Micromorphology Techniques for Soil Organic Carbon Studies

Abstract

Most research about soil organic C (SOC) has dealt with its composition, fractionation, degree of stability and turnover time, through analyses that involve the complete or partial destruction of the soil structure. Different fractionation techniques on soil aggregates have produced information about the relationships between SOC, minerals and soil structure. There is still a gap between aggregates or organo-mineral associations isolated from the soil matrix and the soil structure and organic matter distribution in the field. Micromorphology and micromorphometry can be very useful to fill this gap. Classical micromorphology is capable of producing true-scale images of the 2D porosity of undisturbed soils. The study of soil organic matter (SOM) through light microscopy is however limited by the isotropic nature of most soil organic components. A set of new techniques developed more or less recently exist that can complement the information obtained using classical micromorphology. Fluorescence microscopy, SEM and microanalyses applied to undisturbed samples provide a more detailed information on the arrangement of soil components, although the results do not fully provide information about the distribution of SOM types. TOF-SIMS, NanoSIMS, FTIR microscopy and XANES through synchrotron facilities are able to yield information about the location of SOM functional groups and microorganisms in relation to soil structure, and thus are promising for associating specific microsites and SOM characteristics with different degrees of activity or stability. In this work the fundamentals and usefulness of these techniques for SOM studies are described.