Preferential Flow Drives Coupled Nitrogen Migration and Transformation in the Vadose Zone: Microbial Hotspots and Functional Gene Dynamics

). High hydraulic gradients induced by Pf enhanced oxygen/nutrient transport, creating spatially heterogeneous redox gradients that restructured microbial communities. This interplay between hydrologic forcing and microbial activity established Pf zones as critical nitrogen transformation hotspots characterized by diverse functional potentials shaped by spatially variable environments. Our findings provide a mechanistic framework to refine nitrogen cycle models in the vadose zone and inform strategies to mitigate agricultural nitrogen loss through microbial metabolic control.