The behavior of nickel isotopes at the biogeochemical interface between ultramafic soils and Ni accumulator species

Abstract

Ultramafic derived soils are characterized by low nutrient soils, a low Ca:Mg ratio, and high metal contents such as Ni, Co and Cr. The vegetation growing on these soils is highly adapted and includes both Ni hyperaccumulator and accumulator species. Today, approximately 530 Ni hyperaccumulator species are listed worldwide and the Ni concentration can be extremely high, e.g. up to 25% in latex from Pycnandra acuminata (Sapotaceae), a tree found in New Caledonia. The aim of this study is to identify the potential role of Ni hyperaccumulator plants in the Ni biogeochemical cycle at the soil surface by using Ni isotopes. A set of Ni hyperaccumulator and Ni accumulator plants as well as topsoils were sampled on the Barro Alto and Niquelândia ultramafic complexes (Goiás State, Brazil). Three Ni hyperaccumulator plants were collected: Justicia lanstyakii, Heliotropium aff. salicoides, Cnidoscolus aff. urens, as well as one Ni accumulator plant, Manihot sp. The isotopic compositions of the whole plants were determined and compared to those of the bulk topsoils and DTPA-extractable Ni. The topsoils exhibited δ 60 Ni values ranging from −0.30 ± 0.06‰ to 0.16 ± 0.05‰. The DTPA-extractable Ni in the topsoils ranged from 94 to 623 mg kg −1 , i.e. 0.9-4.9% of the total soil Ni and was found to be isotopically heavier than the corresponding topsoil (from −0.30 ± 0.05‰ to 0.34 ± 0.08‰). The δ 60 Ni values for the Ni accumulator plants showed an enrichment in heavy Ni isotopes in the aerial parts of the plant compared to the roots, whereas similar δ 60 Ni values for the roots, stems and aerial parts suggested that no significant fractionation results from Ni uptake and translocation in Ni hyperaccumulator plants. Moreover, the aerial parts (i.e. leaves and flowers) from all of the plants analyzed showed the highest Ni concentrations and the heaviest δ 60 Ni values up to 1.21 ± 0.05‰. The enrichment in heavy Ni isotopes in the leaves (0.09 ± 0.06‰ < Δ 60 Ni leaves-soil < 1.06 ± 0.03‰) may result in a heavy Ni input in the litter during organic matter restitution. There is a non-negligible amount of Ni uptake by Ni accumulator and Ni hyperaccumulator plants and this may modify both the Ni isotope composition at the soil-plant interface and the overall cycle of Ni in surface soils Highlights ► DTPA extractable Ni in topsoil is isotopically heavier than the total Ni pool. ► Ni-accumulators exhibit enrichment in Ni heavy isotopes in aerial parts. ► Similar δ 60 Ni values for each plant compartment are observed for Ni-hyperaccumulators. ► Enrichment in heavy Ni isotopes in leaves may lead to a heavy Ni input in the litter.

Field availability and mobility of metals in Ferralsols developed on ultramafic rock of Niquelândia, Brazil

“…• the presence of certain "hyperaccumulators" of metals (Ni) ( Jaffré et al 1976, Proctor and Nagy 1992, Reeves et al 2007, Kazakou et al 2008, Anacker 2014, Bini et al 2017, Kanellopoulos et al 2015, 2019.…”

Intensive cycling of nickel in a New Caledonian forest dominated by hyperaccumulator trees

“…, 2015; Ratié et al. , 2019). It has been suggested that plant isotopic composition is mainly controlled by the root uptake process (Estrade et al.…”

“…The use of multi‐collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS) is increasingly used to investigate the fate and pathways of non‐traditional metals such as Ni in soil–plant systems through isotopic fractionation (Ratié et al. , 2019; Zelano et al. , 2018).…”

The potential of Blepharidium guatemalense for nickel agromining in Mexico and Central America

“…Therefore, the above-mentioned Ni resource in soils per hectare would be completely depleted in 3 years of culture considering an annual yield of 142 kg Ni yr -1 after which the site will be suitable for other types of cropping. Research is currently underway to better understand the role of Ni hyperaccumulators in the geochemical cycle of Ni and the replenishment of Ni labile pools in soils over time Ratié et al, 2019). Intensive geochemical investigations are needed to determine the total extent of Ni-enriched substrates and to select the most suitable sites for Ni agromining in southeastern Mexico.…”