The concentration of^15 N in roots was higher than in shoots for all treatments at both stages of growth
(Table 4). Adsorption of ammonium ions to the root surfaces or infusion of ions into apparent free space
within roots, as suggested by Pessarakli and Tucker [60–63] and Pessarakli [55,86,94,95], could be a pos-
sible reason for the higher^15 N concentrations in cotton roots. At both stages of growth, the^15 N concen-
tration of shoots significantly increased for salinized plants (0.8 MPa) compared with the controls. This
can be explained as a dilution effect as suggested by Frota and Tucker [82], Saad [84], Pessarakli and
Tucker [60–63], and Pessarakli [55,94,95], as being due to a greater reduction in plant growth than^15 N
absorption under stress conditions. The relative translocation of^15 N from roots to shoots was not appre-
ciably affected by salt concentration.
- Total N Uptake by Plants
Total N uptake by plants decreased as the culture medium became more saline (Table 5). The reduction
in total N uptake values at 0.8 MPa osmotic potential was to approximately 50 and 70% of the control
RESPONSES OF COTTON TO SALT STRESS 687TABLE 3 Distribution of^15 N Absorbed as Ammonium in Cotton Shoots and Roots Under Different
NaCl Salinity Levels at the Beginning of the Reproductive Stage of Growth(^15) N uptake/pot (two plants) (mg)
Treatment, osmotic potential Uptake time, hr
Plant parts (MPa) 6 12 24
Shoots Control 1.77 4.11 8.57
0.4 1.91 3.78 8.64
0.8 1.49 3.55 8.45
1.2 1.15 2.18 4.67
LSD (.05)a 0.43 0.64 1.67
Roots Control 1.32 2.44 5.49
0.4 1.62 3.07 5.68
0.8 1.58 2.85 5.65
1.2 1.01 1.81 3.39
LSD (.05)a 0.39 0.65 1.80
Total Control 3.09 6.54 13.99
0.4 3.53 6.85 14.32
0.8 3.07 6.40 14.10
1.2 2.16 3.99 8.06
LSD (.05)a 0.21 0.60 1.71
aThe least significant difference among the means at the .05 probability level.
Source: Ref. 62.
TABLE 4 Nitrogen (^15 N) Concentration of Cotton Plants During Vegetative and
Reproductive Stages of Growth as Influenced by NaCl Salinity
(^15) N concentration
Treatment, osmotic potential (mg
(^15) N/kg dry wt)
Growth Stage (MPa) Shoots Roots
Vegetative Control 917 3462
0.4 1261 4330
0.8 1609 4195
1.2 1059 3180
LSD (.05)a 384 586
Reproductive Control 422 1408
0.4 517 1427
0.8 698 1605
1.2 615 1401
LSD (.05)a 109 245
aThe least significant difference among the means at the .05 probability level.
Source: Ref 62.