Agriculture Reference
In-Depth Information
Time of day (h)
noon
6
12
18
−
5
−
10
−
15
−
20
−
25
−
30
Figure 12.4
Diurnal changes in
)ofan
irrigated apple tree on a sunny day in July in southeast England and
diurnal change in
ψ
w
(o-o) and
ψ
s
(
-
•) growing at
Griffith,NSW (fr om Klepper,1968). Reproduced from Goode and
Higgs (1973) with permission.
ψ
w
of an irrigated pear tree (
•
--
Control of leaf relative water content (RWC)
ψ
l
. In orchard trees of 'Golden
RWC is approximately linearly related to
Delicious'/'M.
' in England it varied from nearly
% at leaf (xylem) po-
tentials of around
−
.
MPa or less, to
-
%at
−
.
MPa ( Jones and
Higgs,
). Previously water-stressed trees had
higher RWC values at any given water potential. At Geneva, New York, RWC
declined through the morning from around
; Fanjul and Rosher,
%to
%as
ψ
l
declined from
−
MPa to
−
.
MPa. The changes were reversed in the afternoon (Davies
and Lakso,
).
Control of leaf osmotic (
ψ
s
) and turgor (
ψ
p
) potential
As transpiration-stream water tensions increase, i.e. as its water potential
ψ
w
becomes more negative, cells lose water to it along gradients of potential.
This may, in many plants, simply continue until the resultant increase in
