Available online at www.sciencedirect.com European Journal of Protistology 48 (2012) 161–168 Testate amoebae in 31 mature forest ecosystems – Densities and micro-distribution in soils Otto Ehrmann a , Daniel Puppe b,c , Manfred Wanner b,∗ , Danuta Kaczorek c,d , Michael Sommer c,e a Bureau for Soil Micromorphology and Soil Biology, Münster 12, 97993 Creglingen, Germany b Brandenburg University of Technology Cottbus, Chair General Ecology, 03013 Cottbus, Germany c Leibniz-Centre for Agricultural Landscape Research (ZALF) e.V., Institute of Soil Landscape Research, 15374 Müncheberg, Germany d Department of Soil Environment Sciences, Warsaw University of Life Sciences (SGGW), Nowoursynowska 159, 02-776 Warsaw, Poland e University of Potsdam, Institute of Earth and Environmental Sciences, 14476 Potsdam, Germany Received 25 May 2011; received in revised form 22 December 2011; accepted 11 January 2012 Available online 16 February 2012 Abstract We studied testate amoebae and possible correlated abiotic factors in soils of 31 mature forest ecosystems using an easily applicable and spatially explicit method. Simple counting on soil thin-sections with a light microscope resulted in amoeba densities comparable to previously reported values, i.e. 0.1 × 10 8 to 11.5 × 10 8 individuals m -2 (upper 3 cm of soil). Soil moisture and soil acidity seem to be correlated with amoeba densities. At sites of moderate soil moisture regimes (SMR 2–7) we found higher densities of testate amoebae at pH < 4.5. At wetter sites (SMR ≥ 8) higher individual densities were recorded also at less acidic sites. The in situ description of amoebae, based on the analysis of a complete soil thin-section, showed a relatively uniform spatial micro-distribution throughout the organic and mineral soil horizons (no testate amoeba clusters). We discuss the pros and cons of the soil thin-section method and suggest it as an additional tool to improve knowledge of the spatial micro-distribution of testate amoebae. © 2012 Elsevier GmbH. All rights reserved. Keywords: Microhabitats; Soil thin-section; Soil moisture regimes; Soil reaction Introduction Protozoa in soils are not only important bioindicators of environmental conditions and changes in natural and human-influenced ecosystems (Foissner 1999), but they also play a pivotal role as regulators of ecosystem processes (Darbyshire 1994; Wetzel 2001), especially for nutrient dynamics. Their potential importance for terrestrial Si cycling Abbreviations: MPN, Most Probable Number; WRB, World Reference Base for Soil Resources; SMR, soil moisture regime; SOC, soil organic carbon; C t , total carbon; N t , total nitrogen; C carb , carbonate – C. ∗ Corresponding author. E-mail address: wanner@tu-cottbus.de (M. Wanner). has been addressed, but quantitative knowledge still is very scarce (Clarke 2003; Sommer et al. 2006; Aoki et al. 2007). Testate amoebae constitute the dominant protozoan group, e.g., in coniferous forest soils (Schönborn 1992). Schröter et al. (2003) demonstrated that testate amoebae from forest soils have an overwhelming contribution to C and N min- eralization; among the fauna, testate amoebae made by far the largest contributions to mineralization. In some forest soils, testate amoebae, with an annual biomass production of more than 200 g m -2 (Meisterfeld 2002), are as important as earthworms for processes such as decomposition. Due to their shells, they are very resistant to soil drought and other adverse conditions. Additionally, they are one of the very first colonizers of newly exposed soil substrates. They 0932-4739/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.ejop.2012.01.003