BIOL 4120: Principles of Ecology Lecture 6: Plant adaptations to the Environment

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BIOL 4120 Principles of Ecology Lecture 6
Plant adaptations to the Environment

• Dafeng Hui
• Room Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Topics

• 6.1 Plant photosynthesis to fix carbon
• 6.2 Light influences photosynthesis
• 6.3 Photosynthesis is coupled with water exchange
• 6.4 Water movement through plants
• 6.5 Temperature influences photosynthesis
• 6.6 Carbon allocation
• 6.7 Other photosynthesis pathways
• 6.8 Plants adaptation to different light
  intensity
• 6.9 Plants adaptation to different temperature

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• Earth provides highly diverse environments
• 1.5 million known species now

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Three common basic functions

• 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)
• 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)
• 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

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6.1 Photosynthesis (review)

• 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 tri-p) 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).

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Photosynthesis
Photosynthetic electron transport
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C3 cycle (Calvin cycle)
One major drawback of C3 pathway Rubisco can
catalyze both carbonxylation And RuBP
oxygenation Reduce the efficiency of
photosynthesis.
C3 plant trees, forbs, some grasses
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Cellular respiration
Photosynthesis
Net photosynthesis (Gross) Photosynthesis -
Respiration
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6.2 Light influences photosynthesis

• 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

PAR photosynthetically active radiation
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6.3 Photosynthesis involves exchanges between
atmosphere and plant

• 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

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6.4 Water moves from soil to plant to atmosphere
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Water potential

• 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 0.
• in nature generally negative.
• solute measures the reduction in due to
  dissolved substances.

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Water moves from soil to plant to atmosphere
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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.

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Net photosynthesis and leaf water potential
Declines caused by closure of stomata
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Water use efficiency

• Trade-off
• To carry out photosynthesis, plants must open up
  the stomata to get CO2
• Transpiration loss of water to atmosphere.
• WUE ratio of carbon fixed (photosynthesis) per
  unit of water lost (transpiration)

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Photosynthesis of aquatic plants

• Unique features
• Lack of stomata
• CO2 reacts with H2O first to produce
  biocarbonate.
• Convert biocarbonate to CO2
• Transport HCO3- to leaf then convert to CO2
• Excretion of the enzyme into adjacent waters and
  subsequent uptake of converted CO2 across the
  membrane.

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6.6 Plant temperatures reflects their energy
balance with the surrounding environment

• Different responses of photosynthesis and
  respiration to temperature
• Three basic Temperature points
• Min T, max T and optimal T

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Plant leaf temperatures reflects their energy
balance with the surrounding environment

• Temperature is important to a plants
• Photosynthesis increases as the temperature
  increases
• Energy balance (lt5 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

Different shapes of leaves influence the
convection of heat.
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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.
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Allocation and T, PPT
Hui Jackson 2006
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Plant adaptations and trade-offs

• Environmental factors are inter-dependent 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.

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6.8 Species of Plants are adapted to light
conditions

• 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
• 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
• Changes in leaf structure evolve

Red oak leaves at top and bottom of canopy
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Light also affects whether a plant allocates to
leaves or to roots
Change of allocation to leaf of broadleaved
peppermint.

• Shade tolerant (shade-adapted) species
• Plant species adapted to low-light environments
• Shade intolerant (sun-adapted) species
• Plant species adapted to high-light environments

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Shade tolerance and intolerance
Seedling survival and growth of two tree species
over a year
Shade tolerance
Shade intolerance
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Remember that land plants are not the only plants
on Earth

• Shade adaptation also occurs in algae

Greed algae and diatoms also depend on sunlight
for photosynthesis.
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6.9 Other photosynthesis pathways adaptation to
water and temperature conditions

• 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

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C4 pathway

• Advantages over C3 pathway
• PEP does not interact with O2 (RuBP react with O2
  and reduce the photosynthesis efficiency)
• 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).

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Distribution of C4 grass
Spatial and seasonal gradient
Number are percentage of total grass species are
C4.
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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 Dayclose stomata, re-convert
malic acid to CO2, C3 cycle.
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C3, C4 and CAM

• 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

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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.
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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 Atriplx
everygreen desert C4 plant
Photosyn. rate and Topt

• Topt C3 lt30oC C4 30oC to 40oC CAM, gt40oC

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Illustration of tradeoffs of C4, C3 plants with
temp., CO2 concentration
Increase in CO2 will influence the competition of
C3 and C4
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6.12 Plants exhibit adaptations to variations in
nutrient availability

• 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
• Some nutrients can be inhibitory

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Plants exhibit adaptations to variations in
nutrient availability

• 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

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Photosynthesis and plant growth and nutrient

• Nitrogen can limit photosynthesis
• Need for symbiosis
• Rhizobium
• Peas, beans and a few other plants
• Frankia
• Various woody species in southern Africa

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• Plants respond differently to extra nitrogen
  depending on their natural environments level of
  nitrogen or other nutrient

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The END
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Important set of adaptations for water
conservation involve photosynthesis

• 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

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C3 plant anatomy and biochemistry
Example Geranium
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C4 plant anatomy and biochemistry
Examples Sorghum vulgare (pictured), sugar cane
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C4 photosynthesis has advantages, costs

• Advantages
• CO2 in high concentration
• Water loss reduced
• Costs and tradeoffs
• Recovering PEP from Pyruvate expensive
• Less leaf tissue devoted to photosynthesis
• Not beneficial in cool climates

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CAM photosynthesis separates cycles diurnally
Example Sedum obtusatum
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Macronutrients
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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