the halophytes, can grow under saline conditions. These halophytic species that live under conditions of
high salinity exhibit succulence, which might resort to other physiological adaptations to overcome the
adverse saline environment in the soil. Their extreme tolerance to salinity is related to their ability to
maintain a high salt concentration within their cells. In desert areas salinity is often very prominent,
caused by the input of sodium chloride and other salts for a long period of lack of drainage. On such saline
soils, typical associations dominated by Chenopodiaceae often develop along the salt gradients [6]. Plant
species growing in an area may provide useful information regarding the degree of salinization and con-
sequent soil deterioration. Such information may be helpful in more effective planning for practical uses
of wastelands.
A. Studies of Saline Areas and Their Vegetation Cover
In the early 19th century, an enormous amount of work was done on this special group of plants,
and this topic has been discussed periodically in many reviews and books covering manifold aspects
[7–35]. The major findings reveal that the salt-affected soils have multiple effects on plants. Seed ger-
mination, mortality, and growth of halophytes are controlled in nature by the interaction of soil salin-
ity and moisture. The ionic and toxic effects of various salts, especially of NaCl, play a major role in
halophytism. Increased osmotic stress due to drought and the high rate of evaporation during the sum-
mer months may cause rapid changes in the density and diversity of species in halophyte communities
[15,16]. Seasonal precipitation is often a major factor determining soil water potentials. This factor
in turn affects the establishment of seedlings, often increasing the rate of mortality during drought
periods [17].
Although the salt accumulation nature of halophytes has been recognized for many years, only dur-
ing the last three decades was it shown that sodium is essential for the growth of some Chenopodiaceae
[18]. Strogonov [19] assumed that the survival of plants in saline environments depends upon altered bio-
chemical reactions and on a quantitative ratio between the toxic and protective (i.e., proline) compounds.
Stewart and Lee [20] supported the view that proline functions as a source of solute for intracellular os-
motic adjustment.
II. BIOLOGY OF NATIVE HALOPHYTES
Despite the wide distribution of halophytes in various climatic regions, their taxonomic, structural,
and behavioral uniformity is striking. Salinity is known to affect many aspects of plants, which induces
numerous changes in their morphology. These changes would be adaptations that increase the chance
of plants to endure stress imposed by salinity or damage and disrupt the normal equilibrium of life pro-
cesses [11]. In saline soils, the most common adverse features are delayed germination, high
mortality of seedlings, and poor growth of crops. Plants are stunted, less vigorous, and give poor
yield.
The precise effects of salinity and the sites where salinity may affect plants are not easily assessed.
Because both salt combination and salt concentration differ from one habitat to another, the term “salin-
ity” usually has a loose meaning. In certain cases, it is not the absolute amount of a certain ion that may
affect plants but rather the composition and total concentration of salts. Certain species of plants may be
found in sites where the sodium chloride concentration is beyond their theoretical tolerance but where
high concentrations of calcium, potassium, or sulfate are found as supplementary ions. These ions mod-
erate the toxic effects of sodium and chloride, thus enabling plants to exist.
The ecological limits for distribution of plant communities depend upon the presence of soluble salts
in the water or soil. The water of the habitat is the dominant ecological factor that determines the distri-
bution of species. Thus, the distribution of a halophytic community appears to be limited by salinity and
the depth of the water table as well as by the competitive ability of members of the next community in the
development of halophytic vegetation [31,32]. It is suggested that because sharp boundaries are observed
between halophyte communities even when there is only a gradual change in the physiochemical envi-
ronment, biotic interactions may play a significant role in determining the distribution pattern of species
and the composition of zonal communities [33].
564 SEN ET AL.