite) 2) reduction of water loss i) close stomata - most all plants do this ii) hairs, sunken stomata, waxy cuticle iii) reduce absorbed radiation - leaf orientation (Jojoba) , reflective hairs, waxes iv) decrease leaf area (ocotillo - drought deciduous) 3) storage, cactuses/succulents Drought tolerance at low water potential 1) Maintenance of cell hydrostatic pressure (turgor pressure) I) solute accumulation in cells , osmotic regulation , ii) increase in cell wall elasticity (balloon - box analogy) 2) drought-tolerant tissues Creosote bush resists cavitations in xylem and has leaves that will continue metabilism even at very low leaf water status Examples of animals Kenneth Nagy Ð ÒHow do desert animals get enough water?Ó 1) Desert animals conserve water 2) Desert animals are effective at finding and consuming water 3) Desert animals avoid stressful season or find suitably moist microsites. Water conservation I) Desert animals prevent excessive water loss Evaporative water loss accounts for about 50% of water loss, and much comes from eyes. Thick cuticle of desert invertebrates like scorpionsÉ Lowest water loss rates for vertebrates are found in some desert mamals Kangaroo rats, camels Ð dry feces + extremely concentrated urine Mechanisms: A) extracting more O2 from inhaled air, B) Cooling exhaled air, C) Reduced metabolism (less breathing..) II) Water storage Desert tortoises store water as dilute urine and readsorb. Water Gain I) Energy metabolism (unlikely an important mechanism except in maybe kangaroo rats) II) Osmotic uptake thru skin (desert amphibians that sit in liquid water) ENDED here for lecture (2000) III) Drinking liquid water IV) Taking up water vapor from air V) eating moist food III) Population dynamics