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Ch. 3 Water Relations/Energy Balance

Ch. 3 Water Relations/Energy Balance. Water potential tour. Examine soil to air pathway of water. Fig. 3.2a. Water in the plant: stem xylem. Water in the plant: stem xylem. Xylem cells Vessels vs. tracheids. Water in the plant: stem xylem. Water cohesion (stick together)

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Ch. 3 Water Relations/Energy Balance

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  1. Ch. 3 Water Relations/Energy Balance

  2. Water potential tour..... • Examine soil to air pathway of water Fig. 3.2a

  3. Water in the plant: stem xylem

  4. Water in the plant: stem xylem • Xylem cells • Vessels vs. tracheids

  5. Water in the plant: stem xylem • Water cohesion (stick together) • Water adhesion (stick charged surfaces: cell walls)

  6. Water in the plant: stem xylem • Adhesion: • Slows movement • Strengthens ________ • Small dia. cells: more water-wall contact/unit vol. (withstand ________)

  7. Water in the plant: stem xylem • SO: plants (or parts) under stress make small cells! • Ex, Sequoiadendron gigantea (big tree)

  8. Water in the plant: stem xylem • 102 ft. around • 2,145 tons Boyd Bro: 1984!

  9. Water in the plant: stem xylem • Conifer: tracheids • Smaller @ top (psi lowest)

  10. Water in the plant: stem xylem • Other small cells: • desert plants (Larrea: creosote bush)

  11. Water in the plant: stem xylem • Other exs. small cells: • salt marsh plants Salicornia virginica

  12. Water in the plant: leaf • Steepest drop psi b/w leaf/air

  13. Water in the plant: leaf • Air “dry:” Most plants wilt when soil psi = -1.5 Mpa (permanent wilting point: can’t recover) • Humidity > 97% to be -1.5 MPa or greater -1.5 MPa

  14. Water in the plant: leaf • Water exits thru: • epidermis (cuticular transpiration): <10% • stomates (stomatal transpiration): most loss Fig. 3.9a Fig. 3.9b

  15. How control leaf water loss? • 1) Cuticle • Ex: Cakile constricta

  16. How control leaf water loss? • 2) Stomate properties • Density: few saves water • But

  17. How control leaf water loss? • 2) Stomate properties • Density affected: light, temp., CO2(more CO2 -- density less) • Density change last 200 yr?

  18. How control leaf water loss? • 2) Stomate properties • Arrangement: top/bottom • Often: more

  19. How control leaf water loss? • 2) Stomate properties • Behavior: close stomates--abscisic acid Abscisic acid

  20. How control leaf water loss? • 3) Boundary layer • Boundary layer (BL): Slow-flowing • Water diffuses (slow) • Thick BL slows loss

  21. How control leaf water loss? • 3) BL thickness • BL thickness (delta) • Decreases as wind increases • Increases as leaf size • Big leaves—thick

  22. How control leaf water loss? • 3) BL thickness • How increase BL thickness? • Increase leaf Ceratiola ericoides Magnolia macrophylla

  23. How control leaf water loss? • 3) BL thickness • How increase BL thickness? • entire

  24. How control leaf water loss? • 3) BL thickness • How increase BL thickness? • Do NOT divide blade

  25. How control leaf water loss? • How increase BL w/o change leaf dimensions? • Hairs (trichomes) or spines (modified ______)

  26. How control leaf water loss? • Stomatal crypts: stomates

  27. How control leaf water loss? • Increases dist. H2O diffuses (slows loss) • BL

  28. How control leaf water loss: Review

  29. Dew (Good and Bad) • Dew: Water condensation • Good dew: Reduce loss • increases

  30. Bad Dew • CO2 diffuses 10,000x slower H2O than air • Decrease CO2 uptake • Response: unwettable leaves Leaf from cloud forest plant

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