Nitrogen species coupled with transpiration enhance Fe plaque assisted aquatic uranium removal via rhizofiltration of Phragmites australis Trin ex Steud

Highlights: • The aquatic U retention within Fe plaque was affected by nitrogen species depended redox state conditions. • Higher TR improved the aquatic U and Fe availability for root uptake and retention. • Higher TR encouraged N assimilation for higher areal U accumulation in root via Fe plaque assisted rhizofiltration. • Supplying NH₄⁺ coupled with higher TR was a relatively optimal environmental condition for IP assisted aquatic U retention. - Abstract: The influences of N species and transpiration on the Fe plaque (IP) formation and related aquatic U rhizofiltration had not revealed yet, especially when these factors were co-existed. It was evaluated in a mesocosm experiment in the condition of respective ammonium (NH₄⁺)/nitrate (NO₃⁻) cultivation of Phragmites australis Trin ex Steud. coupled with different transpiration rates (TRs). The results suggested that the enhanced transpiration of P. australis improved the aquatic U rhizofiltration in both NO₃⁻ and NH₄⁺ rich milieus. However, the NO₃⁻ dependent oxidizing milieu restricted aquatic U uptake by the root of P. australis (up to 47.6 ± 1.8 mg kg⁻¹ under high TR) via IP assisted rhizofiltration. The high aquatic U availability and limited IP formation in NO₃⁻ rich milieu benefited the U retention within root tissue. On the contrary, the aquatic U rhizofiltration (up to 62.1 ± 1.0 mg kg⁻¹ under high TR) was enhanced under NH₄⁺ dependent reductive milieu. It was mainly contributed by U retention within IP. The area related U accumulation in different N species cultured roots was enhanced but did not significantly different under higher TR condition. The result suggested that the supplied NH₄⁺ coupled with enhanced transpiration was supposed to be more optimized option for IP assisted aquatic U rhizofiltration via P. australis.