Background and aims <p>Although ferrihydrite transformation and arsenic binding have been widely studied, their coupled, depth-resolved dynamics in rice rhizosphere soil remain unclear. We investigated how soil factors regulate the behavior of arsenic-bearing ferrihydrite (As-Fh) in the rhizosphere.</p> Methods <p>A rice rhizosphere pot experiment combined diffusive gradients in thin films (DGT) profiling with spectral analyses to track the fate of buried As(V)-Fh and infer transformation mechanisms.</p> Results <p>The contents of labile Fe and As originating from buried As(V)–Fh increased with depth within the rhizosphere profile. More labile Fe and As were released from the lower soil layer (-8 to -12&#xa0;cm) than from the upper soil layer (0 to -4&#xa0;cm). As(V)–Fh with an As/Fe molar ratio of 0.005 resulted in relatively high average C_DGT-Fe and C_DGT-As values. Spectral analysis indicated a phase transition of As(V)–Fh toward hematite as the dominant product, with goethite as a minor phase, accompanied by a notable loss of specific surface area. X-ray photoelectron spectroscopy demonstrated that considerable fractions of the initial As(V) were reduced to As(III) and that Fe(II) was formed in solution and adsorbed onto As(V)–Fh. Moreover, soil organic matter was adsorbed onto the As(V)–Fh surface, but carboxyl groups were the predominant organic moieties adsorbed onto As(V)–Fh after 60 d, which is consistent with the increase in the soil organic acid concentration at the tillering stage (60 d).</p> Conclusions <p>Various factors including pH, Eh, depth, As/Fe molar ratio jointly promote ferrihydrite crystallization and associated arsenic mobilization in long-term waterlogged rice rhizosphere soil.</p>