Origin and composition of organic N forms and related stabilization mechanisms in a soil chronosequence

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This project aims at the mechanisms of organic nitrogen (N) stabilization in native rainforest soils with special emphasis on the mineralogical control. It bases on the `long substrate aging gradient¿ chronosequence at Hawaiian Islands (USA) that covers substrate ages from 300 to 4.1 × 106 years at otherwise fairly constant environmental variables. This allows to track changes in organic N accumulation and stabilization as related to mineral composition, which changes during soil formation. The proposal addresses the following aspects: (i) accumulation of organic N forms in bulk and clay-size fractions of soil horizons and transformation of organic N across the differently aged sites as analysed by proteomics, biomarker analysis, and enzyme activity measurements, (ii) investigation of the mineralogical vs. organic matter control on N preservation by relating mineral phase variables and organic matter properties to the composition of organic N, as revealed by wet chemical methods and X-ray absorption near edge structure (N-XANES), and (iii) localization, concentration, and composition of stabilized organic N forms using degradation techniques. Finally we test in batch sorption and incubation experiments if (iv) sorptive interaction of N compounds with mineral phases can account for the observed patterns of organic N accumulation, transformation, and stabilization. We expect novel insight into origin and stabilization mechanisms of organic N forms in soil.