Recruitment of copiotrophic and autotrophic bacteria by hyperaccumulators enhances nutrient cycling to reclaim degraded soils at abandoned rare earth element mining sites

Abstract

Hyperaccumulators harbor potentials for remediating rare earth elements (REEs)-contaminated soils. However, how they thrive in low-nutrient abandoned REE mining sites is poorly understood. Three ferns (REEs-hyperaccumulators Dicranopteris pedata and Blechnum orientale, and non-hyperaccumulator Pteris vittata) along with rhizosphere soils were collected to answer this question by comparing differences in nutrient levels, REEs concentrations, and bacterial composition. Results observed lower soil pH (4.67–4.95 vs. 7.96), total carbon (TC) (0.35–0.62 vs. 2.84 g kg^–1), total nitrogen (TN) (20–23 vs. 133 mg kg^–1), and total phosphorus (TP) (81–91 vs. 133 mg kg^–1) at sites Dp and Bo than site Pv. Hyperaccumulators efficiently extracted soil REEs and translocated them to fronds (6897–7759 mg kg^–1). Bacterial α diversity in three soils did not significantly vary. In contrast, bacterial composition at sites Dp and Bo was dominant by higher abundances of copiotrophic bacteria (18% vs. 12%, p_Actinomycetota; 3.3–8.3% vs. 1.9%, p_Bacteroidota; 8.3–14% vs. 6.9%, c_Gammaproteobacteria) and autotrophic bacteria (18% vs. 13%, p_Chloroflexota; 13% vs. 8.6%, p_Cyanobacteriota) when compared to site Pv. These bacteria likely acted as nutrient cyclers that promoted the growth of hyperaccumulators, based on functional predictions from DiTing analyses. This study provides new insights into nutrient recovery in abandoned REEs mining sites, offering strategies to reclaim degraded soils using phyto-microbial technology.