investigators [2,8,10,15,17,19,24,31] reported similar reductions in different parameters of cotton growth
and development under salinity stress that support the results of the present work.
In the present work, the dry-matter production of the stressed plants was highly negatively correlated
with increasing levels of salinity at both stages of growth (rof0.98 to 0.96). Reduction of plant
growth at higher levels of salinity has also been reported by other investigators for other salt-tolerant
plants, such as barley [43,128,129], mangrove, Avicennia marina[51], and other halophytes including
Suaeda maritimaL. [130]. Several other investigators, in stress physiology, found that the growth of var-
ious plant species substantially decreased under stressful conditions [34,35,37,40,44,45,47,48,
50–61,69–76,81–86,88,95,104–126,131–153]. The present study showed that the shoot dry weight was
reduced more by increasing salinity than the root dry weight. This is supported by the findings of several
other investigators [55–61,82–84,86,94,95,103,104,128,129] and is consistent with the common knowl-
edge in plant physiology that plant roots under stress conditions grow more and penetrate deeper in the
soil or in the root medium in search of water and nutrients. Other studies also indicated a substantial re-
duction in shoot growth under stress conditions. For example, sodium chloride stress severely decreased
shoot growth of rice, Oryza sativaL., cultivar GR-30 [154], and Lactuca sativaplants [155].
In the present study, the effect of salinity was more pronounced at the vegetative growth than at the
reproductive growth stage. Other studies have also indicated that plants at earlier stages of growth were
more sensitive to stress than those at later stages of growth [5,12,50,86,88,105–126,147,156–160]. Ab-
normal plant growth was also observed in experiments using sufficient amounts of salts other than sodium
chloride [81,123,127,130,161,162] as well as under drought stress conditions [71,107,109,124,
125,163,164]. This is an indication of the adverse effects of stress on plant growth regardless of the source
of the salt or the type of the stress.
B. Nitrogen Absorption by Cotton Plants
- Nitrogen (^15 N) Absorption and Concentration in Plant Tissues
The mean values for^15 NH 4 absorption by cotton plants for 24 hr uptake time, under normal Hoagland
solution (control) and salt (NaCl) stress conditions, obtained by analyzing solution samples indicated that
low and medium levels of salinity did not significantly decrease the rate of^15 N absorption (Figures 1 and
2). In fact, absorption was increased slightly at the vegetative stage at a low salinity level (0.4 MPa os-
motic potential). Similar amounts of NaCl drastically reduced the uptake rate of^15 N in red kidney beans
RESPONSES OF COTTON TO SALT STRESS 685Figure 1 Solution loss of^15 N (uptake) by cotton plants under various NaCl salinity conditions during the
vegetative stage of growth. (From Ref. 62.)