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