Summary1. Plant community composition is recognized more and more for playing an important role in ecosystem processes, such as C cycling. In particular, plant functional type (PFT) composition seems to have a key regulatory role, yet the underlying mechanisms in the interaction between PFTs and ecosystem processes are still to be identified. 2. Here, we assess the link between PFTs and dominant microbial consumers along a calcareous poor to extremely rich fen gradient in western Poland. We particularly focussed on dominant microbial consumers (testate amoebae), which can exert large effects on the functioning of peatlands. Using moving-window analyses and path-relation networks subjected to structural equation modelling (SEM), we investigated linkages among abiotic factors, PFTs and testate amoebae. 3. We show that along the poor to extremely rich fen gradient, the dependence of testate amoebae to PFTs is higher than their dependence to abiotic factors. We also found that the link between testate amoebae and PFTs differs between size assemblages of testate amoebae. While large testate amoeba species (i.e. high trophic level) were highly linked to Sphagnum mosses cover, small species (i.e. low trophic level) were linked to brown mosses. Distinction between shallow-rooted and deeprooted vascular plants also showed that shallow-rooted plants play a role on testate amoeba community structure at the 'poor' side of the gradient. 4. Our results further show a dominant role for calcium content and the structure of the bryophyte community on testate amoeba size assemblages at the poor to extremely rich fen scale, both for diversity and abundance of testate amoebae. 5. Synthesis. Variations in plant functional type composition drive niche-size-structure of testate amoebae along the (calcareous) poor to extremely rich fen gradient. Furthermore, strong relationships between moss types and testate amoeba size-structure suggest that mosses specifically influence testate amoeba development through autogenic effects. Therefore, moss cover composition is key to microbial consumers and may be the driving factor determining microbial network structure and associated ecosystem processes, such as carbon cycling. ¶ V. E. J. Jassey and Ł. Lamentowicz contributed equally to the data extraction, statistical analyses and preparation of the manuscript and are therefore considered to be co-first authors.

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We investigated the relationships between testate amoebae (Arcellinida, Euglyphida), vegetation and water chemistry along environmental gradients in minerotrophic peatlands (fens) in western Poland. We hypothesized that: a) hydrochemistry significantly influences structure of testate amoeba communities, and b) testate amoeba communities are more closely correlated with the hydrochemical variables (environment) than with the vegetation data. Testate amoeba communities and vegetation from 71 sample plots were investigated together with the hydro-chemistry and hydrology based on 16 environmental variables and vegetation composition. Testate amoeba communities revealed a distinctive poor-rich gradient in analysed fens. Mineral-rich habitats, which were dominated by brown mosses, were preferred by a higher number of taxa than acidic habitats, which were dominated by Sphagnum. We recorded a total of 107 testate amoebae taxa. The average species richness of testate amoebae for brown mosses was higher (20) than for Sphagnum (13). We found that testate amoebae communities were similarly correlated with vascular plants, mosses and environmental parameters. Results of direct ordination demonstrate that hydrology, pH, Mg 2+ and sodium remain the most important environmental control for the entire data set. CCA showed that in case of brown mosses hydrology, sodium and oxygen affect testate amoeba communities significantly whereas in Sphagnum only sodium emerge as most significant determining testate amoeba assemblages. IntroductionKnowledge about microorganisms is important for understanding peatland ecosystems (GIL- BERT and MITCHELL, 2006). A holistic ecosystem approach, however, is not possible because the number of variables, groups of organisms and interactions is too large to be described in one study. Relationships between soil microbes and plants have not been well explored and increasing numbers of studies are focusing on belowground interactions (WARDLE, 2006;BEVER et al., 2010). In the case of peatlands (especially rich fens), a lot of work is needed to fully explore microbial communities. Among them testate amoebae (Arcellinida, Euglyphida) are an important group of biotic indicators. These organisms live in the soil and mosses in fens and are useful for thoroughly exploring environmental gradients. Their biomass and density in wetlands depends strongly on the abundance and the level of the complicated spatial structure of the plants (MIECZAN, 2010) . They graze on other microbes, such as bacteria, algae and fungi, and play an important role in the soil microbial loop and nutrient cycle in soils (GILBERT et al., 1998;WILKINSON and MITCHELL, 2010). Furthermore, testate amoebae have been used in ecological studies of the response of terrestrial ecosystems to climate change (LAMENTOWICZ et al., 2010b;TSYGANOV et al., 2010) and also are usefull paleoindicators of hydrological changes on ombrotrophic peatlands (BOOTH, 2002) however until now most of the research have been conducted in raised bogs or Sphagnum...

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The paper presents a brief review of published so far and recently recorded unpublished bryological data concerning the distribution in Poland of two neophytic (sensu Meusel 1943) mosses: Campylopus introflexus (Hedw.) Brid. and Orthodontium lineare Schwaegr.to estimate their current influence on native bryoflora. The data clearly indicate the constant spreading of these species towards the east, however, there is no direct evidence that they have been limiting the occurrence of native moss species. They are acidophilous species, so the acidification of the environment probably promotes their expansion. Maps of the most current distribution of Campylopus introflexus and Orthodontium lineare in Poland (in a system of ATMOS-grid squares) are provided, as well as a description of the first locality in Poland of another European bryo-neophyte species Leptophascum leptophyllum Mull. Hal