Microtopography differentiates soil bacterial and fungal communities and modifies assembly processes in the Mu Us sandy land

Dune microtopography creates fine-scale environmental contrasts, yet bacterial and fungal responses across diversity, community composition, assembly processes and predicted function remain poorly resolved. We compared soil bacterial and fungal communities among windward slopes, leeward slopes and interdune lowlands within a stabilized dune complex in the Mu Us Sandy Land. Alpha diversity remained similar among positions, whereas community composition differed in both microbial domains without corresponding differences in multivariate dispersion, indicating position-related compositional differentiation. Stochastic processes predominated in bacterial and fungal community assembly, but the two domains differed in how process contributions varied among positions. Bacteria retained the same dominant-process hierarchy despite quantitative variation in individual processes, whereas the dominant fungal process differed among positions. Broad bacterial COG profiles and fungal guild composition showed no significant positional differences after multiple-testing correction. Microtopographic differentiation was therefore expressed mainly in community composition and assembly rather than in local α diversity or broad predicted functional profiles. These results show that α diversity alone may underestimate microbial spatial differentiation within stabilized dunes, underscoring the need to distinguish among microtopographic positions in belowground biodiversity assessments.