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a maximum in autumn, when photosynthetic activity was maintained to account
for transpiration losses. There was a general trend of increasing salinity and
concentration of different ions along the salinity gradient. The periodical variation
in the water table was insignificant, while a significant drop in salinity and the
concentration of different ions was detected in spring, which was attributed to
the diluting effect of rain water during that season. Analysis of cover vegetation
of each visually divided zone along a micro-scale level has assisted to determine
the dominant species in each zone, identified based on the total soluble salts in
the soils. In the first zone (named as wet solonchaks), where there was a high
mineral content, species of genus
Salicornia
,
Aeluropus
,
Suaeda
,
Halostachys
,
Halimocnemis
,
Climacoptera
were widely distributed. The vegetative period of all
these species begins fairly late because the marshes are under water for a long part
of the year.
4.2
Plant Density of
´
4
Species in Relation to Na
and K Accumulation and Biomass Productivity
´
3
-and
The highest density of xeropsammophyte and xerohalophyte plant communities
belongs to C
3
species consisting of 89-94 % and 74-91 %, respectively (Fig.
13.7
).
The ratio of C
4
plants showed smaller values than C
3
plants for both plant
communities. As its name implies, the plant density of haloxerophyte community
represented considerably rapid changes during the seasons in term of the ratio
of C
3
and C
4
plants. In spite of the dominancy of C
3
species in haloxerophyte
community, the proportion of C
4
species noticeably increased compared with other
plant communities. The contribution of C
4
species showed 19, 70 and 45 %
during spring, summer and autumn seasons, respectively. However, during the
summer season relatively increased values of C
4
species is observed for all plant
communities.
Data collected during many field expeditions throughout Kyzylkum desert and
Priaralie including plateau Ustyurt show clearly that there are changes between
perennial and annual rangelands species ratio along salinity and soil moisture
gradients. As is seen from Fig.
13.7
the biggest numbers of perennials occurs within
semi shrub plant community on non saline soils. With increasing of soil salinity
on typical halophytic plant community on solonchaks desert depression in botanic
diversity the perennials is decreasing up to 50 %, while percent of annual species
out of total plant diversity is sharply increased along salinity gradient.
Results showed that ratio of C
3
and C
4
plants in vegetation communities differ
both along the salinity gradient and on seasons of the year.
´
3
species such as
A. Lehmannii
,
A
.
diffusa
,
A
.
pseudoalhagi
, which occurred mostly on 1-3 ecological
zones and some of tree species accumulate insignificant amount of sodium in leaves
(0.63-7.34 g kg
1
of dry matter). Considerably high content of sodium (about ten
times higher) was found in the leaves of
P
.
harmala
(52.33 g kg
1
) which is one
of the plant components of haloxerophyte vegetation association. Such
´
4
species
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