Metagenomic insight into microbial regulation of nutrient cycling in amended bauxite residue under various planting strategies: Implications for soil formation

Sustainable rehabilitation of bauxite residue relies on a consistent supply of plant-available nutrients, with functional microbial communities playing a pivotal role in nutrient cycling. However, the mechanisms by which microbial functional genes regulate nutrient cycling during vegetation establishment in amended bauxite residue remain poorly understood. This study examined shifts in microbial functional genes related to carbon (C), nitrogen (N), and phosphorus (P) cycling in bauxite residue under various planting strategies, including single and mixed-planting of Lolium perenne, Cynodon dactylon, and Trifolium repens, using metagenomic sequencing. The results showed that vegetation establishment significantly reduced alkalinity while enhancing nutrient availability and enzyme activities in the residue. Dominant C cycling pathways were the reductive tricarboxylic acid (rTCA) cycle and the dicarboxylate-4-hydroxybutyrate (DC4HB) cycle, while N cycling was primarily mediated through organic nitrogen metabolism, and P cycling was driven by translocation processes. Planting with Lolium perenne enhanced C sequestration, whereas Cynodon dactylon promoted N and P cycling. Notably, mixed-planting with Trifolium repens weakened certain metabolic pathways related to C, N, and P cycling. Co-occurrence network analysis indicated that most nutrient cycling genes were positively correlated, with glpx-SEBP, gltB, and phoU identified as key regulatory genes. Partial least squares pathway modeling (PLS-PM) revealed that vegetation establishment directly enhanced enzyme activity by improving residue physicochemical properties and indirectly regulated C, N, and P cycling genes through shifts in bacterial community composition. Metagenomic analysis also showed similar phylum-level microbial community structure across C, N, and P cycling groups. These findings offer mechanistic insights into microbial regulation of nutrient cycling and offer guidance for optimizing planting strategies to support the long-term ecological restoration of bauxite residue disposal areas.