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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.
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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 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 • 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
Dark reactions carboxylation
RESPIRATION C6H12O6 + 6O2 6CO2 + 6H2O + ATP
Controls on photosynthesis • Light • Water • Nutrients • Temperature
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
Tradeoff • Shade plants survive well in either sun or shade • Sun plants cannot tolerate shade Shade plant Sun plant
Phenotypic plasticity • Most plants have the ability to alter their morphology (within limits) in response to light conditions
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 Transpiration
For transpiration to occur atmosphere < leaf <root<soil
Water potential w = p ++m p= = hydrostatic pressure = = osmotic pressure m= = matric pressure
Stomata • Reduction in soil --> stomata close • Species differ in tolerance to drying soils
Strategies for drought • Avoiders • Short lifespan • Wet season • Seeds survive drought • Drought deciduous species • Leaves shed in dry season
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
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 • 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
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 • Plants adapted to nutrient-poor conditions tend to have evergreen leaves
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 • Have higher temperature optima than C3