Agriculture Reference
In-Depth Information
−
1.0
−
2.0
−
3.0
Ψ
s
at 100% RWC
−
4.0
l
=
0.1 cm s
−
1
Ψ
w
at g
−
5.0
June
July
Aug.
Sept.
Date
Figure 12.3
Seasonal changes in mature apple leaf osmotic
potential (
ψ
)
at 100% relative water content (RWC) and in the water
s
potential (
ψ
w
) required to close stomata to a conductance of
0.1 cm s
−1
. Reproduced from Lakso
et al.
(1984) with permission.
a fairly steady increase in stomatal conductance of 'Golden Delicious' apple
leaves as ambient CO
concentration was reduced from about
ll
−
to
µ
ll
−
but for some other cultivars there was a step-change with very
low conductances at more than
about
µ
ll
−
and high conductances at less than
µ
ll
−
. West and Gaff (
about
µ
) found that whereas leaf resistance in
ll
−
CO
) increased rapidly as water potential fell
normal air (around
µ
below
−
.
MPa in CO
-free air it was independent of water potential to
−
.
MPa.
The long-established effect of light on stomatal opening may operate, at least
in large part, through its effects on internal CO
concentration. West and
Gaff (
) found maximum conductance in 'Granny Smith' apple leaves to
be attained at
Wm
−
(about
% of full sunlight) with no response to further
increases in intensity. Others have found light-saturation at about
% of full
sunlight (Lakso,
).
