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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.

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Plant Adaptations

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  1. Plant Adaptations Outline: Photosynthesis and respiration Environmental controls on photosynthesis Plant adaptations to: High and low light Water limitation Nutrient availability Readings: Chapter 6

  2. 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, …

  3. Plant Resources • Plants are autotrophs - make their own organic carbon form inorganic nutrients • Need light, ions, inorganic molecules • Plants are sessile • Grow towards nutrients

  4. PHOTOSYNTHESIS Conversion of carbon dioxide into simple sugars 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O LIGHT

  5. Light reactions

  6. Dark reactions carboxylation

  7. Photosynthetically Active Radiation, PAR

  8. RESPIRATION C6H12O6 + 6O2 6CO2 + 6H2O + ATP

  9. Net photosynthesis = Photosynthesis - Respiration

  10. Photosynthesis involves gas exchange

  11. Controls on photosynthesis • Light • Water • Nutrients • Temperature

  12. 1. Light

  13. PAR

  14. 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

  15. Tradeoff • Shade plants survive well in either sun or shade • Sun plants cannot tolerate shade Shade plant Sun plant

  16. 9 tree species of Macaranga from Borneo, Malaysia

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

  18. Phenotypic plasticity • Sun and shade leaves can exist within the same tree More deeply lobed --> More rapid heat loss

  19. Sun leaf • thicker • more cell layers • more chloroplasts • Shade leaf • flat • thin • larger surface area / unit weight

  20. 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

  21. 2. Water Transpiration

  22. For transpiration to occur atmosphere < leaf <root<soil

  23. Water potential w = p ++m p= = hydrostatic pressure  = = osmotic pressure m= = matric pressure

  24. Stomata • Reduction in soil  --> stomata close • Species differ in tolerance to drying soils

  25. Strategies for drought • Avoiders • Short lifespan • Wet season • Seeds survive drought • Drought deciduous species • Leaves shed in dry season

  26. 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

  27. CAM photosynthesis C4 photosynthesis

  28. C4

  29. CAM

  30. CAM

  31. % of grasses that are C4

  32. Water absorption • Root hairs increase surface area

  33. 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

  34. 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

  35. Table 6-1

  36. Nutrient uptake rates • Reach plateau with increasing nutrient concentration

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

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

  39. 4. Effects of temperature = Condition • Increase temperature --> increase biochemical reaction rate • At high temperature, enzymes denature --> death

  40. 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

  41. Leaf temperature • > 95% of sunlight absorbed by a leaf becomes heat • Cooling of leaves: • Transpiration • Convection (movement of cool air around a leaf)

  42. C4 plants • Have higher temperature optima than C3

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