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Abstract
Soil organic carbon management is a nature-based carbon dioxide removal technology at the same time contributing to soil health and agricultural productivity. The soil science communities are refuting the traditional assumptions of the nature of soil organic matter (SOM) as based on ‘humic substances’ that are operationally-defined and have not been observed by contemporary, in situ spectromicroscopic techniques. Instead, new theories suggest that the interactions between molecular diversity of organic compounds, their spatial heterogeneity and temporal variability controls the formation and persistence of SOM. A mechanistic understanding of these processes occurring within organo-mineral and organo-organic assemblages requires non-invasive techniques that minimize any disturbance to the physical and chemical integrity of the sample. Here, we present a theory-driven review where a combination of in situ methods serve as potential solutions to better understand the persistence and dynamics of SOM and its effects on nutrient distribution at a micro- and nano-scale. We explore underlying theories in light of advances in available methodologies, their historical development and future opportunities. Examples of interdisciplinary approaches that have been utilized in other areas of science but not in soils offer both deductive and inductive analytical opportunities. We show how different conceptual methods across scales inform each other, and how important and indispensable high-resolution investigations are to resolving next-generation questions.
Graphical Abstract
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Acknowledgements
The authors thank the Grains Research and Development Corporation (GRDC) for funding this research (UOQ1910-003RTX). Part of this research was undertaken on the Soft X-ray spectroscopy beamline and the Infrared microscopy beamline at the Australian Synchrotron, part of ANSTO (grant numbers AS1_SXR_15754 and AS1_IRM_15940). Part of the research was funded by La Trobe University’s Research Focus Area in Securing Food, Water and the Environment (Grant Ready: SFWE RFA 2000004295; Collaboration Ready: SFWE RFA 2000004349). The authors acknowledge the facilities, and the scientific and technical assistance from Dr. Hui Diao for 3D-FIB-SEM, of the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis, The University of Queensland. We thank Dr. Julian Ratcliffe for cryo-ultramicrotome preparation at the Bioimaging Platform, La Trobe University. We also thank Kristina Witzgall, Carmen Hoeschen and Johann Lugmeier (Technical University of Munich, Germany) for the assistance with NanoSIMS measurements and the data acquisition.
