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• Peatland degradation caused a significant loss of testate amoeba (TA) biodiversity. • Unexpectedly, this loss was accompanied by an increase in TA biosilicification. • TA biodiversity was not coupled to protozoic biogeochemical silicon (Si) cycling. • New insights into microbial biogeochemical Si cycling on a continental scale. Anthropogenic peatland degradation is a global threat. As peatlands store large amounts of carbon (C) their potential for mitigation of climate change has been emphasized recently. Global C cycling is linked to silicon (Si) fluxes from the continents into the oceans. These fluxes in turn are driven by biosilicification, the incorporation of inorganic Si into living organisms, in terrestrial ecosystems. Biosilicification by testate amoeba (TA) communities and its potential for Si cycling has been highlighted since the beginning of the 21st century. However, the effects of peatland degradation on TA biodiversity and corresponding protozoic biosilicification on a continental scale remained unresolved so far. We show that TA biodiversity in Asian peatlands is strongly affected by the grade of human impact. This biodiversity decline was accompanied by an unexpected increase in protozoic biosilicification. Our findings provide new insights into the interactions between the biodiversity of soil microorganisms and biogeochemical Si cycling. [ABSTRACT FROM AUTHOR]

Testate amoebae (TA) are a common and diverse group of protists and are especially abundant in peatlands. The structure of peatland TA communities is well correlated to surface moisture and water table depth (WTD). For that reason, TA are widely used as proxy indicators in ecological and palaeoecological studies. Peatlands are abundant across Asia, but the diversity and ecology of the TA that inhabit these systems are poorly documented. It is therefore unclear whether TA can be used as palaeohydrological indicators in the manner in which they commonly are in Europe and North-America. There is particular uncertainty as to the efficacy of this approach in the lower latitudes. We compiled existing and new data on testate amoebae from 1124 Sphagnum -dominated samples from 42 individual peatlands covering broad latitudinal (25°–66° N) and longitudinal (68°–129° E) ranges. Using a consensus taxonomic framework, we built a checklist of TA and developed TA-based hydrological transfer functions for Asian peatlands. The results showed that three models, weighted averaging (WA), weighted average partial least squares (WA-PLS), and maximum likelihood (ML), predicted similar WTD values for full samples, while the modern analogue technique (MAT) produced the strongest (R2 boot = 0.58) relationship between observed and estimated water-table depths (WTDs). Removing outlier samples improved the R2 values of observed vs. estimated WTDs, with ML then demonstrating the strongest predictive power (R2 boot = 0.68, RMSEP boot = 8.98 cm). The predictive capability of the developed WTD transfer function is comparable to equivalent models for Europe and North America and thus can be used for palaeohydrological reconstructions for boreal to subtropical peatlands in Asia. • A testate amoebae taxonomic checklist was compiled from Asian peatlands. • We developed continental scale testate amoeba-based hydrological transfer functions. • The water-table depth transfer functions can be used for paleohydrological reconstructions. [ABSTRACT FROM AUTHOR]