4. Discussion
The effects of slope gradient and slope position on soil properties and vegetation have been studied extensively (Bennie et al., 2006), but their effects on soil microbial communities have remained largely unexamined. Soil bacterial and fungal communities are ecologically important groups, as soil bacteria have the largest biomass among soil microorganisms to maintain soil structure. Soil fungi are essential in soil aggregation and improving plant tolerance to drought and heavy metal contamination (Fitter, 2005; Rillig and Mummey, 2006; van der Heijden, 2008). In this study, the lower slope gradient may have suited habitat for soil bacterial communities due to significantly higher bacterial alpha-diversity and species richness. The community was dominated by Proteobacteria, which is similar to the observations from other soils collected from the Arctic (Chu et al., 2010), subalpine (Shen et al., 2013), and agricultural soil environments (Sun et al., 2015). The subsequent analysis of soil bacterial community composition according to different groups in each slope gradient revealed increasing differences among slope gradients. These results clarified soil bacterial community distribution with increasingly apparent effects of topography. Unlike bacterial alpha-diversity, the fungal alpha-diversity was untouched among slope gradients (Table 3), suggesting its resistance to slope gradients-induced interpretation in moisture, root biomass, and soil C, N fractions (Sun et al., 2018). However, fungal community composition showed strong sensitivity to slope gradients (Table 4), indicating that the phyla-type composition of the fungal communities could adapt accordingly to environmental changes without a general loss in diversity (Yuste et al., 2014).
Soil physicochemical characteristics influence the soil microbial community’s composition, activity, and microbial mass level (Dick, 1994; Xue et al., 2022). Clay content were higher in the lower slope gradient which might be the reason of high presence of microbial communities. Previous studies clarified that different soil textures influence the structure of the microbial community, especially bacterial populations (Fang et al., 2005). A possible explanation for the higher number of bacteria in soil with high clay contents was documented by Carney and Matson (2005). They mentioned that fine-textured soils support more microbial biomass than coarse-textured soils. The distribution of microorganisms in varied soil textures might be related to soil moisture and nutrient contents, as Herioge et al. (2003) explained. RDA analysis shows that pH highly correlated with microbial community (Fig. 3). The importance of soil pH in shaping the bacterial population by vertical soil profile has long been recognized (Yun et al., 2016). The close relationship of soil pH with the bacterial community is owning to the dependency of most of the bacterial community under narrow pH (Charokopos et al., 2010), and the slight change in pH significantly affects the bacterial community (Fernández-Calviño et al., 2010). Wei et al. (2019) revealed that N, P, K, and pH are essential sources of variation in soil fungal richness. Fungi play crucial roles in decomposing organic matter and forming an association with the roots for belowground carbon transport and respiration in the boreal forest (Clemmensen et al., 2013). Soil nutrients released by microbes are available for aboveground communities, supporting essential ecosystem services such as food and fiber production (Wardle et al., 2004).