Decadal nitrogen addition alters chemical composition of soil organic matter in a boreal forest

• N addition alters chemical composition of soil organic matter in boreal forest. This is driven by increased lignin derivatives at the expense carbohydrate. Relative abundance microbial origin compounds increases with level. Boreal forests store approximately 470 Pg carbon (C) soil, and rates C accumulation are significantly enhanced long-term nitrogen (N) enrichment. Dissecting compositional profile soils could help better understand potential mechanisms driving changes cycling under enriched conditions. We examined impacts on (SOM) a mature Two large experimental plots (15 ha each) were established: control fertilised plot. The latter received NH 4 NO 3 fertilizer an average rate 75 kg ?1 year for 12 years. While centre this plot prescribed amounts fertilizer, year-to-year variation distribution around designated edges created gradient N-loading. Along gradient, shift SOM horizon was assessed using two methods: pyrolysis-gas chromatography/mass spectrometry (GC/MS) solid-state 13 nuclear magnetic resonance spectroscopy ( NMR). Both these methods revealed that changed increasing loading, fraction (i.e., aromatic, methoxy/ -alkyl C) relative to carbohydrate O C), accompanied mass (kg m ?2 ) Also, pyrolysis products mainly due methyl -acetyl-?- D -glucosaminide F/H horizon, plausibly origin. Microbial processing likely contributed fertilizer-derived N. Our results corroborate hypothesis inorganic suppresses enzymatic white-rot decomposition non-enzymatic brown-rot oxidation. Taken together, our study suggests enrichment leads selective lignin-derived points key role such N-induced accumulation.