Changes in testate amoebae (Protists) communities in a small raised bog. A 40-year study

We analyzed the testate amoebae communities from two sets of moss samples taken forty years apart (1961 and 2001) in the same locations of a peat bog of the Swiss Jura Mountains. Peat cutting and lateral drainage of Le Cachot bog have caused a clear increase in tree cover, especially near the edges. Changes affecting herbaceous plants, mosses, or soil organisms can be subtle, and may easily be overlooked. We hypothesized that we would see changes in the dominant Sphagnum species and the structure of testate amoebae communities living in the mosses. More specifically, we hypothesized that the frequency of bryophyte and testate amoebae species indicative for dry conditions would increase and that the frequency of species indicative for wet conditions would decrease. The mean testate amoebae species richness per sample decreased from 11.9 to 9.6, but the overall species richness was identical (33 species) in both years. Three species increased significantly in mean relative abundance: Nebela tincta s.l. (+97%), Bullinularia indica (+810%), and Cyclopyxis eurystoma (+100%; absent in 1961), while two species decreased significantly: Assulina muscorum (-63%) and Euglypha compressa (-93%). The testate amoebae communities clearly differed among microhabitat types (hummocks, lawns, hollows), but no overall significant change in the community was detectable between the two sampling dates (Mantel test). These results could signify that changes at the microscopic level had already taken place by 1961 and no further overall significant changes in micro-environmental conditions took place during the 40-year period of this study. This would agree with the faster response time usually attributed to microorganisms and would also imply that the bushes and trees may be poor predictors of the response of microorganisms if they are themselves in a non-equilibrium stage. Other possible causes for the lack of overall differences are discussed.

Cutover peatland regeneration assessment using organic matter and microbial indicators (bacteria and testate amoebae)

Alexandre Buttler, Edward Mitchell

Cutover peatlands cover large surfaces of high potential value for biodiversity and carbon sequestration function if successfully restored but the evaluation of restoration success is not straighforward. We assessed the bioindicator value of organic matter (OM), testate amoebae (protozoa) and bacteria in peat from two regeneration stages and a reference site of a cutover bog. 2. Contrasting biochemical signatures of peat OM were observed along the regenerating profiles allowing clear differentiation between the newly regenerated peat and the old peat. Where peat macrofossils were absent sugar biomarkers allowed to infer peat botanical origin and OM alteration. 3. Over the succession, the OM composition of the new peat differed: peat from the recent stage was more dominated by Sphagnum-derived tissues and was characterised by lesser carbohydrate preservation and higher bacterial biomass than the advanced regeneration stage. 4. Surface testate amoeba communities also changed from the recent to the advanced stages of regeneration indicating a shift from wet and moderately acidic conditions to drier and more acidic conditions. Over this regeneration sequence (i) biomass and average size of species declined but were higher in the unexploited site (ii) species richness and diversity increased but density declined. 5. Synthesis and applications. Although the secondary succession in the cutover bog leads to an ecosystem similar to that of the reference site in terms of surface vegetation, OM and testate amoebae continue to reflect disturbances associated with peat harvesting. Nevertheless, the described dynamics of both microbial and biochemical variables over the succession showed similarities between the advanced stage and the reference: a higher testate amoeba diversity is associated with better carbohydrate preservation and a more heterogeneous botanical composition of the peat. The quantitative inference of water table depth and pH based on testate amoebae indicators represents an alternative to labour-intensive repeated measurements in the field. Botanical and biochemical composition of peat OM provides additional information on past anthropogenic perturbations of the bog and can be used for restoration monitoring. The combination of several indicators therefore provides a more complete assessment of ecological conditions which could be valuable for the management of cutover peatlands.

2008

Horizontal distribution patterns of testate amoebae (Protozoa) in a Sphagnum magellanicum carpet

Daniel Borcard, Alexandre Buttler, Jean-Michel Gobat, Edward Mitchell

The distribution of soil microorganisms is generally believed to be patchy and to reflect habitat heterogeneity. Despite this general rule, the amount of existing data oil species distribution patterns is scarce. Testate amoebae (Protozoa; Rhizopoda) are an important component of soil microbial communities and are increasingly used in ecological and paleoecological studies of Sphagnum-dominated peatlands, but data on the spatial structure of communities are completely lacking. This is an important aspect since quantitative models used for paleoecological reconstruction and monitoring are based on species assemblages. We explored the distribution patterns of testate amoebae distribution in a macroscopically homogeneous Sphagnum carpet, down to a scale of several centimeters. Distributions maps of the species and spatially constrained sample groups were produced. Multivariate and individual spatial autocorrelations were calculated. The importance of spatial structure was quantified by canonical correspondence analysis. Our ultimate goal is to find the finest resolution of environmental monitoring using testate amoebae. The distribution patterns differed among species, resulting in a complex spatial structure of the species assemblage in a whole. Spatial structure accounted for 36% of the total variation of species abundance in a canonical correspondence analysis constrained by spatial variables. This structure was partly correlated to altitude (microtopography) at a very fine scale. These results confirmed the existence of significant broad-and fine-scale spatial structures within restate amoebae communities that could in parr be interpreted as effects of ecological gradients. This shows that, on a surface area of 0.25 m(2), ecological conditions which look uniform from a macroscopic point of view are not perceived as such by Sphagnum-inhabiting organisms. Therefore, restate amoebae could prove very useful to monitor fine-scale ecological processes or disturbances. Studies of the species' spatial distribution patterns in combination with autoecological studies are needed and should be included in the toolbox of biomonitoring itself.

2000

Functional traits as a new approach for interpreting testate amoeba palaeo-records in peatlands and assessing the causes and consequences of past changes in species composition

Bertrand Fournier, Vincent Eric Jules Jassey, Enrique Lara, Edward Mitchell

Subfossil remains of various groups of organisms preserved in peat and sediment archives are commonly used to infer past environmental changes using transfer functions based on species composition. However, the changes in community structure can also be explored using the functional trait approach. Investigation of functional traits in palaeoecological records can inform about the mechanisms through which abiotic variables such as temperature or moisture impact communities. Moreover, changes in functional traits provide information about changes in ecosystem functioning and can potentially lead to the reconstruction of past processes at the ecosystem scale. Here, we use five key functional traits of arcellinid testate amoebae (TAs), a group of protozoa that are key actors in the microbial foodwebs in peatlands. We apply this approach to the subfossil TA Holocene record of four geographically independent peatlands from Alaska, Switzerland, Poland and Russia. We found that species with larger shells were frequently eliminated from the communities most likely as a result of a switch towards drier conditions. However, when conditions were wetter, species with large shells and species with small shells could coexist because they differed in their trophic niche (i.e. preys). Our results show direct but site-specific links between TA trait data and the depth to water table and pH data inferred from TA species composition. This suggests that past environmental changes influenced both species composition and community function in these ecosystems. Overall, this study demonstrates that species- and trait-based approaches yield complementary information on past environmental changes. For instance, while taxonomic approaches reveal the changes in community composition over time, investigation of traits informs both on the causes and the consequences of these changes on ecosystem functioning.

Sage Publications Ltd2015