1. Mar. 3rd, 2011 B4730/5730 Plant Physiological Ecology
Water Transport I

2. Root Anatomy and Water Relations
Tradeoffs between safety and efficiency
Exodermis
Roots hairs, mycorrhizae
Casparian strip
Apoplast and symplast
Transcellular
Endodermis
Root branching
Stele
Secondary growth, cambium
Xylem and phloem
Root cap

3. Agave deserti; North et al. 2004 PCE

4. Root Water and Aquaporins Transport
Agave deserti;
North et al PCE

5. Pressure Volume Curves
Relationship between tissue pressure and volume describe effect of dehydration
Uses Boyle-Mariotte Law that PV=constant
Ψ is substitute for pressure
Extrapolation to Ψπ
Relative Water Content substitute for volume
Graphs drawn with 1/RWC
ε derived from nonlinearity between full turgor and turgor loss point
Osmotic adjustment shifts turgor loss point to lower RWC

6. Niinemets Ecology 2001

7. Glyricidia sepium Brodribb & Holbrook Plant Phys. 2003

8. Brodribb & Holbrook Plant Phys. 2003;
dotted lines 80% and 20% maximum gs

9. Salt Effects
Phillyrea latifolia; Tattini et al. 2002

10. Cohesion-Tension Theory
Dixon in late 19th century proposed water transport to top of tall plants by cohesion/tension
Driven by soil to air water potential gradient
Hydrogen-bonding creates tension
Challenged throughout 1990s
Alternatives included metabolic pumping
Centrifuge and killed wood provided very strong support of cohesion-tension

11. Soil Water Movement
Soil Texture Changes Soil Water Characteristic curves
Coarse textured soils hold less water less tightly than fine texture soils
Soil hydraulic conductance changes
Calculating available water requires knowledge of soil water content dynamics and rooting depth
H2O = Θ·depth
Benefit of fine textured soils for plant water drops with decreasing precipitation
Transition at 400mm (Noy-Meir 1973)

12. Water Transport in Xylem
Overproduction of vascular tissue is wasteful and underproduction restricts growth
Plant transport system is efficient yet a large proportion of the decrease in leaf water potential is from hydraulic conductance (20-60%)
Hydraulic conductance dynamics depends on
length
Area of Xylem
Number, type and size distribution of xylem conduits
Cavitation

13. Pinus taeda, PCE Ewers et al. 2000

14. Mencuccini et al PCE