Potential interference of organic acids and ferrous iron in the interpretation of Fe and Mn indicators of reduction in soil

Loffredo, Joseph; Rabenhorst, Martin C.; Stolt, Mark H.; Amador, José A.

doi:10.1002/saj2.20560

Cited by 3 publications

(2 citation statements)

References 36 publications

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“…We attribute this effect to the root release of protons and organic acids (Jones, 1998) as well as increased levels of soil CO2 through plant and microbial respiration (Koop-Jakobsen et al 2018). IRIS sticks have proven robust against pH changes at pH > 4.5 (Loffredo et al, 2023). Soil pH was > 7 in both mesocosm and field.…”

Section: Methodological Considerationsmentioning

confidence: 99%

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Preprint

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The redox potential in wetland soils exerts strong control over microbial decomposition and consequently carbon cycling. Wetland plants influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil. However, quantitative insight into plant effects on wetland soil redox are scarce. We investigated plant effects on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated and unvegetated treatments were created along salt-marsh flooding gradients both in a mesocosm facility and in situ. We show that the presence of plants resulted in both increased and decreased soil reduction compared to non-vegetated controls in the mesocosm study and that the direction of the plant effect (i.e. reducing versus oxidizing) depended on the background redox conditions observed in non-vegetated controls. When background soil reduction was high, plants tended to act as net oxidizers, whereas under more oxidizing conditions plants acted as net reducers of the soil. High-resolution oxygen profiling via planar optode imaging further supported these findings. Plant effects on soil reduction in the field study were negative across all elevational zones. We attribute this effect to the comparably well aerated soils of Wadden Sea salt marshes. Reduction correlated positively with belowground biomass, indicating that a higher availability of plant-derived electron donors increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect.

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Section: Methodological Considerationsmentioning

confidence: 99%

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…Following these experiments for synthesizing Mn-coated sand, selected samples of coated sands were extracted using 0.5 M NH 2 OH•HCl for 1 h at room temperature (which previously had been demonstrated to completely solubilize the synthetic birnessite) (Chao, 1972;Loffredo et al, 2023). Extracts were appropriately diluted and analyzed using atomic absorption (AA) spectroscopy (using a PerkinElmer PinAAcle 500 AA Spectrometer) to quantify the amount of Mn coating the sands.…”

Section: Mn Extractions and Color Analysismentioning

confidence: 99%

Advances in making Mn oxide‐coated sands

Rabenhorst,

Wardrup

2024

Soil Science Soc of Amer J

Self Cite

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Manganese (Mn) oxide‐coated sand has been suggested as an amendment for scrubbing metals in water filtration beds and also as a less concentrated medium for uniformly amending soils with Mn oxides in mesocosm scale studies. Earlier work at the lab bench scale, using potassium permanganate (KMnO4) solutions that were reduced with sodium (Na) lactate, resulted in sands coated with about 0.13% Mn. The goal of this project was to increase the amount of Mn oxide that could be coated on sand to make it a more useful amendment and also to attempt to scale up the procedure to produce larger (kg) quantities of coated sand. Titration experiments examined the effects of (1) varying the molar ratio of Na lactate to KMnO4, (2) varying the rate at which the titration was accomplished, and (3) varying the concentration (molarity) of the original KMnO4 solution. The results of this work led to an optimal approach utilizing 0.32 M KMnO4 solution that was titrated to a final lactate:permanganate ratio of ∼1.1 with 10% of the lactate being added every 10 min while the suspension was being stirred. The proportion of sand to an initial solution was also increased 5–20 fold to between 50 and 200 g per 100 mL of solution. Applying this method and using a large 20‐ to 30‐L reaction vessel yields sands coated with up to 0.7% Mn in batches 5–10 kg is size, which could be useful as an amendment in mesocosm scale studies, or as a component of treatment filter beds. The examination of various size fractions of the coated sands demonstrated that more Mn was coated on finer sand fractions, which appears to be a function of the particle surface area available for the coating of Mn oxides, and at a rate of 0.3–0.5 µg Mn mm−2 of the particle surface.

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Root-Driven Soil Reduction in Wadden Sea Salt Marshes

Mittmann-Goetsch,

Wilson,

Jensen

et al. 2024

Wetlands

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The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables.

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Potential interference of organic acids and ferrous iron in the interpretation of Fe and Mn indicators of reduction in soil

Cited by 3 publications

References 36 publications

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Wetland roots as soil reducers – Insights from a Wadden Sea salt-marsh study

Advances in making Mn oxide‐coated sands

Root-Driven Soil Reduction in Wadden Sea Salt Marshes

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