Strategic pH regulation as an engineering pathway to enhance microbial phosphate solubilization and vegetation growth in constructed wetlands

Phosphate-solubilizing microorganisms (PSMs) can enhance phosphorus availability in constructed wetlands (CWs), but their performance in acidic Fe/Al-dominant soil matrices—representative of humid temperate regions like the Korean peninsula—is poorly understood. This study evaluated the solubilization behavior of PSMs isolated from the Phragmites australis rhizosphere in a bench-scale CW. Modified Pikovskaya (PVK) and National Botanical Research Institute’s phosphate (NBRIP) media were used with Ca-, Fe-, and Al-bound phosphate to simulate various soil chemistries. Halo assays revealed high solubilization for Ca–P (median PSI = 3.5) but markedly lower capacities for Fe–P and Al–P (PSI < 1.3), indicating inhibition by Fe/Al complexation. Broth-based quantification confirmed this pattern, with final soluble phosphate of 190.0 ± 5.0 mg/L for Ca–P, and significantly lower yields for Al–P (33.6 ± 1.5 mg/L) and Fe–P (18.4 ± 0.8 mg/L). Acidification during incubation suggested organic acid secretion as the primary mechanism, with pH dropping to 2.4–3.1. These results were integrated into a mass-balance simulation for a CW treating secondary effluent. Results showed that pH-driven shifts from Fe/Al-P to Ca-P stabilized phosphate availability, potentially increasing biomass by 26.1%. This study utilizes Korea’s pedoclimatic conditions as a representative test-bed, demonstrating that PSM efficiency in Fe/Al-dominated wetlands is constrained by mineralogical composition and pH. Strategic pH control or calcium enrichment is a critical prerequisite for enhancing phosphorus bioavailability and supporting vegetation establishment in urban CWs.