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Abstract Soil organic carbon (SOC) associated with minerals is considered to be one of the most fundamental long-term SOC storage strategies, but little research has integrated the organo-mineral complexes regulated by long-term fertilization. Here, soil samples under three fertilization treatments (Control, no fertilization; NPK, chemical nitrogen, phosphorus and potassium fertilization; NPKM, NPK plus manure) from four 23–34 years long-term field experiment sites across China were examined. Chemical analyses indicated that vigorous iron (Fe) mobilization could be regulated by long-term fertilization regimes. Meanwhile, Fe K-edge X-ray absorption near-edge fine structure (XANES) demonstrated that compared to NPK treated soils, NPKM treated soils contained significantly higher concentration of poorly crystalline ferrihydrite. Results from both the Fourier transform infrared combined with two-dimensional correlation spectroscopy analyses (FTIR-2DCOS) and C 1 s X-ray photoelectron spectroscopy (XPS) revealed that aliphatic carbohydrate might play an important role in binding exogenous Fe(III) in all tested four soils. In addition, greater amounts of aromatic C (the most resistant soil C fraction) were under long-term treated NPKM than NPK soils. Furthermore, multiple regression analyses showed a significantly positive relationship between poorly crystalline Fe minerals and SOC or aromatic C. Such relationships indicated that aromatic functional groups had been attached to the poorly crystalline Fe minerals, which could also be protected from being transformed to the crystalline counterpart. In conclusion, results from our integrated spectroscopic analyses have evidenced greater improvement of both poorly crystalline Fe minerals and aromatic C in organically fertilized than in chemically fertilized soils. Graphical abstract Unlabelled Image Highlights • Fertilization regimes had contrasting effects on Fe C associations in soils. • Combined spectroscopic methods were applied to evaluate the species of Fe and C. • Poorly crystalline Fe minerals were closely correlated to aromatic C accumulations. • Long-term organic fertilization improved the capacity of soil organic carbon storage. [ABSTRACT FROM AUTHOR]

Although the precipitation and dissolution of iron (Fe)-containing-minerals are driven by microbially-mediated iron-redox cycling, we still have a limited understanding of complex response of such microbial communities to fertilisation. Here, using chemical and synchrotron-based spectral analyses, we show that the distribution of poorly crystalline Fe minerals and crystalline Fe minerals is different in organically- and inorganically-fertilised soils, and that compared to no fertilisation (Control), Fe redox cycling bacteria were present at higher abundance and diversity in organically-fertilised soils but lower in inorganically-fertilised soil. During Fe(III) reduction, Geobacter were important active Fe(III) reducers, with a higher relative abundance in both organically- and inorganically-fertilised soils than in Control, and their higher abundance was responsible for greater dissolution of ferrihydrite in inorganically-fertilised soil than in organically-fertilised soil. However, during the Fe(II) oxidation, Pseudomonas and Anaerolinea were more abundant, and produced higher levels of poorly crystalline Fe oxides under organic fertilisation. Thus, for the first time, we demonstrate that inorganic and organic fertilisation regimes have contrasting effects on the Fe redox bacterial communities, which then influence Fe cycling in soils. [ABSTRACT FROM AUTHOR]

Mineral-organo associations (MOAs) are a mixture of identifiable biopolymers associated with highly reactive minerals and microorganisms. However, the in situ characterization and correlation between soil organic matter (SOM) and highly reactive Al and Fe minerals are still unclear for the lack of technologies, particularly in the long-term agricultural soil colloids at submicron scale. We combined several novel techniques, including nano-scale secondary ion mass spectrometry (NanoSIMS), X-ray absorption near edge structure (XANES) and confocal laser scanning microscopy (CLSM) to characterise the capacity of highly reactive Al and Fe minerals to preserve SOM in Ferralic Cambisol in south China. Our results demonstrated that: (1) highly reactive minerals were strongly related to SOM preservation, while SOM had a more significant line correlation with the highly reactive Al minerals than the highly reactive Fe minerals, according to the regions of interest correlation analyses using NanoSIMS; (2) allophane and ferrihydrite were the potential mineral species to determine the SOM preservation capability, which was evaluated by the X-ray photoelectron spectroscopy (XPS) and Fe K-edge XANES spectroscopy techniques; and (3) soil organic biopolymers with dominant compounds, such as proteins, polysaccharides and lipids, were distributed at the rough and clustered surface of MOAs with high chemical and spatial heterogeneity according to the CLSM observation. Our results also promoted the understanding of the roles played by the highly reactive Al and Fe minerals in the spatial distribution of soil organic biopolymers and SOM sequestration. [ABSTRACT FROM AUTHOR]