Synergistic effect of oxalic acid and siderophore on uranium fractions and microbial community traits in rhizosphere soil enhances uranium accumulation in plant roots.

Chelating agent contributes to the remediation of heavy metal contaminations, but it remains unclear how they affect the transformation of radioactive pollutants and microbial traits in phytoremediation. We comprehensively investigated on the uranium (U) speciation and microbial communities in the rhizosphere of Macleaya cordata, Paspalum scrobiculatum and Bamboo willow, and analyzed the accumulation of U in the three plants after the addition of chelating agents including 0.1 mmol kg siderophore (DFO) and 2.0 mmol kg oxalic acid (OA). Results showed that OA (2.0 mmol kg) significantly enhanced the exchangeable U (EU) content in bulk soils compared to the control groups, whereas almost all concentrations of DFO did not substantially affect U fractions. Compared with the control groups, the EU content in the rhizosphere soils of the three plants gradually increased under the treatment of OA, DFO and OA + DFO. The accumulation of U in the roots of P. scrobiculatum and B. willow in the DFO and OA + DFO groups was significantly higher than that in the control groups at day 63. The α-diversity of bacterial communities and the negative interactions between fungal communities in the rhizosphere soils of the three plants significantly decreased in the OA, DFO, and OA + DFO. Partial least squares path models indicated that DFO and OA enhanced the EU content by influencing the intraspecific interactions of fungal communities, the α-diversity of bacterial communities, and the enrichment of key taxa. This study highlights the roles of OA and DFO in affecting U speciation and microbial functional traits, and has important implications for enhancing the phytoremediation of U-contaminated soils.