Accumulation, transformation, and stabilization of organic nitrogen along a mineralogical soil gradient

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Soil organic matter is considered the major source of bioavailable N, but the role of functionally different OM pools in N cycling is poorly understood. This project aims at highlighting the role of mineral−organic associations on accumulation, transformation, and bioavailability of organic nitrogen (ON) in soils of a temperate rainforest chronosequence in New Zealand. The soils developed over 120,000 years in silica-rich parent materials (schist, greywacke) giving rise to pronounced gradients in soil mineralogy and soil formation. This allows to study the mineralogical controls on changes in ON accumulation, its chemical composition, and bioavailability as well as the feedbacks of soil mineralogy on microbial composition and function. To reach this goal, we will (i) characterize the mineralogical composition of the soils, (ii) quantify the amount of ON held in mineral−organic associations, (iii) analyse respective ON forms by molecular biomarker, X-ray photoelectron and absorption spectroscopy, (iv) assess the consequences of mineral−ON interactions for N bioavailability, and (v) characterize the microbial communities involved in N cycling using real-time polymerase chain reaction for 16S rRNA and functional gene quantification, and enzyme activity measurements. This study will emphasize the ubiquitous role of minerals in the cycling of soil ON and thus add an important component to current N cycling models.