Microscopic Processes Ruling the Bioavailability of Zn to Roots of Euphorbia pithyusa L. Pioneer Plant

Abstract

Euphorbia pithyusa L. was used in a plant growth-promoting assisted field trial experiment. To unravel the microscopic processes at the interface, thin slices of E. pithyusa roots were investigated by micro-X-ray fluorescence mapping. Roots and rhizosphere materials were examined by X-ray absorption spectroscopy at the Zn K-edge, X-ray diffraction, and scanning electron microscopy. Results indicate some features common to all the investigated samples. (i) In the rhizosphere of E. pithyusa, Zn was found to exist in different phases. (ii) Si and Al are mainly concentrated in a rim at the epidermis of the roots. (iii) Zn is mostly stored in root epidermis and does not appear to be coordinated to organic molecules but mainly occurs in mineral phases such as Zn silicates. We interpreted that roots of E. pithyusa significantly promote mineral evolution in the rhizosphere. Concomitantly, the plant uses Si and Al extracted by soil minerals to build a biomineralization rim, which can capture Zn. This Zn silicate biomineralization has relevant implications for phytoremediation techniques and for further biotechnology development, which can be better designed and developed after specific knowledge of molecular processes ruling mineral evolution and biomineralization processes has been gained.

Mineralogy and Zn Chemical Speciation in a Soil-Plant System from a Metal-Extreme Environment: A Study on Helichrysum microphyllum subsp. tyrrhenicum (Campo Pisano Mine, SW Sardinia, Italy)

“…In this study, SEM and EDS analysis showed the presence of a mineral rim made up of Al-silicates coating the epidermis of H. tyrrhenicum roots (Figure 2), as previously observed in other autochthonous plant species growing in similar environments, like E. pithyusa subsp. cupanii, P. lentiscus, P. australis, and J. acutus [23,[76][77][78]109]. This structure was also detected by STXM ( Figure 6), also showing that Zn is mainly stored in the root epidermis.…”

“…XAS spectra for each sample were collected at least in triplicate for averaging and statistics. According to literature data [23,26,50,52,[74][75][76][77][78], in the soil-plant system, Zn can occur in different coordination environments, both bound to organic compounds (e.g., organic acids, phytochelatins, metallothioneins, etc.) and to inorganic molecules (e.g., sulfur, sulfate, carbonate, etc.)…”

The role of natural biogeochemical barriers in limiting metal loading to a stream affected by mine drainage

“…Soft X-ray Microscopy combined with Low Energy XRF LEXRF mapping analyses (STXM) were performed at the TwinMic (Kaulich et al, 2006;Gianoncelli et al 2016a and b) beamline at ELETTRA, Trieste (Italy) on plant root samples (see De Giudici et al, 2015 andMedas et al, 2015 for a detailed description on root sections preparation). The TwinMic microscope was operated in Scanning Transmission mode (Gianoncelli et al, 2009(Gianoncelli et al, , 2013(Gianoncelli et al, , 2006Morrison et al, 2006).…”

Towards a multi‐element silicon drift detector system for fluorescence spectroscopy in the soft X‐ray regime

“…The plant is grown in a mine site and accumulates different metals. [28] The same root area was mapped simultaneously with both the standard TwinMic LEXRF system and the novel detector system under development. For this measurement, two of the eight SDDs of the standard TwinMic LEXRF system were replaced by one trapezoid containing six hexagonal monolithic SDD elements.…”