Mar. 3rd, 2011B4730/5730
Plant Physiological Ecology
Water Transport I
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
Agave deserti; North et al. 2004 PCE
Root Water and Aquaporins Transport
Agave deserti;North et al. 2004 PCE
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
Niinemets Ecology 2001
Glyricidia sepium Brodribb & Holbrook Plant Phys. 2003
Brodribb & Holbrook Plant Phys. 2003; dotted lines 80% and 20% maximum gs
Salt Effects
Phillyrea latifolia; Tattini et al. 2002
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
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)
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
Pinus taeda, PCE Ewers et al. 2000
Mencuccini et al. 2003 PCE
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