92
R.H. Waring and W.E. Winner
1.0 ....-cn--.---.-----.-----,---,---,
o
-1.0
-2.0
-3.0
Predawn Water Potential, MPa
Figure 6.2. As soils dry, predawn water potentials in Douglas fir decrease.
Maximum relative stomatal conductance during the day also decreases until
complete closure is attained at -1.6MPa. From Waring and Schlesinger (1985) .
Below-freezing air temperatures and cold soil temperatures also restrict
the uptake of water and the degree that stomata open. Conifers in
the Pacific Northwest show some differences in sensitivity to cold soil
temperatures only up to about lOoC, as shown in Figure 6.3. All the
w
U
Z
~
Ci5
w
a:
w
>
~ w a:
15
o
5
10
ROOTTEMPERATURE (0C)
Figure 6.3. Five species of Northwest conifers-Abies amabilis (0), A . procera
(6), Thuja plicata (.), Tsuga heterophylla (0), and Pseudotsuga menziesii
(.)-show differences in their relative resistance to water uptake when root
temperatures are only below woe.
R.H. Waring and W.E. Winner
1.0 ....-cn--.---.-----.-----,---,---,
o
-1.0
-2.0
-3.0
Predawn Water Potential, MPa
Figure 6.2. As soils dry, predawn water potentials in Douglas fir decrease.
Maximum relative stomatal conductance during the day also decreases until
complete closure is attained at -1.6MPa. From Waring and Schlesinger (1985) .
Below-freezing air temperatures and cold soil temperatures also restrict
the uptake of water and the degree that stomata open. Conifers in
the Pacific Northwest show some differences in sensitivity to cold soil
temperatures only up to about lOoC, as shown in Figure 6.3. All the
w
U
Z
~
Ci5
w
a:
w
>
~ w a:
15
o
5
10
ROOTTEMPERATURE (0C)
Figure 6.3. Five species of Northwest conifers-Abies amabilis (0), A . procera
(6), Thuja plicata (.), Tsuga heterophylla (0), and Pseudotsuga menziesii
(.)-show differences in their relative resistance to water uptake when root
temperatures are only below woe.