Isotope fractionation of zinc in the paddy rice soil-water environment and the role of 2’deoxymugineic acid (DMA) as zincophore under Zn limiting conditions

Weiß, Dominik J.; Northover, George; Hanif, M. D.; Garcı́a-España, Enrique; Vilar, Ramón; Arnold, Tim; Marković, Tamara; Wissuwa, Matthias; Delgado, Estefania

doi:10.1016/j.chemgeo.2021.120271

Cited by 16 publications

(27 citation statements)

References 172 publications

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“…Figure 4 shows intrinsic stability constants for the formation of [Zn(Cit)] − and [Zn(HCit)] determined (i) using the Davies equation and the conditional association constants determined at different ionic strengths and (ii) fitting the parameterised EDH equation to the full ionic strength dataset. We find statistically significant (p < 0.05) differences for the various logβ 0 , emphasizing that the method used for activity corrections is critical when studying the small changes in speciation happening during geochemical processes in the rhizosphere 3 , 30 , 34 . Intrinsic association constants seem over predicted below 0.1 mol dm −3 and underpredicted above 0.1 mol dm −3 .…”

Section: Resultsmentioning

confidence: 84%

“…The other method uses an extended Debye Hückel expression where activity coefficients depend only on ionic charge and ionic strength, and it accounts for the solution particular properties by introducing ionic pairing between solution ions and species involved in the equilibrium reactions. The accurate determinations of logβ and logβ 0 values remain challenging and reported values can vary significantly 29 , 30 . For example, the stability constant reported for [Zn(Cit)] - in 0.1 mol dm -3 KNO 3 differ by 1.36 log units 31 , 32 .…”

Section: Introductionmentioning

confidence: 99%

“…To unravel the role of siderophores and other organic ligands during micronutrient transport in the rhizosphere is of particular interest to understand zinc efficiency mechanisms in rice genotypes 14 , 30 , 35 – 40 . The pH of the rice rhizosphere can vary by more than 2 pH units within 5 mm from the root surface and tends to remain within pH 4 and 8 irrespective of the mineralogical composition of the parent material 41 – 44 .…”

Section: Introductionmentioning

confidence: 99%

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Synergistic use of siderophores and weak organic ligands during zinc transport in the rhizosphere controlled by pH and ion strength gradients

Northover

Mao

Blasco

et al. 2022

Sci Rep

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Citrate (Cit) and Deferoxamine B (DFOB) are two important organic ligands coexisting in soils with distinct different affinities for metal ions. It has been theorized that siderophores and weak organic ligands play a synergistic role during the transport of micronutrients in the rhizosphere, but the geochemical controls of this process remain unknown. Here we test the hypothesis that gradients in pH and ion strength regulate and enable the cooperation. To this end, first we use potentiometric titrations to identify the dominant Zn(II)–Cit and Zn(II)–DFOB complexes and to determine their ionic strength dependent stability constants between 0 and 1 mol dm−3. We parametrise the Extended Debye-Hückel (EDH) equation and determine accurate intrinsic association constants (logβ0) for the formation of the complexes present. The speciation model developed confirms the presence of [Zn(Cit)]−, [Zn(HCit)], [Zn2(Cit)2(OH)2]4−, and [Zn(Cit)2]4−, with [Zn(Cit)]− and [Zn2(Cit)2(OH)2]4− the dominant species in the pH range relevant to rhizosphere. We propose the existence of a new [Zn(Cit)(OH)3]4− complex above pH 10. We also verify the existence of two hexadentate Zn(II)–DFOB species, i.e., [Zn(DFOB)]− and [Zn(HDFOB)], and of one tetradentate species [Zn(H2DFOB)]+. Second, we identify the pH and ionic strength dependent ligand exchange points (LEP) of Zn with citrate and DFOB and the stability windows for Zn(II)–Cit and Zn(II)–DFOB complexes in NaCl and rice soil solutions. We find that the LEPs fall within the pH and ionic strength gradients expected in rhizospheres and that the stability windows for Zn(II)–citrate and Zn(II)–DFOB, i.e., low and high affinity ligands, can be distinctly set off. This suggests that pH and ion strength gradients allow for Zn(II) complexes with citrate and DFOB to dominate in different parts of the rhizosphere and this explains why mixtures of low and high affinity ligands increase leaching of micronutrients in soils. Speciation models of soil solutions using newly determined association constants demonstrate that the presence of dissolved organic matter and inorganic ligands (i.e., bicarbonate, phosphate, sulphate, or chlorides) do neither affect the position of the LEP nor the width of the stability windows significantly. In conclusion, we demonstrate that cooperative and synergistic ligand interaction between low and high affinity ligands is a valid mechanism for controlling zinc transport in the rhizosphere and possibly in other environmental reservoirs such as in the phycosphere. Multiple production of weak and strong ligands is therefore a valid strategy of plants and other soil organisms to improve access to micronutrients.

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Section: Resultsmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synergistic use of siderophores and weak organic ligands during zinc transport in the rhizosphere controlled by pH and ion strength gradients

Northover

Mao

Blasco

et al. 2022

Sci Rep

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“…After the review of Caldelas and Weiss (2017) ; a field study on paddy soil-rice systems showed more positive Δ 66 Zn rice-source values at low Zn than at regular Zn supply ( Weiss et al, 2021 ; Figure 9 ). This shift toward heavy Zn isotopes at low Zn supply can be explained by chelators (e.g., the phytosiderophores 2’deoxymugineic acids) that are secreted by roots to strip Zn from the soil matrix and subsequent uptake of the entire Zn-phytosiderophore complex by a membrane transporter ( Smolders et al, 2013 ; Arnold et al, 2015 ; Weiss et al, 2021 ). Since 2’deoxymugineic acids bind heavy Zn isotopes at equilibrium ( Marković et al, 2017 ), the uptake of Zn-phytosiderophore complexes may have induced the shift toward heavy isotopes.…”

Section: Isotope Fractionation In Plantsmentioning

confidence: 99%

“…Here we provide recommendations to better exploit the information provided by varying isotope compositions in plants to further advance non-traditional isotope process tracing in plants. Once these recommendations are implemented, isotope process tracing could be applied to detect and quantify changes in uptake and translocation pathways in response to changing nutrient supply as suggested for Mg ( Wang et al, 2020 ), Cu ( Blotevogel et al, 2022 ), and Zn ( Weiss et al, 2021 ).…”

Section: Future Perspectivesmentioning

confidence: 99%

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

et al. 2022

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This work critically reviews stable isotope fractionation of essential (B, Mg, K, Ca, Fe, Ni, Cu, Zn, Mo), beneficial (Si), and non-essential (Cd, Tl) metals and metalloids in plants. The review (i) provides basic principles and methodologies for non-traditional isotope analyses, (ii) compiles isotope fractionation for uptake and translocation for each element and connects them to physiological processes, and (iii) interlinks knowledge from different elements to identify common and contrasting drivers of isotope fractionation. Different biological and physico-chemical processes drive isotope fractionation in plants. During uptake, Ca and Mg fractionate through root apoplast adsorption, Si through diffusion during membrane passage, Fe and Cu through reduction prior to membrane transport in strategy I plants, and Zn, Cu, and Cd through membrane transport. During translocation and utilization, isotopes fractionate through precipitation into insoluble forms, such as phytoliths (Si) or oxalate (Ca), structural binding to cell walls (Ca), and membrane transport and binding to soluble organic ligands (Zn, Cd). These processes can lead to similar (Cu, Fe) and opposing (Ca vs. Mg, Zn vs. Cd) isotope fractionation patterns of chemically similar elements in plants. Isotope fractionation in plants is influenced by biotic factors, such as phenological stages and plant genetics, as well as abiotic factors. Different nutrient supply induced shifts in isotope fractionation patterns for Mg, Cu, and Zn, suggesting that isotope process tracing can be used as a tool to detect and quantify different uptake pathways in response to abiotic stresses. However, the interpretation of isotope fractionation in plants is challenging because many isotope fractionation factors associated with specific processes are unknown and experiments are often exploratory. To overcome these limitations, fundamental geochemical research should expand the database of isotope fractionation factors and disentangle kinetic and equilibrium fractionation. In addition, plant growth studies should further shift toward hypothesis-driven experiments, for example, by integrating contrasting nutrient supplies, using established model plants, genetic approaches, and by combining isotope analyses with complementary speciation techniques. To fully exploit the potential of isotope process tracing in plants, the interdisciplinary expertise of plant and isotope geochemical scientists is required.

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