Comparative Analysis of Rhizosphere Bacteria of Phragmites australis and Suaeda salsa (L.) Pall . on Chenier Islands

The Chenier Islands are depositional areas within intertidal zones, characterized by unique soil textures and distinctive environmental conditions that shape specific vegetation distribution patterns. However, the adaptive mechanisms of Phragmites australis (common reed) and Suaeda salsa (L.) Pall. (common seepweed) two prevalent plant species in this region-in saline stress environments, as well as the composition and functional characteristics of their rhizosphere bacterial communities, remain largely unclear. In this study, rhizosphere soil samples were collected from common reed and common seepweed. DNA was extracted and subjected to high-throughput sequencing to analyze the composition and predictive functional profiles of the rhizosphere microbial communities. The results indicated that no significant differences were observed in the alpha diversity indices (Chao1, ACE, Simpson, and Shannon), indicating similar microbial species richness and evenness in the rhizospheres of common reed and common seepweed. Taxonomic analysis at the phylum level showed that the dominant bacterial phyla shared by both plants were Proteobacteria, Bacteroidota, Chloroflexota, and Actinomycetota. Notably, Acidobacteriota and Cyanobacteria were uniquely enriched in the common reed and common seepweed rhizospheres, respectively. At the genus level, the microbial communities of both plants were largely composed of unclassified taxa and minor groups, with Zeaxanthinibacter being the only cultivable dominant genus identified. Principal Coordinates Analysis (PCoA) explained 75.02% of the total β-diversity variance, and the clear separation of samples along the first coordinate axis revealed visually distinct community structures between the two plants. PERMANOVA further confirmed that plant species significantly influenced microbial community assembly, with a moderate explanatory strength (R2 = 0.205, p = 0.008). Integrated results from LEfSe, PICRUSt2, and FAPROTAX analyses demonstrated that common seepweed rhizospheres were enriched with 19 photosynthesis-related biomarkers, suggesting a stronger photoautotrophic potential compared to common reed. In contrast, the common reed rhizosphere retained only two oligotrophic degraders Acidobacteriota and Chloroflexota. Although PICRUSt2 predictions indicated high overlap in core metabolic pathways between the two plants, FAPROTAX profiling revealed markedly divergent energy-acquisition strategies. Specifically, the common seepweed microbiome exhibited a "photoautotrophy nitrogen fixation" coupling strategy, whereas common reed relied predominantly on a "chemoheterotrophy nitrate reduction" pathway, reflecting niche partitioning in the saline environment. It should be noted that functional predictions derived from PICRUSt2 and FAPROTAX are computational inferences rather than empirical measurements, and thus mechanistic interpretations should be treated with caution. This study identifies a rhizosphere bacterial community assembly pattern characterized by "structural differentiation but functional convergence" offering valuable insights into microbial-mediated plant adaptation to saline stress.