『Abstract
　Large portions of organic N (ON) in soil exist tightly associated with minerals. Mineral effects on the type of interactions, chemical composition, and stability of ON, however, are poorly understood. We investigated mineral-associated ON along a Hawaiian soil chronosequence (0.3-4100 kyr) formed in basaltic tephra under comparable climatic, topographic, and vegetation conditions. Mineral-organic associations were separated according to density (ρ＞1.6 g/cm³), characterized by X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge fine structure (NEXAFS) and analyzed for amino acid enantiomers and amino sugars. The ¹⁴C activity of mineral-bound OC was estimated by accelerator mass spectrometry. The close OC-ON relationship (r = 0.96) and XPS results suggest that ON exists incorporated in bulk mineral-bound OM and likely becomes associated with minerals as part of sorbing OM. The youngest site (0.3 kyr), with soils mainly composed of primary minerals (olivine, pyroxene, feldspar) and with little ON, contained the largest proportion of hydrolyzable amino sugars and amino acids but with a small share of acidic amino acids (aspartic acid, glutamic acid). In soils of the intermediate weathering stage (20-400 kyr), where poorly crystalline minerals and metal(hydroxide)-organic precipitates prevail, more mineral-associated ON was present, containing a smaller proportion of hydrolyzable amino sugars and amino acids due to the preferential accumulation of other OM components such as lignin-derived phenols. Acidic amino acids were more abundant, reflecting the strong association of acidic organic components with metal(hydroxide)-organic precipitates and variable-charge minerals. In the final weathering stage (1400-4100 kyr) with well-crystalline secondary Fe and Al (hydr)oxides and kaolin minerals, mineral-organic associations held less ON and were, relative to lignin phenols, depleted in hydrolyzable amino sugars and amino acids, particularly in acidic amino acids. XPS and NEXAFS analyses showed that the majority (59-78％) of the mineral-associated ON is peptide N while 18-34％ was aromatic N. Amino sugar ratios and D-alanine suggest that mineral-associated ON comprises a significant portion of bacterial residues, particularly in the subsoil. With increasing ¹⁴C age, a larger portion of peptide N was non-hydrolyzable, suggesting the accumulation of refractory compounds with time. The constant D/L ratios of lysine in topsoils indicate fresh proteinous material, likely due to continuous sorption of or exchange with fresh N-containing compounds. The ¹⁴C and the D/L signature revealed a longer turnover of proteinous components strongly bound to minerals (not NaOH-NaF-extractable). This study provides evidence that interactions with minerals are important in the transformation and stabilization of soil ON. Mineral-associated ON in topsoils seems actively involved in the N cycling of the study ecosystems, accentuating N limitation at the 0.3-kyr site but increasingly N availability at older sites.』

1. Introduction
2. Materials and methods
　2.1. Study sites and sampling
　2.2. Separation and characterization of mineral-organic associations
　2.3. Radiocarbon dating
　2.4. X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) analysis
　2.5. Hydrolyzable amino acid enantiomers
　2.6. Hydrolyzable amino sugars
　2.7. Estimation of non-hydrolyzable peptide nitrogen
　2.8. Definitions and statistics
3. Results
　3.1. Organic N contents and OC/ON ratios of mineral-organic associations
　3.2. ¹⁴C ages and δ¹³C values
　3.3. Nitrogen XPS of organic matter in mineral-organic associations
　3.4. Nitrogen XPS and NEXAFS of extracted organic matter
　3.5. Amino acids and amino sugars in mineral-organic associations
　　3.5.1. Concentrations of hydrolyzable amino acids and amino sugars
　　　3.5.1.1. Amino acids
　　　3.5.1.2. Amino sugars
　　3.5.2. Non-hydrolyzable peptide nitrogen
　　3.5.3. Composition of N compound classes and their contribution to mineral-associated organic matter
　　　3.5.3.1. Amino acids
　　　3.5.3.2. Amino sugars
　　3.5.4. Amino acid D- and L-enantiomers
　3.6. Hydrolyzable amino acids in extraction residues
4. Discussion
　4.1. Distribution and dynamics of mineral-associated organic matter and nitrogenous components
　　4.1.1. A horizons
　　4.1.2. B horizons
　4.2. Nitrogen species at particle surfaces
　4.3. Bacterial versus fungal contribution to mineral-associated organic N
　4.4. Association of peptide N with mineral surfaces
　4.5. Variations in organic N content and composition with changing mineral assemblage
5. Summary and implications
Acknowledgments
Appendix A. Supplementary data
References