『Abstract
　Amino sugars in fungal cell walls (such as chitin) represent an important source of nitrogen (N) in many forest soil ecosystems. Despite the importance of this material in soil nitrogen cycling, comparatively little is known about abiotic and biotic controls on and the timescale of its turnover. Part of the reason for this lack of information is the inaccessibility of these materials to classic bulk extraction methods. To address this issue, we used advanced visualization tools to examine transformation pathways of chitin-rich fungal cell wall residues as they interact with microorganisms, soil organic matter and mineral surfaces. Our goal was to document initial micro-scale dynamics of the incorporation of ¹³C- and ¹⁵N-labeled chitin into fungi-dominated microenvironments in O-horizons of old-growth forest soils. At the end of a 3-week incubation experiment, high-resolution secondary ion mass spectrometry imaging of hyphae-associated soil microstructures revealed a preferential association of ¹⁵N with Fe-rich particles. Synchrotron-based scanning transmission X-ray spectromicroscopy (SEXM/NEXAFS) of the same samples showed that thin organic coatings on these soil microstructures are enriched in aliphatic C and amide N on Fe (hydr)oxides, suggesting a concentration of microbial lipids and proteins on these surfaces. A possible explanation for the results of our micro-scale investigation of chemical and spatial patterns is that amide N from chitinous fungal cell walls was assimilated by hyphae-associated bacteria, resynthesized into proteinaceous amide N, and subsequently concentrated onto Fe (hydr)oxide surfaces. If confirmed in other soil ecosystems, such rapid association of microbial N with hydroxylated Fe oxide surfaces may have important implications for mechanistic models of microbial cycling of C and N.』

1. Introduction
2. Materials and methods
　2.1. Sample characteristics
　　2.1.1. Soil characteristics
　　2.1.2. Soil incubations
　　2.1.3. Specimen preparation
　2.2. Synchrotron-based scanning transmission X-ray microscopy (SRXM) in combination with near edge X-ray absorption fine structure (NEXAFS) spectroscopy
　　2.2.1. Imaging analysis
　　2.2.2. Data processing
　2.3. High-resolution secondary ion mass spectrometry imaging
　　2.3.1. Imaging analysis
　　2.3.2. Data processing
3. Results
　3.1. Selection of regions of interest (ROIs)
　3.2. NanoSIMS imaging of the δ¹⁵N and Fe distribution
　3.3. STXM/NEXAFS characterization of δ¹⁵N-enriched features on Fe-rich surfaces
　　3.3.1. C NEXAFS spectroscopy
　　3.3.2. N NEXAFS spectroscopy
　　3.3.3. Fe NEXAFS spectroscopy
　3.4. STXM/NEXAFS characterization of spatial and chemical patterns in hyphae-associated microstructures
　　3.4.1. C NEXAFS spectroscopy
　　3.4.2. N NEXAFS spectroscopy
　3.5. Characterization of the δ¹⁵N and Fe distribution of distinct morphological and chemical features
4. Discussion
　4.1. Microbial C cycling in hyphal-dominated microenvironments
　4.2. Microbial amide N cycling in hyphal-dominated microenvironments
　4.3. High affinity of Fe (hydr)oxides for microbial C and N
5. Conclusions
Acknowledgments
Appendix A
References