Soil Plant Water Relations

Water travels from

high potential to low

Rate of water transfer is proportional to (2)

difference in potential

Jw

Water flux

E=(pa-ps)/(rs+ra)

p=vapor concentration r=resistance

Ψs

submergence (hydrostatic pressure)

Plant water potential =

matric +solute+gravitational+turgor

Typical value of dry air

-100MPa

PWP

-1.5Mpa or -2.5Mpa trees

FC

-0.033MPA or -0.010Mpa sand

Hydraulic Conductivity and Hydraulic Resistance relationship

inverse x=1/y

Hydraulic Conductivity with W

Declines Exponentially

Xylem Resistance decreases with

increased root length

Stomatal Resistance increases with

decreasing leaf turgor potential

How do Plants Adapt to Water Deficits?

Drought escape

Drought Avoidance

Drought Tolerance

Drought escape

1. short life cycle during wet periods

2. avoid critical growth in dry periods (short season crops have a lower yield ceiling)

Drought avoidance (water conservation)

1. sensitive stomatal response

2. pubescence (increased boundary layer resistance)

3. roll and/or shed leaves early

4. store water in root/stems or deeper rooting patterns

increasing root:shoot

decreased hydraulic resistance

Drought tolerance (withstanding low water potentials)

1. maintain higher turgor (high stomatal conductance)

2. tolerate tissue desiccation

WUE order

C3≤woddy plants<C4<CAM

WUE is relationship between

NPP and ET

WUE =

yield per area per water/NPP