Biogeography of testate amoebae in the soils of Mexico

We studied testate amoebae (testates) in the soils of coniferous and deciduous forests and in the wetland and aquatic habitats of Mexico. In 141 samples we found 205 taxa identified to the species or intraspecies level and 68 testate amoebae, which could not be identified to the species level. The highest species diversity of testates was found in the soils of the tropical rainforest (126 species and intraspecific taxa, including spp.) and in tropical wetlands (144 species and intraspecific taxa, including spp.). The study documented testate amoebae with a limited geographical distribution (genera Centropyxis, Cornuapyxis, Ellipsopyxis, Hoogenraadia, Planhoogenraadia, Apolimia, Certesella, Apodera, and Alocodera). We found that testate amoebae in the soils of Mexico had a high level of polymorphism and individual variability. We discuss the value of soil testate amoebae for defining biogeographical regions of Mexico.     

Testate amoebae communities in the southern tundra and forest-tundra of Western Siberia

The species composition and community structure of soil-inhabiting testate amoebae communities have been studied in biotopes of different types in the southern tundra and forest-tundra of the Tazovskaya Lowland, Western Siberia. A total of 93 species and forms have been identified. It has been found that the species richness of testate amoebae is much lower in dry than in moist biotopes due to a lower level of beta-diversity, with alpha diversity being the same (on average, 16.9 and 17.1 species per sample, respectively). Factors acting at the microbiotope level (biotope type and moisture) play the most important role in the formation of species richness; biotope features (soils and vegetation) are second in importance. In moist habitats, local communities of testate amoebae from different microbiotopes (mosses, lichens, or litter) are fairly similar in species structure, and communities from different moist biotopes are heterogeneous. In dry areas, the opposite situation is observed: local communities differ at the microbiotope level but are similar at the biotope level. The abundance of testate amoebae in moist biotopes reaches 200 × 10³ ind./g dry soil, being an order of magnitude lower in dry biotopes.     

Light variability and mixotrophy: Responses of testate amoeba communities and shell δ13C values to a peatland shading experiment

Paleoecological records suggest that growing season length and/or cloudiness may affect peatland carbon accumulation and testate amoeba-based environmental reconstructions, highlighting a need to understand how light intensity affects microbial communities. We shaded plots on two peatlands for two years to examine effects on testate amoeba communities, the relative abundance of mixotrophic and heterotrophic testate amoebae, transfer-function performance, and δ¹³C values of two species of mixotrophic testate amoebae. Surprisingly, relative abundance of mixotrophic species increased in shade, although compositional changes did not affect transfer-function performance. Shading did not affect δ¹³C values of Hyalosphenia papilio and Heleopera sphagni, which ranged from −23.5 to −19.6‰ and −23.2 to −19.2‰, respectively. These δ¹³C values were higher than those of potential food sources and lower than literature-derived values for Chlorella, the zoochlorellae inhabiting mixotrophic testate amoebae. δ¹³C values thus suggest that these mixotrophic species obtain some carbon from Chlorella, although coupled dietary and isotope studies are needed to quantify this contribution. More research is needed to assess impacts of light variability on peatland microbial communities; however, carbon sources are recorded by δ¹³C values of testate amoebae, indicating potential for studies of carbon cycling and how mixotrophy varies temporally and spatially.     

Species composition and structure of testate amoebae community in a sphagnum bog at the initial stage of its formation

A total of 42 species and forms have been revealed in the testate amoebae community of a transitional bog at the initial stage of transformation into a typical sphagnum bog. A distinctive features of its species composition is dominance of widespread species Assulina muscorum, Arcella arenaria, Phryganella hemisphaerica, and Euglypha laevis in the absence of common sphagnobionts of the genera Nebela, Hyalosphenia, and Heleopera. Vertical heterogeneity of the community structure is weakly manifested, since dominant species are abundant in all horizons. The highest species richness is characteristic of the marginal community formed at the boundary between a sphagnum quagmire and a reed grass-dominated fen.     

Diversity and Distribution of Freshwater Testate Amoebae (Protozoa) Along Latitudinal and Trophic Gradients in China

Freshwater microbial diversity is subject to multiple stressors in the Anthropocene epoch. However, the effects of climate changes and human activities on freshwater protozoa remain poorly understood. In this study, the diversity and distribution of testate amoebae from the surface sediments were investigated in 51 Chinese lakes and reservoirs along two gradients, latitude and trophic status. A total of 169 taxa belonging to 24 genera were identified, and the most diverse and dominant genera were Difflugia (78 taxa), Centropyxis (26 taxa) and Arcella (12 taxa). Our analysis revealed that biomass of testate amoebae decreased significantly along the latitudinal gradient, while Shannon-Wiener indices and species richness presented an opposite trend (P?P?相似文献   

Distribution of soil-inhabiting testate amoebae along a mountain slope (Baikal Lake region, Khamar-Daban ridge, Cherskii peak)

The specific composition and distribution of soil-inhabiting testate amoebae along the Cherskii peak slope (Khamar-Daban mountain ridge, Lake Baikal region) were studied within the altitude range from 1000 to 1570 m above sea level according to the changes in biogeocenoses from birch-aspen to cedar-fir forests to cedar-fir-bush forest-tundra. One-hundred-four taxa were identified. The most common species are ubiquits with a wide geographical distribution: Trinema lineare, Euglypha levis, Euglypha rotunda, Trinema enchelys, Phryganella acropodia, Tracheleuglypha dentata, Assulina muscorum, Trinema complanatum, and Centropyxis aerophila. The species richness varies from 12 to 40 species per sample, and the abundance varies from 500 to 120000 ind. per gram of absolutely dry soil. The spatial heterogeneity of the specific composition grows with altitude, and the community composition changes. The absence of a common pattern in the cenotic changes in the communities of testate amoebae in Western Europe and the Lake Baikal region is discussed.     

Testate amoebae community structure in the moss biotopes of streams

The specific composition and community structure of testate amoebae in the moss biotopes of streams were studied in the Sura River basin (Middle Volga region). Twenty-nine species and forms were identified. The eurybiont species Trinema enchelys, Euglypha ciliata glabra, Centropyxis aerophila, Tracheleuglypha dentata, Crythion dubium, Centropyxis cassis, Trinema complanatum, and Trinema lineare are dominant. The species richness varies from 2 to 11 species per sample, the abundance is 100 to 4000 ind./g of absolutely dry moss. The degree of forest covering in the basin, hydrochemical peculiarities (the amount of biogenic elements and water hardness) of streams, the size of streams, and environmental contamination are possible factors that determine the specific character of the composition and structure of testate amoebae communities.     

The Impact of Simulated Sulfate Deposition on Peatland Testate Amoebae

Peatlands subjected to sulfate deposition have been shown to produce less methane, believed to be due to competitive exclusion of methanogenic archaea by sulfate-reducing bacteria. Here, we address whether sulfate deposition produces impacts on a higher microbial group, the testate amoebae. Sodium sulfate was applied to experimental plots on a Scottish peatland and samples extracted after a period of more than 10 years. Impacts on testate amoebae were tested using redundancy analysis and Mann–Whitney tests. Results showed statistically significant impacts on amoebae communities particularly noted by decreased abundance of Trinema lineare, Corythion dubium, and Euglypha rotunda. As the species most reduced in abundance are all small bacterivores we suggest that our results support the hypothesis of a shift in dominant prokaryotes, although other explanations are possible. Our results demonstrate the sensitivity of peatland microbial communities to sulfate deposition and suggest sulfate may be a potentially important secondary control on testate amoebae communities.     

Are soil biota buffered against climatic extremes? An experimental test on testate amoebae in arctic tundra (Qeqertarsuaq,West Greenland)

Climate warming is likely to have pronounced impacts on soil biota in arctic ecosystems. In a warmer climate, heatwaves are more frequent and intense, but it is unclear to what extent soil communities are buffered against this. We studied the effects of an artificially induced heatwave on the structure of testate amoebae communities in dry heath tundra in Qeqertarsuaq (Disko Island, West Greenland) during the summer of 2003. While the heatwave was severe enough to induce significant leaf mortality in the aboveground vegetation, overall testate amoebae abundance did not react to the difference in temperature. However, in the heated plots transient shifts in species populations occurred during the exposure, followed by increases in species richness weeks after the heatwave had ended. The most important taxa appearing after the heating period belonged to bacterivorous genera, in agreement with a transient peak in bacterial colony forming units, caused by the heatwave. Lobose testate amoebae resisted the heating and its associated desiccation better than their filose counterparts.     

Flourish or Flush: Effects of Simulated Extreme Rainfall Events on Sphagnum-dwelling Testate Amoebae in a Subarctic Bog (Abisko, Sweden)

Extreme precipitation events are recognised as important drivers of ecosystem responses to climate change and can considerably affect high-latitude ombrotrophic bogs. Therefore, understanding the relationships between increased rainfall and the biotic components of these ecosystems is necessary for an estimation of climate change impacts. We studied overall effects of increased magnitude, intensity and frequency of rainfall on assemblages of Sphagnum-dwelling testate amoebae in a field climate manipulation experiment located in a relatively dry subarctic bog (Abisko, Sweden). The effects of the treatment were estimated using abundance, species diversity and structure of living and empty shell assemblages of testate amoebae in living and decaying layers of Sphagnum. Our results show that increased rainfall reduced the mean abundance and species richness of living testate amoebae. Besides, the treatment affected species structure of both living and empty shell assemblages, reducing proportions of hydrophilous species. The effects are counterintuitive as increased precipitation-related substrate moisture was expected to have opposite effects on testate amoeba assemblages in relatively dry biotopes. Therefore, we conclude that other rainfall-related factors such as increased infiltration rates and frequency of environmental disturbances can also affect testate amoeba assemblages in Sphagnum and that hydrophilous species are particularly sensitive to variation in these environmental variables.     

Relationship Between Testate Amoeba (Protist) Communities and Atmospheric Heavy Metals Accumulated in <Emphasis Type="Italic">Barbula indica</Emphasis> (Bryophyta) in Vietnam

We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H′ was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.     

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.     

TESTATE AMOEBAE FROM THE EARLY JURASSIC OF THE WESTERN TETHYS,NORTH‐EAST ITALY

Abstract: Fossil testate amoebae and their non‐marine finds are rare so their ecological importance through Earth history is poorly understood. The Lower Jurassic shallow water black‐shales of Trento Platform (north‐east Italy) are rich in micro‐organisms and contain a thecamoebian and ostracod assemblage representing the first known record of Early Jurassic oligohaline forms from the European mainland. The thecamoebians are represented by the genera Difflugia, Pontigulasia and Centropyxis. The present discovery of Lower Jurassic thecamoebians in fine carbonate organic‐rich deposits indicates, for the first time, that these sediments can preserve testate amoebae very well. The occurrence of difflugid testate amoebians confirm a transitional marine‐terrestrial habitat, outside large bodies of water, and suggests occasional eutrophication in ephemeral restricted aquatic environment in the Sinemurian–Pliensbachian Trento Platform.     

Does microhabitat influence the testate amoebae communities in the Nameri National Park,northeastern India? A tropical forest perspective

The community structure of testate amoebae inhabiting different microhabitats (soil and tree-moss) within a tropical forest biome in Nameri National Park, northeastern India, was investigated. A total of 33 testate amoebae species belonging to 13 genera were identified. Species belonging to the class Lobosea constituted 73% of total testate amoebae density in the soil habitat, whereas the class Filosea constituted the most dominant forms (58%) in the moist tree-moss habitat. The relative abundance of species was higher in the tree-moss habitat compared to the soil habitats of the forest. Although multivariate analysis suggested a significant difference in assemblage patterns between the habitats, the turnover in species (i.e., beta diversity) was insignificant. Species accumulation curves (SAC) constructed using both parametric and non-parametric species richness estimators revealed that the asymptote of species richness was achieved by a low number of sample replicates in both habitats. The temperature and pH of the substratum on testate amoebae distribution patterns suggest the importance of additional background factors on testate amoebae community structure. Further studies involving more biotopes, seasons, and trophic interactions are recommended to document a complete record of testate amoebae diversity and their interactions with environmental gradients in the tropical forest biomes of northeastern India.     

Structure of a community of testate amoebae in a sphagnum dominated bog in upper sura flow (Middle Volga Territory)

Fifty nine species of testate amoebae were found in a sphagnum moss bog located in the upper Sura flow (Volga highland). The active diversity in communities of sphagnum moss biotopes was formed by 24 species. Minimal species diversity (3 species) and maximum density of organisms were noted in the driest habitat. In the habitats with the medium humidity levels, the level of species richness was similar (13–16 species) and the total density was determined by redox characteristics of the environment: under the conditions of oxygen deficit, it was two to three times lower than in an oxidized environment. The species composition specificity in sphagnum moss biotopes was determined by the degree of humidity: in the driest habitats, Arcella arenaria predominated; in the biotopes with medium humidity, Nebela tenella and Hyalosphenia elegans; and in the most humid biotopes, Hyalosphenia papilio and Heleopera sphagni. Communities of testate amoebae differed by species composition and integral characteristics at different sphagnum moss horizons: the abundance and species richness increased with depth. The proportion of living individuals in the total number of tests was 35 to 75%.     

Diversity of Antarctic terrestrial protozoa

Heterotrophic protozoa have a global distribution in terrestrial habitats. The functional groups significantly represented are zooflagellates, cillates, gymnamoebae and testate amoebae. Their range extends into the Antarctic zone, but the species richness of the communities is rarely of the same order of magnitude as those in temperate latitudes. Species diversity is usually very low owing to dominance of the communities by single, or a few, species which are best adapted to the Antarctic terrestrial environment. This is characterized by seasonal, diurnal or unpredictable fluctuations in moisture, temperature and bacterial food supply of high amplitude. The fauna shows pauperization with latitude and climatic severity. Nearly all records of species distribution are consistent with the model that community composition is determined by local conditions. An important exception is the distribution of the testate amoeba genus Nebela whose species distribution is influenced by biogeographical factors. Successional changes in community composition in fellfield habitats are characterized by the sequence: pioneer microflagellate colonizers, larger flagellates and small ciliates, and finally testate amoebae. The succession is most closely correlated with the accumulation of organic matter. A model of the strategies of dominant microflagellate species can be constructed by ordinating them on a two-dimensional habitat template of A-r-K selection continuum. The globally ubiquitous microflagellate Heteromita globosa emerges as the most strongly A-selected and K-selected. The occurrence of terrestrial protozoa near their latitudinal limits of distribution can serve as sensitive indicators of the biological effects of climatic change. Having short generation times and effective means of cyst dispersal, changes in the gross distribution can provide rapid warning of critical changes in thermal regimes.     

Effects of an invasive plant transcend ecosystem boundaries through a dragonfly-mediated trophic pathway

Trophic interactions can strongly influence the structure and function of terrestrial and aquatic communities through top-down and bottom-up processes. Species with life stages in both terrestrial and aquatic systems may be particularly likely to link the effects of trophic interactions across ecosystem boundaries. Using experimental wetlands planted with purple loosestrife (Lythrum salicaria), we tested the degree to which the bottom-up effects of floral density of this invasive plant could trigger a chain of interactions, changing the behavior of terrestrial flying insect prey and predators and ultimately cascading through top-down interactions to alter lower trophic levels in the aquatic community. The results of our experiment support the linkage of terrestrial and aquatic food webs through this hypothesized pathway, with high loosestrife floral density treatments attracting high levels of visiting insect pollinators and predatory adult dragonflies. High floral densities were also associated with increased adult dragonfly oviposition and subsequently high larval dragonfly abundance in the aquatic community. Finally, high-flower treatments were coupled with changes in zooplankton species richness and shifts in the composition of zooplankton communities. Through changes in animal behavior and trophic interactions in terrestrial and aquatic systems, this work illustrates the broad and potentially cryptic effects of invasive species, and provides additional compelling motivation for ecologists to conduct investigations that cross traditional ecosystem boundaries.     

Testate Amoeba (Arcellinida,Euglyphida) Ecology along a Poor‐Rich Gradient in Fens of Western Poland

We investigated the relationships between testate amoebae (Arcellinida, Euglyphida), vegetation and water chemistry along environmental gradients in minerotrophic peatlands (fens) in western Poland. We hypothesized that: a) hydrochemistry significantly influences structure of testate amoeba communities, and b) testate amoeba communities are more closely correlated with the hydrochemical variables (environment) than with the vegetation data. Testate amoeba communities and vegetation from 71 sample plots were investigated together with the hydro‐chemistry and hydrology based on 16 environmental variables and vegetation composition. Testate amoeba communities revealed a distinctive poor‐rich gradient in analysed fens. Mineral‐rich habitats, which were dominated by brown mosses, were preferred by a higher number of taxa than acidic habitats, which were dominated by Sphagnum. We recorded a total of 107 testate amoebae taxa. The average species richness of testate amoebae for brown mosses was higher (20) than for Sphagnum (13). We found that testate amoebae communities were similarly correlated with vascular plants, mosses and environmental parameters. Results of direct ordination demonstrate that hydrology, pH, Mg²⁺ and sodium remain the most important environmental control for the entire data set. CCA showed that in case of brown mosses hydrology, sodium and oxygen affect testate amoeba communities significantly whereas in Sphagnum only sodium emerge as most significant determining testate amoeba assemblages. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Testate amoebae and tintinnids as spatial and seasonal indicators in the intertidal margins of Guadiana Estuary (southeastern Portugal)

The present study gathers pioneering taxonomical and community data on testate amoebae and agglutinated tintinnids, analyzing their seasonal and spatial distribution patterns in the mesotidal system of the Guadiana Estuary, southeastern Portugal. To evaluate both groups’ potential as bioindicators in climate monitoring and paleoenvironmental reconstructions, their abundance, diversity and living proportions were compared to elevation in relation to mean sea-level, marine influence and to periods of elevated water levels. The distributions of testate amoebae and tintinnid total assemblages were also related to major physicochemical variables by means of multivariate analysis.From 49 surface sediment samples collected in winter and summer 2010, 17 species (25 strains) of testate amoebae were identified (in the 63 μm fraction). The Centropyxidae, mainly represented by Centropyxis aculeata, Centropyxis arcula and Centropyxis constricta, had the greatest density (71% of total individuals), while the Difflugidae represented the most species (82% of total species). Higher diversities and densities were observed in winter in the upper estuary, where salinity is negligible, and in the middle estuary where they are concentrated at the lower levels of the intertidal zone. Few or no individuals were observed in the highest marsh zones. In winter, dead testate amoebae were dominant, with empty tests accumulating in the sediments from post-mortem transport by high river discharge. In summer, an increase in the living fraction is observed, with living testate amoebae along the entire estuary, which could indicate that some species are able to live in the lower reaches of the estuary.Along with the testate amoebae, two species of agglutinated tintinnids (>63 μm), Stenosemella ventricosa and Tintinnopsis cf. lata, were abundant in the sediments. Their highest abundances were observed in summer. Living individuals were only recorded in summer, mainly in the vicinities of freshwater and sewage outflows, where elevated nutrient concentrations may be expected.The present study demonstrates that both testate amoebae and tintinnids have well defined patterns in their temporal and spatial distribution, offering high bioindicator potential in environmental/climate monitoring studies as well as in paleoenvironmental reconstructions.     

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.