Phytomanagement with forage grasses for sustainable remediation of contaminated tailings soil: enhancing soil functionality and microbial communities
Description
Tailings-contaminated soils represent an underutilized land resource. Reclaiming these soils with forage grasses can restore landscapes, mitigate metal pollution, and support phytoremediation and forage production. This study evaluates five forage grasses for reclamation in heavily contaminated tailings soil. All grasses demonstrated strong adaptability, likely due to their metal exclusion traits, with bioconcentration factors < 0.11 for Cd and < 0.06 for Pb and Zn. Notably, Pennisetum purpureum “Sweet” accumulated metals below the permissible limits for fresh grass silage. Grass reclamation significantly improved soil multifunctionality, enhancing physicochemical properties, enzyme activities, and rhizosphere bacterial α-diversity and biomass. It also altered bacterial and fungal community composition and enriched nitrogen-cycling bacteria, with higher abundances of denitrification-related genes (nirK, nosZ) relative to bare tailings soil. Greenhouse experiments further demonstrated that naturally restored rhizosphere microbial communities improved forage grass adaptability and facilitated heavy metal stabilization in roots, reducing translocation and promoting plant growth. Among the tested grasses, P. purpureum “Sweet” exhibited the lowest metal accumulation, making it promising options for forage production on contaminated soils. This study underscores the potential of forage grasses and their associated microbial communities to enhance soil rehabilitation and promote ecological restoration in mining-impacted environments.
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Figure 1 /Figure S1: Plant samples and soil samples were digested using a mixture of HNO₃-HClO₄ (4:1, v/v) for plant tissues, and HNO₃-HClO₄-HF (5:1:2, v/v) for soil samples. The total metal concentrations were then measured using a flame atomic absorption spectrometer (Hitachi, FAAS ZA-3000, Japan. The bioavailability of heavy metals in the soils was evaluated through extraction using a diethylenetriaminepentaacetic acid (DTPA) extraction solution. BCF and TF were calculated as: BCF = Croot / Csoil and TF = Cshoot / Croot (Croot, Cshoot, Csoil: total heavy metal concentrations in roots, shoots, and soil). Figure 2: Soil physico-chemical properties, soil glomalin-related soil proteins and enzyme activity data were standardized using Z-scores. The average Z-score was then calculated to determine the soil multifunctionality index. Figure 6 Absolute qPCR Quantification of Microbial Functional Genes. Soil DNA (FastDNA™ SPIN Kit) was amplified for 16S/18S rRNA, narG/nirK/nosZ/phoD (primers in Table S1). PCR products cloned into pMD™19-T (Takara) via DH5α, with plasmid copies calculated as: Copies/μL = (6.02×10²³ × [ng/μL]) / (bp × 660) ×10⁻⁹. Plasmid standards with 8-point 10-fold serial dilutions were amplified via routine qRT-PCR (Roche LightCycler 480). Target gene copy numbers were calculated using the actual amplification efficiency of internal reference genes, based on gene copy number vs. CP value standard curves, validated by R²>0.99. Figure 8 Plant growth (80 days) was evaluated by height, biomass, chlorophyll (SPAD-502), and heavy metal content were digested using a mixture of HNO₃-HClO₄ (4:1, v/v). The total metal concentrations were then measured using a flame atomic absorption spectrometer (Hitachi, FAAS ZA-3000, Japan.
Institutions
- Yunnan University