Carbonaceous soot priming shields bamboo seeds from lead toxicity by limiting lead uptake and enhancing antioxidative defense

Lead contamination poses a major constraint to bamboo establishment, yet low-cost strategies to improve seed germination under heavy-metal stress remain limited. Here we report, for the first time, the use of carbonaceous soot derived from candle combustion as a priming agent for a bamboo species, Phyllostachys edulis, under lead stress. Germination parameters, lead accumulation, and antioxidant responses were assessed in primed and non-primed seeds exposed to 0-400 mg L⁻¹ lead. Dynamic light scattering analysis revealed that soot particles had a hydrodynamic diameter of ∼210 nm and a stable zeta potential (-33.5 mV). Scanning electron microscopy confirmed strong adherence of aggregated particles on the seed coat. Soot priming significantly improved germination percentage, reduced mean germination time, and enhanced seedling vigor compared with non-primed seeds across all treatments. X-ray fluorescence analysis showed that priming reduced lead uptake by 24-52%. Primed seedlings exhibited lower catalase, peroxidase, and proline levels, indicating reduced oxidative stress. These improvements are attributed to the soot layer functioning as a physical barrier and metal-adsorptive surface, limiting lead entry during imbibition. Overall, candle-derived soot particles effectively enhance germination under lead stress, offering a simple and inexpensive priming strategy for bamboo establishment in contaminated environments.