A novel testate amoebae trait-based approach to infer environmental disturbance in Sphagnum peatlands

Biomonitoring tool for New Zealand peatlands: Testate amoebae and vascular plants as promising bioindicators

In the last two centuries, a high proportion of peatlands have been lost or severely degraded across the world. The value of peatlands is now well-recognised for biodiversity conservation, flood management, and carbon mitigation, with peatland restoration now central to many government policies for climate action. A challenge, however, is to determine 'natural' and 'disturbed' conditions of peatlands to establish realistic baselines for assessing degradation and setting restoration targets. This requires a tool or set of tools that can rapidly and reliably capture peatland condition across space and time. Our aim was to develop such a tool based on combined analysis of plant and testate amoebae; a group of shelled protists commonly used as indicators of ecological change in peatlands. The value of testate amoebae is well established in Northern Hemisphere Sphagnum-dominated peatlands; however, relatively little work has been undertaken for Southern Hemisphere peat forming systems. Here we provide the first assessment and comparison of the bioindicator value of testate amoebae and vascular plants in the context of Southern Hemisphere peatlands. Our results further demonstrate the unique ecohydrological dynamics at play in New Zealand peat forming systems that set them apart from Northern Hemisphere peatlands. Our results show that plant and testate amoeba communities provided valuable information on peatland condition at different scales, we found that testate amoebae tracked changes in the abiotic variables (depth to water table, pH, and conductivity) more closely than vascular plants. Our results further demonstrate that functional traits of testate amoebae showed promising relationships with disturbance. Amoeba test compression, aperture position and test size were linked to changes in hydrology driven by fluctuations in ground water tables; however, trait responses manifested differently in ombrotrophic and minerotrophic peatlands. Overall, testate amoebae provide a promising bioindicator for tracking degradation in New Zealand peatlands and a potential additional tool to assess peatland condition.

Protist Diversity Responses to Experimental N Deposition in Biological Crusts of a Semiarid Mediterranean Ecosystem

Biological soil crusts (BSC) are associations of different macro and microorganisms and aggregated soil particles located on the surface of soils in many different habitats. BSC harbour a diverse and complex community of ciliates and testate amoebae. These phagotrophic protists play an important role in C and N recycling in soil ecosystems but have not been frequently studied in BSC. In this context, the effects of three increasing N inputs on ciliates and testate amoebae in crusts from a semi-arid Mediterranean ecosystem were evaluated. A field experiment with artificial N-deposition was designed to mimic the effects caused by anthropogenic N depositions. The results have shown that the protist populations of these semi-arid Mediterranean environments have lower species richness than other soil environments. The increase in N produces a net loss of diversity in the populations studied and shifts in the community structure. It has also been shown that some ciliates and testate amoebae, due to their population responses to increased N concentrations, could potentially be used as bio-indicators of N contamination in these BSCs.

Anthropocene history of rich fen acidification in W Poland - Causes and indicators of change

In the time of the global climate crisis, it is vital to protect and restore peatlands to maintain their functioning as carbon sinks. Otherwise, their transformations may trigger a shift to a carbon source state and further contribute to global warming. In this study, we focused on eutrophication, which resulted in the transition from rich fen to poor fen conditions on the Kazanie fen (central Greater Poland, western Poland Central Europe). The prior aim was to decipher how i) climate, ii) human, and iii) autogenic processes influenced the pathway of peatland changes in the last ca. 250 years. We applied a high-resolution palaeoecological analysis, based mainly on testate amoebae (TA) and plant macroremains. Our results imply that before ca. 1950 CE, dry shifts on the fen were generally climate-induced. Later, autogenic processes, human pressure and climate warming synergistically affected the fen, contributing to its transition to poor fen within ca. 30 years. Its establishment not only caused changes in vegetation but also altered TA taxonomic content and resulted in a lower diversity of TA. According to our research Microchlamyspatella is an incredibly sensitive testate amoeba that after ca. 200 years of presence, disappeared within 2 years due to changes in water and nutrient conditions. As a whole, our study provides a long-term background that is desired in modern conservation studies and might be used to define future restoration targets. It also confirms the already described negative consequences connected with unsustainable exploitation of nature.

Diversity of Testate Amoebae as an Indicator of the Conservation Status of Peatlands in Southwest Europe

Testate amoebae are one of the most studied groups of microorganisms in Sphagnum peatland ecosystems and, therefore, one of the most reliable bioindicators of their ecological status. Peatland ecosystems are supported by a delicate biogeochemical balance that leads to the formation of peat, one of the main sinks of C, as a result of soil–atmosphere interaction, but currently they are one of the most threatened wetland types at their southern distribution limit. In the European continent, where climatic conditions limit peat formation, they have endured significant anthropic pressure for centuries, and the risk of loss of biodiversity linked to these ecosystems is critical. In addition, peatlands are poorly known ecosystems in the Iberian Peninsula compared with other wetlands; therefore, we have studied the chemical parameters of water and the diversity patterns of testate amoebae in the western Iberian Peninsula to better understand the current status of these ecosystems. The analysis of testate amoeba communities showed an inverse relationship between the diversity and conservation status of these peatlands, both in relation to chemical parameters (i.e., pH, electrical conductivity, phosphates) and to the proportion of anthropized area, with a marked geographical pattern in the degree of anthropogenic disturbance.

Freshwater Testate Amoebae (Arcellinida) Response to Eutrophication as Revealed by Test Size and Shape Indices

We review the potential for applying traits-based approaches to freshwater testate amoeba, a diverse protist group that are abundant in lakes and are valuable ecological indicators. We investigated the efficacy of geometric morphometric analysis to define Arcellinida test size and shape indices that could summarize freshwater testate amoeba community dynamics along a temporal gradient of eutrophication in Loch Leven, Scotland (United Kingdom). A cluster analysis of test size and shape indices yielded three clusters, each dominated by a single shape: elongate, spherical and ovoid. When plotted stratigraphically, we observed increases in spherical tests, decreases in elongate tests and shrinking of test size coeval with eutrophication in Loch Leven. Decreases in the elongate cluster may reflect benthic conditions with reduced oxygen levels, while increases in the spherical cluster are likely associated with an expanding macrophyte community that promoted pelagic and epibiotic life habits. Shrinking of test size may be a stress response to eutrophication and/or warming temperatures. Tracking community dynamics using test size and shape indices was found to be as effective as using species-based approaches to summarize key palaeolimnological changes, with the added benefits of being free from taxonomic bias and error. The approach thus shows significant potential for future studies of aquatic community change in nutrient impacted lakes.

Molecular investigation of Phryganella acropodia Hertwig et Lesser, 1874 (Arcellinida, Amoebozoa)

Phryganella acropodia Hertwig and Lesser, 1874, is one of the most common and abundant testate amoeba species. It represents the type species of the genus Phryganella Penard, 1902, which in turn is the type genus for the suborder Phryganellina (Arcellinida) Bovee, 1985, but despite its taxonomic importance it was not yet analyzed with molecular methods. We established two cultures of putative Phryganella acropodia, designed Phryganellina-specific primers, amplified SSU rDNA data and subjected these sequences to phylogenetic analyses. Morphological and genetic differences were found between both strains. With SSU rDNA phylogenetic analyses we confirm that Phryganella acropodia branches with Phryganella paradoxa Penard, 1902 and Cryptodifflugia Penard, 1890 in the Phryganellina. We thus give further evidence that pseudopodia morphology in the Arcellinida is a character of high taxonomic value, as suggested by Bovee and Jung when erecting the suborder Phryganellina. Moreover, we provide evidence for cryptic diversity and for the first time confirm the existence of a naked life stage in Arcellinida by molecular means.

Testate amoebae taxonomy and trait diversity are coupled along an openness and wetness gradient in pine-dominated Baltic bogs

Sphagnum peatlands host a high abundance of protists, especially testate amoebae. Here, we designed a study to investigate the functional diversity of testate amoebae in relation to wetness and forest cover in Baltic bogs. We provided new data on the influence of openness/wetness gradient on testate amoebae communities, showing significant differences in selected testate amoebae (TA) traits. Three key messages emerged from our investigations: 1) we recorded an effect of peatland surface openness on testate amoebae functional traits that led us to accept the hypothesis that TA traits differ according to light intensity and hydrology. Mixotrophic species were recorded in high relative abundance in open plots, whereas they were nearly absent in forested sites; 2) we revealed a hydrological threshold for the occurrence of mixotrophic testate amoebae that might be very important in terms of peatland functioning and carbon sink vs. source context; and 3) mixotrophic species with organic tests were nearly absent in forested sites that were dominated by heterotrophic species with agglutinated or idiosomic tests. An important message from this study is that taxonomy of TA rather indicates the hydrological gradient whereas traits of mixotrophs the openness gradient.

Human-induced fire regime shifts during 19th century industrialization: A robust fire regime reconstruction using northern Polish lake sediments

Fire regime shifts are driven by climate and natural vegetation changes, but can be strongly affected by human land management. Yet, it is poorly known how humans have influenced fire regimes prior to active wildfire suppression. Among the last 250 years, the human contribution to the global increase in fire occurrence during the mid-19^th century is especially unclear, as data sources are limited. Here, we test the extent to which forest management has driven fire regime shifts in a temperate forest landscape. We combine multiple fire proxies (macroscopic charcoal and fire-related biomarkers) derived from highly resolved lake sediments (i.e., 3–5 years per sample), and apply a new statistical approach to classify source area- and temperature-specific fire regimes (biomass burnt, fire episodes). We compare these records with independent climate and vegetation reconstructions. We find two prominent fire regime shifts during the 19^th and 20^th centuries, driven by an adaptive socio-ecological cycle in human forest management. Although individual fire episodes were triggered mainly by arson (as described in historical documents) during dry summers, the biomass burnt increased unintentionally during the mid-19^th century due to the plantation of flammable, fast-growing pine tree monocultures needed for industrialization. State forest management reacted with active fire management and suppression during the 20^th century. However, pine cover has been increasing since the 1990s and climate projections predict increasingly dry conditions, suggesting a renewed need for adaptations to reduce the increasing fire risk.

Metatranscriptomics reveals unsuspected protistan diversity in leaf litter across temperate beech forests, with Amoebozoa the dominating lineage

Forest litter harbors complex networks of microorganisms whose major components are bacteria, fungi and protists. Protists, being highly selective consumers of bacteria and fungi could influence decomposition processes by shifting competitive microbial interactions. We investigated the eukaryotic diversity from 18 samples of one-year beech (Fagus sylvatica) leaf litter by RNA-based high-throughput sequencing of the small-subunit ribosomal RNA gene. By applying a metatranscriptomics approach, we avoided biases inherent to PCR-based methods, and could therefore focus on elusive protistan groups. We obtained 14 589 eukaryotic assembled sequences (contigs) representing 2223 unique taxa. Fungi dominated the eukaryotic assemblage, followed by an equal proportion of protists and plants. Among protists, the phylum Amoebozoa clearly dominated, representing more than twice the proportion of Alveolata (mostly ciliates) and Rhizaria (mostly Cercozoa), which are often retrieved as the dominant protistan groups in soils, revealing potential primer biases. By assigning functional traits to protists, we could assess that the proportion of free-living and heterotrophs was much higher than that of parasites and autotrophs, opening the way to a better understanding of the role played by the protistan communities and how biodiversity interacts with decomposition processes.

Small-scale Variation of Testate Amoeba Assemblages: the Effect of Site Heterogeneity and Empty Shell Inclusion

Studies on testate amoeba species distribution at small scales (i.e., single peatland sites) are rare and mostly focus on bogs or mineral-poor Sphagnum fens, leaving spatial patterns within mineral-rich fens completely unexplored. In this study, two mineral-rich fen sites of contrasting groundwater chemistry and moss layer composition were selected for the analysis of testate amoeba compositional variance within a single site. At each study site, samples from 20 randomly chosen moss-dominated plots were collected with several environmental variables being measured at each sampling spot. We also distinguished between empty shells and living individuals to evaluate the effect of empty shell inclusion on recorded species distribution. At the heterogeneous-rich Sphagnum-fen, a clear composition turnover in testate amoebae between Sphagnum-dominated and brown moss-dominated samples was closely related to water pH, temperature and redox potential. We also found notable species composition variance within the homogeneous calcareous fen, yet it was not as high as for the former site and the likely drivers of community assembly remained unidentified. The exclusion of empty shells provided more accurate data on species distribution as well as their relationship with some environmental variables, particularly moisture. Small-scale variability in species composition of communities seems to be a worthwhile aspect in testate amoeba research and should be considered in future sampling strategies along with a possible empty shell bias for more precise understanding of testate amoeba ecology and paleoecology.

Testate amoeba records indicate regional 20th-century lowering of water tables in ombrotrophic peatlands in central-northern Alberta, Canada

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 ~315 years, 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 ~15 cm. Over the last 50 years, 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 .