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Water Relations and Energy Balance in Plant Physiology

Explore the path of water from soil to air in plants, focusing on the role of stem xylem, adhesion, cohesion, and water potential. Learn about the mechanisms controlling leaf water loss and the impact of environmental factors on plant hydration.

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Water Relations and Energy Balance in Plant Physiology

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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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