Complementary Rhizosphere Microbial Strategies Drive Functional Specialization in Coastal Halophyte Succession: Differential Adaptation of Suaeda glauca and Phragmites communis to Saline–Alkali Stress

While rhizosphere microbiome functions in saline soils are well documented, complementary microbial strategies between pioneer and late-successional halophytes remain unexplored. Here, we used 16S rRNA sequencing and FAPROTAX functional prediction to compare the rhizosphere bacterial communities of two key halophytes-<i>Suaeda glauca</i> and <i>Phragmites communis</i>-in a reclaimed coastal wetland. The results demonstrate that both plants significantly restructured microbial communities through convergent enrichment of stress-tolerant taxa (<i>Firmicutes</i>, <i>Pseudomonas</i>, <i>Bacillus</i>, and <i>Planococcus</i>) while suppressing sulfur-oxidizing bacteria (<i>Sulfurovum</i> and <i>Thiobacillus</i>). However, they exhibited distinct microbial specialization: <i>S. glauca</i> uniquely enriched organic-matter-degrading taxa (<i>Promicromonospora</i> and <i>Zhihengliuella</i>) and upregulated aromatic compound degradation (2.29%) and ureolysis (0.86%) according to FAPROTAX analysis, facilitating carbon mobilization in early successional stages. Notably, <i>P. communis</i> selectively recruited nitrogen-cycling <i>Serratia</i>, with increased nitrate respiration (3.51% in <i>P. communis</i> vs. 0.91% in <i>S. glauca</i>) function, reflecting its higher nitrogen demand. Environmental factors also diverged: <i>S. glauca</i>'s microbiome correlated with potassium and sodium, whereas <i>P. communis</i> responded to phosphorus and chloride. These findings uncover distinct microbial recruitment strategies by halophytes to combat saline stress-<i>S. glauca</i>-<i>P. communis</i> synergy through microbial carbon-nitrogen coupling-offering a template for consortia design in saline soil restoration.