A combined compost and endophyte addition improves phytostabilization by a native perennial grass in metal contaminated mine tailings

Abstract Background and Aims: Re-vegetation of contaminated and disturbed landscapes can reduce the transport of toxic elements while improving soil fertility. This study evaluated whether the planting of a perennial grass with diazotrophic microbial endophytes and municipal waste compost—alone and in combination—improved phytostabilization of potentially toxic trace elements in dolomite-amended tailings from a historically mined polymetallic mineral deposit. Methods We grew Bouteloua curtipendula seedlings in tailings with hazardous concentrations of As, Cd, Pb, Mn, and Zn. We evaluated how plant growth, organic matter accumulation, and minor and trace element mobilization responded to microbial endophyte and organic amendments. Results Although most of the added endophytes were not uniquely identified, the best plant growth and fertility outcomes were achieved with a combination of amendments: dolomite to reduce acidity, a compost topdressing to accumulate nitrogen in the tailings, and a mixed consortium endophyte seed coating to synergistically increase organic carbon and grass biomass yields. Combining amendments also improved phytostabilization: compost reduced the shoot forage toxicity of B. curtipendula seedlings without reducing phytostabilized contaminant yields in the rhizosphere, while endophyte inoculated grass marginally reduced total and water-extractable concentrations of toxic trace elements through enhanced mobilization. Conclusion The most effective means of reclaiming these acidic, polymetallic tailings is with a simultaneous dolomite, compost, and endophyte seed treatment.