Organic matter character as a critical factor determining the fate and stability of its association with iron in sediments

Osafo, Nana O.-A.; Jan, Jiří; Valero, Astolfo; Porcal, Petr; Petrash, Daniel A.; Borovec, Jakub

doi:10.1007/s11368-022-03207-x

Cited by 4 publications

(2 citation statements)

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“…However, in addition to this problem, we must mention that in most studies relating Fe oxyhydroxides with SOM storage, dithionite is the main extractor [17,44], either alone or combined with other chemicals. Dithionite, through the reduction of Fe(III) to Fe(II), solubilizes massively all free iron forms, either amorphous or crystalline, being therefore quite unspecific.…”

Section: Insight About the Role Of Free Fe Formsmentioning

confidence: 99%

“…Several precise mechanisms through which Fe and Al forms would stabilize SOM have been described [3]: sorptive processes, including preferential sorption in micropores of Fe oxides, or the precipitation of organic compounds via formation of complexes, often with Ca 2+ [16]. The stability of the organo-Fe complexes seems to depend strongly on the specific type of the organic moiety (humic substances, proteins, and carbohydrates) [17].…”

Section: Introductionmentioning

confidence: 99%

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Constraints on Organic Matter Stability in Pyrenean Subalpine Grassland Soils: Physical Protection, Biochemical Quality, and the Role of Free Iron Forms

Rovira,

Sauras-Yera,

Poch

2024

Environments

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The stability of soil organic matter (SOM) depends on its degree of physical protection, biochemical quality (q), and mineralogical features such as the abundance of iron or aluminum oxyhydroxides: All constraints stabilize SOM, but the relevance of each is herein discussed. We studied from this point of view the stability of SOM in four grassland soils. The SOM in these profiles was characterized for its physical protection (ultrasonic dispersion + size fractionation) and its q (acid hydrolysis, carbohydrates, phenolics, and unhydrolyzable carbon). The profiles were also analyzed for free iron forms extracted with several chemicals: dithionite-citrate-bicarbonate, citric acid, oxalic-oxalate (Tamm’s solution), and DTPA. Soil horizons were incubated under optimal conditions to obtain the C lost after 33 days (Cresp33) and basal respiration rate (BRR). The microbial C was obtained at the end of the incubation. The microbial activity rate (MAR: mg C respired per g microbial C per day) was obtained from these measures. The sum soluble + microbial C was taken as the active C pool. As expected, the stability of SOM depends on its distribution between the size fractions: The higher the proportion of particulate organic matter (POM: >20 µm size), the higher the soil respiration rate. In contrast, q barely affects SOM decomposition. Both physical availability (size fractionation) and q (acid hydrolysis) affect the size of the microbial C pool, but they barely affect MAR. The effects of free iron on SOM stability are complex: While dithionite-extracted Fe negatively affected Cresp33, BRR, and MAR, the Fe extracted by smoother methods (Tamm’s reagent and DTPA) positively relates to Cresp33, BRR, and MAR. Free iron apparently modulates soil microbial metabolism because it is the only studied parameter that significantly affected MAR; however, the precise effect depends on the precise free Fe fraction. From our data, SOM stability relies on a net of constraints, including physical availability and free Fe forms, with q being of minor relevance. Our dataset suggests a role for free iron as a modulator of microbial activity, deserving future research.

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Section: Insight About the Role Of Free Fe Formsmentioning

confidence: 99%