Bacterial community assembly in a typical estuarine marsh with multiple environmental gradients.

Bacterial communities play essential roles in estuarine marsh ecosystems, but the interplay of ecological processes underlying their community assembly are poorly understood. Here, we studied the sediment bacterial communities along a linear gradient extending from the water-land junction toward a high-marsh, using the 16S rRNA gene amplicon sequencing. Bacterial community composition differed significantly between sediment transects. Physico-chemical properties, particularly sediment nutrient levels [i.e., total nitrogen (TN) and available phosphorus (AP)], as well as sediment physical structure and pH (P < 0.05) were strongly associated with the overall community variations. In addition, the topological properties of bacterial co-occurrence networks varied with the distance to the water-land junction. Both node- and network-level topological features revealed the bacterial network of sediments farthest from the junction to be less intense in complexity and interactions compared with other sediments. Phylogenetic null modelling analysis showed a progressive transition from stochastic to deterministic community assembly for the water-land junction sites toward the emerging terrestrial system. Taken together, this study provides a detailed outline of the distribution pattern of sediment bacterial community across the estuarine marsh and inform on the mechanisms and processes mediating bacterial community assembly in marsh soils. [ABSTRACT FROM AUTHOR]