3.2 Soil nutrient and stoichiometric characteristics
Soil degradation was one of the important characteristics of
desertification. With the development of desertification, the
degradation of soil physical and chemical factors had gradually
increased (Wang et al., 2018). Related studies have found that, with the
succession and development of desertification, and the content of soil
organic matter and total N decrease significantly (Meng et al., 2018).
In this study, from TS, TSD to TD, the total porosity, total N and soil
organic matter were significant decreased, and soil bulk density and pH
were significant increased. But the total P, total K and available P
were in order of TSD < TD < TS. Due to the long-term
warming and drying of the climate, the succession of temperate steppe to
Temperate Steppe Desert has been induced. The vegetation type had
evolved from herbaceous to semi-shrub (Wu et al., 2017). The decrease in
vegetation litter amount and the decrease in decomposition rate
(decomposing bacteria activity decreased) were co-leading of the reduced
soil carbon, nitrogen, and phosphorus nutrients, which turned the
changes of soil pH, porosity and bulk density. At the same time, soil
changes had a negative effect on vegetation, which was caused the
heterogeneity absorption of trace elements by vegetation (Tao et al.,
2019). Soil ecological stoichiometric characteristics (C/N, C/P and N/P)
have a strong regulatory effect on the carbon fixation process in
terrestrial ecosystems (Zhang et al., 2016), which is an important
parameter to measure soil quality (Liu et al., 2021), reflecting the
ability of soil to release nitrogen and phosphate mineralized nutrients.
The optimal C/N required for microbial life activities was 25 (Tessier
and Raynal, 2019), which is the most favorable ratio for the conversion
of organic carbon. In this study, from TS, TSD to TD, C/N rate was
decreased, and C/N of TS, TSD to TD was 15.70, 10.13 and 5.80,
respectively. That was, TS was good for microbial life activities, but
TSD and TD was bad for microbial life activities. Soil C/P ratio was an
important indicator of soil phosphorus mineralization capacity, which
could measure the potential of soil organic matter mineralization to
release phosphorus or absorb phosphorus fixation (Zhang et al., 2018).
In this study, from TS, TSD to TD, C/N was decreased, and C/P of TS, TSD
to TD was 63.17, 10.04 and 2.98, respectively. The N/P ratio was used as
an index for determining the nutrient factors that limit productivity,
and N/Pīš¤10 and N/P>20 were used as indicators to evaluate
the productivity of vegetation limited by nitrogen or phosphorus(Li et
al., 2018). In this study, from TS, TSD to TD, C/N was decreased, and
N/P of TS, TSD to TD was 4.02, 1.00 and 0.53, respectively. That was,
productivity was increasingly limited by soil nitrogen from TS, TSD to
TD.