Microtopography mediates the community assembly of soil prokaryotes on the local-site scale

Microbial community assembly is a central topic in soil microbiology and remains controversial at small scales. Microtopography, a common feature of terrestrial ecosystems, strongly affects energy, water, and nutrient cycling at local-site scale; however, its influence on the community assembly of soil microbes has rarely been explored. Here, we investigated how different microtopographic types (depressions, gentle and steep slopes, and gullies) and slope positions (upstream, middle, and downstream) mediate the community assembly of soil prokaryotes on a local-site scale. Our results showed that α-diversity significantly differed across microtopographic types, being highest on the gentle slope and lowest in the gully. The relative abundance of 30% dominant phyla as well as the prokaryotic community composition were also significantly affected by microtopography. Notably, the relative abundance of Bacteroidetes, an easy-dispersal phylum, increased from upstream to downstream. Further analyses showed that although stochastic processes (mainly homogenizing dispersal) dominated the community assembly, abiotic environmental filtering (mainly imposed by soil moisture and total phosphorus) could still explain 27.4–28.8% of the total variations in the soil prokaryotic community. These results suggested that microtopography shapes the diversity, community composition, and assembly of soil prokaryotes at local-site scale via two pathways: direct influence through prokaryotic dispersal and indirect influence through the re-allocation of soil water and phosphorus. Our findings provide novel insights into the local controls over community assembly of soil microbes. It emphasises the importance of focusing on the microtopography-derived heterogeneity in soil microbial functions when applying microtopographic modifications to ecological restoration in the future.