Application of synchrotron-based X-ray fluorescence (XRF) mapping, and X-ray absorption spectroscopy (XAS) to study the mineral-organic matter associations in the rhizosphere soils of Canola genotypes
Abstract
Synchrotron-enabled high-resolution spectroscopic and imaging techniques can be efficiently used to study the spatial heterogeneity and mineral-associations of soil organic matter (SOM) without the physical disruption of soil aggregation. We used synchrotron-enabled X-ray fluorescence (XRF) mapping, and X-ray absorption spectroscopy (XAS) to study the molecular speciation, distribution and mineral correlations of SOM in the rhizospheric soils for different genotypes of the canola crop. Root and soil samples for sixteen canola lines were collected on a weekly basis from a Dark Brown Chernozemic soil at the Llewelyn Road Research site in Saskatoon, Canada. The rhizosphere soils collected from around the roots of Canola lines were analyzed for differences in SOM molecular composition by using ATR-FTIR and XAS spectroscopies. Rhizospheric soils of the Canola lines showed differences in the relative abundances of simple polysaccharide-like substances and microbially-derived aliphatic-C groups. Three out of the sixteen canola lines that showed maximum differences in SOM speciation within the rhizosphere were selected for analysis using XRF imaging to map various elements including C, N, O, Fe, and Al in the rhizosphere soils. The roots and soils were prepared for mapping by utilizing two different methods - a) by directly making the thin sections of the fresh roots along with the soil particles adhered to them, and b) by cryogenically cooling the roots along with adhered soils, followed by acquisition of thin sections used for imaging analysis. Additionally, microfocused XANES (uXANES) spectra for C and N K-edges were acquired at the hot spots within the spatially-heterogenous images of the root-soil systems, in order to constrain the C and N speciation at micrometre spatial resolutions. The hydrophobic organic matter forms, including aromatic-C and aliphatic-C groups showed a patchy distribution at the micrometer scale, while the oxidised forms were distributed more uniformly across the mineral surfaces. C association with Fe and Al showed some differences amongst the Canola lines, possibly due to the differences in the chemical speciation of OM between the different lines.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B21L2312D
- Keywords:
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- 0409 Bioavailability: chemical speciation and complexation;
- BIOGEOSCIENCES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0452 Instruments and techniques;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES