Divergent co- occurrence patterns and assembly processes structure the abundant and rare bacterial communities in a salt marsh ecosystem.

Understanding how species interaction and assembly processes structure the abundant and rare bacterial biosphere in soils is crucial for predicting how biodiversity influences ecosystem functioning. Here, we profiled the bacterial communities across a salt marsh ecosystem gradient to investigate the co-occurrence patterns across taxa and the relative influence of ecological processes mediating the assembly of the abundant and rare biospheres in soil. Our results revealed abundant taxa to be ubiquitous across all sample sites, whereas the distributions of the rare taxa were relatively more site-specific. The alpha-diversity indices and beta-diversity of rare sub-communities were significantly higher than those of the abundant sub-communities. Besides, both the taxonomic and functional composition of soil bacterial communities significantly differed between the two biospheres. Furthermore, the influence of stochasticity differed in each sub-community. In particular, stochastic processes were relatively more important in constraining the rare taxa assembly. Co-occurrence network analysis revealed that a few abundant taxa occupy central nodes within the networks, possibly indicating crucial roles as keystone taxa. Collectively, these findings suggest that abundant and rare bacterial biospheres have distinct distributions underpinned by a dynamic interplay of ecological processes and taxa co-occurrence patterns. [ABSTRACT FROM AUTHOR]