Impact of indigenous soil microbes on switchgrass tolerance to lead stress

Lead (Pb) contamination of soil poses a significant and pressing environmental threat to a multitude of ecosystems. Phytoremediation assisted by the collaborative activities of rhizosphere soil microbes holds considerable promise for the removal of metal contaminants from affected sites. Nevertheless, there remains a substantial shortage of knowledge regarding the impact of indigenous rhizosphere soil microbes on plant strategies for Pb accumulation and Pb speciation within plant-microbial root associations. In this study, switchgrass (Panicum virgatum) was grown in soils with varied Pb stress (0, 200, 800, 1400, and 2000 mg/kg), with and without native microbial inoculants, to investigate how plant-microbe interactions influence Pb transfer and speciation in native soils. Notably, our findings highlight the remarkable Pb tolerance of switchgrass. The plants sustained robust growth and resilience even at 2000 mg/kg, a concentration far exceeding the recommended Pb limit for human health. Native microbial inoculation significantly increased Pb retention in roots and reduced its translocation to leaves, likely due to a stable symbiosis with arbuscular mycorrhizal (AM) fungi. The combination of switchgrass and microbial inoculants altered soil pH and rhizosphere processes, consequently leading to changes in the bioavailability of Pb. A numerical model based on the mass balance equation predicted that over 80 % of bioavailable soil Pb could be removed within 120 days. Our study advances the understanding of Pb accumulation and transfer in plants and the benefits of inoculation with indigenous soil microbial communities, thereby laying the foundation for the development of enhanced phytoremediation strategies of efficient Pb removal from contaminated soils.