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).