Geoscience Reference
In-Depth Information
Fig. 13.9
Leaf carbon isotope ratio of
´
3
(
T. hispida
)and
´
4
(
H. aphyllum
) species along salinity
gradient
community its amount becomes comparable to the proportion of C
3
species.
´
4
species are mostly due to the salt affected soils and Na
C
is essential for C
4
species
(for the translocation of pyruvate across the chloroplast envelope) where it functions
as a micronutrient and to some extent all Chenopodiaceae species (studied
´
4
chenopods) are halophytes (Akhani et al.
1997
; Toderich et al.
2007
). Although in
the case of vegetation cover of Karakum desert (Pyankov et al.
2002
) and grasslands
of Argentina (Feldman et al.
2008
) the increased amount of C
4
species compared to
C
3
species has been shown along the gradient of deterioration of soil condition and
soil salinization. Significant dependence of C
3
species on soil salinization indicates
a reduction of carbon isotope discrimination (
13
C value) of studied C
3
species along
the salinity gradient (from
27.39 to
24.79 ‰) (Fig.
13.9
). A 2 ‰ differences
13
C value of
in
´
3
plants indicates a difference in water-use efficiency of about
30 % (Ehleringer and Cooper
1988
; Ehleringer et al.
1998
;Dawson
1993
). In this
case, C
4
species demonstrates independence of
13
C value along the salinity gradient
(Fig.
13.9
).
A positive correlation of total productivity of main plant communities along
the gradient of salinity with vegetative cover of C
4
species, especially due to the
perennial C
4
tree and shrubs like
Haloxylon aphyllum
and
Calligonum leocacladum
was identified. The dominance of C
3
species in spring and early summer seasons in
the studied areas is determined by abundance of short-live species of ephemerals
and ephemeroids. The high ratio of C
4
species in summer comes from annuals
halophytes from genus
Salsola
,
Climacoptera
,
Suaeda
etc. (more than 40 % among
total C
4
species of haloxerophytic plant community). Species with C
4
type of
photosynthesis with high transpiration efficiency are better adapted to soil water
deficit or physiological drought that is strongly expressed in summer period, thus,
the productivity of C
4
species within different desert plant communities are not very
dependent on the regime of rainfall.
Search WWH ::
Custom Search