compared to non-stressed plants. Shoot dry
weight of cv Madison decreased compared
to its control at the same time (Table 3). Salt
stress also had a significant negative effect
on root dry weight. The effect of salinity on
root dry weight was greater than shoot dry
weight because root dry weight of both cvs
decreased even at the lowest level of
salinity. Root dry weight at the lowest level
(50 mM) of salinity decreased by 34.8%
compared to root dry weight of non-stressed
plants (Table 3). This might be due to the
type of sugar beet root (storage root) and
also water deficiency caused by
concentration of salt in the growth medium.
Abdollahian-Noghabi (1999) found that
shoot/root ratio of Beta vulgaris increased
under drought stress condition. The root
percentage reduction of cv P29 was less than
that of Madison at high level of salinity
(Table 3), although both were severely
influenced. A possible reason for dry matter
reduction could be the greater reduction in
uptake and utilization of mineral nutrients
by plants under salt stress. Pessarakli and
Tucker (1985, 1988) reported that total
nitrogen uptake of cotton plants decreased
with increasing salinity, reflecting primarily
a dry matter reduction. The uptake of
nitrogen (N) in salt stressed plant might be
competitively limited by Cl-
(Aslam et al.,
1984; Ward et al., 1986).
Leaf Gas Exchange
Net Photosynthesis (ACO2) significantly
(P≤ 0.001) decreased with increasing salt
concentration (Figure 1-a). Plants grown at
low and high levels of salinity had rates that
were , respectively, 80% and 8.3% of the
controls. Analysis of variance revealed that
there were no significant differences
between the two cultivars in the rates of net
photosynthesis, but cv Madison had higher
net photosynthesis than P29. Net
photosynthesis rate generally decreased with
leaf age (Figure 1-b) and this was paralleled
by a lower stomatal conductance. Net
photosynthesis rate of cv Madison was
significantly decreased at the lowest level of
salinity (50 mM), while P29 had a higher net
photosynthesis rate compared to its control
at the same salt concentration but this was
not significant. The photosynthetic rates of
old leaves of Madison plants grown at 250
mM salt concentration were below the
compensation point, while P29 still
maintained rates above the compensation
point. The photosynthetic rates of old leaves
of plants grown at 350 mM of salt
concentration were at the compensation
point and below it for, respectively, P29 and
Madison cultivars (Figure 1-b). Therefore,
old leaves of these plants were effectively
parasitic, whereas old leaves of non-stressed
plants and those grown at low levels of
salinity still made a positive contribution to
the carbon economy of the plant.
The adverse effects of salinity on net
photosynthesis (ACO2) was associated with a
significant (P≤ 0.001) decrease in stomatal