Land-use change reshapes soil nitrogen (N) cycling, yet the mechanistic links between microbial functional potential and soil N supply remain poorly quantified on China's Loess Plateau. We examined the effects of converting native grassland to afforested land and 10-year abandoned cropland on N supply potential (net N mineralization, Nmin) and soil N-cycling functional genes across two soil depths (0-15 and 15-30 cm). Afforested soils exhibited the highest Nmin (30.15 mg center dot kg- 1), significantly exceeding that of grassland (15.36 mg center dot kg- 1) and abandoned land (10.82 mg center dot kg- 1). Nmin showed strong vertical stratification, declining significantly by 37% - 70% from the 0-15 cm to the 15-30 cm layer across all land-use types. Metagenomic profiling revealed pathway-specific shifts in the functional gene repertoire: Afforestation promoted a genetic configuration enriched in genes for nitrate reduction, nitrification, and N assimilation, while abandoned land was characterized by genes associated with N retention. Hierarchical partitioning and structural equation modeling identified soil physicochemical properties (e.g. water content, pH, organic carbon, total and available N, and total and available phosphorus) and fungal diversity as the dominant direct controls on Nmin. Functional gene abundance provided a smaller but non-negligible contribution. These findings demonstrate that land-use change enhances N supply potential not only by modifying abiotic conditions but also by promoting fungal communities and microbial genetic potential that support active N cycling. This study highlights the importance of integrating both biotic and abiotic drivers into soil N management strategies in semi-arid landscapes.