Bioresource amendment promotes early mineralization and nitrification recovery in ammonium-rich rare earth tailings

Rare earth tailings soil retains high residual NH₄⁺-N after in-situ leaching with ammonium sulfate, creating coupled risks of nitrogen loss and poor revegetation. The substrate and microbial pathways that reopen ammonia oxidation and mediate nitrification restart in this ammonium rich rare earth tailings soil remain unclear. To address this gap, a microcosm incubation over time compared an unamended soil, MgO, and manure, integrating nitrogen transformations, net mineralization, enzymes, qPCR, and shotgun metagenomics. Under OM, extractable NH₄⁺-N declined by 88.3 % from its initial value, while oxidized inorganic N accumulated. Three related functional patterns were observed under OM. First, an early apparent net N mineralization pulse occurred under DCD inhibition, peaking at 15.45 mg N kg^-1 d^-1, alongside evidence of peptide cleavage and amino sugar turnover. Second, ammonia oxidation was reactivated, as indicated by enrichment of amoABC and hao and increases of 2.8 to 15-fold in archaeal and bacterial amoA. Third, manure enhanced functional network integration between nitrogen cycling and substrate metabolism genes, with functional coupling associated with inorganic N, CEC, and SOM. These findings suggest a role for biological functional reconstruction in restoring nitrogen cycling in ammonium rich rare earth tailings soil.