The Qinghai-Tibetan Plateau (QTP) is called “Asia’s water tower” because it is the headwaters of Asia’s major rivers, on which approximately 40% of the world population depends (Kuang and Jiao, 2016). The QTP is an important ecological barrier in China and even Asia. Alpine grassland is the main ecosystem on the QTP (Liu et al., 2018), accounting for more than half of the total plateau area. It has important ecological and socio-economic roles, such as storing carbon, altering biodiversity by evolving grass species that shape grassland environments (Gieselman et al., 2013), and impacting livestock by producing forage (Harris, 2010). Alpine grassland on the QTP is one of main pastoral areas in China and provides important grazing grounds for livestock. Furthermore, the QTP is highly sensitive to global climate change (Xu et al., 2008; Yao et al., 2012), and the warming rate on the QTP has been almost twice that of general global warming over recent decades (Kuang and Jiao, 2016). This means that the alpine grassland ecosystem on the QTP is sensitive and fragile (Guo et al., 2018).
Alpine grassland on the QTP has suffered from severe degradation due to climate change and human activities in recent decades (An et al., 2017; Harris 2010). Furthermore, alpine grassland degradation has led to a decline in grassland productivity, a decrease in biodiversity, and environmental deterioration (An et al., 2017). It has caused fragmentation of grassland coverage, a decrease in the proportion of edible herbage, a reduction in soil fertility, and soil erosion (Li et al., 2013). The alpine grassland ecosystem is under threat and grassland degradation has attracted substantial national attention.
There have been many studies on grassland degradation, and technological restoration solutions and measures have been proposed. Some researchers have investigated grassland degradation and restoration from the view point of plant community, including grass coverage (Zhang et al., 2014), grassland net primary production (Chen et al., 2014), and grassland yield (Cai et al., 2015). Some studies have investigated environmental issues, such as topographic parameters (Li et al., 2018) and soil condition (Harris, 2010), and a series of studies have analyzed the relationship between plant community and environmental parameters. Based on species dominance, some studies have investigated the effect of environmental factors on species diversity patterns among different plant community types (Jiang et al., 2016). In addition, natural gradient studies have been conducted to explore the mechanisms of species character changes. For instance, the relationships between the physico-chemical parameters of soil and plant species have been analyzed in terms of geological structure and lithology (Do Carmo and Jacobi 2016; Hanaka et al., 2019). Topography plays a crucial role in grassland degradation because it affects the distribution of moisture and energy (Li et al., 2018). The QTP has complex topographic features with contiguous mountains and hills. However, there have been few studies on how the relationships between plant species and soil parameters along the elevation gradient affect grassland degradation on the QTP.
This study focused on the relationship between species composition/diversity and soil parameters. We explored the effect of soil physico-chemical properties on plant species along an elevation gradient to provide information that could be used to improve the restoration of damaged grassland ecosystems and responses to climate change. The specific objectives were to (1) clarify significant differences in soil parameters at different elevations; (2) determine which soil parameters affect species composition and diversity, and (3) elucidate the effects of key soil parameters on species diversity at different elevations.