Landscape Mapping Reveals Depth‐Dependent Regional Heterogeneity in Soil Microbial Diversity

Abstract

To identify microbial hotspots and investigate the spatial distribution and assembly mechanisms of soil bacterial and archaeal communities across a coastal ecosystem, and to assess implications for biodiversity conservation and sustainable land management. Yellow River Delta, China (YRD, ~13,680 km 2 coastal plain). A total of 112 sites were sampled across diverse land‐use types along strong gradients of salinity, moisture and nutrients. At each site, soils were collected from three depth intervals (0–20, 20–40 and 40–100 cm), yielding a total of 336 samples for analysis. Microbial community composition and diversity were analysed using high‐throughput sequencing, and spatial patterns were evaluated using diversity mapping, distance–decay relationships (DDR) and community assembly modelling. Hotspot analysis revealed that microbial diversity exhibited marked spatial heterogeneity, with these hotspots primarily located in agricultural and grassland soils characterized by high soil organic matter (SOM) and low salinity. Hotspots became increasingly fragmented with depth. DDR analysis revealed weak but significant patterns: community turnover in the surface layer was primarily associated with nestedness (i.e., species loss), whereas in subsoils, turnover showed a weak positive association with species replacement. Community assembly was consistently shaped by a mixture of homogeneous selection (~40%), dispersal limitation (30%–31%) and drift (22%–24%), but the dominant environmental drivers transitioned from nutrient‐based filtering in topsoil to more complex multivariate constraints in deeper layers. Spatially structured and depth‐dependent microbial processes reveal that surface‐layer diversity hotspots, though accounting for only 7%–13% of the region, harbour up to 40% of microbial taxa and 83% of total abundance. These findings, based on taxonomic diversity, highlight the need for depth‐resolved conservation planning that considers both hotspots and the unique taxa in peripheral areas to sustain microbial contributions to ecosystem functions in coastal systems undergoing rapid environmental change.