Phosphorus mediated rhizosphere mobilization and apoplast precipitation regulate rare earth element accumulation in Phytolacca americana

Aims The plant available phosphorus (P) is deemed as the main soil factor affecting the accumulation of rare earth elements (REEs) in the hyperaccumulator plant Phytolacca americana, but the underlying mechanisms are largely unknown. Methods Soil P amendment and exogenous organic acids addition experiments were employed to determinate the P-induced soil chemical properties changes and subsequent REE accumulation variations in P. americana. Manipulations of P and REE concentration were also conducted under hydroponic conditions, and the translocation of P and REE from roots to shoots was analyzed. Results P-deficiency induced a decrease of pH (0.8 unit) and secretion of organic acids in the rhizosphere, thus contributing to the mobilization of P and REEs, and the increased REE accumulation in P. americana eventually. However, an elevated soil P supply reduced REE accumulation by 90% in shoots. P spray did not affect the accumulation of yttrium (Y) in P. americana under 1-10 mu mol L-1 Y treatment, but limited Y translocation from roots to shoots under 100 mu mol L-1 Y treatment. Moreover, compared to 1 mu mol L-1 Y treatment, under 100 mu mol L-1 Y the root P concentration was nearly tripled and more P was allocated to the apoplast. The linear regression slope between Y and P concentrations in the roots of hydroponic P. americana was 3.4, being close to the Y/P ratio of YPO4 precipitates (2.9). Conclusions Our study demonstrates that P mediated REE mobilization in the rhizosphere and apoplast precipitation within the endosphere can regulate the REE accumulation in P. americana.

Automated summary

This study demonstrates that phosphorus mediates the migration of rare earth elements in the rhizosphere and the precipitation in the endosphere, thereby regulating the accumulation of rare earth elements in Phytolacca americana.