Lecture 14: Plants in arid environments Flashcards
Desert examples:
- Mohave
- Arizona
- Sahara
- Atacama
Water supply to deserts varies…
- varies over time
- – seasonal (reg rainfall at particular time of year)
- – occasional
- varies with topography
- varies in distribution in the soil profile (rainfall accumulates in riverbed or depressions before draining several metres to stable water table)
more water needed at ____ temperatures because of increased ______
higher
evapotranspiration
water potential =
- the work required to raise bound water to the level of pure water
- pure water = 0WP
- wp in soils and plants is therefore negative
plant water potential =
- osmotic potential
- turgor pressure in plant cell
- matric potential
- – osmotic dominates in plant cells
soil water potential =
- osmotic potential
- gravitational potential
- matric potential
- matric potential most important in soils
dry air water potential =
approx -100 MPa
water potential gradient drawing water from soil to plant to air
soil around -0.6, as you move through plant centre to tips wp decreases (-0.9 to -4 in day) this to air is mass difference (dry air -100MPa)
plant adaptions to low water supply
- avoidance
- – short term acclimation to water deficit –> using stomatal control of water loss
leaves are warmer than the air temperature, heating of leaves drives
transpiration by increase wp gradient
___ Are key in controlling water loss
stomata
gradual drop of water potential of leaves, roots and soil
wiggly graph.
- as soil grad drops across seven days
- in day leaf and root drops and comes back up
- leaf lower than root
- at night all three come back together
- as soil wp decreases, leaf must get lower in the day to draw water up
limit water loss from leaves: (i.e. in desert plants)
- cuticle helps keep water
- hide stomata,
- i.e in a crypt w hairs or just sunken
- reduce photosynthetic rate as a cost
Desert life and CAM metabolism
- prevent water loss
- photosynthesise in day, carbon exchange at night (take in CO2 at night)
- cell becomes more acidic at night, less acidic in day
- shut stomata in the day
both C3 and CAM plant example
- facultative CAM plant
- Mesembryanthemum crystallinum
- they start as C3 plant, max photosynthesise,
- when dry switches to CAM, prevent water loss but continues to grow
desert plant: morphological adaptions
- store water
- change root morphology
desert plant: two types of adaptions
- physiological
- CAM
- stomata sunken/crypt
- morphological
- store water
- -change root morphology
water storers have ___ roots
shallow
water storage = & example
- stem water storage
- example Barrel cactus
- no leaves
- high SA:V
- ribbing allows expansion and contraction & increases SA
- waxy cuticle
- CAM metabolism
- large water buffers heat exchange
barrel cacti spines =
- modified leaves
- protects from herbivores
- shade surface
water storage in leaves examples and why is it good
agave and aloe
– increases window in which u can photosynthesise
Nobel 1977: Barrel cactus
- investigated barrel cactus
- plant reacts to unpredictable rainfall
- roots near surface, captures rain, photosynthesises for as long as it then can
- during drying = restricts time of day it photosynthesises (stomata are open)
- low temp optimum for photosynthesis as photosynthesises at night when desert is cold
adaptive roots
- Search deep: spindling deep root (tap root), when finds water it proliferates
- Search widely: spread out root system
- search widely and deeply: BOTH
