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The size and dynamics of biogenic silicon (BSi) pools influence silicon (Si) fluxes from terrestrial to aquatic
ecosystems. The research focus up to now was on the role of plants in Si cycling. In recent studies on old forests annual biosilicification rates of idiosomic testate amoebae (i.e. TA producing self-secreted silica shells) were shown to be of the order of Si uptake by trees. However, no comparable data exist for initial ecosystems. We analyzed the protozoic BSi pool (idiosomic TA), corresponding annual biosilicification rates and readily available and amorphous Si fractions along a 10-year chronosequence in a post-mining landscape in Brandenburg, Germany. Idiosomic Si pools ranged from 3 to 680 g Si ha−1 and were about 3–4 times higher at vegetated compared to uncovered spots. They increased significantly with age and were related to temporal development of soil chemical properties. The calculation of annual biosilicification resulted in maxima between 2 and 16 kg Si ha−1 with rates always higher at vegetated spots. Our results showed that the BSi pool of idiosomic TA is built up rapidly during the initial phases of ecosystem development and is strongly linked to plant growth. Furthermore, our findings highlight the importance of TA for Si cycling in young artificial ecosystems.
Accumulation and recycling of biogenic silicon (BSi) in terrestrial ecosystems influence fluxes of dissolved Si from the continents to the oceans, thus act as a filter in the global Si cycle. Although the biogenic control mechanism especially of phytogenic Si pools (phytoliths) has been generally recognized since decades quantitative information on other terrestrial BSi pools is surprisingly rare. For the first time terrestrial protophytic (diatom frustules), protozoic (testate amoeba shells) and zoogenic (sponge spicules) Si pools were quantified in soils of initial ecosystem states. We analyzed spatiotemporal changes of these Si pools in differently aged soils of the artificial catchment ‘Chicken Creek’ in NE Germany. Within a relatively short time span (<10 years) of ecosystem development protophytic, protozoic and zoogenic Si pool sizes increased markedly, whereat protozoic Si pools were the smallest ones with a maximum of 6.2 mg m−2. Zoogenic Si pool size (max. 22.6 mg m−2) is comparable to the one of protophytic Si pools (max. 30.5 mg m−2) although only few sponge spicules (n = 10) and spicule fragments (n = 2) were found. Differences in quantities, dynamics and resistibility against dissolution of various BSi pools indicate their possibility to influence biogeochemical Si cycling relatively rapid (protophytic and protozoic Si pools) or slow (zoogenic Si pool). Spatiotemporal changes of protophytic and protozoic Si pools within the first decade of ecosystem development seem to be mainly controlled by (biotic) small-scale environmental conditions (e.g., vegetation, food sources).