Boron isotope variability related to boron speciation (change during uptake and transport) in bell pepper plants and SI traceable n(¹¹B)/n(¹⁰B) ratios for plant reference materials

Abstract

Rationale: Boron (B) is an essential micronutrient in plants and its isotope variations are used to gain insights into plant metabolism, which is important for crop plant cultivation. B isotope variations were used to trace intra-plant fractionation mechanisms in response to the B concentration in the irrigation water spanning the range from B depletion to toxic levels. Methods: A fully validated analytical procedure based on multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), sample decomposition and B matrix separation was applied to study B isotope fractionation. The validation was accomplished by establishing a complete uncertainty budget and by applying reference materials, yielding expanded measurement uncertainties of 0.8‰ for pure boric acid solutions and ≤1.5‰ for processed samples. With this validated procedure SI traceable B isotope amount ratios were determined in plant reference materials for the first time. Results: The B isotope compositions of irrigation water and bell pepper samples suggest passive diffusion of the heavy 11 B isotope into the roots during low to high B concentrations while uptake of the light 10 B isotope was promoted during B depletion, probably by active processes. A systematic enrichment of the heavy 11 B isotope in higher located plant parts was observed (average Δ 11 B leaf-roots = 20.3 ± 2.8‰ (1 SD)), possibly by a facilitated transport of the heavy 11 B isotope to growing meristems by B transporters. Conclusions: The B isotopes can be used to identify plant metabolism in response to the B concentration in the irrigation water and during intra-plant B transfer. The large B isotope fractionation within the plants demonstrates the importance of biological B cycling for the global B cycle.

Dynamic of boron in forest ecosystems traced by its isotopes: A modeling approach

“…Leaves are enriched in the heavy isotope by about 20‰ relative to the root/wood compartment (Figure SI_7a), in agreement with the observations of Geilert et al, (2015) and Geilert et al (2019) who measured for various plant species isotopic differences between the upper leaves and the roots between 24‰ and 27‰. The model predicts an enrichment in 11 B of the leaf exudates relative to the leaves of about 14‰, also in agreement with the observations of Cividini et al (2010) and Gaillardet and J o u r n a l P r e -p r o o f Lemarchand (2018).…”

“…Thus, changes of coordination between different phases induce large isotopic fractionations for example during incongruent dissolution of minerals, adsorption onto mineral or organic surfaces. Moreover, J o u r n a l P r e -p r o o f boron isotopes are potentially fractionated during its uptake by roots (Marentes et al, 1997;Cividini et al, 2010;Geilert et al, 2019) and strong evidences exist that intra-plant isotopic fractionations exist (Geilert et al, 2015;Gaillardet and Lemarchand, 2018). At the scale of the ecosystem, the B isotopic compositions, expressed in the classical δ notation, of different compartments cover a range up to 80‰ (Cividini et al, 2010;Gaillardet and Lemarchand, 2018) and vegetation (leaves) and leaf exudates appear to be enriched in the heavy isotope relative to atmospheric inputs and soil.…”

NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ11B and Trace Element Ratio Value Assignment

“…Value assignment such as this, by consensus approach involving multiple participants, is not conducive to obtaining a fully comprehensive uncertainty budget (e.g., Vogl and Rosner 2012, Geilert et al . 2019). The DerSimonian‐Laird method was therefore chosen to account for ‘dark uncertainty’ (unaccounted sources of uncertainty among laboratories) as the reported data only included uncertainties related to replication.…”

Stable Isotope Fractionation of Metals and Metalloids in Plants: A Review

“…These differences are possibly linked to distinct B demand at similar B supply. In bell pepper, heavy B isotopes were preferentially transported from roots to leaves (Δ 11 B leaves-roots +0.8 to +27‰, Geilert et al, 2015 , 2019 ). Within the shoots, leaves were isotopically heavier than stems and fruits were in most cases lighter than leaves.…”