Phytomanagement with forage grasses for sustainable remediation of contaminated tailings soil: Enhancing soil functionality and addressing forage safety risks

Abstract

Tailings-contaminated soils represent an underutilized land resource, and reclaiming them with forage grasses can restore landscapes, mitigate metal pollution, and support phytoremediation. This study evaluates five forage grasses for reclamation in contaminated tailings soil. All grasses demonstrated strong adaptability, likely due to their metal exclusion traits, with bioconcentration factors (BCF) < 0.11 ± 0.02 for Cd, Pb, and Zn. Grass reclamation significantly improved soil multifunctionality, enhancing physicochemical properties, enzyme activities, and rhizosphere bacterial α-diversity and biomass compared with bare soil. Furthermore, grass reclamation reshaped the microbial community, towards a plant-beneficial microbiome, including the enrichment nitrogen-cycling bacteria (e.g., increased bacteria containing nirK, nosZ genes), and a rise in symbiotic mycorrhizal fungi. Greenhouse experiments further demonstrated that the microbial communities naturally restored in the rhizosphere, similar to those associated with established AMF symbioses, improved forage grass adaptability. These microbial communities facilitated heavy metal stabilization in roots, reduced metal translocation, and lowered the risk of food chain contamination, thereby promoting plant growth. Our results suggest that these naturally restored microbiotas should be prioritized in tailings soil reclamation with forage grasses as an alternative to AMF. However, the potential risk of heavy metal contamination in forage grasses requires careful consideration, as all species investigated pose a risk of exceeding heavy metal limits, except for P. purpureum 'Sweet', remaining within permissible levels for silage. Combining microbial heavy metal mitigation with strategies such as soil amendments and selecting low-metal-accumulating grasses, like, P. purpureum 'Sweet', provides a promising, sustainable approach for phytomanagement of severely contaminated tailings soils.