Direct evidence for the enhanced acquisition of phosphorus in the rhizosphere of aquatic plants: A case study on Vallisneria natans

摘要

Highlights•Fe and P inVallisneria natansrhizosphere were measured at mm and submm resolutions.•Fe plaque formed on the root surface and enriched the Fe and P.•Labile P decreased in rhizosphere due to enrichment by Fe plaque.•Fe and P were released in rhizosphere with enhanced soluble concentrations.•Root-excreted organic acids complexed Fe(III) in Fe plaque and liberated Fe and P.Graphical abstractDisplay OmittedAbstractThere are few studies about the processes and mechanisms for aquatic plants to take up phosphorus (P) in wetland soils and sediments. Direct observation of P mobilization in rhizosphere is lacking. In this study, high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) techniques were used to capture the small-scale changes of soluble reactive P (SRP) and soluble Fe, and labile P in the rhizosphere ofVallisneria natans(V. natans), respectively. The results showed 5.92- and 3.12-fold enrichments of P and Fe in the Fe plaques formed on the root surfaces, respectively, in comparison with the P and Fe concentrations in the non-rhizosphere sediments. Moreover, simultaneous releases of P and Fe appeared in rhizosphere and the SRP concentration showed up to 114-fold increases compared to the non-rhizosphere sediments. Five kinds of low-molecular weight organic acids (LMWOAs) were detected in the root exudates; oxalic acid accounted for 87.5% of the total. Extraction of Fe and P in the Fe plaques was greatly enhanced by root exudates compared to deionized water, and oxalic acid contributed to 67% and 75% of the total extracted Fe and P, respectively. The coupling processes of Fe plaque enrichment of P and oxalic acid complexation of Fe(III) led to significantly enhanced P acquisition in the rhizosphere ofV. natans.