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The Quaternary glaciations profoundly shaped the biogeography of plants and animals, yet their impact on microbial eukaryotes remains largely unexplored. We tested the “genetic legacy of the Quaternary” (GLQ) paradigm in terrestrial protists using Arcellinida testate amoebae diversity distribution across the Iberian Peninsula, a well‐established glacial refugium. To do so, we compiled the most extensive Arcellinida metabarcoding dataset to date (ArKOI), including 615 samples from multiple continents and ecosystems. Our results showed that hotspots of intra‐OTU genetic diversity align with known Iberian refugia, supporting the concept of “refugia within refugia,” and displaying clear ecoregion‐specific climatic niches. Patterns of spatial clustering, niche breadth, and historical demographic reconstruction revealed repeated range contractions and expansions during the Pleistocene, mirroring those observed in macro‐organisms. These findings extend the GLQ paradigm to protists, highlighting shared historical and ecological processes across the eukaryotic tree of life and contributing to a unified theory of biogeographic responses to climatic change.

Climate change models point to a possible rise in air temperature, ranging from 2 °C to 4 °C. Global changes will therefore have a particularly pronounced effect on the functioning of shallow water bodies known as peat ponds, i.e., habitats formed after peat extraction in peatlands. However, the extent of this impact is still unknown. The main objective of the study was to determine the impact of water level and water physicochemical properties on the functioning of selected groups of aquatic organisms in peat ponds of different origins. The study was conducted in spring, summer and autumn of the years 2024 and 2025, in 10 peat ponds with different trophic status and typology, located in the Polesie National Park in eastern Poland. Considerable fluctuations in water levels, resulting from a scarcity of precipitation, accelerated the drying out and overgrowth of peat ponds, particularly the alkaline and acidic types. Within the zoocoenotic communities, a significant decline in the abundance of planktonic species and an increase in the abundance of littoral or periphytic species were recorded (F = 6.24, p < 0.015). Regarding trophic structure, an increase in the abundance of mixotrophic species and a decrease in the abundance of top-level predators were observed. Hydrological changes were reflected in an increase in species richness and abundance of communities of organisms with broad ecological tolerance (mainly ciliates), and a decrease in the number of species and abundance of planktonic crustaceans and macroinvertebrates. The RDA model explains over 84% of the total variability, indicating excellent model fit to the data and a strong correlation between environmental variables and species composition. Based on p values, water level, temperature, pH, and COD were selected as significant variables, with conductivity, O2, and Ptot demonstrating less statistical significance. Peat ponds ecosystems can serve as an excellent model system for studying the impact of intensifying climate change on the functioning of shallow water bodies.

Testate amoebae are known among the proxies for paleolimnological investigations but, despite their recognized importance and recent findings, they have not been sufficiently studied in alpine lakes, particularly in Europe. The present study analyzes fossil testate amoeba assemblages from the Upper Balma Lake (2216 m a.s.l., Western Alps, Italy) to reconstruct ecological changes over the past 1200 years. 21 species belonging to 5 genera were identified, with Centropyxis and Difflugia being the most abundant. Multivariate statistical analyses, combined with sedimentological and geochemical data, revealed five paleoenvironmental phases corresponding to known climatic events, including the Medieval Climate Anomaly, the Little Ice Age, and the Recent Warming period. Assemblage composition and diversity were related to grain size variations, nutrient input, and trace element concentrations (e.g., As, Mn, Mo) and periods of climatic stability were associated with higher biodiversity, while cold or disturbed intervals, marked by floods or sediment reworking, resulted in reduced abundances and diversity. In recent decades, a decline was observed for the genus Centropyxis , possibly indicating reduced oxygenation and changes in contaminant levels. Comparative analysis with the Lower Balma Lake, located downstream in the same area, highlighted the influence of morphological/hydrological differences between lakes on species distributions. The findings underscore the value of testate amoebae as sensitive bioindicators and their applicability in paleoecological reconstructions of alpine lakes. This study contributes to understanding long-term ecological responses to climate change and provides insights into flood regime variability in high-mountain environments.

Non-pollen palynomorphs (NPPs) are important ecological indicators and are increasingly used in the study of Arctic ice-wedge polygon mires in Siberia. This paper provides an overview of NPPs found in high-spatial-resolution (1 m sample distance) surface samples along transects crossing various polygon microtopographical elements, and in high-temporal-resolution (sample distance 0.5 cm) contiguous samples in peat profiles. Whereas algal palynomorphs - of e.g. Botryococcus, Pediastrum, and various Zygnemataceae - show a distinct presence in open water settings, testate amoebae tests - of Arcella, Assulina, and Amphitrema flavum - are typical for dry peatland settings such as polygon rims. Various other NPPs were encountered including types not yet described. The latter have been denominated using morphological terms to facilitate future identification. These types are often typical for distinct polygon microhabitats and thus have indicator values that allow the reconstruction of past ecological settings without knowing the taxa that produce them.

Peatlands are susceptible not only to direct disturbance, but also to indirect changes in their surroundings, including land management. Changes in agricultural practices or forest management can significantly influence peatland functioning, for example, their trophic status or surface vegetation. Here, we investigate the effects of planned forestry on two Sphagnum -dominated peatlands in northern Poland’s Tuchola Forest. We use testate amoebae and compare them to available pollen and historical data to reconstruct past environmental conditions and assess anthropogenic pressure. The Tuchola Forest has undergone significant transformations as a result of human activities, notably during Prussia’s promotion of pine monoculture in the 19th century. We hypothesized that forest management activities and other related disturbances have led to wetland acidification and water table alterations. Our results show that these changes have had profound effects on both peatlands. Radiocarbon dating revealed a correlation between forest management practices and peatland dynamics. Quantitative reconstructions based on testate amoebae showed that, as a result of the introduced pine monoculture, both peatlands experienced rapid acidification (pH levels dropping from ca. 6.2 to 3.5) and water table lowering of over 15 cm. The predominance of pine monoculture has not only reduced biodiversity but also enhanced the susceptibility of the forest to fires and pest outbreaks, further affecting peatland conditions. These findings contribute to understanding of how historical land-use changes continue to influence present-day peatland dynamics, offering insights into restoration and conservation efforts in forested peatland landscapes.

Peatlands have been among the world's fastest-disappearing ecosystems, facing human pressure, especially over the last two centuries. The drainage of peatlands has long been pursued to expand agricultural and forestry areas as well as for peat extraction. One of the most degraded peatlands in western Poland is the Bagno Chlebowo, of which a small part is legally protected, having a raised bog status. The peatland has been undergoing drainage and peat mining since the 19th century, and regardless of its partial protection since 1959, it continues to be subjected to drainage, further compromising the function of the nature reserve. Our research focuses on reconstructing the impact of anthropogenic pressure on the state of the peatland over the last 600 years. We applied palaeoecological methods to reconstruct changes in water table levels, acidity (pH) and local plant cover over time. Additionally, we utilized historical maps to gather data on the area's land use and land cover changes. Our findings reveal that drainage and peat harvesting significantly increased the pH level of the peatland, consequently promoting Sphagnum expansion. These recent changes in vegetation cover and increased acidity have led to inaccuracies in correctly identifying peatland type. Therefore, the palaeoecological record makes us question its current protection status as a true raised bog, suggesting that the site was a fen for most of the time of its functioning. We demonstrate that long-term reconstructions are, therefore, substantial for nature conservation to (1) properly assess the status of wetlands, (2) identify baseline conditions, and (3) plan suitable restoration and protection methods. • Drainage and peat extraction have altered peatland, revealing human impact on ecosystem. • Paleoecology offers insights into peatland changes and aids in setting restoration goals. • Overlooking ecological history may misclassify peatlands, stressing history's role in conservation. • Using outdated data in conservation plans may mislead efforts and harm fragile peatlands.

Due to the temperate and relative dry climate of south-eastern Australia, there are relatively few moisture-sensitive palaeoenvironmental records in the region. The region is of significance as it is influenced by several major ocean-atmospheric modes including El Niño–Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO). In this research we applied a transfer function between (sub)fossil testate amoebae and water table depth to consider local surface wetness, which may reflect effective moisture conditions, at Snowy Flat, a high-altitude Sphagnum -shrub bog in south-eastern Australia over the late Holocene. The reconstruction water table depth, covering the last ∼3100 cal yr B.P., suggested several distinct periods of enhanced surface wetness, perhaps reflecting moisture availability, including from 2400 to 2200, 1350–1100, 920–860 and 670 to 60 cal yr B.P.. After 1800 cal yr B.P., depth to water table (DWT) was more variable and followed well-known trends of the Northern Hemisphere including the Medieval Climatic Anomaly (MCA; increased DWT) and the Little Ice Age (LIA; decreased DWT). We also investigated the instrumental record of rainfall and found a significant negative relationship with the IPO and an IPO-like tripole spatial pattern between rainfall and sea surface temperatures in the Pacific Ocean. This suggests that the late Holocene hydroclimate at the Snowy Flat site, and across south-eastern Australia and more widely, can be related to the IPO and this is especially true after 1800 cal yr B.P. when the relationship apparently strengthened. The reconstruction also indicated that a positive IPO (El Niño-like) mean state prevailed in the MCA and a negative IPO (La Niña-like) mean state dominated the LIA. Surface moisture (DWT) was also related to total solar irradiance (from 10 Be in polar ice): periods of enhanced surface moisture (reduced DWT) (mean negative IPO states) coincided with minima (e.g. 920–860 and 670–60 ca. yr B.P.) and reduced moisture (increased DWT) coincided with maxima (e.g. 850–700 cal yr B.P.). Together these results shed further light on the variability of moisture in south-eastern Australia, and further afield, and the potential mechanisms for these. • Water table depth was reconstructed, over the last ∼3.1 ka, using testate amoeba. • Wetter periods were found 2500–2200, 1350–1100, 920–860 and 670–60 cal yr B.P. • The MCA/LIA were periods of reduced/enhanced moisture availability. • Enhanced moisture availability reflected negative IPO and lower solar irradiance.

High-latitude ecosystems are undergoing rapid ecological changes in response to climate warming. While some changes are well studied, the responses of microbial communities remain less understood. Testate amoebae, shell-producing protists well preserved in peat, provide a means to reconstruct past microbial dynamics. Mixotrophic taxa such as Archerella flavum host algal endosymbionts (zoochlorellae), allowing both heterotrophic and phototrophic energy acquisition. Previous work has demonstrated that these pathways result in different δ 13 C values. We applied a novel stable isotope approach to a peat core from the North Slope of Alaska to reconstruct changes in phototrophy by Archerella flavum . δ 13 C values were measured on Archerella flavum tests (i.e. shells) and Sphagnum , and a two-endmember mixing model was used to estimate relative usage of phototrophy through time. δ 13 C values were compared with testate amoeba community composition, test size, vegetation, and historical climate. Archerella flavum δ 13 C values were consistently more positive than Sphagnum δ 13 C values in the peat core, and patterns indicated greater phototrophy use after the late 1980s CE. This shift was followed by expansion of Archerella flavum populations and a trend of decreasing test length in several testate amoeba taxa. Increased phototrophy was associated with higher peat C:N ratios, indicating more oligotrophic conditions. From 2007 to 2019 CE, the length of the snow-free growing season was correlated with estimates of phototrophy usage, with more phototrophy during longer growing seasons. δ 13 C analyses of mixotrophic testate amoebae are a powerful tool for reconstructing microbial nutritional strategies and responses to past environmental change.

Functional traits provide key insights into ecological strategies and evolutionary diversification. In this study, we analyzed a comprehensive trait dataset to investigate morphological predictors of feeding ecology in testate amoebae from the Northern Holarctic realm, focusing on variability across 372 species. We also examined whether trait diversity mirrors taxonomic richness at the family level. Morphological traits included shell length, shell width, aperture dimensions, shape, and covering. The Principal Component Analysis (PCA) indicated that Axis 1 predominantly represented variation in shell and aperture size, while Axis 2 was associated with differences in overall shape proportions. Bacterivorous species exhibited the greatest morphological and taxonomic diversity, spanning 21 families and 48 genera, with mixotrophs and predators occupying nested subsets of their broader morphospace. The regression analyses demonstrated significant associations between species richness and variation in protective features, including aperture rim morphology and the presence of spines. Decision tree models identified the aperture width-to-length ratio as a key predictor of feeding strategy, although classification accuracy was lower for mixotrophs and predators. Future research should integrate shell morphology with phylogenetic data to enhance ecological strategy predictions in testate amoebae and explore hypotheses regarding functional diversification across a broader geographical scale and within different environments.

Abstract. The frequency of extreme events worldwide is steadily increasing. Therefore, it is crucial to recognize the accompanying response of different ecosystems. Monoculture tree plantations with simplified ecosystem linkages in food webs are particularly vulnerable to catastrophic events like fires, wind throws, droughts, and insect outbreaks. These events threaten forests and other associated ecosystems, including peatlands, which are extremely important in regulating the global carbon cycle and, thus, mitigating the effects of a warming climate. Here, we traced a 2000-year history of the Miały peatland, which is located in one of Poland's largest pine plantation complexes, and we examined how this peatland responded to some of the largest environmental disasters observed in the 20th century across central Europe: the 1922–1924 Panolis flammea outbreak and the 1992 fire. As a disturbance proxy, we used a multi-proxy palaeoecological analysis (plant macrofossils, testate amoebae, pollen, non-pollen palynomorphs, and micro- and macrocharcoal) supported by a neodymium isotope record. We showed several critical transitions in the peatland associated with extreme events and anthropogenic impacts, which triggered significant changes in the peatland's ecological status.