Introduction
”Desertification” refers to land degradation caused by climate change
and human activities in arid, semi-arid and semi-humid arid regions
(Liu, 1998), which is a global environmental problem that plagues human
development, and one of the current ecological research hotspots (Gao et
al., 2019). Relevant studies have shown that the global arid area is
6.1×108 hm2, among which China has
2.97×108 hm2, and the arid areas
have different degrees of desertification. From 1984 to 1991, the global
land desertification accelerated at an annual rate of 3.4% (Office of
Desertification Prevention and Control, Ministry of Forestry of the
People’s Republic of China, 1994). With global warming, the disorderly
development of resources and the urbanization process, desertification
may become a major ecological problem and challenge in the 21st century
(Li et al., 2019; Rong, 2019). Therefore, understanding the rules of
desertification, that is, the change characteristics and mutual
relationship of vegetation and soil, has important ecological
significance for slowing down the desertification process and vegetation
restoration and reconstruction in desertified areas.
Qilian Mountain is located on the eastern edge of the Qinghai-Tibet
Plateau in China, adjacent to the Mongolian Plateau and the Loess
Plateau (Gao et al., 2019). The Qilian mountains is the intersection of
the Qinghai-Tibet Plateau, the Loess Plateau and the Inner Mongolia
Plateau, with a fragile ecological environment, and is also one of the
most sensitive regions for global climate change (Wang et al., 2001).
Grassland is the largest vegetation type in Qilian Mountains (Li et al.,
2019). Therefore, the health of the grassland ecosystem in the Qilian
Mountains is not only related to the water source security in the Hexi
region, but also related to the ecological security and social stability
in northwest China (Yao et al., 2018). Related studies have found that
the climate change in the eastern part of Qilian is warm and humid,
while the central and western regions is warm and dry (Rong, 2019).
Therefore, climate change poses a serious challenge to the ecology of
the Qilian Mountains. The warming and humidification of the climate in
the eastern region had caused the degradation of alpine meadows and the
shift of the snow line, while the warming and drying of the climate in
the central and western regions led to the succession of temperate
steppe to temperate desert steppe and temperate desert (Rong, 2019).
Succession of grassland desertification will lead to a series of
grassland ecological changes, such as changes in vegetation community
structure, soil nutrients, microbial composition, etc. (Rong, 2019).
Tang et al. (2016) found that the effects of desertification on total
phosphorus and available phosphorus were not significant, and
desertification decreased productivity in the desert steppe as a result
of direct changes to soil physical properties, which can directly affect
soil chemical properties. Li et al. (2006) found that soil organic
matter is also reduced with desert development, which leads to
destruction of the stability of soil physical structure and nutrient
content, such as progressive N, P and K loss in surface and subsoil
layers, and in response to changes in soil properties, vegetation
altered as regards species composition, species diversity, coverage,
structure and life-form (Tang et al., 2016). Therefore, a systematic
understanding of the vegetation and soil change characteristics in the
process of grassland desertification is of great significance to the
restoration of desert grassland.
At present, most of the research on grassland desertification focused on
the degradation of desert grassland. According to the degradation
standard, the desert grassland is divided into several degradation
gradients to study the relationship between vegetation community
structure and soil nutrients (Rong, 2019; Li et al., 2006; Tang et al.,
2016). Because grassland desertification is a process of long-term
succession of grassland under warm and dry climate, this study used the
method of replacing time with space, and selects three types grassland
(temperate steppe, temperate steppe desert and temperate desert) as
research objects replacing desertification succession. The
characteristics changes and relationship of vegetation and soil factors
were analyzed during the succession of temperate steppe to temperate
desert, which could provide theoretical basis and data support for
curbing grassland desertification and inducing forward succession of
desert grassland.