HOW DO INDIGENOUS MICROORGANISMS INFLUENCE SWITCHGRASS RESPONSE TO LEAD STRESS IN NATIVE SOIL?

Lead (Pb) contamination of soils poses a significant threat to numerous ecosystems. Increasing evidence indicates that phytoremediation, supported by the collaborative activities of rhizosphere soil microbes, provides a cost-effective and eco-friendly approach to remove heavy metal contaminants from the soil environments. However, the knowledge regarding the impact of indigenous rhizosphere soil microbes on plant strategies for Pb accumulation and Pb speciation within plant-microbial root associations remains limited. To fill the knowledge gap, we subjected switchgrass (Panicum virgatum) to varied Pb stress (0, 200, 800, 1400, and 2000 mg Pb /kg soil) with and without native microbial inoculants. The interactions between biological factors (the plant and its associated microbes) that influence the transfer and speciation of Pb in native soils has been examined.

Our results demonstrate that switchgrass has the ability to uptake Pb from soils with considerable resilience in environments with Pb concentrations as high as 2000 mg/kg. The inoculation of native microbes exhibited a consistent effect by elevating Pb concentration and content within the plant roots while simultaneously reducing these in the leaves. This phenomenon is likely attributed to the symbiotic relationship between switchgrass and arbuscular mycorrhizal (AM) fungi, as the percentage of AM fungal root colonization was more than 70% in all microbial inoculated plant and the colonization is unaffected by various Pb concentration. Furthermore, AM fungal structures were observed across all Pb concentrations, indicating that these structures are resistant to the presence of Pb. The combination of switchgrass and microbial inoculants induced an increase in soil pH, consequently leading to the increases in the bioavailability of Pb. Our study advances the understanding of Pb accumulation and transfer in plant-soil systems and the benefits of inoculation with indigenous soil microbial communities. Our results can also serve as the foundation for the future development of phytoremediation strategies aimed at efficiently removing Pb from contaminated soils.