Lectures%208%20Low%20water%20availability

Lectures%208%20Low%20water%20availability - Quiz Quiz...

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Unformatted text preview: Quiz Quiz Adaptations to water Adaptations to water Too little Too much Water availability Water availability Desert plants Desert plants Dessication avoidance Dessication tolerance Desert annuals, drought­deciduous, phreatophytes Succulents Evergreens Resurrection plants Intermediates Dessication avoidance: annuals Dessication avoidance: annuals Species with little or no physiological tolerance of drought. Annuals (ephemerals) have water­soluble germination inhibitors so they germinate only when soil water is great enough to leach out inhibitors. Short life cycle (6 weeks or less) High PS, high LA, high transpiration rates Examples: Annuals Annuals Desert ephemerals Desert ephemerals Camissonia boothii Completes life cycle in > 100 d Plantago insularis (ovata) Completes life cycle in < 60 d Camissonia Plantago Good strategy if it rains more than once Good strategy if it only rains once Desert ephemerals Desert ephemerals Plantago allocates more biomass to reproduction earlier in the season. Camissonia allocates more biomass to production and maintenance of vegetative tissue. Plantago has greater reproductive output in years with no further rainfall. Camissonia has greater reproductive output in years when it rains later in the season. Variability in rainfall supports populations of both species. Dessication avoidance: deciduous Dessication avoidance: deciduous Species with little or no physiological tolerance of drought. Low water potential triggers reduction in leaf area and dormancy. Can lose leaves several times per year High PS and growth under favorable conditions but significant cost to produce new leaves. Example: Fougueria splendens (ocotillo) Ocotillo Ocotillo Drought deciduous species Drought deciduous species Dessication avoidance: Dessication avoidance: phreatophytes Species with little or no physiological tolerance of drought. Extremely deep roots that tap water table High PS and transpiration Need sufficient moisture for seedlings to establish (desert washes) Examples: mesquite, salt cedar Salt cedar Salt cedar Dessication Dessication tolerance:succulents Saguaro cactus Cacti are the best known CAM pathway; high WUE Store water in vacuoles (organic acids, salt dilution). Reserves can extend PS for weeks. Stem succulents Stem succulents Saguaro Saguaro Pleats allow it to expand. Spongy flesh serves as a reservoir for water. No conventional leaves = reduced transpiration. Photosynthesis is performed in the trunk and branches. Spines discourage herbivory, shade the plant, and shield it from drying winds. Waxy skin. Saguaro Saguaro Most vulnerable in seedling stage (nurse plants) Growth is very slow. 1 yr, ¼ inch 15 years, 1 foot 30 years before they flower and produce fruit 50 years, 7 feet 75 years, sprout “arms: 100 years, 25 feet >150 years, 50 feet, 8 tons Dessication Dessication tolerance:succulents Desert prickly pear (Opuntia phaeacantha) Leaves reduced to spines; stems conduct PS. Shallow root system can respond to light rains. Slow growth but long­ lived (hundreds of years) Most not frost­resistant (distribution related to isolines of average hours frost) Prickly pear is exception (can be found in IN) Leaf succulents Leaf succulents Dessication tolerance:evergreens Dessication tolerance:evergreens 1­3 m tall Widely spaced Leaves adapted for extremely dry conditions. Deeproots Retain leaves Defended against herbivory Xeromorphic leaves Xeromorphic leaves 1. 2. 3. 4. 5. 6. Small size (reduced to spines in cacti). Reduced number Waxy cuticle High internal leaf surfance to outer leaf surface Pubescence Vertical orientation Succulence 1. 2. 3. 4. 5. 6. More efficient energy dissipation Prevents dessication Decreases mesophyll resistance Increases boundary layer and regulates light absorptance (T) Reduced heat absorption Storage Adaptations to temperature Adaptations to temperature Adaptations to heat Adaptations to heat Evaporation (580 cal energy used to evaporate 1 g water at 28 C). Small, dissected and lobed leaves lose heat more effectively Exposed leaves lose heat more effectively Fewer leaves, leaf dropping Heliotropism Reflectivity Adaptations to heat Adaptations to heat Atriplex hymenelytra Desert Holly Adaptations to cold Adaptations to cold Height? Leaf density? Heliotropism? Leaf angle? Reflectivity? Leaf properties Leaf properties Incident radiation (heat and cold) Reflection (wax layers, white hairs, salt crystals) Leaf angle Heliotropism (arctic & alpine plants move continually to face the sun; shape of flowers directs radiation to ovary to maximize development and attract pollinators Kjellberg et al. 1982) Leaf size Heat retention Heat retention Alpine plants can raise leaf temperature by keeping leaves closely packed and close to the ground (rosettes) Non­reflective leaf hairs can increase boundary layer thickness. Celmisia longifolia can maintain 27 °C, 99% humidity vs. 10 °C, 50% humidity, 4 m s­1 windspeed. Club moss in tundra Club moss in tundra Leaves with dark pigment absorb heat Silena acaulis Cushion plants Andes Adaptation to cold Adaptation to cold Freezing kills plant cells by damaging membranes/organelles and dehydration. Supercooling Extracellular ice formation ­40 °C; oak, elm, maple, beech, hickory, apple, pear, peach Coincides with altitude of timberline Water is withdrawn from cells and freezes in extracellular spaces. Requires slow acclimation Dormancy Dormancy “Adaptive mechanism whereby plants avoid periods of unfavorable weather or periods of high competition.” Buds Seed germination Seasonal (stop, start) Photoperiod Temperature Cold requirement Sumorization ...
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This note was uploaded on 02/19/2011 for the course BTNY 211 taught by Professor Gibson during the Spring '11 term at Purdue.

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