Phosphorus Cycling Dominates Microbial Regulation of Synergistic Carbon, Nitrogen, and Phosphorus Gene Dynamics During Robinia pseudoacacia Restoration on the Loess Plateau

Carbon (C), nitrogen (N), and phosphorus (P) are key soil nutrients whose synergistic interactions regulate ecosystem nutrient cycling, yet the functional gene-level coordination and driving factors of these cycles remain poorly understood. This study addresses this gap by investigating the dynamic changes in C, N, and P cycling functional genes and their microbial and environmental drivers across Robinia pseudoacacia plantations of different restoration stages (10, 20, 30, and 40 years) on the Loess Plateau. We analyzed soil physicochemical properties and conducted metagenomic sequencing, redundancy analysis (RDA), and Partial Least Squares Structural Equation Modeling (PLS-SEM). Results showed that P-cycling functional genes, particularly pqqC and spoT, exhibited the highest network centrality, indicating their dominant role in regulating nutrient dynamics. Compared with farmland, STC, SOC, SAP, pH, and SWC significantly changed (p < 0.05) with restoration age, directly shaping key microbial groups such as Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi. These microbial shifts were strongly correlated with the synergistic changes in C, N, and P functional gene abundance (p < 0.01). The findings highlight the central role of phosphorus-solubilizing genes in linking C, N, and P cycles and emphasize the microbial community responses to soil environmental changes as a key driver of nutrient cycling during ecological restoration. This study provides novel insights into microbial functional gene interactions and their ecological significance in soil nutrient dynamics, offering theoretical support for improving restoration strategies on the Loess Plateau.