The experimental determination of equilibrium Si isotope fractionation factors among H4SiO4o, H3SiO4− and amorphous silica (SiO2·0.32 H2O) at 25 and 75 °C using the three-isotope method

Stamm, Franziska M.; Zambardi, Thomas; Chmeleff, Jérôme; Schott, Jacques; Blanckenburg, Friedhelm von; Oelkers, Eric H.

doi:10.1016/j.gca.2019.03.035

Cited by 32 publications

(14 citation statements)

References 97 publications

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“…The high nutrient content and the organic acids in the nutrient solution potentially impair the chromatographic purification of Si. Thus the nutrient solution was digested following the "sample preparation of water samples" by Steinhoefel et al (2017) without employing an additional step for the removal of dissolved organic carbon. Briefly, based on the concentration measured, an aliquot of each nutrient solution containing approximately 1000 µg Si was dried down in silver crucibles on a hotplate at 80-95 • C. The crucibles were then filled with 400 mg NaOH (Merck pellets, pro analysi grade, previously checked for low Si blank levels) and ultrapure water to the initial fill level and dried down.…”

Section: Nutrient Solution Purificationmentioning

confidence: 99%

Silicon uptake and isotope fractionation dynamics by crop species

et al. 2020

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Abstract. That silicon is an important element in global biogeochemical cycles is widely recognised. Recently, its relevance for global crop production has gained increasing attention in light of possible deficits in plant-available Si in soil. Silicon is beneficial for plant growth and is taken up in considerable amounts by crops like rice or wheat. However, plants differ in the way they take up silicic acid from soil solution, with some species rejecting silicic acid while others actively incorporate it. Yet because the processes governing Si uptake and regulation are not fully understood, these classifications are subject to intense debate. To gain a new perspective on the processes involved, we investigated the dependence of silicon stable isotope fractionation on silicon uptake strategy, transpiration, water use, and Si transfer efficiency. Crop plants with rejective (tomato, Solanum lycopersicum, and mustard, Sinapis alba) and active (spring wheat, Triticum aestivum) Si uptake were hydroponically grown for 6 weeks. Using inductively coupled plasma mass spectrometry, the silicon concentration and isotopic composition of the nutrient solution, the roots, and the shoots were determined. We found that measured Si uptake does not correlate with the amount of transpired water and is thus distinct from Si incorporation expected for unspecific passive uptake. We interpret this lack of correlation to indicate a highly selective Si uptake mechanism. All three species preferentially incorporated light 28Si, with a fractionation factor 1000×ln (α) of −0.33 ‰ (tomato), −0.55 ‰ (mustard), and −0.43 ‰ (wheat) between growth medium and bulk plant. Thus, even though the rates of active and passive Si root uptake differ, the physico-chemical processes governing Si uptake and stable isotope fractionation do not. We suggest that isotope fractionation during root uptake is governed by a diffusion process. In contrast, the transport of silicic acid from the roots to the shoots depends on the amount of silicon previously precipitated in the roots and the presence of active transporters in the root endodermis, facilitating Si transport into the shoots. Plants with significant biogenic silica precipitation in roots (mustard and wheat) preferentially transport silicon depleted in 28Si into their shoots. If biogenic silica is not precipitated in the roots, Si transport is dominated by a diffusion process, and hence light silicon 28Si is preferentially transported into the tomato shoots. This stable Si isotope fingerprinting of the processes that transfer biogenic silica between the roots and shoots has the potential to track Si availability and recycling in soils and to provide a monitor for efficient use of plant-available Si in agricultural production.

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Section: Nutrient Solution Purificationmentioning

confidence: 99%

Silicon uptake and isotope fractionation dynamics by crop species

et al. 2020

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“…This soil property has never been taken into account when studying Si isotope fractionation during clay mineral formation in natural soil environments, while geochemical equilibria in solid-water interfaces are strongly controlled by the chemistry and residence time of the soil solution (Sverdrup, 1996). It is therefore especially important to study the influence of contrasting geochemical conditions on Si isotope fractionation during the formation of pedogenic clay minerals given that solidwater silicon isotope fractionation is essentially kinetically driven as a function of the precipitation rate of Si solid phases (Geilert et al, 2015), as well temperature and pH conditions (Stamm et al, 2019). This system-dependent feature is mainly controlled by original Si concentration in solution (Oelze et al, 2014), concentration of Fe and Al hydroxide precursors (Oelze et al, 2015), and temperature and pH of the solid-water interface (Geilert et al, 2014;Stamm et al, 2019) during the kinetically-dominated first step of precipitation (Roerdink et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…It is therefore especially important to study the influence of contrasting geochemical conditions on Si isotope fractionation during the formation of pedogenic clay minerals given that solidwater silicon isotope fractionation is essentially kinetically driven as a function of the precipitation rate of Si solid phases (Geilert et al, 2015), as well temperature and pH conditions (Stamm et al, 2019). This system-dependent feature is mainly controlled by original Si concentration in solution (Oelze et al, 2014), concentration of Fe and Al hydroxide precursors (Oelze et al, 2015), and temperature and pH of the solid-water interface (Geilert et al, 2014;Stamm et al, 2019) during the kinetically-dominated first step of precipitation (Roerdink et al, 2015). To understand the role of initial geochemical conditions on Si stable isotope fractionation, we analyzed Si isotope and Ge/Si ratios in soil solution, bulk soil, clay and silt fractions of a unique soil profile, an Ethiopian Vertic Planosol, characterized by the presence of a bleached, silty ash-derived soil horizon (with 25, 71, and 4% clay, silt and sand, respectively) that abruptly overlays a heavy clayey lacustrine-derived vertic horizon (with 68, 26 and 6% clay, silt and sand, respectively).…”

Section: Introductionmentioning

confidence: 99%

Past and current geochemical conditions influence silicon isotope signatures of pedogenic clay minerals at the soil profile scale, Ethiopia

et al. 2019

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Soil processes strongly govern silicon (Si) mobility in terrestrial environments and its relation to other global biogeochemical cycles. The nature of inherited soil clay minerals can be highly diverse given the variability of their weathering environment. The influence of Si isotope fractionation factor in the initial geochemical conditions of clay precipitation can therefore be still expressed in inherited clay minerals in their new environment. We studied top-and subsoil of an Ethiopian Vertic Planosol derived from parent materials of similar sources of volcanism. The selected Planosol has an abrupt textural change at a depth of~40 cm separating a bleached, silty (25 ± 1.8% clay) ash-derived soil horizon with a crumby structure from a heavy clayey (68 ± 3.4% clay) lacustrine-derived vertic soil horizon. The mineralogical assemblage of the clay fraction in top-and subsoil is characterized by similar proportions of 1:1 (kaolinite) and 2:1 (illite and smectite) layer-type clay minerals. This specific soil profile provides a unique opportunity to elucidate the influence of clay formation processes (inheritance versus neoformation) on the Si isotope signature of pedogenic clay minerals. Minerals of the clay fraction in the clayey vertic horizon are significantly enriched in light Si isotope (δ 30 Si = −1.41 ± 0.02‰) compared to the bleached, silty horizon (δ 30 Si = −0.69 ± 0.03‰). These results are corroborated by the preferential enrichment in Ge, relative to Si, in the clay fraction of the clayey subsoil compared to the silty topsoil (Ge/Si = 6.3 ± 0.14 and 4.0 ± 0.10 μmol mol −1 , respectively). Our results demonstrate that geochemical conditions in lacustrine environment favor kinetically-driven Si isotope fractionation factor leading to lower Si isotope ratios in 2:1 clay minerals inherited in the new soil profile environment. The inherited soil textural conditions in the soil profile also contribute to ongoing processes that result in larger Si isotope differences between the soil solution (CaCl 2 extractable) and clay minerals. This implies that Si isotope signatures of clay minerals in the studied soil profile are influenced by a combination of inheritance processes in lacustrine environment and ongoing neoformation processes in the soil profile. This finding has important implications for environmental studies using geochemical and Si stable isotope tracers to better understand current soil processes, to model elemental cycling in soil-plant systems and to quantify land-ocean element mass-balances.

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“…In comparison with the equilibrium experiment, here the ∆ 30 Si p-s shows a continuous trend towards more negative ∆ 30 Si p-s values with the relative amount of Si lost from the starting solution. Previous studies have shown that pH can impact the stability and structure of silica precipitates 38 , and that at high pH (pH ∼ 9) the Si isotope exchange rate between precipitate and solution is higher, and so can affect the fractionation of Si isotopes by over 1 39 . Figure 3 shows the relationship between pH and ∆ 30 Si p-s for both equilibrium and kinetic experiments.…”

Section: Equilibrium Versus Kinetic Fractionationmentioning

confidence: 99%

A Biomimetic Peptide has no Effect on the Isotopic Fractionation during in Vitro Silica Precipitation

Cassarino

Curnow

Hendry

2021

Preprint

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The stable isotopic composition of diatom silica is used as a proxy for nutrient utilisation in natural waters. This approach provides essential insight into the current and historic links between biological production, carbon cycling and climate. However, estimates of isotopic fractionation during diatom silica production from both laboratory and field studies are variable, and the biochemical pathways responsible remain unknown. Here, we investigate silicon isotopic fractionation through a series of chemical precipitation experiments that are analogous to the first stages of intracellular silica formation within the diatom silicon deposition vesicle. The novelty of our experiment is the inclusion of the R5 peptide, which is closely related to a natural biomolecule known to play a role in diatom silicification. Our results suggest that the presence of R5 induces a systematic but non-significant difference in fractionation behaviour. It thus appears that silicon isotopic fractionation in vitro is largely driven by an early kinetic fractionation during rapid precipitation that correlates with the initial amount of dissolved silica in the system. Our findings raise the question of how environmental changes might impact silicon isotopic fractionation in diatoms, and whether frustule archives record information in addition to silica consumption in surface water.

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The experimental determination of equilibrium Si isotope fractionation factors among H4SiO4o, H3SiO4− and amorphous silica (SiO2·0.32 H2O) at 25 and 75 °C using the three-isotope method

Cited by 32 publications

References 97 publications

Silicon uptake and isotope fractionation dynamics by crop species

Silicon uptake and isotope fractionation dynamics by crop species

Past and current geochemical conditions influence silicon isotope signatures of pedogenic clay minerals at the soil profile scale, Ethiopia

A Biomimetic Peptide has no Effect on the Isotopic Fractionation during in Vitro Silica Precipitation

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