Testate amoebae in pollen slides

A preliminary investigation into the use of testate amoebae for the discrimination of forensic soil samples

Testate amoebae are phylogenetically a very diverse group of eukaryotic microorganisms. They can be found in marine and freshwater habitats and in soil. Some of these single-celled organisms inhabit both surface and cave habitats, but their diversity in caves has barely been explored. Recent studies in the Dinaric region imply that testate amoebae in caves show a high diversity. The aim of this study was to identify the alpha diversity of testate amoebae in the Lika region (Dinaric karst, Croatia) and to compare the habitats of different caves based on testate amoebae assemblages. In eight caves we found more than 40 testate amoebae taxa, including a new testate amoeba species, Psammonobiotus dinaricasp. nov. The greatest diversity of testate amoebae was found in Markov ponor (27 taxa). The Bray-Curtis Similarity Index showed that testate amoebae assemblages in caves inhabited by the endemic and endangered cave bivalve Congeria jalzici (Markov ponor, Dankov ponor and Dražice ponor) differ from caves not inhabited by this species. This differentiation is attributed to the impact of the sinking Lika river, which occasionally completely submerges these caves, creating specific habitats for eukaryotic microorganisms. This study contributes to our understanding of the diversity, biogeography and ecology of testate amoebae in caves, as well as providing further insight into the conditions that sustain populations of C. jalzici.

Restoring degraded peatlands is vital for sustaining their capacity as carbon sinks and long-term carbon stores. Microbial assemblages serve as valuable indicators for monitoring environmental change and assessing the success of ecosystem restoration efforts. Testate amoebae are a group of unicellular shelled protists that are commonly used for Holocene palaeohydrological reconstruction in peatlands. While progress is being made, the use of testate amoebae for biomonitoring in peatland restoration is still in its early stages. The aim of this study is to assess testate amoebae response to restoration measures (drain blocking) across three lowland raised bogs in Northern Ireland. To accomplish this, Sphagnum samples were collected from each site using a before-after control-impact (BACI) experimental design. After peatland drainage ditches were blocked, subtle yet significant responses in testate amoebae were observed: (1) key unambiguous wet-indicator taxa became more abundant in samples adjacent to blocked dams; (2) a widespread increase in the abundance of taxa with sub-spherical tests was observed, most notably in samples near to blocked drains. The findings of this study demonstrate the reliable response of testate amoebae to wetter conditions across all sites after restoration. Functional trait analysis paired with an indicator-taxa based approach, demonstrate the value of testate amoebae as contemporary bioindicators for tracking peatland restoration success, even when detailed hydrological monitoring data is not available. However, testate amoebae should be used with some degree of caution for peatland biomonitoring until long-term assemblage-level response to restoration is better understood.

Valentine, Julie, Davis, Stephen R., Kirby, Jason R., Wilkinson, David M. (2013): The Use of Testate Amoebae in Monitoring Peatland Restoration Management: Case Studies from North West England and Ireland. Acta Protozoologica 52 (3): 129-145, DOI: 10.4467/16890027AP.13.0013.1110, URL: https://www.mendeley.com/catalogue/3b06ce53-3e6f-38be-87b5-83caeffceeef/

In peatland palaeoecological studies, the preparation of peat samples for testate amoebae (TA) analysis involves boiling of samples and microsieving them through a 15-μm sieve. We studied the effect of these preparation stages on the estimation of TA assemblages and on the reconstruction of water table depths (WTD). Our results indicate that the TA assemblages of boiled and unboiled samples are not significantly different, while microsieving reduces the concentration of small TA taxa and results in significantly different TA assemblages. The differences between microsieved and unsieved TA assemblages were reflected also in predicted values of WTD, which indicated drier conditions in case of unsieved samples than in microsieved samples. We conclude that the boiling of samples might be omitted if TA are extracted from the fresh peat samples. Microsieving may lead to erroneous palaeoecological WTD reconstructions and should be avoided if small TA taxa are present in samples.

Testate amoebae are sensitive indicators of substrate moisture in peatlands. Over the last decades, they have been studied to reconstruct hydrological changes since the Holocene. However, these studies have been geographically restricted to North America and Europe. We conducted the first investigation of testate amoebae on the largest continental fresh water wetland in the Sanjiang Plain, China. The objectives of this study were to provide baseline data on the ecology of testate amoebae in the peatlands of Northeast China and to assess the potential of using them as environmental indicators in this ecosystem. We examined modern testate amoeba assemblages and species-environmental relationships at 46 microsites within 5 waterlogged depressions. The environmental parameters measured included: depth to water table, pH, and loss on ignition. The results showed that the dominant species were Trinema complanatum type, Euglypha rotunda type, Euglypha strigosa type, and Centropyxis cassis type. Redundancy analysis demonstrates that water table depth has the most important effect on testate amoeba assemblages, explaining 16.7% (p = 0.002) of the total variance. pH was not a statistically significant factor for testate amoeba assemblages. Weighted averaging and weighted averaging partial least squares models were used to build transfer functions for depth to water table. The best performing transfer function was generated by the weighted averaging partial least squares model with an r 2 LOSO of 0.62 and RMSEPLOSO of 6.96 cm. Results indicate that testate amoebae in waterlogged depression peatland have the potential to be used as indicators for hydrological changes and for palaeohydrologic reconstructions in the Sanjiang Plain.

Salt-marsh testate amoebae as precise and widespread indicators of sea-level change

Twelve peat clasts were recovered from a paleochannel deposit on Skidaway Island, Chatham County, Georgia. An AMS radiocarbon date from a plant stem in one of these clasts indicates original peat deposition 36,830 ± 340 14C years B.P., and the stratigraphic position of the clasts supports this age assignment. Fossil Pinus needles, pollen, and testate amoebae provide a snapshot of the environment and biota at a time when most other sites in coastal Georgia were not accumulating sediment. Pollen from the peat clasts is dominated by Pinus and other genera common on the coastal plain today (e.g., Quercus , Carya ). Morphological and anatomical analyses of the fossil Pinus needles indicate they are either Pinus taeda or Pinus serotina , which both currently inhabit the Coastal Plain of Georgia. Seven testate amoeba taxa, all characteristic of relatively dry peatland conditions, were encountered in the clasts. Testate amoeba assemblages are dominated by Hyalosphenia subflava , a taxon that is not typically dominant in modern assemblages. More investigations describing the occurrence and distribution of Quaternary testate amoebae, as well as modern ecology and biogeography of testate amoebae, are necessary before the significance of these assemblages can be assessed fully. Deposition of the peat clasts occurred at a time when pollen evidence from Florida indicates warm and wet climatic conditions, and the paleoecology of the peat clasts indicates that a relatively warm climate also existed in coastal Georgia.

Sphagnum-dwelling Testate Amoebae in Subarctic Bogs are More Sensitive to Soil Warming in the Growing Season than in Winter: the Results of Eight-year Field Climate Manipulations

Testate amoebae are abundant in the surface layers of northern peatlands. Analysis of their fossilized shell (test) assemblages allows for reconstructions of local water-table depths (WTD). We have reconstructed WTD dynamics for five peat cores from peatlands ranging in distance from the Athabasca bituminous sands (ABS) region in western Canada. Amoeba assemblages were combined with plant macrofossil records, acid-insoluble ash (AIA) fluxes and instrumental climate data to identify drivers for environmental change. Two functional traits of testate amoebae, mixotrophy and the tendency to integrate xenogenic mineral matter in test construction, were quantified to infer possible effects of AIA flux on testate amoeba presence. Age-depth models showed the cores each covered at least the last ~315years, with some spanning the last millennium. Testate amoeba assemblages were likely affected by permafrost development in two of the peatlands, yet the most important shift in assemblages was detected after 1960 CE. This shift represents a significant apparent lowering of water tables in four out of five cores, with a mean drop of ~15cm. Over the last 50years, assemblages shifted towards more xerophilous taxa, a trend which was best explained by increasing Sphagnum s. Acutifolia and, to a lesser extent, mean summer temperature. This trend was most evident in the two cores from the sites located farthest away from the ABS region. AIA flux variations did not show a clear effect on mineral-agglutinating taxa, nor on S.s.Acutifolia presence. We therefore suggest the drying trend was forced by the establishment of S.s.Acutifolia, driven by enhanced productivity following regional warming. Such recent apparent drying of peatlands, which may only be reconstructed by appropriate indicators combined with high chronological control, may affect vulnerability to future burning and promote emissions of CO2 .

Summary 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. 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. 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 deep‐rooted vascular plants also showed that shallow‐rooted plants play a role on testate amoeba community structure at the ‘poor’ side of the gradient. 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. 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.

Knowledge of the effect of geographic factors on the assemblages of protozoan testate amoebae is still limited, despite there having been a number of studies on this fauna. We applied statistical analyses to data on the distribution of testate amoebae from nine major lakes in the Yunnan Plateau, southwest China. Cluster analysis, based on community structure, separated the lakes into two groups—the ligotrophic/mesotrophic lakes and the hypereutrophic lakes—confirming the idea that the testate amoebae assemblages in lakes are closely related to the trophic status. Additionally, within the oligotrophic/mesotrophic lakes, there was distinct geographic clustering. Linear regression analysis and the Mantel test both revealed that similarity of species composition decreased with increasing geographic distance among the oligotrophic/mesotrophic lakes.

Evaluating the potential of testate amoebae as indicators of hydrological conditions in boreal forested peatlands

Testate amoebae (Protozoa) were studied in spring, summer, and fall from the same microhabitats in a small Sphagnum-dominated peatland in southern Ontario, Canada. A total of 32 sampling stations were established in two wetland plant communities, 19 in an open Ericaceae low-shrub community and 13 in a closed Picea mariana and Larix laricina swamp community. Sphagnum was collected in each station for analysis of testate amoebae and measurement of soil water content parameters and water table depth in May, August, and October 2001. pH and dissolved oxygen of the groundwater under the Sphagnum were measured also. A total of 52 taxa including the rotifer, Habrotrocha angusticollis, were identified. Soil water content and water table variables emerged as the primary factors separating testate amoebae between the open bog/fen community and swamp community. Testate amoebae in the open bog/fen community showed a clear separation between the May sampling period and the August and October sampling periods. Sampling stations in May had much higher water table and were wetter than those in August and October. Conversely, testate amoebae in the swamp community did not show a clear difference between sampling periods. Soil moisture and water tables appear to be more constant in the swamp communities. Biological factors or other microscale environmental factors may need to be considered to explain seasonal changes in testate amoebae. A greater understanding of relationships between testate amoebae and microenvironmental factors is necessary to track seasonality in testate amoebae distributions.

The use of testate amoebae in studies of peatland hydrology and palaeohydrology has been increasing, and considerable efforts have been made over the past decade to standardise techniques as much as possible. In this article we briefly describe the common procedures used to collect, prepare and analyse testate amoebae in peat-based studies of palaeohydrology and palaeoclimatology. Although specific methods are dependent on the questions and objectives of individual studies, the methods presented here should serve as a good starting point for peatland palaeoenvironmental applications.