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Plant adaptations

Earth provides highly diverse environments:

1.5 million known species now

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 energyE bt i d di tl f b li i i i– 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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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 ofOnly 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

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 O2yg 2– The hydrogen is linked to CO2 to form a three carbon

organic molecule (3-PGA, phosphoglycolate; C3photosynthesis). This is carried out by the enzyme ribulosebiphosphate carboxylase- oxygenase (Rubisco)

– The C3 molecules are then converted into carbonhydrateslike 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).

Photosynthetic electron transport PGARuBPCO −→+ 322

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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

Cellular respiration

2612622 666 OOHCOHCO +→+

PhotosynthesisPhotosynthesis

Cellular respiration

ATPOHCOOOHC ++→+ 2226126 666

Net photosynthesis = (Gross) Photosynthesis - Respiration

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 photosynthesisphotosynthesis

• 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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Exchanges between atmosphere & 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 p y

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

Water moves from soil to plant to atmosphere

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 , p gypure water in reference conditions – Pure Water = 0.

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

substances.

ψψ ψ

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– w = p + o + m

– Hydrostatic pressure or physical pressure.– Osmotic potential: tendency to attract water

l l f f hi h t ti t l

ψ ψ ψ ψ

Water potential of compartment of soil-plant-atmosphere

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

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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 atmosphereTranspiration loss of water to atmosphere.

• WUE: ratio of carbon fixed (photosynthesis) per unit of water lost (transpiration)

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.

• Different responses of photosynthesis and respiration to temperature;

• Three basic Temperature points– Min T, max T and optimal T

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• 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)

Different shapes of leaves influence the convection of heat.

(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

Carbon allocation is an important issue and has not been well studied.

Difficult to measure, especially below ground.

Carbon gained in photosynthesis is allocated to production of plant tissues

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.

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– In dry area: more radiation, high temperature, low relative humidity, high water demandsmaller leaves, more roots

– Trade-offs: more carbon allocated to below-ground.

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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 t ti li htsaturation 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

Light also affects whether a plant allocates to leaves or Light also affects whether a plant allocates to leaves or to rootsto rootsChange 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

Shade tolerance and intolerance

Shade tolerance

Seedling survival and growth of two tree species

Shade intolerance

spec esover a year

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Remember that land plants are not the only plants on Earth

• Shade adaptation also occurs in algaein algae

Greed algae and diatoms also depend on sunlight for photosynthesis.

• 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 sheathPh h l t

Other photosynthesispathways: adaptation to water and temperature conditions

– Phosphoenolpyruvatesynthase (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 d CO2 h b dl h hacids 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 that 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, re-convert malic acid to CO2, C3 cycle.

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 photosynthesisenergy) 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.

Plants need to make serious evolutionary adaptations to temperature

Topt: CTopt: C3: 3: <30<30ooC; CC; C4: 4: 3030ooC to 40C to 40ooC; CAM, >40C; CAM, >40ooCC

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

Illustration of tradeoffs of

C4, C3 plants with temp.,

CO2concentration

Increase in CO2 will influence the competition of C3 and C4

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• Uptake of a nutrient through the roots depends on its concentration

• However there is a

Plants exhibit adaptations to variations in nutrient availability

maximum• Effect of nutrient

availability can also reach a maximum

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

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

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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

C3 plant anatomy and biochemistry

Example:Geranium

C4 plant anatomy and biochemistry

Examples: Sorghum

lgarevulgare (pictured),

sugar cane

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C4 photosynthesis has advantages, costs

• Advantages:• 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

CAM photosynthesis separates cycles diurnally

Example: pSedum obtusatum

Macronutrients

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Micronutrients

• 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