Abstract
Abstract. The significance of biogenic silicon (BSi) pools as a key factor for the control of Si fluxes from terrestrial to aquatic ecosystems has been recognized for decades. However, while most research has been focused on phytogenic Si pools, knowledge of other BSi pools is still limited. We hypothesized that different BSi pools influence short-term changes in the water-soluble Si fraction in soils to different extents. To test our hypothesis we took plant (Calamagrostis epigejos, Phragmites australis) and soil samples in an artificial catchment in a post-mining landscape in the state of Brandenburg, Germany. We quantified phytogenic (phytoliths), protistic (diatom frustules and testate amoeba shells) and zoogenic (sponge spicules) Si pools as well as Tiron-extractable and water-soluble Si fractions in soils at the beginning (t0) and after 10 years (t10) of ecosystem development. As expected the results of Tiron extraction showed that there are no consistent changes in the amorphous Si pool at Chicken Creek (Hühnerwasser) as early as after 10 years. In contrast to t0 we found increased water-soluble Si and BSi pools at t10; thus we concluded that BSi pools are the main driver of short-term changes in water-soluble Si. However, because total BSi represents only small proportions of water-soluble Si at t0 (< 2 %) and t10 (2.8–4.3 %) we further concluded that smaller (< 5 µm) and/or fragile phytogenic Si structures have the biggest impact on short-term changes in water-soluble Si. In this context, extracted phytoliths (> 5 µm) only amounted to about 16 % of total Si contents of plant materials of C. epigejos and P. australis at t10; thus about 84 % of small-scale and/or fragile phytogenic Si is not quantified by the used phytolith extraction method. Analyses of small-scale and fragile phytogenic Si structures are urgently needed in future work as they seem to represent the biggest and most reactive Si pool in soils. Thus they are the most important drivers of Si cycling in terrestrial biogeosystems.
Highlights
Various prokaryotes and eukaryotes are able to synthesize hydrated amorphous silica (SiO2 q nH2O) structures from monomeric silicic acid (H4SiO4) in a process called biosilicification (Ehrlich et al, 2010)
For t10 we hypothesized section-specific differences in biogenic silicon (BSi) pool quantities related to section-specific vegetation dynamics. To evaluate these differences after a decade of ecosystem development and to cover the biggest possible BSi accumulation in soil we focused on spots where Si-accumulating plant species, i.e., Calamagrostis epigejos and Phragmites australis, became dominant (Zaplata et al, 2010)
The major proportion of Tiron-extractable Si at Chicken Creek seems to be of pedogenic origin (e.g., Si included in Al / Fe oxides / hydroxides)
Summary
Various prokaryotes and eukaryotes are able to synthesize hydrated amorphous silica (SiO2 q nH2O) structures from monomeric silicic acid (H4SiO4) in a process called biosilicification (Ehrlich et al, 2010). BSi has been recognized as a key factor in the control of Si fluxes from terrestrial to aquatic ecosystems as it is in general more soluble compared to silicate minerals (e.g., Fraysse et al, 2006, 2009). These fluxes influence marine diatom production on a global scale (Dürr et al, 2011; Sommer et al, 2006; Struyf and Conley, 2012). Puppe et al.: The influence of biogenic silicon pools tities of carbon dioxide via photosynthesis, because up to 54 % of the biomass in the oceans is represented by diatoms; diatoms have an important influence on climate change (Tréguer and De La Rocha, 2013; Tréguer and Pondaven, 2000)
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