Long-Term Nitrogen Fertilization Accelerates Labile Biomolecules Decomposition and Retains Recalcitrant Compounds in a Temperate Agroecosystem

The influence of long-term nitrogen (N) fertilization on the quantity, molecular constituents, and origin of soil organic matter (SOM) within the soil profile remains an area of ongoing investigation. We employed a comprehensive set of biomarkers (including free lipids, bound lipids, lignin phenols, neutral sugars, and amino sugars), 13C NMR techniques, and soil extracellular enzyme activities, to evaluate the SOM characteristics in response to 18-year N fertilizer gradients (i.e., 0, 57.5, 97.5, 137.5 kg N ha(-1) yr(-1)) to a depth of 60 cm in Northeast China. The results showed that N fertilization distinctly modified the molecular signature of SOM (e.g., biomolecules, degradation, and source) within the soil profile, particularly within the top 20 cm layer. N ad-ditions led to a 13.6-17.3 % increase in microbial-derived free lipids (predominantly short-chain lipids, 更多