Chemistry Reference
In-Depth Information
Figure 5.
Some plants have roots growing in the deeper soil layers toward the water table,
Helianthemum lipii
.
3.2. Halophytic plants
Halophyte plants in Qatar are living near the coastal line, and in other inland areas like
Subkhas, including some species of the genera
Anabasis, Arthrocnemum
,
Atriplex
,
Avicennia
,
Halocnemum
,
Halopeplis, Limonium
,
Salsola, Seidlitzia
,
Suaeda
and may be many others.
These
plants have two main mechanisms to cope with saline environments: (a) Avoidance
mechanisms, (b) Tolerance mechanisms [9, 15, 26, 41, 43].
(a) Avoidance mechanisms
These mechanisms involve structural and physiological adaptations to minimize salt
concentrations in the cells or physiological exclusion by root membranes. Plants can use one
or more of the following secondary mechanisms to avoid salt stress at their environment:
exclusion, extrusion and dilution.
i.
Exclusion mechanism: plants having such mechanism may exclude ions at different
locations along plant organs: (a) at the surface of the roots (b) between shoot system and
root system, and (c) between leaves and petioles or sheaths. The best example of
exclusion mechanism at the root surface was found in Date Palm trees (
Phoenix
dactylefera
), which seems excluding Na
+
and Cl
-
from the root, by having a barrier at the
root surface, since the uptake of Na
+
and Cl
-
was not proportional to the concentration
of these ions in the external solution. The efficiency of exclusion increases with
increasing salinity in the growth medium, and as a result, the accumulation of Na
+
and
Cl
-
in the tissue was not much greater at high than at low salinity levels, and there were
no visible symptoms of salt injury [15, 44]. Halophytes and may be many glycophytes
