Sphagnum peatlands host a high abundance of protists, especially testate amoebae. Here, we designed a study to investigate the functional diversity of testate amoebae in relation to wetness and forest cover in Baltic bogs. We provided new data on the influence of openness/wetness gradient on testate amoebae communities, showing significant differences in selected testate amoebae (TA) traits. Three key messages emerged from our investigations: 1) we recorded an effect of peatland surface openness on testate amoebae functional traits that led us to accept the hypothesis that TA traits differ according to light intensity and hydrology. Mixotrophic species were recorded in high relative abundance in open plots, whereas they were nearly absent in forested sites; 2) we revealed a hydrological threshold for the occurrence of mixotrophic testate amoebae that might be very important in terms of peatland functioning and carbon sink vs. source context; and 3) mixotrophic species with organic tests were nearly absent in forested sites that were dominated by heterotrophic species with agglutinated or idiosomic tests. An important message from this study is that taxonomy of TA rather indicates the hydrological gradient whereas traits of mixotrophs the openness gradient.

泥炭藓泥炭地拥有大量的原生生物，尤其是有遗迹的变形虫。在这里，我们设计了一项研究，以调查波罗的海沼泽地区的睾丸变形虫的功能多样性与湿度和森林覆盖率的关系。我们提供了有关开放度/湿度梯度对睾丸变形虫群落影响的新数据，显示了所选的睾丸变形虫（TA）性状的显着差异。我们的研究得出了三个关键信息：1）我们记录了泥炭地表表面开放度对睾丸变形虫功能性状的影响，这使我们接受了TA性状根据光照强度和水文学而不同的假设。在开阔地带记录到混合营养物种相对较高的丰度，而在森林地带则几乎没有。2）我们揭示了混合营养型睾丸变形虫发生的水文阈值，对于泥炭地功能和碳汇与源环境而言，这可能非常重要；3）在森林地区几乎没有经过有机测试的混养物种，而被凝集或异基因组测试的异养物种占主导地位。这项研究的一个重要信息是，TA的分类学更确切地表明了水文梯度，而混合营养的特征则表明了开放度梯度。