Habitat and lifestyle affect the spatial dynamics of prokaryotic communities along a river–estuary–sea continuum

TL;DR

This study explores how prokaryotic communities change along a river-estuary-sea gradient, showing that spatial distance and environmental factors strongly influence their diversity and assembly.

Contribution

The study reveals distinct spatial dynamics and assembly mechanisms of prokaryotic communities across different habitats and lifestyles in a river-estuary-sea continuum.

Findings

Community variability increases with spatial distance more than with habitat or lifestyle differences.

Dispersal limitation and salinity differences strongly influence microbial assembly in this gradient.

Abiotic and biotic factors interact more in free-living communities than in particle-associated ones.

Abstract

Microbial biogeography and its controlling mechanisms are central themes in microbial ecology. However, we still lack a comprehensive understanding of how habitats and lifestyles affect microbial biogeography across complex environmental gradients. In this study, we investigated the planktonic (including free‐living [FL] and particle‐associated [PA] lifestyles) and benthic prokaryotic communities along a river–estuary–sea continuum of the Changjiang River to explore their distinct spatial dynamics. We observed greater community variability across spatial distances than between habitat and lifestyle types. Spatial variations were evident in FL, PA, and benthic communities, with the highest turnover rates observed in benthic communities, followed by PA, and the lowest turnover rates observed in FL. The replacement effect dominated PA and benthic community variations, whereas the richness effect was more significant in FL communities. Microbial assembly was primarily governed by homogeneous selection and dispersal limitation regardless of habitats/lifestyles, with their ratios decreasing as the spatial distance increased, particularly in the FL fraction. Dispersal limitation had a stronger effect on benthic communities compared to planktonic communities. While heterogeneous selection generally played a minor role, its influence became more pronounced over larger spatial distances and with increasing salinity differences. Finally, we showed that abiotic and biotic factors individually exerted a greater influence on PA communities, whereas their interactions had a stronger effect on FL communities. Our results revealed complex spatial dynamics and assembly mechanisms among microorganisms across different habitats and lifestyles, providing insights into the spatial scaling of community assembly across complex environmental gradients.

The river–estuary–sea continuum presents a natural environmental gradient that fosters rich microbial communities. However, our understanding of microbial community succession patterns and underlying ecological mechanisms remains limited. In this study, we observed significant changes in prokaryotic communities along the river–estuary–sea continuum. We found that spatial effect was more important in structuring community variations than that exerted by habitat or lifestyle types. Increasing spatial distance led to a greater effect of dispersal limitation on community assembly, and heterogeneous selection intensified its role at higher salinity differences. These findings provide new insights into the assembly processes of microbial communities in natural ecosystems, characterized by high spatial connectivity and environmental heterogeneity.

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