Mechanistic insights into enhanced rare earth element phytoextraction by Dicranopteris pedata in leached soils: Integrating rhizosphere DGT-LA-ICP-MS imaging and metabolomic profiling

Phytoextraction shows promise for decontaminating and recovering rare earth elements (REEs) from REEs tailings. In this study, soils from a leached (L) and nearby un-leached (UL) hill were taken from an ion adsorption rare earth mine, using the REEs hyperaccumulator Dicranopteris pedata in potting experiments, we investigated the influence of its root exudates on REEs mobilization and transport at the root-soil interface by thin-film diffusive gradient (DGT) coupled with Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The REEs concentrations in L were significantly higher than those in UL (p < 0.05), with Ce, La, Y, and Nd being the most abundant. Leaching increased REEs mobility and bioavailability, altering their fractions in the topsoil. After 3 months, D. pedata in L exhibited significantly higher REEs concentrations in roots, stems, and fronds compared to UL, with enhanced root-to-frond translocation of REEs, especially HREEs. The bioconcentration factor (BF) and translocation factor (TF) were also higher in L, indicating greater REE enrichment capacity. DGT and LA-ICP-MS indicated that the closer to the D. pedata rhizosphere, the higher the signal of the REEs, suggesting a tendency for REEs to enrich in the rhizosphere soil. The untargeted liquid chromatography coupled to mass spectrometry (LC-MS) identified 42 key differential metabolites in D. pedata root exudates, many associated with stress responses and cell membrane fluidity, which are crucial for plant stress resilience under leaching conditions. This study provides insights into REEs mobilization and enrichment mechanisms in the rhizosphere and metabolite changes of D. pedata under leaching conditions, highlighting its potential as an effective hyperaccumulator for REEs-contaminated sites and contributing to the advancement of REEs phytoextraction strategies.