Dispersal limitation relative to environmental filtering governs the vertical small‐scale assembly of soil microbiomes during restoration

Uncovering the plant‐soil feedback mechanisms underlying the assembly of belowground microbial communities is essential for terrestrial biodiversity conservation. However, little is known about the small‐scale spatial assembly processes of distinct soil microorganisms, especially during natural restoration of ex‐arable ecosystems. We examined the spatial structure of soil microbiomes in arable land and reforested soils to elucidate the underlying assembly processes at a small spatial scale. The analysis was based on a MiSeq sequencing database, detecting the diversity of archaeal, bacterial and fungal communities, simultaneously, from 300 soil samples along vertical and horizontal profiles during 30‐year reforestation. Compared with environmental filtering, dispersal limitation made crucial contributions to microbial community assembly. Archaeal and bacterial communities with a wider niche breadth were governed more by dispersal limitation than were fungal communities. The effect of dispersal limitation on archaeal and bacterial communities increased first and then decreased over time, while the effect on fungi temporally increased. Synthesis and applications. Our results highlight the variation of assembly processes governing distinct soil microbiomes during reforestation, with dispersal limitation playing a prominent role. This finding suggests that the increase in soil microbial diversity during natural restoration is mainly due to the stochastic influx and dispersal of microorganisms. This greater understanding of microbial community assembly can contribute to more targeted and efficient environmental management practices for the restoration of terrestrial ecosystems, for example, by promoting the restoration practices and shortening the restoration period. These practices may thus be incorporated into policies developed for effective biodiversity conservation, especially the restoration and maintenance of subsurface soil microbial diversity and associated functions. Our results highlight the variation of assembly processes governing distinct soil microbiomes during reforestation, with dispersal limitation playing a prominent role. This finding suggests that the increase in soil microbial diversity during natural restoration is mainly due to the stochastic influx and dispersal of microorganisms. This greater understanding of microbial community assembly can contribute to more targeted and efficient environmental management practices for the restoration