BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 6: Plant adaptations Lecture 6: Plant adaptations to the Environmentto the Environment

Dafeng HuiDafeng Hui

Room: Harned Hall 320Room: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

TopicsTopics 6.1 Plant photosynthesis to fix carbon6.1 Plant photosynthesis to fix carbon 6.2 Light influences photosynthesis6.2 Light influences photosynthesis 6.3 Photosynthesis is coupled with water exchange6.3 Photosynthesis is coupled with water exchange 6.4 Water movement through plants6.4 Water movement through plants 6.5 Temperature influences photosynthesis6.5 Temperature influences photosynthesis 6.6 Carbon allocation6.6 Carbon allocation 6.7 Other photosynthesis pathways6.7 Other photosynthesis pathways 6.8 Plants adaptation to different light intensity6.8 Plants adaptation to different light intensity 6.9 Plants adaptation to different temperature6.9 Plants adaptation to different temperature

Earth provides highly diverse Earth provides highly diverse environments:environments:

1.5 million known species now1.5 million known species now

Three common basic functionsThree common basic functions Assimilation:Assimilation: acquire energy and matter from external acquire energy and matter from external

environmentenvironment Reproduction:Reproduction: to produce new individuals to produce new individuals Response to external stimuli:Response to external stimuli: able to respond to both able to respond to both

physical (light, temperature etc) and biotic (predator etc).physical (light, temperature etc) and biotic (predator etc).

All organisms require energyAll organisms require energy• Energy obtained directly from an energy source by a living Energy obtained directly from an energy source by a living

organism is called autotrophy (autotroph)organism is called autotrophy (autotroph) Plants are autotrophs, primary producersPlants are autotrophs, primary producers So are certain bacteria like So are certain bacteria like Thiobacullus ferrooxidansThiobacullus ferrooxidans

• Energy obtained indirectly from organic molecules by a living Energy obtained indirectly from organic molecules by a living organism is called heterotrophy (heterotrophy)organism is called heterotrophy (heterotrophy)

All animals are heterotrophs, secondary producersAll animals are heterotrophs, secondary producers Some organisms can be a a mixture like lichens where you have an Some organisms can be a a mixture like lichens where you have an

alga and a fungus living togetheralga and a fungus living together

6.1 Photosynthesis (review)6.1 Photosynthesis (review) All life on Earth is carbon basedAll life on Earth is carbon based COCO22 was the major form of free carbon was the major form of free carbon

available in past and still isavailable in past and still is Only photosynthesis is capable of Only photosynthesis is capable of

converting COconverting CO22 into organic molecules into organic molecules Only plants (some algae, bacteria) are Only plants (some algae, bacteria) are

capable of photosynthesiscapable of photosynthesis All other living organisms obtain their All other living organisms obtain their

carbon via assimilation from plantscarbon via assimilation from plants

Photsynthesis is a biochemical process that uses light to Photsynthesis is a biochemical process that uses light to convert COconvert CO22 into a simple sugar such as glucose into a simple sugar such as glucose

• Light of the certain wavelength (PAR) is absorbed by Light of the certain wavelength (PAR) is absorbed by chlorophyll in the organelle called a chlorophyll in the organelle called a chloroplastchloroplast and and converted via the converted via the light reactionslight reactions into ATP (adenosine tri- into ATP (adenosine tri-p) and NADPH (reduced nicotinamide adenine dinucleotide p) and NADPH (reduced nicotinamide adenine dinucleotide phosphate)phosphate)

• HH22O is split into oxygen and hydrogenO is split into oxygen and hydrogen• The oxygen is released as OThe oxygen is released as O22

• The hydrogen is linked to COThe hydrogen is linked to CO22 to form a three carbon to form a three carbon organic molecule (3-PGA, phosphoglycolate; Corganic molecule (3-PGA, phosphoglycolate; C33 photosynthesis). This is carried out by the enzyme photosynthesis). This is carried out by the enzyme ribulose biphosphate carboxylase- oxygenase ribulose biphosphate carboxylase- oxygenase (Rubisco)(Rubisco)

• The C3 molecules are then converted into carbonhydrates The C3 molecules are then converted into carbonhydrates like glucose via the like glucose via the dark reactionsdark reactions

• This glucose can then be used to produce energy by This glucose can then be used to produce energy by respiration in respiration in mitochondriamitochondria or used to produce other or used to produce other organic compounds (proteins, fatty acids etc).organic compounds (proteins, fatty acids etc).

PhotosynthesisPhotosynthesis

PGARuBPCO 322Photosynthetic electron transport

One major drawback of C3 pathway:

Rubisco can catalyze both carbonxylation

And RuBP oxygenation

Reduce the efficiency of photosynthesis.

C3 cycle (Calvin cycle) C3 cycle (Calvin cycle)

PGARuBPCO 322

C3 plant: trees, forbs, some grasses

22 CORuBPO

Cellular respirationCellular respiration

ATPOHCOOOHC 2226126 666

Net photosynthesis = (Gross) Photosynthesis - Respiration

2612622 666 OOHCOHCO

PhotosynthesisPhotosynthesis

Obviously the amount of Obviously the amount of light received by a plant light received by a plant will affect the light will affect the light reactions of photosynthesisreactions of photosynthesis

Light Compensation PointLight Compensation Point• As light declines, it As light declines, it

eventually reaches a eventually reaches a point where respiration point where respiration is equal to is equal to photosynthesisphotosynthesis

Light Saturation PointLight Saturation Point• As light increases, it As light increases, it

reaches a point where reaches a point where all chloroplasts are all chloroplasts are working at a maximum working at a maximum raterate

PhotoinhibitionPhotoinhibition• In some circumstances, In some circumstances,

excess light can result in excess light can result in “overloading” and even “overloading” and even damage to chlorophyll damage to chlorophyll by bleachingby bleaching

6.2 Light influences photosynthesis

PAR: photosynthetically active radiation

Photosynthesis takes place in Photosynthesis takes place in plants in specialized cells in the plants in specialized cells in the mesophyllmesophyll

Needs movement of CONeeds movement of CO22 and O and O22 between cells and atmospherebetween cells and atmosphere

Diffuses via stomata in land Diffuses via stomata in land plants (CO2, 370ppm to 150ppm)plants (CO2, 370ppm to 150ppm)• Stomata close when Stomata close when

photosynthesis is reduced and photosynthesis is reduced and keeps up partial pressure of keeps up partial pressure of COCO22

Stomata also control Stomata also control transpirationtranspiration• Reduces water lossReduces water loss• Minimizing water needs from Minimizing water needs from

soil (dry area)soil (dry area)• Ratio of carbon fixed to water Ratio of carbon fixed to water

lost is the lost is the water-use efficiencywater-use efficiency

6.3 Photosynthesis involves exchanges between

atmosphere and plant

6.4 Water moves from soil to plant to atmosphere

Water potentialWater potential

Water moving between soil and plants Water moving between soil and plants flows down a water potential gradient.flows down a water potential gradient.

Water potentialWater potential ( ) is the capacity of water ( ) is the capacity of water to do work, to do work, potential energypotential energy of of waterwater relative to pure water in reference relative to pure water in reference conditions conditions • Pure Water = 0.Pure Water = 0.

in nature generally negative.in nature generally negative. solutesolute measures the reduction in due to dissolved measures the reduction in due to dissolved

substances.substances.

Water moves from soil to plant to atmosphere

Water potential of compartment of soil-plant-atmosphereWater 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 efficiencyWater use efficiency

Trade-offTrade-off• To carry out photosynthesis, plants must To carry out photosynthesis, plants must

open up the stomata to get CO2;open up the stomata to get CO2;• Transpiration loss of water to Transpiration loss of water to

atmosphere.atmosphere. WUE: ratio of carbon fixed WUE: ratio of carbon fixed

(photosynthesis) per unit of water (photosynthesis) per unit of water lost (transpiration)lost (transpiration)

Photosynthesis of aquatic plantsPhotosynthesis of aquatic plants

Unique featuresUnique features• Lack of stomataLack of stomata• CO2 reacts with H2O first to produce CO2 reacts with H2O first to produce

biocarbonate.biocarbonate.

• Convert biocarbonate to CO2Convert biocarbonate to CO2 Transport HCOTransport HCO33

-- to leaf then convert to CO2 to leaf then convert to CO2 Excretion of the enzyme into adjacent Excretion of the enzyme into adjacent

waters and subsequent uptake of converted waters and subsequent uptake of converted CO2 across the membrane. CO2 across the membrane.

Different responses of Different responses of photosynthesis and photosynthesis and respiration to temperature;respiration to temperature;

Three basic Temperature Three basic Temperature pointspoints• Min T, max T and optimal TMin T, max T and optimal T

6.6 Plant temperatures reflects their energy balance with the surrounding environment

Temperature is important to a plantsTemperature is important to a plants• Photosynthesis increases as the Photosynthesis increases as the

temperature increasestemperature increases Energy balance (<5% used in Energy balance (<5% used in

photosynthesis)photosynthesis) Radiation not used increases Radiation not used increases

internal leaf temperature internal leaf temperature significantlysignificantly

Some heat can be lost by Some heat can be lost by convection (leaf sizes and shapes)convection (leaf sizes and shapes)

Some heat can be lost by radiation Some heat can be lost by radiation (leaf color)(leaf color)

• Respiration increases as the Respiration increases as the temperature increasestemperature increases

• Damage to enzymes etc increases Damage to enzymes etc increases with temperaturewith temperature

• Water loss increases with temperatureWater loss increases with temperature Evaporation of water helps to Evaporation of water helps to

keep the temperature lowerkeep the temperature lower Thus relative humidity and Thus relative humidity and

available water is importantavailable water is important

Plant leaf temperatures reflects their energy balance with the surrounding environment

Different shapes of leaves influence the convection of heat.

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, PPTAllocation and T, PPT

Hui & Jackson 2006

Plant adaptations and trade-offsPlant adaptations and trade-offs

Environmental factors are inter-Environmental factors are inter-dependent: light, temperature and dependent: light, temperature and moisture are all linked together.moisture are all linked together.• In dry area: more radiation, high In dry area: more radiation, high

temperature, low relative humidity, high temperature, low relative humidity, high water demandwater demand smaller leaves, more smaller leaves, more rootsroots

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

6.8 Species of Plants are adapted 6.8 Species of Plants are adapted to light conditionsto light conditions

Plants adapted to a shady Plants adapted to a shady environmentenvironment• Lower levels of rubiscoLower levels of rubisco• Higher levels of chlorophyll Higher levels of chlorophyll

(increase ability to capture (increase ability to capture light, as light is limiting)light, as light is limiting)

• low light compensation and low light compensation and saturation lightssaturation lights

Plants adapted to a full sun Plants adapted to a full sun environmentenvironment• Higher levels of rubiscoHigher levels of rubisco• Lower levels of chlorophyllLower levels of chlorophyll• Because leaf structure is Because leaf structure is

limitinglimiting• High compensation and High compensation and

saturation lightssaturation lights Changes in leaf structure Changes in leaf structure

evolveevolve

Red oak leaves at top and bottom of canopy

Shade tolerant (shade-Shade tolerant (shade-adapted) speciesadapted) species• Plant species adapted to Plant species adapted to

low-light environmentslow-light environments Shade intolerant (sun-Shade intolerant (sun-

adapted) speciesadapted) species• Plant species adapted to Plant species adapted to

high-light environmentshigh-light environments

Change of allocation to leaf of broadleaved peppermint.

Light also affects whether a plant allocates to Light also affects whether a plant allocates to leaves or to rootsleaves or to roots

Shade tolerance and intoleranceShade tolerance and intolerance

Shade tolerance

Shade intolerance

Seedling survival and growth of two tree species over a year

Remember that land plants are not Remember that land plants are not the only plants on Earththe only plants on Earth

Shade Shade adaptation adaptation also occurs also occurs in algaein algae

Greed algae and diatoms also depend on sunlight for photosynthesis.

To increase water use To increase water use efficiency in a warm dry efficiency in a warm dry environment, plants have environment, plants have modified process of modified process of photosynthesisphotosynthesis

CC33

• Normal in mesophyll Normal in mesophyll with rubiscowith rubisco

CC44

• Warm dry environmentWarm dry environment• Additional step in Additional step in

fixation of COfixation of CO2 2 in the in the bundle sheathbundle sheath

• Phosphoenolpyruvate Phosphoenolpyruvate synthasesynthase (PEP) does (PEP) does initial fixation into initial fixation into Malate and aspartate Malate and aspartate

• Malate and aspartate Malate and aspartate are transported to are transported to bundle sheath as an bundle sheath as an intermediate moleculeintermediate molecule

• Rubisco and CORubisco and CO22 convert them to convert them to glucoseglucose

6.9 Other photosynthesis pathways: adaptation to water and temperature conditions

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 grassDistribution of C4 grass

Number are percentage of total grass species are C4.

Spatial and seasonal gradient

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.

CC33, C, C4 4 and CAMand CAM

CC44 makes more effective use of CO makes more effective use of CO22 COCO22 concentration in bundle cell can be 6X that of concentration in bundle cell can be 6X that of

atmosphere and mesophyll cellatmosphere and mesophyll cell As rate limiting aspect of photosynthesis is usually the As rate limiting aspect of photosynthesis is usually the

availability of COavailability of CO22, then C, then C44 is more efficient is more efficient Also can keep stomata closed longer and therefore better Also can keep stomata closed longer and therefore better

water usewater use But needs large amount of extra enzyme (PEP, need more But needs large amount of extra enzyme (PEP, need more

energy) and there only well adapted to high photosynthesis energy) and there only well adapted to high photosynthesis environmentsenvironments

In deserts with really low water availability and high In deserts with really low water availability and high temperaturetemperature• Third type – Crassulacean acid pathway – CAMThird type – Crassulacean acid pathway – CAM• CO2 fixed converted to malate by PEP during night and CO2 fixed converted to malate by PEP during night and

stored, while stomata are openstored, while stomata are open• Malate is converted back to CO2 during day and using Malate is converted back to CO2 during day and using

photosynthesis, light and rubisco changed into sugarphotosynthesis, light and rubisco changed into sugar• High level of water conservationHigh level of water conservation• Both processes in the mesophyll cellsBoth processes in the mesophyll cells

Plants need to make serious evolutionary adaptations to Plants need to make serious evolutionary adaptations to water availabilitywater 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 6.11 Plants need to make serious evolutionary adaptations to temperatureevolutionary 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

C3

C4

C4

Photosyn. rate and Topt

Illustration of Illustration of tradeoffs of tradeoffs of

C4, C3 plants C4, C3 plants with temp., with temp.,

COCO22

concentrationconcentration

Increase in CO2 will influence the competition of C3 and C4

Plants need nutrient for Plants need nutrient for metabolic processes and metabolic processes and synthesize new tissuessynthesize new tissues

According to amount of According to amount of nutrient required:nutrient required:• Macronutrients: needed in Macronutrients: needed in

large amountlarge amount N, P, KN, P, K

• Micronutrients: needed in Micronutrients: needed in lesser quantitieslesser quantities

Zn, B Zn, B

Some nutrients can be Some nutrients can be inhibitoryinhibitory

6.12 Plants exhibit adaptations to variations in nutrient availability

Uptake of a Uptake of a nutrient through nutrient through the roots depends the roots depends on its on its concentrationconcentration

However there is a However there is a maximummaximum

Effect of nutrient Effect of nutrient availability can availability can also reach a also reach a maximummaximum

Plants exhibit adaptations to variations in nutrient availability

Photosynthesis and plant growth and Photosynthesis and plant growth and nutrientnutrient

Nitrogen can limit Nitrogen can limit photosynthesisphotosynthesis

Need for symbiosisNeed for symbiosis• RhizobiumRhizobium

Peas, beans and a Peas, beans and a few other plantsfew other plants

• FrankiaFrankia Various woody Various woody

species in southern species in southern AfricaAfrica

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

The ENDThe END

Important set of adaptations for Important set of adaptations for water conservation involve water conservation involve

photosynthesis:photosynthesis:

CC33 plants the norm in cool, moist climatesplants the norm in cool, moist climates

CC44 plants adapted to hot, dry climates because plants adapted to hot, dry climates because of efficiency of COof efficiency of CO22 uptake uptake

CAMCAM plants are another fundamental variation plants are another fundamental variation on Con C44 plants, also adapted to hot, dry climates plants, also adapted to hot, dry climates

CC33 plant anatomy and plant anatomy and biochemistrybiochemistry

Example: Geranium

CC44 plant anatomy and plant anatomy and

biochemistrybiochemistry

Examples: Sorghum vulgare (pictured),

sugar cane

CC44 photosynthesis has photosynthesis has

advantages, costsadvantages, costs

Advantages:Advantages:• COCO22 in high concentration in high concentration

• Water loss reducedWater loss reduced Costs and tradeoffs:Costs and tradeoffs:

• Recovering PEP from Pyruvate expensiveRecovering PEP from Pyruvate expensive• Less leaf tissue devoted to photosynthesisLess leaf tissue devoted to photosynthesis• Not beneficial in cool climatesNot beneficial in cool climates

CAM photosynthesis separates CAM photosynthesis separates cycles diurnallycycles diurnally

Example: Sedum obtusatum

MacronutrientsMacronutrients

MicronutrientsMicronutrients

Pine species are adapted to live in low nitrogen Pine species are adapted to live in low nitrogen environments like sandy soilsenvironments like sandy soils

Pines retain their leaves for a long timePines retain their leaves for a long time This saves the recycling of nitrogen through the soilThis saves the recycling of nitrogen through the soil