Agriculture Reference
In-Depth Information
200
180
160
140
120
100
80
0
2
4
6
Days since treatment
8
10
12
Figure 12.2
Daily growth increment of apple plants following
treatment on the 24th day after water was withheld. Plants with half of
their roots in dry soil [—]; rewatered plants [
]; plants with roots in dry
soil excised [
] and plants well watered throughout [
]. Reproduced
from Gowing
et al.
(1990) with permission.
•
a number of ways while there is still appreciable available water in some soil
zones.
Stem water relations
The longitudinal resistance to water flow in stems is small, being least in the
main trunk and increasing towards the branch ends (Landsberg and Jones,
).
At high levels of tension, shown by very negative leaf water potentials, the
watercolumnsinxylemvesselscansnap,leadingtoembolisms. JonesandPena
(
) found that the cross-sectional area of wood that was conducting was
markedly reduced by a single drought to a leaf water potential of
MPa.
This effect may be partially offset by continued differentiation of new vessels
throughout the season.
Water stored in the trunk is withdrawn during the day and replenished
at night. This has a buffering effect, reducing the impact of transpirational
−
.
