Abstract
New Caledonian endemic Mn-hyperaccumulator Grevillea meisneri is useful species for the preparation of ecocatalysts, which contain Mn–Ca oxides that are very difficult to synthesize under laboratory conditions. Mechanisms leading to their formation in the ecocatalysts are unknown. Comparing tissue-level microdistribution of these two elements could provide clues. We studied tissue-level distribution of Mn, Ca, and other elements in different tissues of G. meisneri using micro-X-Ray Fluorescence-spectroscopy (μXRF), and the speciation of Mn by micro-X-ray Absorption Near Edge Structure (µXANES), comparing nursery-grown plants transplanted into the site, and similar-sized plants growing naturally on the site. Mirroring patterns in other Grevillea species, Mn concentrations were highest in leaf epidermal tissues, in cortex and vascular tissues of stems and primary roots, and in phloem and pericycle–endodermis of parent cluster roots. Strong positive Mn/Ca correlations were observed in every tissue of G. meisneri where Mn was the most concentrated. Mn foliar speciation confirmed what was already reported for G. exul, with strong evidence for carboxylate counter-ions. The co-localization of Ca and Mn in the same tissues of G. meisneri might in some way facilitate the formation of mixed Ca–Mn oxides upon preparation of Eco-CaMnOx ecocatalysts from this plant. Grevillea meisneri has been successfully used in rehabilitation of degraded mining sites in New Caledonia, and in supplying biomass for production of ecocatalysts. We showed that transplanted nursery-grown seedlings accumulate as much Mn as do spontaneous plants, and sequester Mn in the same tissues, demonstrating the feasibility of large-scale transplantation programs for generating Mn-rich biomass.
Highlights
More than 700 plant species worldwide are so far known to be hyperaccumulators of metals
We were interested in the co-distribution patterns of Mn and Ca, in the hope of obtaining clues about the mechanisms leading to the formation of mixed Mn–Ca oxides in the ecocatalysts prepared from Mn-(hyper) accumulators. Such mixed oxides are present in ecocatalysts prepared from prepared from different Grevillea species and Garcinia amplexicaulis[27], we focused on Grevillea meisneri, as its performance shows the greatest potential for use in revegetation and in supplying biomass for production of ecocatalysts
Soils of the site are enriched in Ni, this element was not detected in any part of G. meisneri plants
Summary
More than 700 plant species worldwide are so far known to be hyperaccumulators of metals. Like the endemic Ni-hyperaccumulating species, these Mn-(hyper)accumulating trees are highly adapted to the local climatic and edaphic constraints of mining s ites[28,29,30,31,32,33,34] These pioneer trees have been introduced with success on degraded sites characterized by open environments, frequent water stress, and poor s oil[10]. Foliar Mn concentrations in Mn-hyperaccumulating species such as Grevillea meisneri can exceed 10,000 μg g−17,30,36 Their Mn-rich biomass is valorized by the use of powdered leaves as green and highly efficient catalysts in organic c hemistry[10,13,14,37]. Apart from New Caledonia, other Mn-hyperaccumulating plant species are known from A ustralia39,40, Japan41, China[42,43] and M alaysia[44]
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