Biochar source heterogeneity drives simultaneous detoxification and stochastic microbial assembly in extreme mine...

The extreme acidification and nutrient deficiency of lead-zinc (Pb-Zn) mine tailings severely limit phytoremediation efficacy. While biochar is widely applied as a soil amendment, how its source heterogeneity drives interfacial chemistry and microbial ecological recovery remains unclear. Herein, an 8-month pot experiment was conducted using Miscanthus combined with different biochar sources and dosages. Results demonstrated that the source effect significantly outweighed the dosage effect. Manure-derived biochar exhibited superior heavy metal immobilization through a dual mechanism of mineral-induced coprecipitation (via high-ash alkaline minerals) and surface inner-sphere complexation (via abundant oxygen-containing and aliphatic groups). At the micro-ecological level, biochar disrupted stringent environmental filtering, driving bacterial community assembly toward stochastic processes governed by dispersal limitation and ecological drift, while deterministic selection persisted for fungi. Bacterial recovery was primarily associated with reduced metal toxicity, whereas fungal diversity responded more directly to carbon alleviation. Furthermore, the superior immobilization by manure-derived biochar was attributable to its ash/mineral content rather than carbon input. These findings underscore that effective phytoremediation strategies must achieve both detoxification (via mineral-rich amendments) and carbon replenishment as complementary objectives, activating a cross-kingdom synergistic network that enhances soil fertility.