Abstract: Biochar has gained increasing attention as a soil amendment, yet its effects on soil nutrients and plant growth across wetland salinity gradients remain unclear. This study examined the efficacy of biochar, inorganic fertilizer, and their combined addition in enhancing Phragmites australis growth under low-salinity (1‰) and high-salinity (20‰) levels through in situ field experiments within its native community in the Yellow River Delta. The results indicated that compared with the control, the biochar-based inorganic fertilizer treatment significantly increased total biomass (90.6%) and plant height (17.2%) of Phragmites australis under low-salinity levels, respectively. Meanwhile, under high-salinity levels, both biochar alone and the combined addition significantly enhanced the total biomass, shoot biomass, belowground biomass, and leaf area of the Phragmites australis, with total biomass increasing by 88.3% and 97.5%, respectively. Compared with inorganic fertilizer addition alone, both biochar alone and the biochar-based inorganic fertilizer treatment significantly enhanced the total biomass and plant height under high-salinity conditions. Both biochar alone and the biochar-based inorganic fertilizer addition significantly improved the root system architecture of Phragmites australis. The different addition treatments did not significantly affect soil dissolved organic carbon, inorganic nitrogen, or bacterial community composition. However, salinity significantly influenced bacterial relative abundance, particularly reducing dominant Proteobacteria under high-salinity levels. The structural equation model showed that biochar-based fertilizer addition treatments could explain 56% of the total biomass and 33% of the belowground biomass of Phragmites australis. Overall, biochar-based inorganic fertilizer exhibits a promoting effect comparable to or significantly better than that of biochar treatment, while it is significantly superior to inorganic fertilizer treatment. It is recommended to conduct long-term field experiments to systematically evaluate the sustained impact mechanisms of biochar-based inorganic fertilizer additions on saline wetland ecosystems