Differences of key processes in soil nitrogen cycling and their driving factors under different land-use types.

To investigate the responses and drivers of soil microbial nitrogen (N)-cycling functional genes under different land-use types, we analyzed five representative ecosystems in the Yellow River alluvial plain: Tamarix chinensis forests, Fraxinus chinensis forests, grasslands, wetlands, and farmlands. With metagenomic sequencing, we quantified the relative abundances of 22 functional genes associated with six critical N-cycling processes. Soil physicochemical properties were characterized. There were significant variations in soil nitrogen (N)-cycling functional gene abundances across land-use types. Wetlands exhibited the highest relative abundances of nitrogen fixation (1.28×10^-5), nitrification (4.91×10^-4), and denitrification (7.03×10^-4) genes, but the lowest assimilatory nitrate reduction potential (1.84×10^-4). Farmlands showed maximal assimilatory nitrate reduction gene abundance (3.31×10^-4), while grasslands dominated in ammonification gene expression (2.35×10^-4), significantly higher than other ecosystems. T. chinensis forests maintained the most constrained N-cycling profile, with minimal nitrification (2.77×10^-4) and denitrification (5.25×10^-4) relative gene abundances. Redundancy analysis identified soil total nitrogen, organic carbon, total potassium, and electrical conductivity as the key environmental drivers of these variations. Our findings demonstrated that land-use types could shape microbial N-cycling functional gene abundances by altering soil nutrient conditions, with consequence on fundamental processes of soil nitrogen transformation.