BIO120H1 Lecture Notes - Lecture 17: Sclerophyll, Volumetric Heat Capacity, Larix Laricina

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12 Jul 2017
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BIO120: Physiological Ecology of Plants (Lecture 17)
Main Themes in Plant Physical Ecology
-stresses on plants are especially challenging because plants can’t evade stress by moving
-plants solve problems by growth and development, not behaviour, carbon balance
central
-tradeoffs on photosynthesis: compromises involving 3 necessities (light, temperature,
water)
-adaptations to an extreme habitat: deserts
-adaptations to an extreme lifestyle: epiphytes
-sclerophylly: paradox
Keeping Cool While Conserving Water
-desert: plant roots in dry matrix of sandy soil
-palo verde: green stick”, common shrubby species
photosynthetic bark on trunks and branches, can grow without incurring heat load and
water loss through leaves
microphylly: highly reduced leaves, fairly thick (thermal inertia), don’t heat up much
beyond air around them
-mesquite: more common shrub, doesn’t have photosynthetic bark, greatly reduced leaves
keep plant from overheating
-extreme microphylly: leaves dispensed with entirely
e.g. prickly pear: expanded stems, no leaves, leaves modified into thorns that protect
plants from animals that would like to get at pads (full of water)
-cacti: extensive but shallow roots
harvest rainfall
-episodic patterns of H2O availability: Rillito River, Arizona
Saguaro Cactus
-adapted to episodic rains
-grows to 15m, 200 years old, 5+ tonnes (wet weight)
-extensive, shallow roots
-accordion-pleated trunk allows expansion
-can absorb 800L of water from one storm, use it gradually for growth
-downside of being succulent: can’t grow very fast, even in optimal conditions (no
leaves)
Stress-Evading Behaviour
-deciduous habit: dropping leaves during dry or cold seasons can reduce water stress and
tissue damage
Evergreen
-most important groups of land plants are angiosperms and conifers
-loosely, “evergreen” is synonym for “conifer”
-some conifers are not evergreen, many evergreens are not conifers (especially in wet
tropics)
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