Correlative Microscopy: a tool for understanding soil weathering in modern analogues of early terrestrial biospheres

R L Mitchell,P Kenrick,R Johnston,C Pleydell-Pearce,T Volkenandt,P Davies

doi:10.1038/s41598-021-92184-1

R L Mitchell, P Kenrick + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-92184-1

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Abstract

Correlative imaging provides a method of investigating complex systems by combining analytical (chemistry) and imaging (tomography) information across dimensions (2D-3D) and scales (centimetres-nanometres). We studied weathering processes in a modern cryptogamic ground cover from Iceland, containing early colonizing, and evolutionary ancient, communities of mosses, lichens, fungi, and bacteria. Targeted multi-scale X-ray Microscopy of a grain in-situ within a soil core revealed networks of surficial and internal features (tunnels) originating from organic-rich surface holes. Further targeted 2D grain characterisation by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (SEM–EDS), following an intermediate manual correlative preparation step, revealed Fe-rich nodules within the tunnels. Finally, nanotomographic imaging by focussed ion beam microscopy (FIB-SEM) revealed coccoid and filamentous-like structures within subsurface tunnels, as well as accumulations of Fe and S in grain surface crusts, which may represent a biological rock varnish/glaze. We attribute these features to biological processes. This work highlights the advantages and novelty of the correlative imaging approach, across scales, dimensions, and modes, to investigate biological weathering processes. Further, we demonstrate correlative microscopy as a means of identifying fingerprints of biological communities, which could be used in the geologic rock record and on extra-terrestrial bodies.

Highlights

Correlative imaging provides a method of investigating complex systems by combining analytical and imaging information across dimensions (2D-3D) and scales
The first plant-dominated biospheres were akin to modern cryptogamic ground covers (CGCs)[4,9,10], which are composed of a consortia of early divergent and evolutionary ancient non-vascular bryophyte plants, lichens, fungi, algae, and bacteria
The tunnels appear to originate from holes at the grain surface (Figs. 1, 2a, g–j), which extend to varying depths within the grain, and appear to contain accumulations of organic material (Figs. 2g–j), but these are at the limit of resolution of Versa X-ray Microscopy (XRM)

Summary

Introduction

Correlative imaging provides a method of investigating complex systems by combining analytical (chemistry) and imaging (tomography) information across dimensions (2D-3D) and scales (centimetres-nanometres). Investigating the intricate nano-to-micro scale interactions in modern analogous CGCs can shed light on how ancestors of Scientific Reports | (2021) 11:12736 These primitive organisms contributed to soil-forming processes, biologically mediated weathering, and potential nutrient-acquisition from their substrates. Previous research on modern CGCs developing on primordial land surfaces from Iceland (i.e. lava flows and volcanic sedimentary terrains that are relatively new and unweathered land surfaces devoid of ‘higher’ vascular plants) were mostly limited to 2D investigations, mainly of grain surface p rocesses[21] These revealed biologicallymediated weathering features (BWFs) on volcanic glass and scoria within soils that were attributed to the actions of different organisms (e.g. bacteria, fungi) and processes (e.g. symbiosis, root-mediated dissolution)[21]. We propose that this approach could be used in the search for biological influences on extra-terrestrial bodies

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