Diversity and assemblage patterns of microorganisms structured by the groundwater chemistry gradient in spring fens

Abstract

-We examined the associations of microorganism assemblages with a complete mineral richness gradient spanning from extremely mineral-rich tufa-forming calcareous fens to mineral-poor acidic Sphagnum-fens. We also compared the distribution of two dominant taxa, testate amoebae and monogonont rotifers, among the sites differing in water chemistry and among three microhabitats sampled at each site differing in substrate and moisture conditions. Microorganism assemblages primarily changed in relation to the mineral richness gradient; moisture was the second most important factor structuring microorganism assemblages among microhabitats (i.e., wet bryophytes, submerged bryophytes and waterlogged bottom sediments). Densities of testate amoebae taxa and individuals were the highest in rich Sphagnum-fens, indicating a unimodal pattern along the mineral richness gradient. Numbers of testate amoebae taxa decreased notably in wet bryophytes, especially in poor Sphagnum-fens. This pattern might result from a strong effect of Sphagnum acidification due to minimal or no dilution of the acidic environment by mineral-rich groundwater. As a consequence, acid tolerant and relatively xerophilous taxa chiefly dominated in wet bryophytes of poor Sphagnum-fens, while poor Sphagnum-fen bottom sediments could provide a refuge for less tolerant and hydrophilous species. In contrast to testate amoebae, monogonont rotifers preferred bryophytes in all sites, with the number of monogonont taxa distinctly increasing from calcareous fens to poor Sphagnum-fens. In poor Sphagnum-fens, monogononts were the most abundant in wet bryophytes, probably due to reduced food competition and/or predaceous pressure resulting from the limited occurrence of other groups of microorganisms by virtue of the hostile acidic conditions in wet Sphagnum carpets.

Testate Amoeba Functional Traits and Their Use in Paleoecology

“…They contribute to soil nutrient cycling (Wilkinson and Mitchell, 2010), especially the cycles of C, N, and Si in soils (Schröter et al, 2003;Nguyen-Viet et al, 2004;Aoki et al, 2007;Jassey et al, 2015;Puppe, 2020). Their community structure is also strongly correlated to peatland water table depth, soil moisture regime (Woodland et al, 1998;Mitchell et al, 1999;Sullivan and Booth, 2011), shade/hydrology (Marcisz et al, 2014b;Lamentowicz et al, 2020), and chemistry (Tolonen et al, 1992;Hajkova et al, 2011;Singer et al, 2018); contaminant runoff into lakes (Neville et al, 2014;Roe and Patterson, 2014;Gavel et al, 2018); sea level change (Patterson et al, 1985;Charman et al, 1998Charman et al, , 2002; and has been shown to respond to experimental water table changes both in the field (Marcisz et al, 2014a) and in mesocosm studies (Koenig et al, 2017(Koenig et al, , 2018b. Testate amoeba community dynamics and how they relate to ecosystem functions is a dynamic field of research, although many knowledge gaps remain (but see Fournier et al, 2012;Jassey et al, 2013aJassey et al, , 2015Lamentowicz et al, 2013a;Macumber et al, 2017).…”

“…Studies on testate amoeba-environment relationships in Sphagnum-dominated peatlands have been mainly carried out on raised ombrotrophic bogs (but see Opravilova and Hajek, 2006;Hajkova et al, 2011). Peatlands of this type are highly acidic (pH 3.5-5.5), have no contact with groundwater, and are supplied exclusively by rainwater (Rydin and Jeglum, 2006).…”