Our results also suggest that moderate water stress
has a speci
fi
c effect on root hydraulic conductivity because PEG
favoured water transport without affecting the solute concentra-
tion gradient between the root xylem and the growth medium, i.e.,
PEG did not affect the osmotic gradient, which is the main driving
force for root-water transport in non-transpiring plants (
Kramer,
1983
). Thewater
fl
owacrossroots (J
V
) is dependenton the osmotic
pressuregradientbetweenthexylemsapandtheexternalmedium
(
D
p
) and the root hydraulic conductivity (L
P
)(J
V
=
s
L
P
D
p
;
s
is the
overall re
fl
ection coef
fi
cient of the root, the value of which is
assumed to be unity) (
BassiriRab et al.,1991; Quintero et al.,1999
).
Because the water-stressed Olimpia cultivar exhibited greater
water
fl
ow after re-watering, without modi
fi
cation of the osmotic
gradient, we suggest that moderate water stress enhances root
hydraulic conductivity. This effect has also been observed in