Spatial Heterogeneity of Soil Organic Matter and Its Driving Mechanisms in the Dayangshu Area of the Songnen Plain

Understanding the spatial heterogeneity of deep soil organic matter is critical for terrestrial carbon cycling, yet its driving mechanisms remain elusive due to a historical research bias toward surface layers. This study develops a 3D spatial prediction and mechanistic framework for Soil organic matter(SOM) across a 0–200 cm profile in the Mollisols of the Songnen Plain, Northeast China. By integrating systematic sampling with Random Forest modeling and a comprehensive suite of multi-source environmental covariates, we identified pronounced vertical stratification in SOM distribution and its governing factors. Our results reveal that surface SOM is primarily driven by climate, vegetation, and anthropogenic activities, whereas deep soil organic matter is dictated by intrinsic physicochemical properties and surface matrix compositions. Furthermore, significant interaction effects between topography and soil attributes further enhance SOM accumulation. This research clarifies the depth-dependent processes of carbon stabilization, providing a robust scientific basis for the targeted conservation and carbon sequestration enhancement of Mollisols.