Taxonomic and functional traits responses of <i>Sphagnum</i> peatland testate amoebae to experimentally manipulated water table

Biomonitoring tools are useful to assess the impact of environmental changes on the functioning of ecosystems. Existing tools mostly require species identification, thus allowing to estimating changes in biodiversity, and possibly inferring ecosystem functioning, using functional diversity and traits based approaches.<br> Testate amoebae are good indicators of surface moisture conditions in <i>Sphagnum</i> peatlands and are routinely used in palaeoecology. Their shells (tests), on which identification is based, can also be used to define functional traits and thus to infer changes in ecosystem functioning. <br> We investigated the response of testate amoeba communities to manipulated water table depth (wet: −4 cm, intermediate: −15 cm, and dry: −25 cm) over time (seven time points, 19 months) using mesocosms by comparing two approaches: community structure and functional traits responses, using a combination of morphological (biovolume, length, aperture size and position) and physiological (mixotrophy/heterotrophy, shell material) traits. <br> This is the first study investigating the effect of water table depth on testate amoeba assemblages over time using a mesocosm approach. Taxonomical and functional approaches showed similar response patterns, confirming that water level acted as a strong environmental filter. After one year <i>Hyalosphenia papilio</i> decreased in the dry treatment, and the community structure shifted towards a dominance of dry indicators (<i>Nebela tincta</i> complex, <i>Corythion dubium</i>, <i>Euglypha compressa</i>) and the selected functional traits (smaller, heterotrophic, compressed species, with a ventral aperture) corresponded to drought adaptations. <br> In line with recent observational and transfer function studies exploring the use of testate amoebae functional traits, our experimental results illustrate how well-selected traits could be used to monitor the impact of present and past climatic changes on <i>Sphagnum</i> peatlands.