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A method using diffusive gradients in thin films (DGT) for the accurate quantification of trace-level (μg L

Brazil is an agricultural giant that plays a crucial role in the Global Phosphorus Challenge (GPC), and whose highly weathered soils are currently dependent on phosphorus (P) fertilizers derived from phosphate rock, a dwindling and critical resource. Brazil imports > 50% of its P fertilizers and P recovery from waste is not yet explored in the country, making it vulnerable to market instabilities, phosphate rock availability, and geopolitical conflicts. To make matters worse, Brazilian research budget has been shrinking for 7 years straight, hindering scientific efforts and causing significant ‘brain drain’, further undermining the country’s capacity to tackle this critical problem. However, an opportunity comes with the new Brazilian Federal government (starting January 2023), which promises to make significant investments in science and higher education. We call for all stakeholders to seize this important moment and timely collaborate in creating multidisciplinary P-related projects, taking advantage of the soon-to-be available resources to develop knowledge, technologies, and training networks to shape a new generation of experts in P management in the tropics. We are confident that through agriculture intensification, intelligent use of resources, new legislation and governance, Brazil will stride towards sustainable food production, bringing immediate value to Brazil and the world by protecting the Amazon forest and advancing to overcome the GPC.

Soil P testing has been widely used to predict crop yields, P uptake, and fertilizer demands in agriculture. Diffusive gradients in thin films (DGT) provides a zero-sink soil P test which mimics diffusion-controlled plant uptake and has previously been found to predict P availability to crops better than conventional quantity-based P tests in highly weathered Australian, though not in European soils. Here we tested the performance of DGT and the Austrian and German standard P quantity test calcium acetate lactate (CAL) to explain the variation of crop yield and P uptake response of winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) in long-term P fertilization experiments at four different sites in eastern Austria. Phosphorus extracted with DGT (P-DGT) and CAL (P-CAL) correlated well in similar soils but not across sites with large variation in soil and site properties such as carbonate equivalent and water availability. The predictive power of DGT for barley (R2 = 0.42) and wheat grain yield (R2 = 0.32), and P uptake in wheat grains (R2 = 0.36) was clearly superior to that of the CAL, and less dependent on soil properties. The better performance of DGT compared to the quantity test is consistent with diffusion-limited P uptake in the water-limited cultivated soils of eastern Austria. The critical values of P deficiency derived from the Mitscherlich-type fits for barley and wheat at 80% relative yield are 64.9 and 26.2 µg L−1, respectively, consistent with differential P demands of the crops.

Synchrotron-based X-ray fluorescence microscopy (XFM) analysis is a powerful technique that can be used to visualize elemental distributions across a broad range of sample types. Compared to conventional mapping techniques such as laser ablation inductively coupled plasma mass spectrometry or benchtop XFM, synchrotron-based XFM provides faster and more sensitive analyses. However, access to synchrotron XFM beamlines is highly competitive, and as a result, these beamlines are often oversubscribed. Therefore, XFM experiments that require many large samples to be scanned can penalize beamline throughput. Our study was largely driven by the need to scan large gels (170 cm2) using XFM without decreasing beamline throughput. We describe a novel approach for acquiring two sets of XFM data using two fluorescence detectors in tandem; essentially performing two separate experiments simultaneously. We measured the effects of tandem scanning on beam quality by analyzing a range of contrasting samples downstream while simultaneously scanning different gel materials upstream. The upstream gels were thin (99%) transmittance with minimal (

International audience; Understanding phosphorus (P) dynamics in the rhizosphere is crucial for sustainable crop production. P mobilization processes in the rhizosphere include the release of plant and microbially-derived protons and extracellular phosphatases. We investigated the effect of root hairs and soil texture on the spatial distribution and intensity of P mobilizing processes in the rhizosphere of Zea mays L. root-hair defective mutant (rth3) and wildtype (WT) grown in two substrates (loam, sand). We applied 2D-chemical imaging methods in custom-designed root windows installed in the field to visualize soil pH (optodes), acid phosphatase activity (zymography), and labile P and Mn fluxes (diffusive gradients in thin films, DGT). The average rhizosphere extent for phosphatase activity and pH was greater in sand than in loam, while the presence of root-hairs had no impact. Acidification was significantly stronger at young root tissue (4 cm from root cap) and stronger in WT than rth3. Accompanied with stronger acidification, higher P flux was observed mainly around young, actively growing root tissues for both genotypes. Our results indicate that acidification was linked to root growth and created a pH optimum for acid phosphatase activity, i.e., mineralization of organic P, especially at young root tissues which are major sites of P uptake. Both genotypes grew better in loam than in sand; however, the presence of root hairs generally resulted in higher shoot P concentrations and greater shoot biomass of WT compared to rth3. We conclude that soil substrate had a larger impact on the extent and intensity of P solubilization processes in the rhizosphere of maize than the presence of root hairs. For the first time, we combined 2D-imaging of soil pH, phosphatase activity, and nutrient gradients in the field and demonstrated a novel approach of stepwise data integration revealing the interplay of various P solubilizing processes in situ.

Visualization and quantification of corrosion processes is essential in materials research. Here we present a new approach for 2D spatiotemporal imaging of metal corrosion dynamics in situ. The approach combines time-integrated Mg

Pteris vittata (PV) and Pteris quadriaurita (PQ) are reported to hyperaccumulate arsenic (As) when grown in As-rich soil. Yet, little is known about the impact of their unique As accumulation mechanisms on As transformations and cycling at the soil-root interface. Using a combined approach of two-dimensional (2D), sub-mm scale solute imaging of arsenite (AsIII), arsenate (AsV), phosphorus (P), manganese (Mn), iron (Fe) and oxygen (O2), we found localized patterns of AsIII/AsV redox transformations in the PV rhizosphere (AsIII/AsV ratio of 0.57) compared to bulk soil (AsIII/AsV ratio of ≤0.04). Our data indicate that the high As root uptake, translocation and accumulation from the As-rich experimental soil (2080 mg kg−1) to PV fronds (6986 mg kg−1) induced As detoxification via AsV reduction and AsIII root efflux, leading to AsIII accumulation and re-oxidation to AsV in the rhizosphere porewater. This As cycling mechanism is linked to the reduction of O2 and MnIII/IV (oxyhydr)oxides resulting in decreased O2 levels and increased Mn solubilization along roots. Compared to PV, we found 4-fold lower As translocation to PQ fronds (1611 mg kg−1), 2-fold lower AsV depletion in the PQ rhizosphere, and no AsIII efflux from PQ roots, suggesting that PQ efficiently controls As uptake to avoid toxic As levels in roots. Analysis of root exudates obtained from soil-grown PV showed that As acquisition by PV roots was not associated with phytic acid release. Our study demonstrates that two closely-related As-accumulating ferns have distinct mechanisms for As uptake modulating As cycling in As-rich environments., Environmental and Experimental Botany, 177, ISSN:0098-8472, ISSN:1873-7307

Boron is a finite resource, which has been listed as a critical raw material in the EU since 2014. Glass, frits and ceramics production, as well as fertilizers are among the major uses of B. Moreover, about 50 000 t B have been applied as fire retardant and pest repellent in cellulose fiber insulation (CFI) in Europe since the 1980s. Here we propose the end-of-life utilization of borated CFI as B fertilizer, to decrease societal B consumption and to avoid costly and potentially environmentally harmful CFI incineration and deposition in landfills. In a case study, we show that CFI biochar can provide substantial amounts of B to rapeseed and sunflower, with the B plant-availability being comparable to sodium tetraborate, a conventional B fertilizer. The annual B fertilizer consumption of the EU is estimated at ∼4000 t B yr–1, which could be sustained by the B currently installed as CFI for >10 years. In addition, the annual use of B in CFI of 1100 t B yr–1 could cover ∼25% of the annual B fertilizer demand ...

Crops may require Si fertilization to sustain yields. Potential Si fertilizers include industrial byproducts (e.g., steel slags), mined minerals (CaSiO3), fused Ca-Mg-phosphates, biochar, ash, diat...

In the framework of the circular economy, new P fertilizers produced from diverse secondary raw materials are being developed using various technologies. Standard extraction methods (neutral ammonium citrate (NAC) and H2O) provide limited information about the agronomic efficiency of these often heterogenous new products. Here, we compared these extractions with two alternative methods: 0.5molL-1 NaHCO3 and a sink extraction driven by phosphate adsorption onto ferrihydrite (“Iron Bag”) on 79 recycled and mineral reference fertilizers. We compared their capacity to predict shoot biomass and P content of rye (S. cereale L.) grown in a greenhouse on three soils of contrasting pH with a subset of 42 fertilizers. The median extracted P (% of total P) was H2O (1%)3 (25%)3 extraction stood out as a cost-effective and reliable method to predict plant shoot biomass and P content (R2 ranging between 0.65 and 0.86 in the slightly acidic and alkaline soil). Notwithstanding, the other methods provide complementary information for a more detailed characterization of how P solubility may be impacted by e.g. soil pH, granulation, or time. The implications of this work are therefore significant for fertilizer production, regulation, and use.

Purpose: Rhizosphere processes are known to modify uptake of elements from soil, but limited information is available for hyperaccumulators. We investigated labile Ni fractions and their kinetics of replenishment in the rhizospheres of the Ni-hyperaccumulator Odontarrhena serpyliffolia, the Ni-excluder Holcus lanatus and in bulk soils collected at the same serpentine outcrop. Methods: Labile Ni fractions in rhizosphere and bulk soil were evaluated using conventional extractions and also by the Diffusive Gradients in Thin Films (DGT) technique. DGT data were used to predict the kinetics of Ni resupply using DIFS modelling. Chemical imaging of Ni distribution along roots using DGT coupled with laser-ablation was conducted. Results: Labile Ni forms were higher in both rhizosphere than in bulk soils, together with an increase in dissolved organic C, cation exchange capacity and the Ca/Mg ratio. Ni fractionation indicated a shift towards less stable Ni fractions in the rhizosphere, particularly in the hyperaccumulator. DIFS modelling showed that the rhizosphere of the excluder was able to sustain the initially lower soluble Ni concentration through replenishment from the solid phase, while Ni resupply in the rhizosphere of the hyperaccumulator was not sufficient to maintain the initially high concentrations of soluble Ni. However, the amount of DGT-labile Ni was higher in the rhizosphere of the hyperaccumulator compared to the excluder in all deployment times. Conclusion: Our data suggest that compounds derived from root activity, in particular DOC, are important controls of Ni availability to plants growing on serpentine soil.

This study was set up to identify the role of the phosphorus (P) desorption rate in P diffusion and in P bioavailability in soil. The P desorption kinetics were measured with a zero‐sink method in soil suspensions (0–77 days) for a set of soils that either had or had not been mined for P in a glasshouse study. The desorption kinetics was fitted by a serial two‐pool model, discriminating a fast desorbing P pool (Q₁) with desorption half‐lives of 3–8 days, and a slowly desorbing P pool (Q₂), which replenishes the fast P pool with 100‐fold larger half‐lives than the fast pool. Phosphate desorption was smaller and slower after soil P mining compared to that in the original soil samples and mining reduced the Q₁/Q₂ ratio. This kinetic model was embedded in a 1D planar diffusion model predicting that the diffusive flux of P to a zero sink in 5 days varies by a factor of 1.4 among the observed Q₁ desorption rate constants, keeping other parameters constant, and that the reduced Q₁/Q₂ ratio upon P mining sharply reduces the diffusible P in soil. The P uptake model of Barber‐Cushman was extended with P desorption kinetics and was successfully calibrated to the P uptake data of the glasshouse P mining study. The model correctly predicted that reduced nitrogen (N) fertilization enhances the soil P‐use efficiency because of lower critical P demand rates at slower growth. Finally, that new model predicted that maize requires >3‐fold more available P in soil than wheat because of a higher P demand rate per unit root area of maize than that of wheat. This confirms a similar factor difference in critical soil P concentrations observed in P‐response trials in Belgium between 1973 and 2018. This study shows that the P desorption rate limits P bioavailability for fast growing plants with a small effective root area, especially under negative soil P balances that slow down the desorption rate of P in soil. HIGHLIGHTS: The diffusion coefficient of P in soil is reduced by soil P mining Faster growing plants require more available P in soil because they rely on high diffusive P fluxes P desorption rate can limit the P bioavailability ispartof: EUROPEAN JOURNAL OF SOIL SCIENCE vol:72 issue:1 pages:221-233 status: published

The reliable sampling of root exudates in soil grown plants is experimentally challenging. This study aimed at developing a citrate sampling and mapping technique with millimetre-resolution using DGT (diffusive gradients in thin films) ZrOH binding gels. Citrate adsorption kinetics, DGT capacity and stability of ZrOH gels were evaluated. ZrOH gels were applied to generate 2D maps of citrate exuded by white lupin roots grown in rhizotrosn in a phosphorus deficient soil. Citrate was adsorbed quantitatively and rapidly by the ZrOH gels, these gels can be stored after sampling for several weeks prior to analysis. The DGT capacity of the ZrOH gel for citrate depends on the ionic strength and the pH of the soil solution but was suitable for citrate sampling. 2D citrate maps of rhizotron grown plants have been generated for the first time at a millimetre resolution to measure an illustrated plant response to P fertilization. DGT-based citrate sampling is suitable for studying the root exudation in soil environments, at unprecedented spatial resolution. By changing binding material, the technique is also applicable to other exudate classes and might be used for the evaluation of whole root exudation crucial in specific cultivar breeding.HighlightWe present a novel, reliable, easy to use, non-destructive citrate sampling- and two-dimensional high-resolution imaging technique for soil grown plant roots.

The reliable sampling of root exudates in soil grown plants is experimentally challenging. This method shows how to sample citrate from rhizotron grown plants with ZrOH DGT gels to produce high resolution citrate imaging. The DGT technique is based on thin hydrogels with homogeneously distributed analyte-selective binding phases and is used for 2D visualization and quantification of the distribution of labile (i.e., reversibly adsorbed) analytes.

We describe a method for two-dimensional (2D) visualization and quantification of the distribution of labile (i.e., reversibly adsorbed) inorganic nutrient (e.g., P, Fe, Mn) and contaminant (e.g., As, Cd, Pb) solute species in the soil adjacent to plant roots (the ‘rhizosphere’) at sub-millimeter (~100 µm) spatial resolution. The method combines sink-based solute sampling by the diffusive gradients in thin films (DGT) technique with spatially resolved chemical analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The DGT technique is based on thin hydrogels with homogeneously distributed analyte-selective binding phases. The variety of available binding phases allows for the preparation of different DGT gel types following simple gel fabrication procedures. For DGT gel deployment in the rhizosphere, plants are grown in flat, transparent growth containers (rhizotrons), which enable minimal invasive access to a soil-grown root system. After a pre-growth period, DGT gels are applied to selected regions of interest for in situ solute sampling in the rhizosphere. Afterwards, DGT gels are retrieved and prepared for subsequent chemical analysis of the bound solutes using LA-ICP-MS line-scan imaging. Application of internal normalization using 13C and external calibration using matrix-matched gel standards further allows for the quantification of the 2D solute fluxes. This method is unique in its capability to generate quantitative, sub-mm scale 2D images of multi-element solute fluxes in soil-plant environments, exceeding the achievable spatial resolution of other methods for measuring solute gradients in the rhizosphere substantially. We present the application and evaluation of the method for imaging multiple cationic and anionic solute species in the rhizosphere of terrestrial plants and highlight the possibility of combining this method with complementary solute imaging techniques.

Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the leaching of terrestrial DOM into adjacent aquatic ecosystems. In order to close this linkage, we conducted a short-term (45 day) lysimeter experiment with silt loam and sandy loam undisturbed/intact soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha&minus, 1. On average, amounts of leached DOC over 45 days ranged between 20.4 mg (silt loam, mineral fertilizer) and 34.4 mg (sandy loam, organic fertilizer). Both, mineral and organic fertilization of a silt loam reduced concentration of dissolved organic carbon (DOC) in the leachate and shifted its composition towards a microbial-like signature (BIX) with a higher aromaticity (Fi) and a lower molecular size (E2:E3). However, in sandy loam only mineral fertilization affected organic matter leaching. There, lowered DOC concentrations with a smaller molecular size (E2:E3) could be detected. The overall effect of fertilization on DOC leaching and DOM composition was interrelated with soil texture and limited to first 12 days. Our results highlight the need for management measures, which prevent or reduce fast flow paths leading soil water directly into aquatic systems, such as surface flow, fast subsurface flow, or drainage water.

This work aimed to investigate the metal accumulation characteristics as well as biogeochemical changes in the rhizosphere and root foraging strategies of this plant species. Previous reports suggested that Noccaea rotundifolia ssp. cepaeifolia is a Zn, Cd and Pb hyperaccumulator. We used hydroponic, rhizobox and split-pot experiments for studying metal accumulation and related rhizosphere processes. Although this species accumulated up to 1250 mg Pb kg−1 and 27,000 mg Zn kg−1 in shoots, translocation factors

The determination of citrate exuded from soil-grown roots is very challenging due to its rapid microbial degradation and mineralization, sorption to the solid soil phase and ongoing release of organic molecules from organic matter breakdown. For this reason, our knowledge about citrate release is mainly based on experiments carried out in hydroponics. Results obtained in hydroponics cannot directly be transferred to soil-plant systems, as hydroponics represents an artificial environment. This study aimed to develop a localization and quantification technique for citrate exuded from soil-grown plant roots, based on diffusive gradients in thin film (DGT). Polyacrylamide gels containing precipitated zirconium hydroxide (ZrOH) were applied to the rhizosphere of soil grown plants, on which citrate is efficiently immobilized, thereby creating a zero sink to sample the citrate exuded from the roots. Citrate was eluted with 1 mL 0.5 mol L-1 NaOH from the ZrOH gel and quantified by ion chromatography. ZrOH gel discs were able to bind the citrate contained in 10 mL of 2.77 mg citrate L-1 solutions within a 4h uptake period. Elution efficiency was ~89%. ZrOH gel capacity at pH 8 was 200 µg per gel disc and 299 µg per gel disc at pH 4, which is sufficient to act as a zero sink for citrate released from plant roots. As a first exemplary method application, we grew white lupin plants in rhizotrons using a highly phosphorus deficient soil. ZrOH gel sheets were applied for 26 h onto cluster roots for citrate sampling following established DGT protocols. Gels were cut afterwards into 5×5 and 5×2 mm slices for obtaining a citrate exudation map. In both cases we were able to localize and quantify up to 7.89 µg citrate on individual gel slices, as well as to identify longitudinal and lateral citrate gradients around the cluster roots. Moreover, the characterization of ZrOH gels showed its suitability for citrate sampling in terms uptake kinetics and capacity. These results demonstrate that the developed method is suitable for citrate sampling and localization in a non-destructive way from soil-grown plant roots. As it is applicable to soil grown-roots and provides unprecedented spatial resolution, this sampling technique advances the experimental possibilities for researching root exudates considerably. Using suitable binding materials, this approach is also applicable to other carboxylates such as malate or oxalate and other compound classes such as phenolics, flavonolos etc. Furthermore, this technique can be combined with complementary imaging methods for mapping e.g. nutrients, contaminants, pH or enzyme activity distributions.

Besides the importance of dissolved organic matter (DOM) in soil biogeochemical processes, there is still a debate on how agricultural intensification affects the composition and concentration of dissolved organic matter leached from soils into adjacent aquatic ecosystems. In order to investigate the immediate response of DOM leaching to fertilization, we conducted a short-term (45 day) lysimeter experiment with undisturbed silt loam and loamy sand soil cores. Mineral (calcium ammonium nitrate) or organic (pig slurry) fertilizer was applied on the soil surface with a concentration equivalent to 130 kg N ha−1. After fertilization, soil leachate was collected in 6-days intervals. Dissolved organic carbon concentrations (DOC) were measured with gas chromatography, while shifts in DOM composition were analysed using absorbance and excitation- emission fluorescence indices from peak-picking as well as from PARAFAC analysis. During the first 12 days, fertilization of a silt loam reduced DOC concentrations in the leachate and shifted its composition towards more microbial- like compounds. Additionally, the discrepancy in DOM composition between fertilizer and control treatments of a silt loam increased with time. However, in loamy sand only mineral fertilization affected organic matter leaching and decreased DOC concentrations in the leachate during the first 12 days. Furthermore, mineral fertilization of the loamy sand led to DOM compounds with low molecular size in the first 12 days. Our results show that fertilization tends to increase microbial transformed DOM, while it reduces leached DOC concentrations. Furthermore, the magnitude of fertilization on DOC concentrations and DOM composition was highly depending on the soil texture they originate from. However, in our set-up, the experimental soil units were restricted to a soil depth of 16 cm (Ap horizon). At ecosystem level, a sufficiently long soil passage might mitigate the impact of fertilization on soil DOM.

Aims We imaged the sub-mm distribution of labile P and pH in the rhizosphere of three plant species to localize zones and hot spots of P depletion and accumulation along individual root axes and to relate our findings to nutrient acquisition / root exudation strategies in P-limited conditions at different soil pH, and to mobilization pattern of other elements (Al, Fe, Ca, Mg, Mn) in the rhizosphere. Methods Sub-mm distributions of labile elemental patterns were sampled using diffusive gradients in thin films and analysed using laser ablation inductively coupled plasma mass spectrometry. pH images were taken using planar optodes. Results We found distinct patterns of highly localized labile P depletion and accumulation reflecting the complex interaction of plant P acquisition strategies with soil pH, fertilizer treatment, root age, and elements (Al, Fe, Ca) that are involved in P biogeochemistry in soil. We show that the plants respond to P deficiency either by acidification or alkalization, depending on initial bulk soil pH and other factors of P solubility. Conclusions P solubilization activities of roots are highly localized, typically around root apices, but may also extend towards the extension / root hair zone. Electronic supplementary material The online version of this article (10.1007/s11104-017-3542-0) contains supplementary material, which is available to authorized users.

The sustainable exploitation of phosphorus (P) is essential for food and water security. However, our current poor management of this essential nutrient represents a pressing challenge, which cause global scale pollution of water resources(2) while failing to achieve equitable access to fertilizers to support food production worldwide.(3) This is, in part, due to poor uptake of advances, for example, in new technologies to reduce losses of P from agriculture, in our understanding of P thresholds for ecosystem functioning, and in sustainable urban development approaches focused on nutrient recycling systems. We identify, here, a pressing need to develop a new generation of nutrient sustainability professionals working collectively to implement diverse and interdiciplinary approaches within large scale urban and rural planning, for example, following the UNESCO Global Action Programme on Education for Sustainable Development, to meet the diverse needs of communities and countries.

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

Under conditions of climate change, the severity and probability of storm events and droughts are expected to increase, this may affect the partitioning into surface and subsurface runoff. However, there is still a debate on how such extreme weather conditions affect the leaching of soil organic carbon. The aim of this study was to ascertain the impact of rainfall intensity (63 vs 79 mm h−1) and antecedent soil moisture (Matric potential: −10 hPa vs −450 hPa) on flow partitioning in the transportation (fluxes and timing) of dissolved (DOC) and particulate organic carbon (POC). Rainfall simulation experiments using undisturbed soil monoliths (1 m × 0.5 m × 0.3 m) allowed to monitor the transport of water, sediments, DOC, and POC via surface and shallow subsurface runoff. In addition, the composition of the leached organic matter was analysed using photometric and fluorometric methods. Most of the organic carbon was transported as POC via surface runoff. In the surface runoff, the influence of antecedent soil moisture on POC loss was larger than rainfall intensity, while rainfall intensity had a greater influence on DOC losses. Under initially unsaturated conditions, surface sealing reduced the infiltration rate, thus fuelling the total surface runoff, which, in turn, enhanced the transported total sediment and POC load of the surface runoff. While POC dominated surface runoff, DOC played a crucial role in the subsurface runoff with higher DOC concentrations under unsaturated conditions. In contrast to other treatments, DOC exported from unsaturated soils rained with high intensity had a unique composition with the highest proportion of humic-like peaks (A, M, C), protein-like peaks (T) and components (C4), suggesting a concentrating effect on DOC at those soils. Altogether, this research acquires new insights into how flow partitioning under extreme weather conditions affects organic carbon losses and which transport mechanism might pose a risk for aquatic systems.

Innovative non-destructive 2D imaging methods such as zymography and diffusive gradients in thin films (DGT) have been developed recently to assess the distribution of phosphatase activity and labile solutes at the root-soil interface. We report on the first combination of these techniques for the spatial distribution and potential interaction of labile phosphorus (P) and associated acid phosphatase activity in the rhizosphere of blue lupin (Lupinus angustifolius) in two contrasting soils (‘Sand’ and ‘Loam’). Zymography, based on 4-methylumbelliferylphosphate (MU-P) for acid phosphatase activity mapping, and DGT gels capable of binding labile P were deployed to individual root axes to visualise P mobilisation and depletion in the rhizosphere of blue lupin grown in rhizotrons in glasshouse conditions for 45 days. Acid phosphatase activity was evidently higher in the rhizosphere and co-occurred with P-depletion zones around the roots in both soils. Lateral root profiles showed that elevated acid phosphatase activity as well as P-depletion extended up to 2 mm from the root centre into the rhizosphere. Despite larger total and organic P pools in the Loam, P was less plant available (DGT labile P) than in the Sand. However, phosphatase activities in the rhizosphere and plant P contents were similar in both soils. These results indicate that enzyme-catalysed hydrolysis of organic P was limited in the Loam, due to low P availability, hence explaining similar P contents in lupins from both soils. P did not accumulate in labile pools in the rhizosphere indicating that P supply via phosphatase could not compensate the plants demand for P resulting in P depletion zones. While our work demonstrates the applicability of combined zymography and DGT deployments to study rhizosphere processes at microscale, we also discuss limitations and perspectives of this approach.

A diffusive gradient in thin films (DGT) technique, based on a strongly basic anion exchange resin (Amberlite IRA-400), was successfully tested for 34S/32S analysis in labile soil sulfate. Separation of matrix elements (Na, K, and Ca) that potentially cause non-spectral interferences in 34S/32S 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 34S 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 2 = 0.89 and r 2 = 0.74 for the 11 topsoils, respectively). The systematically lower 34S/32S isotope ratios of the DGT-S were ascribed to mineralization of organic S.

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. ispartof: SCIENCE OF THE TOTAL ENVIRONMENT vol:738 ispartof: location:Netherlands status: published

Reliable data on K fixation in soils are of agronomic interest in paddy rice production. Considering the factors flooding time and K concentration, we evaluated fixation characteristics of K-depleted paddy soils of northern Iran using an adopted method to assess K fixation in flooded conditions. Potassium fixation in 68 topsoils (i.e. 0–30 cm) from paddy fields of the Mazandaran and Guilan provinces ranged between ~48 and ~700 mg K kg−1 soil with the maximum occurring within 30 days of flooding. These data indicate that NH4OAc-extractable, readily-available K may be below the critical level in ~220,000 ha of the paddy rice cultivated areas in the two provinces. Clay content, CEC and NH4OAc-extractable K in air-dried soil can predict 73.2% of the variation in K fixation, with K fixation increasing with clay content and CEC. The fact that the K fixation percentage remained unchanged in the range of 39.2–314 mg K added kg−1 soil shows, that large amounts of K are likely be needed to restore K fertility. These may be added in portions over several years. After restoring the K fertility in the soils, K outputs have to be balanced continuously by K fertilization.

Acid soils cover 30–40% of the world’s arable land and represent one of the major constraints to agricultural production. Lime is routinely added to soil to improve fertility and to reduce the solubility of elements such as aluminum (Al) and cadmium (Cd). White lupin is cultivated globally, however, this is done mainly on acidic soils because of its calcifuge characteristics resulting from its limited ability to compartmentalize calcium (Ca). In abiotic stress conditions, lupins exude organic acids and flavonoids from cluster roots. This can increase the availability of essential soil nutrients to the plant but also exacerbate the uptake of contaminants. We aimed to determine the effect of liming on the rhizosphere processes of white lupin plants in two high-fertility soils, which were treated with seven levels of lime. Nutrient availability and plant uptake was assessed with a pot experiment. Three lime levels have been chosen for a further rhizotron study. Diffusive gradient in thin layers (DGT) gels were applied on selected root zones and then analyzed by laser ablation inductively-coupled plasma mass spectrometry (LA ICP-MS). The results showed that lime affected the solubility of extractable elements and the plant uptake. In soils treated with different levels of lime, the uptake of nutrients was sufficient to avoid nutrient deficiency. However, analysis of the DGT gels only showed mobilization around the cluster root of the plant grown in the untreated soil. The results indicate that white lupin can be grown at pH as high as 7.50 with 10 wt% lime without suffering from nutrient deficiencies.

11 páginas.-- 4 figuras.-- 6 tablas.-- 40 referencias, Purpose: This study evaluates the effects of two soil amendments and the growth of two plant species on labile trace element (TE) fractions in two different contaminated soils. Materials and methods: We studied the effects of two organic amendments (biosolid compost and alperujo compost) and two plant species (Medicago polymorpha and Poa annua) on pH, total organic carbon (TOC), and TE availability, by three extraction methods (CaCl2 aqueous solution, soil pore water (SPW), and diffusive gradient in thin film (DGT)), in two contaminated soils with contrasting pH values (Aznalcázar, 6.53, and Vicario, 3.48) in a 118-day pot experiment. The effects of the composts on labile TE fractions were compared with element concentrations in plants. Results and discussion: No relevant effects of amendments and plants were found on the physical and chemical characteristics of the Aznalcázar soil. However, the addition of amendments was essential for plant species growing in the acid Vicario soil. In this soil, amendments and plant growth increased pH and TOC and reduced substantially TE bioavailability. Although absolute values of bioavailable TE contents obtained by the three methods were very different and followed the trend CaCl2 extraction > SPW > DGT, these values follow a similar behavior in the two studied soils and for the two species. Conclusions: The results demonstrate that the application of organic amendments are suitable for remediating acid TE-contaminated soils, for the establishment of a vegetation cover on previously bare soils for reducing wind and water erosion and for reducing labile TE fractions to prevent leaching of pollutants into subsoil or groundwater layers. Moreover, the results obtained in this study pointed out that under microcosm conditions, the three methods tested (CaCl2 extraction, SPW, and DGT) to predict TE bioavailability were highly correlated. © 2015 Springer-Verlag Berlin Heidelberg, AGL2011-23617 was supported by the CICYT of the Ministerio de Ciencia e Innovación of Spain and FEDER (EU). L. Ciadamidaro thanks the CSIC for funding her grant (JAE-PreDoc).

Arsenic and Cu mobility was investigated in the rhizosphere of Lupinus albus L. grown in an iron-amended contaminated soil. White lupin was grown in rhizobags in contaminated soil either left untreated or amended with iron sulphate plus lime (Fe + lime) or biochar (Fe + BC). Porewater was monitored in rhizosphere and bulk soil throughout the experiment and the extractable fraction of several elements and As and Cu plant uptake was analysed after 48 days. The distribution of As, Cu, P and Fe in the lupin rhizosphere was evaluated with chemical images obtained by laser ablation-ICP-MS analysis of diffusive gradients in thin films (DGT) gels. The treatments effectively reduced the soluble and extractable As and Cu fractions in the bulk soil, but they did not affect plant uptake. In all cases, soluble As was slightly enhanced in the rhizosphere. This difference was more pronounced in the Fe + lime-treated rhizosphere soil, where an increase of pH as well as extractable As and Fe concentrations were also observed. Chemical imaging of the lupin rhizosphere also showed slightly higher As- and Fe-DGT fluxes around lupin roots grown in the non-amended soil. Our findings indicate As and Fe co-solubilisation by lupin root exudates, likely as a response to P deficiency. Arsenic mobilisation occurred only in the rhizosphere and was not decreased by the amendments.

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 cm2 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.

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

A novel method based on high-performance ion chromatography inductively coupled plasma mass spectrometry employing strong anion exchange chromatography with HNO3 gradient elution for simultaneous analysis of orthophosphate and myo-inositol hexakisphosphate (IP6 ) in soil solution and plant extracts is presented. As inductively coupled plasma mass spectrometry analysis of phosphorus at m/z 31 is hampered by N-based interferences, (31)P was measured as (31)P(16)O(+) at m/z 47 employing dynamic reaction cell technique with O2 as reaction gas. Orthophosphate and IP6 were separated within a total chromatographic run-time of 12 min revealing a limit of detection of 0.3 μmol/L. The coefficients of determination obtained in a working range of 1-100 and 1-30 μmol/L were 0.9991 for orthophosphate and 0.9968 for IP6, respectively. The method was successfully applied to extracts from three different soils as well as root and shoot extracts of Brassica napus L. The precision of three independently prepared soil extracts was in the range of 4-10% relative standard deviation for PO4 (3-) and 3-8% relative standard deviation for IP6. Soil adsorption/desorption kinetics for IP6/orthophosphate were performed for investigating the sorption behavior of the two P species in the experimental soils.