Grassland ecosystems play important roles in regulating the climate and maintaining global biodiversity (Habel et al., 2013; Binder et al., 2018). Grazing is the most common land use in grassland ecosystems (Allred et al., 2011), and it affects the processes and functions of grassland ecosystems, especially grassland community characteristics (Song et al., 2020) and element cycling (Yan & Lu, 2020).
In recent decades, under the continuous influence of human factors, large grassland areas on the Mongolian Plateau have been degraded to varying degrees (Wang et al., 2017). In particular, in desert grasslands where the average annual precipitation is less than 200 mm and long-term overgrazing occurs, the peak standing crop yield decreases steadily (Wang et al., 2014a). Therefore, understanding the ecological processes taking place in vegetation and soil on desert steppes under grazing stress is very important for the protection and management of plant species and for understanding community feedback and maintenance mechanisms.
As herbivores are responsible for rangeland degradation, it is not tenable to explain plant responses under livestock feeding. The existing literature suggests that grazing not only directly affects the community structure, primary productivity, biodiversity and ecosystem stability of grasslands (White et al., 2000; Schönbach et al., 2011; Cao et al., 2013) but also indirectly affects the chemical properties of soil (Cao et al., 2017) because livestock, vegetation and soil are complete microecosystems. Soil stoichiometry can provide a good framework for such multilevel research. Stoichiometry can explain the energy balance of ecosystems and the interactions of various chemical elements within ecosystems. Stoichiometry provides a new perspective for exploring the biochemical cycles of specific populations, communities and ecosystems (Wang et al., 2014b) and reflects the adaptation strategies of plants in specific habitats (Sterner et al., 2002; Elser et al., 2000; Yan et al., 2016). Through the study of the C, N and P contents of plant leaves and C, N and P stoichiometry, we can clearly understand the nutrients in the soil and the nutrient absorption and assimilation abilities of plants because there is usually a reciprocal nutritional relationship between plants and soil.
In addition, studies have shown that grasslands and grassland ecosystems are affected by grazing intensity. Wang et al. (2014a) indicated that the peak standing crop yield decreases with an increasing grazing intensity. Song et al. (2020) indicated that grazing intensity affects the plant function of grasslands. Grazing intensity may alter the C, N and P contents and stoichiometry of plants, and it affects C, N and P accumulation in soil (Han et al., 2008; He et al., 2020; Yan & Lu, 2020). Han et al. (2008) indicated that the N content increases with an increasing grazing intensity in nonlegume species. He et al. (2020) found that a heavy grazing intensity decreases C:N and C:P. These finding reveal that the direction of grassland development, including plant functions and C, N and P stoichiometry, is affected by grazing intensity.
Previous studies have focused on the changes in underground grass vegetation (such as its composition, structure, diversity and biomass) and soil characteristics (such as the water content and carbon storage) (Zhang et al., 2011; Jing et al., 2014). However, this study analyzed the characteristics of plant communities and C:N:P stoichiometry in a desert steppe under different grazing treatments for three consecutive years. Specifically, we addressed the following questions: 1) How do different grazing treatments affect the coverage, biomass, litter biomass and species richness of a plant community? 2) How do plant and soil C, N and P contents and stoichiometry respond to grazing treatments?