Evaluating soil extraction methods for chemical characterization of ultramafic soils in Kinabalu Park (Malaysia)

Soils derived from ultramafic bedrock are known for hosting distinct vegetation types as a consequence of atypical soil chemistries consisting of high trace elements concentrations (Ni, Cr, Co) and exchangeable cation imbalances (high Mg:Ca quotients). Ecological studies use a range of single-stage extraction methods for chemical characterization of such soils in order to be able to interpret plant response, and ultimately to explain plant community composition. Few studies to date have compared different soil extraction methods in relation to tropical ultramafic soils. This study compares eight commonly used extraction methods on a large number of ultramafic soil samples collected from Kinabalu Park (Malaysia). The tested methods were: for trace elements: NH4AC, DTPA, CaCl2, Sr(NO3)2 and Mehlich-3, for exchangeable cations: NH4Ac and silverthiorea, and for plant-available phosphorus: Mehlich-3 and Olsen-P. These single-stage extraction methods were compared and evaluated for predictive power for chemically characterizing soils, interrelatedness and ecological application. The methods were also contrasted with a sequential extraction scheme. Finally, several operational parameters including molar ratio (0.01 and 0.1 M CaCl2, Sr(NO3)2) and pH buffering (DTPA-TEA) were also evaluated. The majority of single-stage extraction methods are highly inter-correlated and predictive power could be improved by including independent soil parameters (pH, CEC, pseudo-total element concentration) in the multivariate regression equation. Ecological interpretation remains difficult because of lack of experimental studies in relation to plant uptake response and potential phytotoxicity effects on tropical native plants from ultramafic soils

Impacts of ultramafic outcrops in Peninsular Malaysia and Sabah on soil and water quality

This study focused on the influence of ultramafic terrains on soil and surface water environmental chemistry in Peninsular\ua0Malaysia and\ua0in\ua0the State of Sabah also in\ua0Malaysia. The sampling included 27 soils from four isolated outcrops at\ua0Cheroh, Bentong, Bukit Rokan, and Petasih from Peninsular Malaysia and sites near Ranau in\ua0Sabah. Water samples were also collected from rivers and subsurface waters interacting with the ultramafic bodies in these study sites. Physico-chemical parameters (including pH, EC, CEC) as well as the concentration of major and trace elements were measured in these soils and waters. Geochemical indices (geoaccumulation index, enrichment factor, and concentration factor) were calculated. AlO and FeO had\ua0relatively high concentrations in the samples. A depletion in MgO, CaO, and NaO was observed as a result of leaching in tropical climate, and in relation to weathering and pedogenesis processes. Chromium, Ni, and Co were enriched and confirmed by the significant values obtained for Igeo, EF, and CF, which correspond to the extreme levels of contamination for Cr and high to moderate levels of contamination for Ni and Co. The concentrations of Cr, Ni, and Co in surface waters did not reflect the local geochemistry and were within the permissible ranges according to WHO and INWQS standards. Subsurface waters were strongly enriched by these elements and exceeded these standards. The association between Cr and Ni was confirmed by factor analysis. The unexpected enrichment of Cu in an isolated component can be explained by localized mineralization in Sabah

Nickel hyperaccumulation mechanisms: a review on the current state of knowledge

Background: Hyperaccumulator plants are unusual plants that accumulate particular metals or metalloids, such as nickel, zinc, cadmium and arsenic, in their living tissues to concentrations that are hundreds to thousands of times greater than what is normal for most plants. The hyperaccumulation phenomenon is rare (exhibited by less than 0.2% of all angiosperms), with most of the ~500 hyperaccumulator species known globally for nickel. Scope: This review highlights the contemporary understanding of nickel hyperaccumulation processes, which include root uptake and sequestration, xylem loading and transport, leaf compartmentation and phloem translocation processes. Conclusions: Hyperaccumulator plants have evolved highly efficient physiological mechanisms for taking up nickel in their roots followed by rapid translocation and sequestration into the aerial shoots. The uptake of nickel is mainly involved with low affinity transport systems, presumably from the ZIP family. The presence of high concentrations of histidine prevents nickel sequestration in roots. Nickel is efficiently loaded into the xylem, where it mainly presents as Ni. The leaf is the main storage organ, which sequestrates nickel in non-active sites, e.g. vacuoles and apoplast. Recent studies show that phloem translocates high levels of nickel, which has a strong impact on nickel accumulation in young growing tissues

Contrasting nickel and zinc hyperaccumulation in subspecies of Dichapetalum gelonioides from Southeast Asia

Hyperaccumulator plants have the unique ability to concentrate specific elements in their shoot in concentrations that can be thousands of times greater than in normal plants. Whereas all known zinc hyperaccumulator plants are facultative hyperaccumulators with only populations on metalliferous soils hyperaccumulating zinc (except for Arabidopsis halleri and Noccaea species that hyperaccumulate zinc irrespective of the substrate), the present study discovered that Dichapetalum gelonioides is the only (zinc) hyperaccumulator known to occur exclusively on 'normal' soils, while hyperaccumulating zinc. We recorded remarkable foliar zinc concentrations (10 730 µg g, dry weight) in Dichapetalum gelonioides subsp. sumatranum growing on 'normal' soils with total soil zinc concentrations of only 20 µg g. The discovery of zinc hyperaccumulation in this tropical woody plant, especially the extreme zinc concentrations in phloem and phloem-fed tissues (reaching up to 8465 µg g), has possible implications for advancing zinc biofortification in Southeast Asia. Furthermore, we report exceptionally high foliar nickel concentrations in D. subsp. tuberculatum (30 260 µg g) and >10 wt% nickel in the ash, which can be exploited for agromining. The unusual nickel and zinc accumulation behaviour suggest that Dichapetalum-species may be an attractive model to study hyperaccumulation and hypertolerance of these elements in tropical hyperaccumulator plants

The seed germination properties of two hyperaccumulator plant species with the potential for Ni agromining

The aim of this study is to investigate the effect of different nickel concentrations and light in combination with storage conditions and storage time on the seed germination ability of two serpentine-endemic nickel hyperaccumulating species (Bornmuellera emarginata and B. tymphaea). The seeds of both species were collected from natural populations in the Pindus Mountain range, Greece in early July and stored in a refrigerator (4°C) and in laboratory conditions (22°C). The seeds were exposed to a range of nickel concentrations typical of non-ultramafic ‒ ultramafic gradient in two light environments (12 h photoperiod and continuous darkness). The nickel concentration only had a significant effect on B. emarginata, decreasing its seed germination rate with increasing Ni concentrations. The storage temperature significantly affected the germination percentage of both species and it was higher at 4°C compared to 22°C. A higher germination rate (> 60%) was observed for 5‒8-month-old seeds, but both species generally showed significantly higher germination rates in the tests conducted seven months after seed ripening in the field. A higher germination rate was observed in a 12-hour photoperiod than in continuous darkness only for B. tymphaea. This study provides guidelines on the germination capacity of two obligate nickel hyperaccumulators with a potential for use in agromining systems

Herbarium X-ray fluorescence screening for nickel, cobalt and manganese hyperaccumulator plants in the flora of Sabah (Malaysia, Borneo Island)

Sabah (Malaysia) on the Island of Borneo has high plant diversity (>8000 species) occurring on a wide range of soils, including ultramafic soils which are known to host hyperaccumulator plants. In this study a new approach (“Herbarium X-ray Fluorescence Ionomics”) was used to obtain elemental data from herbarium specimens using non-destructive X-ray Fluorescence spectroscopy analysis. In total ~7300 specimens were thus analysed for nickel, cobalt, and manganese concentrations at the Herbarium of the Forest Research Centre (FRC) in Sepilok, Sabah. The measurements led to recording a total of 759 specimens (originating from 17 families in 30 genera and 74 species) as trace element hyperaccumulators, including 28 nickel hyperaccumulator species (in 10 families, 17 genera), 12 cobalt hyperaccumulator species (in 3 families, 7 genera), and 51 manganese hyperaccumulator species (in 12 families, 24 genera). The outcomes of this research demonstrate that handheld XRF is highly useful approach for hyperaccumulator plant discovery in herbarium collections that has the potential to add vast numbers of hyperaccumulating taxa to the global inventory

The first tropical ‘metal farm’: some perspectives from field and pot experiments

Agromining is the chain of processes of phytoextraction of economically valuable elements by selected hyperaccumulator plants, and subsequent processing of biomass to produce targeted metals or commercial compounds of high value. Although substantial unrealized opportunities exist for developing economic nickel (Ni) agromining in the tropics, this technology has remained relatively unexplored. This study investigated the soil chemistry of a newly established tropical ‘metal farm’ and elucidated the performance of a prospective ‘metal crop’ species (Phyllanthus rufuschaneyi) to be used in a large-scale tropical Ni agromining program on ultramafic soils in Sabah (Malaysia). We found that a major portion of the site (>90%) had high total Ni concentrations (>2000 μg g) in the soil (shallow Eutric Cambisol Magnesic). This study also recorded high phytoavailable soil Ni concentrations in the field site, which is a desired property of soils intended for Ni agromining. Moreover, the average soil pH of the field (pH 6.4) is ideal for maximum Ni uptake in the local candidate species. We recorded low concentrations of Ca, K and P, suggesting the need for a fertilizer regime in the farm. The extraordinary shoot Ni concentrations (>2 wt%), coupled with the high purity of the ‘bio-ore’ derived from Phyllanthus rufuschaneyi, confirm its high potential for economic Ni agromining. The success of our first field trial is critical to provide ‘real-life’ evidence of the value of large-scale tropical ‘metal farming’. Research priorities include the need to intensify the search for candidate species, determine their agronomy, develop mass propagation methods, and to test technologies to process the biomass to recover valuable products