Metabolic reconstruction and microbial network assembly immobilised heavy metals during soil function recovery in coal gangue.

Coal gangue stockpiling leads to considerable soil heavy metal contamination and ecological degradation. Vetiveria zizanioides (L.) exhibits strong phytoremediation potential; however, the mechanisms underlying heavy metal immobilisation during soil function recovery remains unclear. In this study, a spatiotemporal substitution method was applied to investigate soil heavy metal distribution, microbial communities, and metabolite profiles during a nine-year cultivation period of V. zizanioides in coal gangue. Long-term cultivation effectively immobilised heavy metals (Cr, Cu, and Zn), reduced their migration and progressively restored soil pH while enhancing soil multifunctionality. Bacterial network vulnerability decreased, whereas network complexity and robustness increased, resulting in greater microbial diversity in the coal gangue-V. zizanioides system. Sulfurifustis, a dominant bacterial genus, strongly influenced microbial network structure and promoted heavy metal immobilisation. Keystone taxa (Proteobacteria, Actinobacteriota, and Chloroflexi) were essential in determining bacterial network structures. In addition, purine metabolism and its intermediate metabolite allantoin were significantly enhanced and were potentially associated with plant detoxification under heavy metal stress in soils. Overall, these findings demonstrate that V. zizanioides cultivation immobilises heavy metals, restores soil functionality, and maintains microecological balance through bacterial network assembly and metabolic reprogramming.