Using the Scanning Electron Microprobe and Secondary Ion Mass Spectrometry to Locate ¹⁴C- and ¹³C-Labelled Plant Residues within Soil Aggregates

Abstract

Increasing concentrations of CO₂ in the atmosphere are placing emphasis on the necessity for sequestering carbon (C) into soil organic matter (SOM). By studying the interior parts of soil aggregates, a better understanding of the incorporation and sequestration of plant residue materials within these aggregates could be obtained. The location of newly added plant residues within soil aggregates may also assist in the investigation of the impact of these newly added plant materials on soil aggregation. This study investigated two different techniques for determining the location of newly added plant residues within soil aggregates by using plant materials labelled with ¹⁴C and ¹³C isotopes incorporated into two different soil types, Black Earth (Pellic Vertisol) and Red Clay (Chromic Vertisol). Both autoradiography combined with scanning electron microprobe analysis (¹⁴C) and secondary ion mass spectrometry (SIMS) (¹³C) were successfully used for detecting the presence and location of the newly added plant residues fragments within soil aggregates of both soil types. The use of labelled plant materials is essential for the study of the location of newly added plant materials within soil aggregates, and this has proven to be a useful tool for studying the impact of residue additions on soil aggregate formation. Furthermore, these methods have been shown to be useful for determining the incorporation and sequestration of C materials within soil aggregates. The development of the ¹³C SIMS technique could alleviate the necessity for the use of the radioactive isotope ¹⁴C in soil studies.