Microbial and mineral drivers of organic carbon sequestration in soilless revegetated zinc smelting slag site: Insights from a 12-year field study.

Soilless revegetation provides a cost-effective and sustainable strategy for rehabilitating metal-contaminated smelting slags, yet the long-term dynamics and mechanisms of organic carbon (OC) sequestration in these extreme anthropogenic substrates remain poorly understood. Here, we quantified OC fractions, microbial attributes, and mineral characteristics in a zinc smelting slag site after 12 years of field-based revegetation to elucidate pathways of carbon accumulation and stabilization. Revegetation markedly increased multiple OC pools, microbial biomass, microbial necromass carbon, enzyme activities, and carbon-cycling functional genes. OC stabilization was governed by two coupled pathways: (i) the formation of mineral-associated OC (MAOC) driven by interactions between microbially transformed substrates and reactive Al-rich mineral phases, and (ii) the accumulation of microbial necromass supported by improved moisture, nutrient availability, and metabolic activity. Enrichment of aromatic and phenol compounds, together with polysaccharide-rich substrates, further contributed to OC persistence through chemical recalcitrance and organo-mineral associations. These integrated microbial-mineral interactions indicate that long-term revegetation promotes the development of soil-like carbon stabilization processes within slag and provide mechanistic insights into OC persistence in technogenic substrates. Collectively, the findings offer a foundation for carbon-oriented revegetation and highlight the potential for managing metallurgical slags as long-term carbon-retaining substrates.