BIOL 4120: Principles of Ecology
Lecture 6: Plant adaptations
to the Environment
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Topics
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6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
Plant photosynthesis to fix carbon
Light influences photosynthesis
Photosynthesis is coupled with water exchange
Water movement through plants
Temperature influences photosynthesis
Carbon allocation
Other photosynthesis pathways
Plants adaptation to different light intensity
Plants adaptation to different temperature
Earth provides highly diverse
environments:
1.5 million known species now
Three common basic functions
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Assimilation: acquire energy and matter from external
environment
Reproduction: to produce new individuals
Response to external stimuli: able to respond to both
physical (light, temperature etc) and biotic (predator etc).
All organisms require energy
• Energy obtained directly from an energy source by a living
organism is called autotrophy (autotroph)
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Plants are autotrophs, primary producers
So are certain bacteria like Thiobacullus ferrooxidans
• Energy obtained indirectly from organic molecules by a living
organism is called heterotrophy (heterotrophy)
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All animals are heterotrophs, secondary producers
Some organisms can be a a mixture like lichens where you have
an alga and a fungus living together
6.1 Photosynthesis (review)
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All life on Earth is carbon based
CO2 was the major form of free carbon
available in past and still is
Only photosynthesis is capable of
converting CO2 into organic molecules
Only plants (some algae, bacteria) are
capable of photosynthesis
All other living organisms obtain their
carbon via assimilation from plants
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Photsynthesis is a biochemical process that uses light to
convert CO2 into a simple sugar such as glucose
• Light of the certain wavelength (PAR) is absorbed by
chlorophyll in the organelle called a chloroplast and
converted via the light reactions into ATP (adenosine trip) and NADPH (reduced nicotinamide adenine dinucleotide
phosphate)
• H2O is split into oxygen and hydrogen
• The oxygen is released as O2
• The hydrogen is linked to CO2 to form a three carbon
organic molecule (3-PGA, phosphoglycolate; C3
photosynthesis). This is carried out by the enzyme
ribulose biphosphate carboxylase- oxygenase (Rubisco)
• The C3 molecules are then converted into carbonhydrates
like glucose via the dark reactions
• This glucose can then be used to produce energy by
respiration in mitochondria or used to produce other
organic compounds (proteins, fatty acids etc).
Photosynthesis
Photosynthetic electron transport
CO2  RuBP  2 3  PGA
C3 cycle (Calvin cycle)
One major drawback of C3
pathway:
Rubisco can catalyze both
carbonxylation
CO2  RuBP  2 3  PGA
And RuBP oxygenation
O2  RuBP  CO2
Reduce the efficiency of
photosynthesis.
C3 plant: trees, forbs,
some grasses
Photosynthesis
6CO2  6H 2O  C6 H12O6  6O2
Cellular respiration
C6 H12O6  6O2  6CO2  6H 2O  ATP
Net photosynthesis = (Gross) Photosynthesis - Respiration
6.2 Light influences photosynthesis
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PAR: photosynthetically active
radiation
Obviously the amount of
light received by a plant
will affect the light
reactions of photosynthesis
Light Compensation Point
• As light declines, it
eventually reaches a
point where respiration
is equal to
photosynthesis
Light Saturation Point
• As light increases, it
reaches a point where
all chloroplasts are
working at a maximum
rate
Photoinhibition
• In some circumstances,
excess light can result in
“overloading” and even
damage to chlorophyll
by bleaching
6.3 Photosynthesis involves exchanges between
atmosphere and plant
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Photosynthesis takes place in
plants in specialized cells in the
mesophyll
Needs movement of CO2 and O2
between cells and atmosphere
Diffuses via stomata in land
plants (CO2, 370ppm to
150ppm)
• Stomata close when
photosynthesis is reduced
and keeps up partial
pressure of CO2
Stomata also control
transpiration
• Reduces water loss
• Minimizing water needs from
soil (dry area)
• Ratio of carbon fixed to water
lost is the water-use
efficiency
6.4 Water moves from soil to plant to atmosphere
Water potential
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Water moving between soil and plants
flows down a water potential gradient.
Water potential ( ) is the capacity of
water to do work, potential energy of
water relative to pure water in
reference conditions
• Pure Water
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= 0.
 in nature generally negative.
 due to dissolved
  solute measures the reduction in
substances.
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Water moves from soil to plant to atmosphere
Water potential of compartment of soil-plant-atmosphere
•

w
=

p
+
o
+

m
• Hydrostatic pressure or physical pressure.
• Osmotic potential: tendency to attract water
molecule from areas of high concentrations
to low. This is the major component of total
leaf and root water potentials.
• Matric potential: tendency to adhere to
surfaces, such as container walls. Clay soils
have high matric potentials.
Net photosynthesis and leaf water potential
Declines caused by closure of stomata
Water use efficiency
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Trade-off
• To carry out photosynthesis, plants
must open up the stomata to get CO2;
• Transpiration loss of water to
atmosphere.
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WUE: ratio of carbon fixed
(photosynthesis) per unit of water
lost (transpiration)
Photosynthesis of aquatic plants
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Unique features
• Lack of stomata
• CO2 reacts with H2O first to produce
biocarbonate.
• Convert biocarbonate to CO2
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Transport HCO3- to leaf then convert to CO2
Excretion of the enzyme into adjacent
waters and subsequent uptake of converted
CO2 across the membrane.
6.6 Plant temperatures reflects their energy balance
with the surrounding environment
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Different responses of
photosynthesis and
respiration to temperature;
Three basic Temperature
points
• Min T, max T and optimal T
Plant leaf temperatures reflects their energy
balance with the surrounding environment
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Different shapes of leaves
influence the convection of
heat.
Temperature is important to a plants
• Photosynthesis increases as the
temperature increases
 Energy balance (<5% used in
photosynthesis)
 Radiation not used increases
internal leaf temperature
significantly
 Some heat can be lost by
convection (leaf sizes and shapes)
 Some heat can be lost by
radiation (leaf color)
• Respiration increases as the
temperature increases
• Damage to enzymes etc increases
with temperature
• Water loss increases with temperature
 Evaporation of water helps to
keep the temperature lower
 Thus relative humidity and
available water is important
6.7 Carbon gained in photosynthesis is allocated to
production of plant tissues
Carbon allocation is an
important issue and has not
been well studied.
Difficult to measure,
especially below ground.
Allocation to different parts
has major influences on
survival, growth, and
reproduction.
Leaf: photosynthesis
Stem: support
Root: uptake of nutrient and
water
Flower and seed: reproduc.
Allocation and T, PPT
Hui & Jackson 2006
Plant adaptations and trade-offs
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Environmental factors are interdependent: light, temperature and
moisture are all linked together.
• In dry area: more radiation, high
temperature, low relative humidity, high
water demand smaller leaves, more
roots
• Trade-offs: more carbon allocated to
below-ground.
6.8 Species of Plants are adapted
to light conditions
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Plants adapted to a shady
environment
• Lower levels of rubisco
• Higher levels of
chlorophyll (increase
ability to capture light, as
light is limiting)
• low light compensation
and saturation lights
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Red oak
leaves at
top and
bottom of
canopy
Plants adapted to a full sun
environment
• Higher levels of rubisco
• Lower levels of chlorophyll
• Because leaf structure is
limiting
• High compensation and
saturation lights
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Changes in leaf structure
evolve
Light also affects whether a plant allocates to
leaves or to roots
Change of allocation to leaf of
broadleaved peppermint.
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Shade tolerant (shadeadapted) species
• Plant species adapted to
low-light environments
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Shade intolerant (sunadapted) species
• Plant species adapted to
high-light environments
Shade tolerance and intolerance
Shade tolerance
Shade intolerance
Seedling
survival and
growth of
two tree
species
over a year
Remember that land plants are not
the only plants on Earth
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Shade
adaptation
also occurs
in algae
Greed algae and diatoms
also depend on sunlight for
photosynthesis.
6.9 Other photosynthesis
pathways: adaptation to
water and temperature
conditions
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To increase water use
efficiency in a warm dry
environment, plants have
modified process of
photosynthesis
C3
• Normal in mesophyll
with rubisco
C4
• Warm dry environment
• Additional step in
fixation of CO2 in the
bundle sheath
• Phosphoenolpyruvate
synthase (PEP) does
initial fixation into
Malate and aspartate
• Malate and aspartate
are transported to
bundle sheath as an
intermediate molecule
• Rubisco and CO2
convert them to
glucose
C4 pathway
Advantages over C3 pathway
1.
PEP does not interact with O2
(RuBP react with O2 and reduce the
photosynthesis efficiency)
2.
Conversion of malic and aspartic
acids into CO2 within bundle sheath
cell acts to concentrate CO2, create
a much higher CO2 concentration.
C4 plants have a much higher
photosynthetic rate and greater
water-use efficiency.
C4 plants are mostly grasses native to
tropical and subtropical regions and
some shrubs of arid and saline
environments (Crop, corn, sorghum,
sugar cane).
Distribution of C4 grass
Spatial and seasonal
gradient
Number are percentage of total grass species are C4.
CAM pathway
CAM (Crassulacean acid
metabolism) pathway
Hot desert area
Mostly succulents in the
family of Cactaceae
(cacti), Euphorbiaceae
and Crassulaceae)
Similar to C4 pathway
Different times:
Night: open stomata,
convert CO2 to malic
acid using PEP
Day:close stomata, reconvert malic acid to
CO2, C3 cycle.
C3, C4 and CAM
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C4 makes more effective use of CO2
CO2 concentration in bundle cell can be 6X that of
atmosphere and mesophyll cell
As rate limiting aspect of photosynthesis is usually the
availability of CO2, then C4 is more efficient
Also can keep stomata closed longer and therefore better
water use
But needs large amount of extra enzyme (PEP, need more
energy) and there only well adapted to high photosynthesis
environments
In deserts with really low water availability and high
temperature
• Third type – Crassulacean acid pathway – CAM
• CO2 fixed converted to malate by PEP during night and
stored, while stomata are open
• Malate is converted back to CO2 during day and using
photosynthesis, light and rubisco changed into sugar
• High level of water conservation
• Both processes in the mesophyll cells
Plants need to make serious evolutionary adaptations to
water availability
As water availability
decreases, plants
allocate more carbon to
the production of roots
relative to leaves. The
increased allocation to
roots increases the
surface area of roots for
the uptake of water,
while the decline in leaf
area decreases water
losses through
transpiration.
6.11 Plants need to make serious
evolutionary adaptations to temperature
C4
C4
C3
Neuropogon: Arctic lichen (C3)
Ambrosia: cool coastal dune plant (C3)
Tidestromia: summer-active desert C4 perennial
Photosyn. rate and Topt
Atriplx: everygreen desert C4 plant
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Topt: C3: <30oC; C4: 30oC to 40oC; CAM, >40oC
Illustration of
tradeoffs of
C4, C3 plants
with temp.,
CO2
concentration
Increase in
CO2 will
influence the
competition
of C3 and
C4
6.12 Plants exhibit adaptations to
variations in nutrient availability
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Plants need nutrient for
metabolic processes and
synthesize new tissues
According to amount of
nutrient required:
• Macronutrients: needed in
large amount
N, P, K
• Micronutrients: needed in
lesser quantities
Zn, B
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Some nutrients can be
inhibitory
Plants exhibit adaptations to variations
in nutrient availability
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Uptake of a
nutrient through
the roots depends
on its
concentration
However there is a
maximum
Effect of nutrient
availability can also
reach a maximum
Photosynthesis and plant growth and
nutrient
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Nitrogen can limit
photosynthesis
Need for symbiosis
• Rhizobium
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Peas, beans and a
few other plants
• Frankia
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Various woody
species in southern
Africa
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Plants respond
differently to extra
nitrogen depending
on their natural
environment’s level
of nitrogen or
other nutrient
The END
Important set of adaptations for
water conservation involve
photosynthesis:
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C3 plants the norm in cool, moist
climates
C4 plants adapted to hot, dry climates
because of efficiency of CO2 uptake
CAM plants are another fundamental
variation on C4 plants, also adapted to
hot, dry climates
C3 plant anatomy and
biochemistry
Example:
Geranium
C4 plant anatomy and
biochemistry
Examples:
Sorghum
vulgare
(pictured),
sugar cane
C4 photosynthesis has
advantages, costs
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Advantages:
• CO2 in high concentration
• Water loss reduced
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Costs and tradeoffs:
• Recovering PEP from Pyruvate expensive
• Less leaf tissue devoted to photosynthesis
• Not beneficial in cool climates
CAM photosynthesis separates
cycles diurnally
Example:
Sedum
obtusatum
Macronutrients
Micronutrients
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Pine species are adapted to live in low nitrogen
environments like sandy soils
Pines retain their leaves for a long time
This saves the recycling of nitrogen through the soil