Root induced soil deformation influences Fe, S and P: rhizosphere chemistry investigated using synchrotron XRF and XAS

Abstract

Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root induced physical changes, chemical changes have not been extensively measured in situ on the pore scale.

In this study we couple structural information, previously obtained using synchrotron X-ray computed tomography (XCT), with synchrotron X-ray Fluorescence (SR-XRF) microscopy and X-ray Absorption Near-Edge Structure (XANES) to unravel chemical changes induced by plant roots.
Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO42-) and that P is increasable adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically suggesting the preferential dissolution and the formation of more stable Fe-oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via X-ray CT.
The fact that these changes are co-located near the root and the compaction zone suggests that decreased permeability due to soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface mediated processes, microbial activity and acidification.

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Identifiers

ORCID for Tiina Roose: orcid.org/0000-0001-8710-1063

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