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Plant Adaptations

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Plant adaptations

Plant Adaptations

Outline:

Photosynthesis and respiration

Environmental controls on photosynthesis

Plant adaptations to:

High and low light

Water limitation

Nutrient availability

Readings: Chapter 6


Conditions and resources

Conditions and Resources

  • Conditions are physical / chemical features of the environment

    • E.g. Temperature, humidity, pH, etc.

    • Not consumed by living organisms (but may still be important to them)

  • Resources are consumed

    • Once used, they are unavailable to other organisms

    • Plants: sunlight, water, mineral nutrients, …

    • Animals: prey organisms, nesting sites, …


Plant resources

Plant Resources

  • Plants are autotrophs - make their own organic carbon form inorganic nutrients

    • Need light, ions, inorganic molecules

  • Plants are sessile

    • Grow towards nutrients


PHOTOSYNTHESIS

Conversion of carbon dioxide into simple sugars

6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O

LIGHT


Light reactions


Dark reactions

carboxylation


Photosynthetically Active Radiation, PAR


RESPIRATION

C6H12O6 + 6O2 6CO2 + 6H2O + ATP


Net photosynthesis = Photosynthesis - Respiration


Photosynthesis involves gas exchange


  • Controls on photosynthesis

    • Light

    • Water

    • Nutrients

    • Temperature


1 light

1. Light


PAR


Tradeoff

Tradeoff

  • Shade plants grow better in the sun than in the shade,

  • but sun plants grow faster than shade plants in direct sun

Shade plant

Sun plant


Tradeoff1

Tradeoff

  • Shade plants survive well in either sun or shade

  • Sun plants cannot tolerate shade

Shade plant

Sun plant


  • 9 tree species of Macaranga from Borneo, Malaysia


Phenotypic plasticity

Phenotypic plasticity

  • Most plants have the ability to alter their morphology (within limits) in response to light conditions


Phenotypic plasticity1

Phenotypic plasticity

  • Sun and shade leaves can exist within the same tree

More deeply lobed --> More rapid heat loss


  • Sun leaf

  • thicker

  • more cell layers

  • more chloroplasts

  • Shade leaf

  • flat

  • thin

  • larger surface area / unit weight


  • Shade leaves

  • Horizontal leaves, single layer

  • Low saturation point

  • Low compensation point

  • Produce less RUBISCO

  • Low respiration

  • More chlorophyll

  • Light availability limits photosynthesis rate

  • Sun leaves

  • Leaves at many angles

  • High saturation point

  • High compensation point

  • Produce more RUBISCO

  • High respiration

  • Less chlorophyll

  • RUBISCO availability limits photosynthesis rate


2 water

2. Water

Transpiration


For transpiration to occur

For transpiration to occur

atmosphere < leaf <root<soil


Water potential

Water potential

w = p ++m

p= = hydrostatic pressure

 = = osmotic pressure

m= = matric pressure


Stomata

Stomata

  • Reduction in soil  --> stomata close

  • Species differ in tolerance to drying soils


Strategies for drought

Strategies for drought

  • Avoiders

    • Short lifespan

    • Wet season

    • Seeds survive drought

    • Drought deciduous species

      • Leaves shed in dry season


Strategies for drought1

Strategies for drought

  • Tolerators

    • Leaves transpire slowly

    • Change orientation of leaves

    • Sunken stomata

      • E.g. pines

    • More efficient photosynthesis

      • E.g. C4 --> reduces photorespiration

      • E.g. CAM --> stomata open at night


CAM

photosynthesis

C4

photosynthesis


C4


CAM


CAM


% of grasses that are C4


Water absorption

Water absorption

  • Root hairs increase surface area


  • Structure of the root system varies between species, depending on the amt. of soil moisture in their env’t

  • Individual species show phenotypic plasticity

    • wet soil --> shallow roots near surface (greater oxygen availability)

    • dry soil --> deep roots


3 nutrients

3. Nutrients

  • Macronutrients – needed in large amounts (e.g. C, H, O, … N, P, K, Ca, Mg, S)

  • Micronutrients – trace elements (e.g. Fe, Mn, B)

  • Micro/macro refer to the quantity needed


Table 6-1


Nutrient uptake rates

Nutrient uptake rates

  • Reach plateau with increasing nutrient concentration


Maximum growth rate of a plant reflects N availability in its natural habitat. A. stolonifera occurs on more nitrogen-rich soils than A. canina.


Evergreen leaves

Evergreen leaves

  • Plants adapted to nutrient-poor conditions tend to have evergreen leaves


4 effects of temperature

4. Effects of temperature

= Condition

  • Increase temperature --> increase biochemical reaction rate

  • At high temperature,

    enzymes denature

    --> death


  • Gross photosynthetic rate increases up to a point with increasing temperature

  • Respiration rate also increases with temperature.

  • Net photosynthesis is maximal at a point slightly below that at which gross photosynthesis is maximal


Leaf temperature

  • > 95% of sunlight absorbed by a leaf becomes heat

  • Cooling of leaves:

    • Transpiration

    • Convection (movement of cool air around a leaf)


C4 plants

C4 plants

  • Have higher temperature optima than C3


Phenotypic plasticity2

Phenotypic plasticity

  • Individual species can modify their Topt according to the changing seasons

    = acclimatization


  • Response to cold

  • Chilling injury - near, > 0 oC

  • - cell membranes rupture

  • Freezing - < 0 oC

  • - ice inside cells = death

  • - ice outside cells = dehydration

    • (may survive)

    • may kill juveniles only


Saguaro cacti (S.W. United States) store large amounts of water; they can tolerate short periods of freezing temperatures


  • CLOSER TO HOME

  • Freeze-tolerant plants: frost hardening

    • When T decreases – plants synthesize sugars, amino acids, other molecules to act as antifreeze.

  • Winter – deciduous plants

    • Lose leaves in autumn

    • Leaves very efficient in summer – high photosynthesis rate

    • Leaves can’t survive freezing

    • Costly in energy, nutrients to rebuild leaves

  • Chilling breaks seed dormancy for temperate/boreal spp.

  • Germinates only in spring


Plants are phenotypically plastic

Plants are phenotypically plastic