Thermodynamic Decoupling of Soil Organic Carbon Stabilization Mechanisms Under Chronic Anthropogenic Nitrogen Deposition: Reassessing the Mineral-Organo Complex Paradigm

Abstract

Conventional frameworks posit that mineral-associated organic matter (MAOM) constitutes the predominant long-term carbon sink in terrestrial pedogenic systems. However, mounting biogeochemical evidence challenges the universality of this paradigm under conditions of chronic atmospheric nitrogen deposition. This study integrates synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy, 13C cross-polarization magic-angle spinning nuclear magnetic resonance (CP-MAS NMR), and density fractionation protocols across twelve nitrogen-enriched forest soils spanning temperate and subtropical biomes. Results demonstrate statistically significant thermodynamic decoupling of organo-mineral bonding at deposition thresholds exceeding 25 kg N ha⁻¹ yr⁻¹, leading to preferential dissolution of iron-humate complexes and accelerated particulate organic matter (POM) turnover. These findings necessitate a fundamental re-evaluation of soil carbon persistence models embedded within current Earth system frameworks, with direct implications for IPCC-aligned climate mitigation projections.