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

Xylem cells –Vessels vs. tracheids

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

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

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

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

Water in the plant: stem xylem Conifer: tracheids top (psi lowest)

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

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

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

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

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

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

How control leaf water loss? 2) Stomate properties –Density: few saves water –But

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

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

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

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

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

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

How control leaf water loss? 3) BL thickness How increase BL thickness? –entire

How control leaf water loss? 3) BL thickness How increase BL thickness? –Do NOT divide blade

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

How control leaf water loss? Stomatal crypts: stomates

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

How control leaf water loss: Review

Dew (Good and Bad) Dew: Water condensation Good dew: Reduce loss –increases

Bad Dew CO 2 diffuses 10,000x slower H2O than air –Decrease CO 2 uptake Response: unwettable leaves Leaf from cloud forest plant