Microbial filtering and functional reprogramming in soil exposed to spent NCM battery black powder

Spent lithium-ion battery black powder is an emerging complex contaminant, which contains transition metals, residual electrolyte salts, and compounds derived from organic electrolytes or binders. Its ecological effects on soil microbiomes remain poorly understood. Here, we designed a soil microcosm experiment with using red soil exposed to a concentration gradient of black powder derived from nickel-cobalt-manganese (NCM) lithium-ion batteries. Samples were collected at two incubation time points and analyzed by shotgun metagenomic sequencing. Black powder exposure produced a nonlinear taxonomic response, with species-level alpha diversity increasing under intermediate exposure, while rare-taxon abundance distributions shifted markedly under medium and high exposure. The LEfSe and PLS-DA analyses identified concentration- and time-dependent indicator taxa, including enrichment of Actinomycetota-related taxa and depletion of Nitrospira and Candidatus Methylomirabilis under high exposure. Community structure diverged significantly along the concentration gradient, and PERMANOVA attributed 23.2% of taxonomic variation to treatment. Structural equation modeling showed no significant direct path from black powder concentration to functional potential; instead, the model was consistent with a possible indirect association through community restructuring. Functional alpha diversity generally declined with increasing black powder concentration. High concentration exposure was associated with reduced relative abundance of KEGG Orthology entries (KOs) related to nitrogen cycling and increased stress-response and organic-matter-decomposition signatures. Overall, these results suggest that NCM-derived black powder can alter soil microbial functional profiles by reshaping community composition.