Increased silicon concentration in fen peat leads to a release of iron and phosphate and changes in the composition of dissolved organic matter

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Hömberg, Annkathrin ; Obst, Martin ; Knorr, Klaus-Holger ; Kalbitz, Karsten ; Schaller, Jörg:
Increased silicon concentration in fen peat leads to a release of iron and phosphate and changes in the composition of dissolved organic matter.
In: Geoderma. Bd. 374 (2020) . - 114422.
ISSN 0016-7061
DOI: https://doi.org/10.1016/j.geoderma.2020.114422

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Abstract

Prior studies have shown that silicon (Si) increases the dissolution of iron (Fe) phosphates, releasing phosphorus (P) into the soil solution of fen peat and thereby changing the composition of organic matter (OM). We hypothesized that this processes occur in the following way: [i] high Si availability causes a mobilization of Fe phosphates, which, in turn, [ii] results in a higher concentration of P, Fe, and dissolved organic carbon, and [iii] changes the composition of organic matter. To this end, we conducted a laboratory experiment adding amorphous silica to fen peat and analyzed Fe mineralogy and carbon quality of the peat material by X-ray absorption spectroscopy (XAS). Under high Si availability, significantly higher concentrations of P and Fe were found in soil solution. Moreover, XAS data indicated a dissolution of Fe (II) phosphates and a change in the composition of available OM with decreasing contributions of carboxylic groups and quinones. We propose to explain the effects as follows: under high Si availability Fe (II) phosphates dissolve and OM rich in carboxylic groups are mobilized. As the nutrient availability in the soil solution increased, the degradation of oxidized components of the OM, such as quinones and carboxylic groups is enhanced.