Elucidating the contribution of arbuscular mycorrhizal fungi to lead and uranium uptake, localisation and speciation within plant roots

  • James Dinsley

Student thesis: Phd

Abstract

The legacy of soil and water pollution generated by historic mining and milling operations has generated an enduring and widespread contamination issue that degrades otherwise viable land. Whilst it is known that microbes can influence soil Pb and U bioaccessibility to plants, the influence of some microbial groups, particularly symbionts (e.g., arbuscular mycorrhizal fungi, AMF), are still poorly understood with respect to soil-plant transfer, accumulation and bioaccessibility of Pb and U. Advancing current understanding of AMF-contaminant interactions is critical for accurately assessing food chain transfer risks for contaminants like Pb and U, alongside improving the feasibility and efficiency of phytoremediation strategies. This NERC-funded research project, partnered with the British Universities Fund Initiative (sponsored by the British Geological Survey), acknowledges the criticality of this research towards exploring the contribution of AMF towards plant uptake, localisation and speciation of Pb and U, firstly by better defining the likely chemical mechanisms that govern Pb and U acquisition and accumulation by roots and AMF hyphae within controlled laboratory conditions via Pb and U dosing trials; and secondly by assessing the contribution of native AMF towards Pb and U uptake by bait plants cultivated within a field-relevant system of mesocosms containing a Pb and U contaminated soil. Soil turfs collected from the abandoned U and Pb mining site of South Terras (Cornwall, UK) were used to create the field-relevant mesocosms. For studying Pb and U localisation, this investigation relied heavily on a suite of high-resolution and highly sensitive techniques such as inductively coupled plasma mass spectrometry (ICP-MS), scanning and transmission electron microscopy (SEM-EDX, STEM-EDX, TEM), nanoscale secondary ion mass spectrometry (NanoSIMS), gas chromatography (GC) and synchrotron radiation techniques for element mapping (micro-X-ray fluorescence, μ-XRF). X-ray absorption spectroscopy (XAS) analyses were conducted to assess the changes in Pb and U speciation within both model (e.g., Plantago lanceolata) and native (e.g., Geum urbanum) plant species, determining how AMF presence alters this speciation chemistry. Overall, it was determined that AMF may not have a significant influence on Pb and U uptake in either laboratory-grown model plants or within plants that grow naturally at the South Terras sites. Nevertheless, it is apparent that the colonisation of P. lanceolata with the AMF model species, R. irregularis, did have an observable impact on Pb and U localisation within plant roots, with mycorrhizal plants demonstrating a greater abundance of Pb and U rich particles within root sections (preferentially bound to cell walls) than for un-colonised plant roots. TEM analysis of Pb and U dosed plants indicated that two different crystalline compounds of both Pb and U were being formed within the roots of P. lanceolata: an acicular form for both elements, alongside a granular Pb crystal habit and an equant, platy U habit. The acicular form was present irrespective of AMF, but the equant platy U crystals were only observed in the mycorrhizal variants of P. lanceolata and the granular Pb form was more common in the mycorrhizal roots relative to the un-colonised. Upon examination of field-relevant plant roots, whilst U localisation aligned with that of lab-grown plants, Pb localisation differed, appearing preferentially bound to intracellular compounds. No notable impact on U or Pb speciation was observed via XAS following AMF inoculation, with uranyl orthophosphate being the likely dominant U contributor in P. lanceolata roots and shoots and the dominant Pb species remaining inconclusive. Field-collected G. urbanum plants also showed U(VI) as the dominant U oxidation state, possibly via the presence of uranyl orthophosphate or autunite. Overall, the results of this thesis presented herein provide a novel account on how AMF
Date of Award1 Aug 2024
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorClare Robinson (Supervisor), Samuel Shaw (Supervisor) & Jon Pittman (Supervisor)

Keywords

  • Elemental Speciation
  • Elemental Mapping
  • Synchrotron
  • Lead
  • Uranium
  • Arbuscular Mycorrhizal Fungi
  • Plant

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