Geoscience Reference
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The total biomass for each subplot was determined by combining density data of
each species present. Cover of individual shrub species was determined from a 50 m-
line intercept along one edge of the 2 m
50 m plot.
Aboveground biomass of investigated species was harvested at the end of
October each year. Seasonal measurements of vegetation parameters (biomass,
density, vegetative cover) along the apparent grazing gradient were conducted
during 2005-2007. A conceptual framework of successive vegetation changes along
the grazing gradient was developed by applying State and Transition (S&T) models.
Vegetation data were analyzed by applying Non Metric Multidimensional Scaling
(NMS) ordination. Seasonal dynamics of the Normalized Difference Vegetation
Index (NDVI) derived from Landsat imagery were examined to detect the vegetation
changes caused by grazing. The vegetation succession was demonstrated as a
presence/absence of unpalatable/palatable species in plant composition as a function
of piosphere effects.
50 m and 5 m
2.1.2
Soil Sampling
Soil samples were collected from different depths (0-20; 21-40; 41-60; 61-90;
91-120 cm). Sodium (Na
C
) ion concentration was analyzed by water extract from
air-dry soil and plant samples (100 mg of sample) and detected on atomic adsorption
spectrophotometer (Hitachi 2007, Japan). Salinity gradient was characterized by
contents of Na
C
ions in the soil profiles. The regression analysis was applied to
investigate correlation between remote sensing data, Na
C
ion content and EC values
calculated from field data in order to predict soil salinity and vegetation changes.
Soil Salinity was also determined using an electromagnetic conductivity device
(EM38) was standardized at reference temperature of 25
ı
C as EC increases at a
rate of approximately 1.9 % (Rhoades et al.
1999
). We used the formula provided in
Sheets and Hendricks (
1995
), who fit the curve to a conversion table given in USDA
(
1954
): EC
25
D
(T/26.815)
], where EC
25
is standardized EC
a
EC
a
* [0.4470
C
1.4034
"
and T-soil temperature.
2.1.3
Carbon Isotope Analysis of Desert Vegetation
The distribution and abundance of desert plant communities were examined. Plant
species were collected along a sequence of increasing ground-water depths in eight
transects. Experimental data from Carbon and Oxygen isotopes were used to assess
the responses of native plants to salinity and the effect of salinization on natural
vegetation in Uzbek dryland ecosystems.
Carbon isotope composition (d
13
C) of plant material is related to intrinsic water
use efficiency in C
3
plants (Farquhar et al.
1989
). The positive correlation was found
between the salinity and the d
13
C of leaf organic matter both in salt-tolerant species
and salt-sensitive species (Seemann and Critchley
1985
). These reports indicate
that salt stress may decrease the CO
2
concentration inside the leaf via the stomata
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