two-dimensional-visualization-quantification-labile-inorganic-plant

Two-Dimensional Visualization and Quantification of Labile, Inorganic Plant Nutrients and Contaminants in Soil

We describe a method for two-dimensional (2D) visualization and quantification of the distribution of labile (i.e., reversibly adsorbed) inorganic ...

polyacrylamide-zroh-hydrogels-for-spatially-resolved-sampling

Polyacrylamide ZrOH Hydrogels for Spatially Resolved Sampling of Carboxylates Exuded from Roots Growing in Soil

Sampling and reliable quantification of root exudates from undisturbed soil-grown plant roots remain challenging. We further developed a non-destructive ...

Montanuniversität Leoben

University of Natural Resources and Life Sciences, Vienna

Justus Liebig University Giessen

Diffusion towards the root surface has recently been shown to control the uptake of metal ions from solutions. The uptake flux of phosphorus (P) from solutions often approaches the maximal diffusion flux at low external concentrations, suggesting diffusion-controlled uptake also for P. Potential diffusion limitation in P uptake from nutrient solutions was investigated by measuring P uptake of Brassica napus from solutions using P-loaded Al(2) O(3) nanoparticles as mobile P buffer. At constant, low free phosphate concentration, plant P uptake increased up to eightfold and that of passive, diffusion-based samplers up to 40-fold. This study represents the first experimental evidence of diffusion-limited P uptake by plant roots from nutrient solution. The Michaelis constant of the free phosphate ion obtained in unbuffered solutions (K(m) = 10.4 µmol L(-1) ) was 20-fold larger than in the buffered system (K(m) ∼0.5 µmol L(-1) ), indicating that K(m) s determined in unbuffered solutions do not represent the transporter affinity. Increases in the P uptake efficiency of plants by increasing the carrier affinity are therefore unlikely, while increased root surface area or exudation of P-solubilizing compounds are more likely to enhance P uptake. Furthermore, our results highlight the important role natural nanoparticles may have in plant P nutrition.

First observation of diffusion-limited plant root phosphorus uptake from nutrient solution.

Sink extraction of phosphorus from soils has been utilised to study soil P desorption kinetics and as index of plant availability, but not for quantitative prediction of P uptake by plants. Here we investigate the potential of a modified sink extraction method for determining P desorption kinetics and for quantifying plant available soil P.

Phosphorus uptake by  L. is quantitatively predicted by infinite sink extraction of soil P.

The increasing appreciation of the small-scale (sub-mm) heterogeneity of biogeochemical processes in sediments, wetlands and soils has led to the development of several methods for high-resolution two-dimensional imaging of solute distribution in porewaters. Over the past decades, localised sampling of solutes (diffusive equilibration in thin films, diffusive gradients in thin films) followed by planar luminescent sensors (planar optodes) have been used as analytical tools for studies on solute distribution and dynamics. These approaches have provided new conceptual and quantitative understanding of biogeochemical processes regulating the distribution of key elements and solutes including O2, CO2, pH, redox conditions as well as nutrient and contaminant ion species in structurally complex soils and sediments. Recently these methods have been applied in parallel or integrated as so-called sandwich sensors for multianalyte measurements. Here we review the capabilities and limitations of the chemical imaging methods that are currently at hand, using a number of case studies, and provide an outlook on potential future developments for two-dimensional solute imaging in soils and sediments. 

Two decades of chemical imaging of solutes in sediments and soils--a review.

A novel diffusive gradients in thin films (DGT) technique for sampling labile soil sulfate was developed, based on a strong basic anion exchange resin (Amberlite IRA-400) for sulfate immobilization on the binding gel. For reducing the sulfate background on the resin gels, photopolymerization was applied instead of ammonium persulfate-induced polymerization. Agarose cross-linked polyacrylamide (APA) hydrogels were used as diffusive layer. The sulfate diffusion coefficient in APA gel was determined as 9.83 × 10(-6) ± 0.35 × 10(-6) cm(2) s(-1) at 25 °C. The accumulated sulfate was eluted in 1 mol L(-1) HNO3 with a recovery of 90.9 ± 1.6 %. The developed method was tested against two standard extraction methods for soil sulfate measurement. The obtained low correlation coefficients indicate that DGT and conventional soil test methods assess differential soil sulfate pools, rendering DGT a potentially important tool for measuring labile soil sulfate. 

Novel diffusive gradients in thin films technique to assess labile sulfate in soil.

A diffusive gradient in thin films (DGT) technique, based on a strongly basic anion exchange resin (Amberlite IRA-400), was successfully tested for S/S analysis in labile soil sulfate. Separation of matrix elements (Na, K, and Ca) that potentially cause non-spectral interferences in S/S analysis by MC ICP-MS (multi-collector inductively coupled plasma-mass spectrometry) during sampling of sulfate was demonstrated. No isotopic fractionation caused by diffusion or elution of sulfate was observed below a resin gel disc loading of ≤79 μg S. Above this threshold, fractionation towards S was observed. The method was applied to 11 different topsoils and one mineral soil profile (0-100 cm depth) and compared with soil sulfate extraction by water. The S amount and isotopic ratio in DGT-S and water-extractable sulfate correlated significantly (r  = 0.89 and r  = 0.74 for the 11 topsoils, respectively). The systematically lower S/S isotope ratios of the DGT-S were ascribed to mineralization of organic S.

Diffusive gradients in thin films measurement of sulfur stable isotope variations in labile soil sulfate.

Erratum to: Diffusive gradients in thin films measurement of sulfur stable isotope variations in labile soil sulfate.

Erratum to: Novel diffusive gradients in thin films technique to assess labile sulfate in soil.

Gel-based, two-dimensional (2D) chemical imaging techniques are versatile methods for investigating biogeochemically active environments at high spatial resolution (sub-mm). State-of-the-art solute imaging techniques, such as diffusive gradients in thin films (DGT) and planar optodes (PO), employ passive solute sampling or sensing. Combining these methods will provide powerful tools for studying the biogeochemistry of biological niches in soils and sediments. In this study we aimed at developing a combined single-layer gel for direct pH imaging using PO and sampling of anionic and cationic solutes by DGT, with subsequent analysis of the bound solutes by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We tested three ultra-thin (<100 μm) polyurethane-based gels, incorporating anion and cation binding materials and the fluorescent pH indicator DCIFODA (2',7'-dichloro-5(6)-N-octadecyl-carboxamidofluorescein). Results showed that PO-based pH sensing using DCIFODA was impossible in the presence of the anion binding materials due to interferences with DCIFODA protonation. One gel, containing only a cation binding material and DCIFODA, was fully characterized and showed similar performance characteristics as comparable DGT-only gels (applicable pH range: pH 5-8, applicable ionic strength range: 1-20 mmol L, cation binding capacity ∼24 μg cm). The dynamic range for PO-based pH mapping was between pH 5.5 and 7.5 with t response time of ∼60 min. In a case study we demonstrated the gel's suitability for multi-analyte solute imaging and mapped pH gradients and concurrent metal solubility patterns in the rhizosphere of Salix smithiana. pH decreases in the rooted soil were co-localized with elevated solute fluxes of Al, Co, Cu, Fe, Mn, Ni and Pb, indicating pH-induced metal solubilisation.

Integrating chemical imaging of cationic trace metal solutes and pH into a single hydrogel layer.

Fertilizers produced from heterogeneous, phosphorus-rich biowastes are becoming increasingly relevant. Treatment and processing (combustion, pyrolysis, anaerobic digestion, etc.) increase the diversity of their physico-chemical composition even further. We investigated several approaches to characterize P availability from a set of 13 contrasting fertilizers. We tested them directly using standard fertilizer extractions, as well as a continuous, sink-based P extraction (iron bag) method. We also performed Olsen, CAL and diffusive gradients in thin films (DGT) tests on fertilized soil. Standard extractions correlated only weakly, whereas the iron bag method correlated highly (0.73<R<0.85) with plant P uptake. Among the tests conducted on fertilized soils, DGT was equivalent or slightly better than Olsen, showing Rs of about 0.90 for P uptake and plant growth. Our results suggest that the validity of standard P fertilizer tests needs to be reassessed in the context of increasingly diverse recycling fertilizers.

Predicting phosphorus availability from chemically diverse conventional and recycling fertilizers.

Trace element concentrations in the rhizosphere were quantified to better understand why soil liming often fails to reduce cadmium (Cd) uptake by plants. Maize seedlings were grown on a soil with natural background levels of Cd and zinc (Zn). Soil liming increased soil pH from 4.9 to 6.5 and lowered the soil solution free ion activities by factor 7 (Cd) and 9 (Zn). In contrast, shoot Cd concentrations were unaffected by liming while shoot Zn concentrations were lowered by factor 1.9. Mapping of labile soil trace elements using diffusive gradients in thin films (DGT) in combination with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) revealed an almost complete depletion of Cd in the rhizosphere in all soil treatments, showing that Cd uptake is controlled by diffusion. The flux of Cd from soil to the DGT, with direct contact between the soil and the binding gel, was unaffected by liming whereas it decreased by factor 3 for Zn, closely mimicking the contrasting effects of liming on Cd and Zn bioavailability. This evidence, combined with additional flux data of freshly spiked Cd and Zn isotopes in soil and with modelling, suggests that the diffusive transport of Cd in unsaturated soil is more strongly controlled by the labile adsorbed metal concentration than by its concentration in solution. This is less the case for Zn because of its inherently slower desorption compared to Cd.

Sub-millimeter distribution of labile trace element fluxes in the rhizosphere explains differential effects of soil liming on cadmium and zinc uptake in maize.

Tungsten (W)-based shots are considered more environmentally safe than lead (Pb)-based shots, but knowledge about the W-shot fate in the soil environment is still limited, especially in terms of minor constituents such as iron, copper, and nickel (Ni). Contaminant behaviour in soil strongly depends on pH; in turn, the corrosion of metal composites may affect the pH locally. The aim of this study was to compare Pb- and W-shot weathering dynamics in soil (silt loam, pH 6.3) and reveal the interplay of shot weathering-induced pH-changes on the mobility of elements using in situ chemical imaging (Diffusive gradients in thin films for labile elements, planar optodes for soil pH) and batch incubation experiments over time (16 months). Despite our expectation to find acidification due to W oxidation, we observed a pH increase by 0.2 units in extracted soil solutions and by 0.6 units in the soil around W-shots as Ni dissolved from the binder phase of the shot. After 10 weeks, release of labile Ni was 3-times higher compared to W despite the low Ni content in the shot (7 %, m/m). Pb-shot oxidation increased soil solution pH by 0.5 units which likely supported mobility of Pb-shot-derived antimony (Sb). Steep gradients of labile W and Pb and soil solution concentrations <0.8 μmol L indicated that transfer from shot to soil was low. Contrastingly, labile Ni and Sb were found up to ~4 mm from the shot surface and in higher soil solution concentrations as suggested by the shot constitution, indicating higher mobility of minor as compared to major shot constituents. After 16 months, 36 % of total Ni were dissolved in the soil solution highlighting the environmental relevance of minor shot constituents in Pb-shot alternatives after short term weathering in soil.

Chemical imaging reveals environmental risk of minor tungsten and lead shotgun pellet constituents during weathering in soil.

This study evaluated the potential of the diffusive gradients in thin films (DGT) technique to assess radiogenic strontium (Sr) and lead (Pb) isotope signatures in bioavailable soil fractions as a proxy for plant uptake. Concentrations (c) and isotope ratios of Sr (Sr/Sr) and Pb (Pb/Pb, Pb/Pb, Pb/Pb) assessed by DGT (TK100, Chelex), along with extractable (NHNO, NHOAc, EDTA) and total Sr and Pb mass fractions and isotope ratios, were compared to those in Lactuca sativa L. (lettuce), Triticum aestivum L. (wheat), and Raphanus sativus L. (radish) grown on five geochemically distinct soils. Relative to conventional soil extraction, DGT significantly reduced matrix loads, facilitating isotope ratio measurements by multi-collector inductively coupled plasma mass spectrometry. DGT-labile Sr and Pb concentrations and isotope ratios reflected soil-specific geochemical signatures, allowing for clear differentiation among soils. Importantly, DGT-labile isotope ratios closely matched those in plant tissues across soils and species within analytical uncertainty, demonstrating that DGT captures the isotopically relevant bioavailable Sr and Pb pool without inducing significant mass-dependent isotopic fractionation. These findings establish DGT as a practical tool for bioavailable multi-isotope tracing with strong potential for applications in environmental forensics, food authentication, and archaeological provenance research.

Prediction of radiogenic Sr and Pb isotope signatures in plants using diffusive gradients in thin films.

Copper (Cu) and zinc (Zn) are essential micronutrients, critical for both crop growth and human health, yet imbalances can result in deficiency or toxicity. Assessments based on total metal concentrations miss key insights into metal bioavailability and mobility. This study addresses the existing gap in data and knowledge on readily available Cu and Zn in EU agricultural soils. We used a subset of the Land Use and Coverage Area frame Survey (LUCAS) topsoil database in 2015 to map distributions of available Cu and Zn in agricultural soils across the EU27 + UK using the electro-ultrafiltration (EUF) technique. The EUF results made it possible to identify reigons where agricultural soils may require Cu and Zn fertilization or face toxicity risks. Using existing thresholds from the Austrian fertilization guideline, around one-third (32%) of the soils were deficient in Cu, mainly in Northern and Eastern Europe, while Zn deficiency affected 14% of samples, notably in Spain, Cyprus, and Finland. Only a small proportion (1.5%) of samples exceeded the estimated Cu toxicity threshold. Overall, our findings indicate that continental regions consistently exhibit higher available Cu and Zn levels than Northern Europe, where igneous parent materials and less weathered glacial soils prevail. In addition, in Southern and Eastern Europe and inland regions of Spain, where calcareous soils are common, low Zn availability was observed. While natural factors largely explain these regional differences, local anthropogenic activities further contribute to elevated metal concentrations. Our results contribute to the monitoring of soil Cu and Zn beyond total concentrations, helping guide fertilization practices that support optimal crop nutrition and ensure safe and nutritious food.

ArticleTotal : 2	Year
Publication title Cited by 13	2020
Publication title	2026

Article	Year
First observation of diffusion-limited plant root phosphorus uptake from nutrient solution. Plant, cell & environment\| PubMed ID: 22452489	2012
Phosphorus uptake by L. is quantitatively predicted by infinite sink extraction of soil P. Plant and soil\| PubMed ID: 25722500	2015
Two decades of chemical imaging of solutes in sediments and soils--a review. Analytica chimica acta\| PubMed ID: 26002324	2015
Novel diffusive gradients in thin films technique to assess labile sulfate in soil. Analytical and bioanalytical chemistry\| PubMed ID: 27491301	2016
Diffusive gradients in thin films measurement of sulfur stable isotope variations in labile soil sulfate. Analytical and bioanalytical chemistry\| PubMed ID: 27687185	2016
Erratum to: Diffusive gradients in thin films measurement of sulfur stable isotope variations in labile soil sulfate. Analytical and bioanalytical chemistry\| PubMed ID: 27866255	2017
Erratum to: Novel diffusive gradients in thin films technique to assess labile sulfate in soil. Analytical and bioanalytical chemistry\| PubMed ID: 27878314	2017
Integrating chemical imaging of cationic trace metal solutes and pH into a single hydrogel layer. Analytica chimica acta\| PubMed ID: 27916135	2017
Predicting phosphorus availability from chemically diverse conventional and recycling fertilizers. The Science of the total environment\| PubMed ID: 28511361	2017
Sub-millimeter distribution of labile trace element fluxes in the rhizosphere explains differential effects of soil liming on cadmium and zinc uptake in maize. The Science of the total environment\| PubMed ID: 32806385	2020
Chemical imaging reveals environmental risk of minor tungsten and lead shotgun pellet constituents during weathering in soil. The Science of the total environment\| PubMed ID: 37088395	2023
Prediction of radiogenic Sr and Pb isotope signatures in plants using diffusive gradients in thin films. Analytical and bioanalytical chemistry\| PubMed ID: 41627397	2026
Copper and zinc thresholds in EU topsoils: Insights from LUCAS and literature datasets. Environment international\| PubMed ID: 41690199	2026

Jakob Santner

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