Chemistry Reference
In-Depth Information
1.
Morphology and behavior of stomata:
stomata are differing in plant species in their
number and distribution on both surfaces of the leaf, size, shape and behavior. These
features are species-specific characteristics, and vary with the adaptation to stress
conditions. In
Cyperus conglomeratus
, stomata appear only on the abaxial surface of the
leaves and these stomata are sunken [18]. Moreover, most plants living in the desert
areas or saline soils close their stomata during periods of osmotic stress except CAM
(Crassulacean Acid Metabolism) plants. However, many plants have special
physiological and biochemical features to cope with the harsh environments [19-21].
Data from glycophytes have revealed considerable reduction in the stomatal
conductance with salinity [22]. In this respect, it should be understood that stomatal
closure may help maintain the water balance inside the plant. Thus, stomatal closure
can be considered as an adaptation characteristic that plants have in various degrees
under conditions of osmotic stress [22-24].
Cyperus conglomeratus
exhibits C4
metabolism and this characteristic might allow the plant to maximize rates of
photosynthesis by sustaining stomatal opening [25].
2.
Increased cuticle thickness by increasing the surface lipid:
the cuticle of plants under
osmotic stress may become more thickened than those living under normal conditions
(well irrigated or / and non-saline) [19, 22, 26]. The thickened cuticle is observed in
many of these plants like
Cyperus conglomeratus
and
Tetraena qatarense
[18].
3.
Decreased transpiring surface: the reduction in the leaf area is a common response to
osmotic stress, and could be a main reason behind the reduction in the total
transpiration rate in most plants [22, 27]. In fact, the reduction of leaf area at stressed
growth conditions has been considered as a complex response and can be seen as an
adaptation feature to reduce the water lost by transpiration process [28]. Some plant
species in the Qatari flora like
Ochradenus baccatus
showed great reduction in the size of
leaves to reduce the transpiring surface. In some other plants, rolling, folding, or
shedding of leaves are possible methods of drought avoidance mechanisms in many
desert plants [26].
Aeluropus lagopoides
is another example of wild plants having some
morphological modifications to cope with dry soils which include leaves linear;
lanceolate with small blades ending in sharp rigid points [4]. These plants might have
green stems to increase the photosynthetic efficiency under the severe environmental
conditions [29].
4.
Root adaptation: plant roots can contribute effectively to the drought avoidance
mechanism by three ways
:
(a) restricting the root surface and decreasing its
permeability to water, (b) quick development of roots to absorb rain water and
disappear soon after soil dries, and (c) roots can reduce transpiration by high resistance
to water [15, 30]. High Root / Shoot ratio, on the other hand, has been considered as a
trait of a plant having drought avoidance mechanism [19, 31],
Cyperus conglomeratus
is a
good example of such trait (Fig. 2) which helps withstand water stress by two ways: (1)
less water is needed for the top, (2) exploring larger volume of soil.
5.
Water storage: many plant species show succulence characteristics (Fig. 3); such plants
could have water cells in stems, leaves and roots, which might confer avoidance
mechanism against drought and water shortage.
CAM plants are good example of how
