Asymmetric connectivity and distinct assembly processes of bacterial communities across the soil-water-sediment environments of the Antarctic Peninsula.

Macro-ecological linkages and bacterial assembly across Antarctic land-sea continuums remain poorly understood, especially regarding environmental filtering boundaries. Hypothesizing that environmental filtering intensifies along the Antarctic Peninsula's terrestrial-marine continuum, we integrated a historical terrestrial bacterial baseline (2008) with modern coastal water and sediment surveys (2017-2018). Using 16S rRNA sequencing and ecological models, we identified distinct communities associated with asymmetric filtering and divergent assembly. Despite ubiquitous Pseudomonadota dominance, significant niche differentiation occurred: historically isolated soils harbored the highest diversity (enriched with Actinomycetota), whereas modern sediments exhibited the lowest. Null modeling (iCAMP) indicated that soil assembly exhibited a strong statistical pattern of dispersal limitation (89%). We posit that this high value reflects a composite signal potentially resulting from the severe spatiotemporal disconnect and methodological variance between the historical terrestrial baseline and modern marine sinks, alongside actual physical isolation constraints. Conversely, homogeneous selection (42%) was primarily associated with modern water communities, while sediments acted as transitional sinks influenced by deposition and local filtering. Source tracking and network analyses showed: a strong "sinking effect" sustained water-derived taxa in sediments, whereas a high depletion index (DI > 26%) indicated strong environmental filtering, PLS-PM suggested that while water depth and salinity act as significantly filters in aquatic niches, bulk nutrients (TOC/TN) lack significant effects in sediments. This indicates the benthic matrix is primarily structured by physical isolation and stochasticity. These findings quantify the asymmetric connectivity segregating Antarctic microbiomes, highlighting marine sediments as complex integrators of modern biological pumps and distinct benthic assembly processes.