• Soil bacterial community composition strongly differed along a short elevational gradient.

The elevational distributions of bacterial communities in natural mountain forests, especially along large elevational gradients, have been studied for many years. However, the distributional patterns that underlie variations in soil bacterial communities along small-scale elevational gradients in urban ecosystems are not yet well understood. Using Illumina MiSeq DNA sequencing, we surveyed soil bacterial communities at three elevations on Zijin Mountain in Nanjing City: the hilltop (300 m a.s.l.), the hillside (150 m a.s.l.), and the foot of the hill (0 m a.s.l.). The results showed that edaphic properties differed significantly with elevation. Bacterial community composition, rather than alpha diversity, strongly differed among the three elevations (Adonis: R² = 0.12, P<0.01). Adonis and DistLM analyses demonstrated that bacterial community composition was highly correlated with soil pH, elevation, total nitrogen (TN), and dissolved organic carbon (DOC). The degree scores, betweenness centralities, and composition of keystone species were distinct among the elevations. These results demonstrate strong elevational partitioning in the distributions of soil bacterial communities along the gradient on Zijin Mountain. Soil pH and elevation together drove the small-scale elevational distribution of soil bacterial communities. This study broadens our understanding of distribution patterns and biotic co-occurrence associations of soil bacterial communities from large elevational gradients to short elevational gradients.