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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.

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.

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.

Abstract. Northern peatlands are significant terrestrial carbon stores but are increasingly threatened by human activities. Ombrotrophic peatlands, being naturally acidic, are particularly vulnerable to alkaline pollution. Despite their importance, the effects of alkalinisation on peatlands remain insufficiently studied. In Estonia, alkaline pollution from a cement industry and oil shale power plant emissions have degraded several peatlands since the 19th century. Although some sites have recovered in recent decades, more severely impacted areas remain in poor condition. We investigated the effects of alkalinisation on Varudi peatland, a forested site in northeast Estonia, which was exposed to 125 years of alkaline emissions from a nearby cement factory. Using a multi-proxy, high-resolution palaeoecological approach combined with a precise and reliable age-depth model, we reconstructed changes in environmental, chemical, botanical, and hydrological conditions over the past millennium. Our findings revealed three successional phases: during the mid-13th century CE, land clearance and increased mineral deposition caused the site to transition from a bog to a poor fen phase between approximately 1250–1570 CE; and while the cement factory operated without efficient filters, the site became a pine-dominated fen between 1871–1995. After the installation of filters in 1996, peatland pH returned to near pre-disturbance levels, and some recovery was observed. However, the site remains degraded. Our results indicate that alkalinisation significantly disrupts peatland functioning, reducing carbon storage and altering vegetation communities. These effects can persist for decades even after the source of contamination is removed, underscoring the need for more comprehensive monitoring of peatlands impacted by alkaline pollution globally.

The global nitrogen cycle has been majorly disrupted by anthropogenic activity. While nitrogen emissions in the UK and Ireland are declining, ammonia (NH 3 ) remains a significant exception. NH 3 emissions are mostly agriculturally sourced and deposited on nearby habitats at high rates in both countries. Peatlands are globally important wetlands that are vulnerable to NH 3 deposition. Essential peatland restoration risks being diminished by excessive NH 3 deposition, leading to the loss of valuable ecosystem services. This study investigates testate amoebae (indicators of contemporary and historic peatland conditions) as bioindicators of seasonal NH 3 deposition on six peatlands across Northern Ireland, UK. Sphagnum , an NH 3 -sensitive bryophyte, was sampled adjacent to NH 3 monitoring sites once per season for a year. When NH 3 deposition was critically high, multivariate analysis demonstrates a link between NH 3 and testate amoebae assemblage change. Similarly, at high NH 3 deposition sites, testate amoebae taxa diversity is observed to be significantly reduced in springtime, when it is expected to be highest. Although, in response to high NH 3 deposition large algivorous taxa do not proliferate as was anticipated, and mixotrophic taxa abundance decreases could not be linked primarily to NH 3 . This research demonstrates the continued potential of testate amoebae as highly informative peatland bioindicators. • The first field study focussing on testate amoebae as bioindicators of seasonal NH 3 deposition on peatland ecosystems. • Multivariate analysis of testate amoebae assemblages showed critically high ammonia deposition in four lowland raised bogs. • Testate amoebae diversity was found to be unseasonably low during spring in critically high ammonia deposition sites. • A decline in mixotrophic testate amoebae was observed during the summer sampling period. • A hypothesised increase in large algivorous taxa in response to rising NH 3 deposition was not evident in this study.

Testate amoebae are widely used paleoindicators of past environmental conditions, particularly in peatlands where they have been used as surface-moisture proxies. Modern ecological studies of the past several decades inform the interpretation of stratigraphic records, and increasingly both modern surface-sample datasets and stratigraphic records are being added to publicly available databases like the Neotoma Paleoecology Database. In this paper, we broadly synthesize results of calibration studies during the past ∼35 years, and then use data from the Neotoma Paleoecology Database to examine morphospecies-environment relationships in calibration datasets from the northern hemisphere and directly compare subfossil and modern testate amoeba communities to assess the strength of modern analogues for subfossil samples in North American stratigraphic records. Results confirm the consistent and central importance of surface-moisture in controlling testate amoeba communities in peatlands, with similar community-moisture relationships across the Northern Hemisphere. However, many subfossil communities have few good modern analogues, likely due to a combination of factors including differential decomposition of taxa extending beyond the well-documented poor preservation of weakly idiosomic tests. Many subfossil samples contain high abundances and unusual combinations of taxa that are not well represented in modern datasets, and the causes and implications of subfossil communities with poor modern analogues deserve greater attention by the research community. The Neotoma Paleoecology Database is a valuable shared resource, and its continued development will enable the examination of research questions focused on understanding the variability and structure of modern and subfossil testate amoeba communities, as well as moisture reconstructions in both time and space. • Surface-moisture is a critical control on the composition of testate amoeba communities in peatlands. • Similar community-moisture relationships occur across the Northern Hemisphere. • Many subfossil communities have few good modern analogues. • Differential decomposition of taxa likely extends beyond the well-documented poor preservation of weakly idiosomic tests. • Causes and implications of subfossil communities with poor modern analogues deserve greater attention.

Urban waters play a crucial role in biodiversity conservation and the provision of ecosystem services. However, the drivers of changes in these habitats remain poorly understood. This study investigates the determinants of microbial community dynamics along a 0.14 km heatwave-impacted hydrological gradient formed by three connected urban ponds in Shenzhen, southern China. The experimentation focused on extremely sensitive microorganisms, testate amoebae, using 30 water samples representing water columns, 30 sediment samples representing beds, and 27 microspatial factors that capture weather conditions (WC), air quality (AQ), and water quality (WQ). Both environmental conditions and testate amoeba communities varied significantly along the heatwave-impacted hydrological gradient. A total of 39 species were recorded, marking a net increase of 5 species relative to the pre-heatwave period (June–July 2020). The mean species richness was 9 ± 1 in water and 16 ± 1 in sediment. The mean absolute abundance reached 30 ± 5 ind. mL⁻¹ in water and 2500 ± 430 ind. mL⁻¹ in sediment. Water depth and pH emerged as the most influential factors, with water depth explaining 12.4% of the total variation in testate amoeba species in water and pH accounting for 21.8% of the total variation in sediment. The variation partitioning analysis (VPA) revealed that WC, AQ, and WQ substantially influenced testate amoeba communities in sediment, accounting for 11%, 20%, and 15.5%, respectively, based on the pure percentage of community variation. Mechanistically, community changes were driven by warming-induced physiological changes, toxicity-induced stress, and hypoxia-induced stress. The neutral model explained 78.8% in water and 69.3% in sediment. Standardized effect sizes (SES) for the checkerboard score (C-score) in the null model were 0.732 (21.2%) in water and 4.437 (30.7%) in sediment, indicating that stochastic processes have a stronger influence on testate amoeba community composition than deterministic ones. These results suggest that determinants of testate amoeba community dynamics in urban waters involve both predictable factors, such as heatwaves, air pollution, and hydrological gradient (deterministic processes), and unpredictable factors, such as dispersal limitation, ecological drift, and homogenizing dispersal (stochastic processes).

Peatlands are globally-important carbon sinks at risk of degradation from climate change and direct human impacts, including drainage and burning. Peat accumulates when there is a positive mass balance between plant productivity inputs and litter/peat decomposition losses. However, the factors influencing the rate of peat accumulation over time are still poorly understood. We examine apparent peat accumulation rates (aPAR) during the last two millennia from 28 well-dated, intact European peatlands and find a range of between 0.005 and 0.448 cm yr^-1 (mean = 0.118 cm yr^-1). Our work provides important context for the commonplace assertion that European peatlands accumulate at ~0.1 cm per year. The highest aPAR values are found in the Scandinavian and Baltic regions, in contrast to Britain, Ireland, and Continental Europe. We find that summer temperature is a significant climatic control on aPAR across our European sites. Furthermore, a significant relationship is observed between aPAR and water-table depth (reconstructed from testate-amoeba subfossils), suggesting that higher aPAR levels are often associated with wetter conditions. We also note that the highest values of aPAR are found when the water table is within 5–10 cm of the peatland surface. aPAR is generally low when water table depths are < 0 cm (standing water) or > 25 cm, which may relate to a decrease in plant productivity and increased decomposition losses, respectively. Model fitting indicates that the optimal water table depth (WTD) for maximum aPAR is ~10 cm. Our study suggests that, in some European peatlands, higher summer temperatures may enhance growth rates, but only if a sufficiently high water table is maintained. In addition, our findings corroborate contemporary observational and experimental studies that have suggested an average water-table depth of ~10 cm is optimal to enable rapid peat growth and therefore carbon sequestration in the long term. This has important implications for peatland restoration and rewetting strategies, in global efforts to mitigate climate change.

Testate amoebae are a valuable group of species for biogeographic research. Current knowledge about the distribution of testate amoebae in the aquatic habitats Arctic is incomplete. In this study, we present the first report on testate amoebae from ponds of eastern part of Chukotka in the Arctic. Testate amoebae were studied in 11 ponds on the coast of Anadyr Bay of the Bering Sea. We identified 46 species belonging to 15 genera, among which Difflugia lobostoma, Netzelia gramen, and Cucurbitella mespiliformis were found in Arctic for the first time. Most common genera in ponds were Difflugia, Centropyxis, and Arcella. This genera structure is similar to that in lacustrine in the temperate climatic zone, but differed from genera structure described in Devon Island, Greenland, and Spitsbergen. Species structure of assemblages differed from that in both aquatic habitats from temperate zone and in other Arctic aquatic habitats. These results are consistent with the concept of a regionalized distribution of testate amoebae in the Arctic and provide new information on the species and genus distribution and species structure of testate amoebae communities from aquatic habitats in the Arctic.