Our results also suggest that moderate water stress
has a specific 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). The water flow across roots (JV) is dependent on the osmotic pressure gradient between the xylem sap and the external medium(D
p
) and the root hydraulic conductivity (L
P
)(J
V
=
s
L
P
D
p
;
s
is the
overall re
flection coefficient 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 flow after re-watering, without modi fication of the osmotic
gradient, we suggest that moderate water stress enhances root
hydraulic conductivity. This effect has also been observed in
Our results also suggest that moderate water stresshas a specific effect on root hydraulic conductivity because PEGfavoured 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 drivingforce for root-water transport in non-transpiring plants (Kramer,1983). The water flow across roots (JV) is dependent on the osmotic pressure gradient between the xylem sap and the external medium(Dp) and the root hydraulic conductivity (LP)(JV=sLPDp;sis theoverall reflection coefficient of the root, the value of which isassumed to be unity) (BassiriRab et al.,1991; Quintero et al.,1999).Because the water-stressed Olimpia cultivar exhibited greaterwater flow after re-watering, without modi fication of the osmoticgradient, we suggest that moderate water stress enhances roothydraulic conductivity. This effect has also been observed in
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