Search

Current projections suggest that climate warming will be accompanied by more frequent and severe drought events. Peatlands store ca. one third of the world's soil organic carbon. Warming and drought may cause peatlands to become carbon sources through stimulation of microbial activity increasing ecosystem respiration, with positive feedback effect on global warming. Micro-eukaryotes play a key role in the carbon cycle through food web interactions and therefore, alterations in their community structure and diversity may affect ecosystem functioning and could reflect these changes. We assessed the diversity and community composition of Sphagnum-associated eukaryotic microorganisms inhabiting peatlands and their response to experimental drought and warming using high throughput sequencing of environmental DNA. Under drier conditions, micro-eukaryotic diversity decreased, the relative abundance of autotrophs increased and that of osmotrophs (including Fungi and Peronosporomycetes) decreased. Furthermore, we identified climate change indicators that could be used as early indicators of change in peatland microbial communities and ecosystem functioning. The changes we observed indicate a shift towards a more ''terrestrial'' community in response to drought, in line with observed changes in the functioning of the ecosystem. [ABSTRACT FROM AUTHOR]

Abstract Methodological advances are essential for robust ecological research. Quantitative reconstructions of environmental conditions using testate amoebae rely on sound taxonomy. While the taxonomy of large species is relatively well resolved, this is not the case for most small taxa (typically <45 μm long). In New Zealand, peatlands contain a diversity of both cosmopolitan and characteristic large southern endemic taxa, but also have a high abundance of small taxa. The latter are often lumped into morphotypes reducing their value as ecological indicators. In this study, we demonstrate how (a) lumping small taxa versus splitting them into unique types, and (b) including or excluding them from community analysis influenced their ecological inference. We assessed testate amoeba composition in six peat bogs from New Zealand, three that were moderately-to-highly impacted, and three that were non-impacted. Environmental variables were measured at each sampling site and the surface testate amoeba community patterns and community-environment relationships compared. We found a clear division between impacted and non-impacted sites. Several distinct small taxa were more strongly related to water-table depth and conductivity, while the larger taxa were more correlated to pH. These results show that improved taxonomic resolution of small taxa can provide more informed environmental assessment. [ABSTRACT FROM AUTHOR]

Endosymbiosis is a central and much studied process in the evolution of eukaryotes. While plastid evolution in eukaryotic algae has been extensively studied, much less is known about the evolution of mixotrophy in amoeboid protists, which has been found in three of the five super groups of Eukaryotes. We identified the green endosymbionts in four obligate mixotrophic testate amoeba species belonging to three major eukaryotic clades, Hyalosphenia papilio and Heleopera sphagni (Amoebozoa: Arcellinida), Placocista spinosa (Rhizaria: Euglyphida), and Archerella flavum (Stramenopiles: Labyrinthulomycetes) based on rbcL (ribulose-1,5-diphosphate carboxylase/oxygenase large subunit) gene sequences. We further investigated whether there were different phylotypes of algal endosymbionts within single H. papilio cells and the degree of host-symbiont specificity by amplifying two genes: COI (mitochondrial cytochrome oxydase subunit 1) from the testate amoeba host, and rbcL from the endosymbiont. Results show that all studied endosymbionts belong to genus Chlorella sensu stricto, closely related to Paramecium bursaria Chlorella symbionts, some lichen symbionts and also several free-living algae. Most rbcL gene sequences derived from symbionts from all testate amoeba species were almost identical (at most 3 silent nucleotides difference out of 780bp) and were assigned to a new Trebouxiophyceae taxon we named TACS (Testate Amoeba Chlorella Symbionts). This “one alga fits all mixotrophic testate amoeba” pattern suggests that photosynthetic symbionts have pre-adaptations to endosymbiosis and colonise diverse hosts from a free-living stage. [Copyright &y& Elsevier]

Abstract: Peatlands are widely exploited archives of paleoenvironmental change. We developed and compared multiple transfer functions to infer peatland depth to the water table (DWT) and pH based on testate amoeba (percentages, or presence/absence), bryophyte presence/absence, and vascular plant presence/absence data from sub-alpine peatlands in the SE Swiss Alps in order to 1) compare the performance of single-proxy vs. multi-proxy models and 2) assess the performance of presence/absence models. Bootstrapping cross-validation showing the best performing single-proxy transfer functions for both DWT and pH were those based on bryophytes. The best performing transfer functions overall for DWT were those based on combined testate amoebae percentages, bryophytes and vascular plants; and, for pH, those based on testate amoebae and bryophytes. The comparison of DWT and pH inferred from testate amoeba percentages and presence/absence data showed similar general patterns but differences in the magnitude and timing of some shifts. These results show new directions for paleoenvironmental research, 1) suggesting that it is possible to build good-performing transfer functions using presence/absence data, although with some loss of accuracy, and 2) supporting the idea that multi-proxy inference models may improve paleoecological reconstruction. The performance of multi-proxy and single-proxy transfer functions should be further compared in paleoecological data. [Copyright &y& Elsevier]

Abstract: Peatland testate amoebae are widely used to reconstruct paleohydrological/climatic changes, but many species are also known to respond to pollutants. Peatlands around the world have been exposed to anthropogenic and intermittent natural pollution through the late Holocene. This raises the question: can pollution lead to changes in the testate amoeba paleoecological record that could be erroneously interpreted as a climatic change? To address this issue we applied testate amoeba transfer functions to the results of experiments adding pollutants (N, P, S, Pb, O3) to peatlands and similar ecosystems. We found a significant effect in only one case, an experiment in which N and P were added, suggesting that pollution-induced biases are limited. However, we caution researchers to be aware of this possibility when interpreting paleoecological records. Studies characterising the paleoecological response to pollution allow pollution impacts to be tracked and distinguished from climate change. [Copyright &y& Elsevier]

Testate amoebae are useful environmental indicators in ecological and palaeoecological studies from peatlands. Previous quantitative studies have focused on the peatlands of Northern and Central Europe, North America, and New Zealand and have considered a relatively restricted variety of peatland types, mostly ombrotrophic or Sphagnum-dominated while more minerotrophic fens have been less studied. Here we present the first quantitative ecological study of testate amoebae from four small mesotrophic fens (pH 5.5–8.1) in the Elatia Forest, northern Macedonia province, Greece. Relationships with the environmental data were investigated using redundancy analysis and mantel tests. Transfer function models were derived using a variety of techniques. Results demonstrate that as for Sphagnum-dominated mires hydrology is the most important control on amoebae community composition. Transfer function models should enable water tables to be predicted within 2.5cm, when data selection is used this is reduced to less than 2cm. pH is also an important environmental control on testate amoebae communities, a transfer function model enables pH prediction within 0.4 pH units. The hydrological transfer function is the best performing such model yet produced in terms of prediction error. This study provides new data on the ecology of testate amoebae in fens, and the transfer function models should allow quantitative palaeohydrological reconstruction. [Copyright &y& Elsevier]

Testate amoebae are a diverse group of shelled protists frequently used as model organisms in microbial biogeography. Relatively few species have been reported for the Southern Hemisphere, however, it remains unclear whether this lower diversity is real or an artifact of under-sampling or misidentifications, which would reduce their potential to address macroecological questions. We evaluated testate amoebae diversity from the full range of habitats occurring within two Tierra del Fuego peatlands and compared it with the reported diversity for the area and from the Northern Hemisphere peatlands. We recorded 87 species, of which 69 are new for the region and 45 of them probably new to science and likely to have restricted geographical distributions. Combined with previous studies, the total diversity of testate amoebae only from Tierra del Fuego peatlands now reaches 119, as compared with 183 reported from all Northern Hemisphere peatlands. Our results demonstrate that the number of Gondwanian and Neotropical endemic testate amoeba may be substantially higher than currently known. Previous reports of Holarctic taxa in Tierra del Fuego may result from forcing the identification of morphotypes to the descriptions in the most common literature (force-fitting) South American species into species common in literature from other regions. [ABSTRACT FROM AUTHOR]

Testate amoebae are a widely-used tool for palaeohydrological reconstruction from peatlands. However, it has been observed that weak idiosomic siliceous tests (WISTs) are common in uppermost peats, but very rarely found as subfossils deeper in the peat profile. This taphonomic problem has been noted widely and it has been established that WISTs disaggregate and/or dissolve in the low pH condition of ombrotrophic peatlands. Here we investigate the effect of this taphonomic problem on water-table reconstructions from thirty European peatlands through the comparison of reconstructions based on all taxa and those with WISTs removed. In almost all cases the decomposition of WISTs does not introduce discernible bias to peatland water-table reconstructions. However, some discrepancy is apparent when large abundances of Corythion-Trinema type are present (9−12 cm deviation with 50–60% abundance of this particular taxon). We recommend that WISTs should be removed before carrying out water-table reconstructions, and that the minimum count of testate amoebae per sample should exclude WISTs to ensure the development of robust reconstructions. [ABSTRACT FROM AUTHOR]

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. • The first assessment and comparison of the bioindicator value of testate amoebae and vascular plants in Southern Hemisphere peatlands. • Testate amoebae are a promising bioindicator for tracking degradation in New Zealand peatlands and are a potential tool for peatland managers. • Testate amoebae tracked changes in the abiotic variables more closely than vascular plants in New Zealand peatlands. • Functional trait analysis of testate amoebae enriches our understanding of microorganism response to degradation in peatlands. [ABSTRACT FROM AUTHOR]

In the decade since the first pan-European testate amoeba-based transfer function for peatland palaeohydrological reconstruction was published, a vast amount of additional data collection has been undertaken by the research community. Here, we expand the pan-European dataset from 128 to 1799 samples, spanning 35° of latitude and 55° of longitude. After the development of a new taxonomic scheme to permit compilation of data from a wide range of contributors and the removal of samples with high pH values, we developed ecological transfer functions using a range of model types and a dataset of ∼1300 samples. We rigorously tested the efficacy of these models using both statistical validation and independent test sets with associated instrumental data. Model performance measured by statistical indicators was comparable to other published models. Comparison to test sets showed that taxonomic resolution did not impair model performance and that the new pan-European model can therefore be used as an effective tool for palaeohydrological reconstruction. Our results question the efficacy of relying on statistical validation of transfer functions alone and support a multi-faceted approach to the assessment of new models. We substantiated recent advice that model outputs should be standardised and presented as residual values in order to focus interpretation on secure directional shifts, avoiding potentially inaccurate conclusions relating to specific water-table depths. The extent and diversity of the dataset highlighted that, at the taxonomic resolution applied, a majority of taxa had broad geographic distributions, though some morphotypes appeared to have restricted ranges. [ABSTRACT FROM AUTHOR]

Abstract: Peatlands represent massive global C pools and sinks. Carbon accumulation depends on the ratio between net primary production and decomposition, both of which can change under projected increases of atmospheric CO2 and N deposition. The decomposition of litter is influenced by 1) the quality of the litter, and 2) the microenvironmental conditions in which the litter decomposes. This study aims at experimentally testing the effects of these two drivers in the context of global change. We studied the in situ litter decomposition from three common peatland species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) collected after one year of litter production under pre-treatment conditions (elevated CO2: 560 ppm or enhanced N: 3 g m−2 y−1 NH4NO3) and decomposed the following year under treatment conditions (same as pre-treatment). By considering the cross-effects between pre-treatments and treatments, we distinguished between the effects on mass loss of 1) the pre-treatment-induced litter quality and 2) the treatment conditions under which the litters were decomposing. The combination between CO2 pre-treatment and CO2 treatment reduced Polytrichum decomposition by −24% and this can be explained by litter quality-driven decomposition changes brought by the pre-treatment. CO2 pre-treatment reduced Eriophorum litter quality, although this was not sufficient to predict decomposition. The N addition pre-treatment reduced the decomposition of Eriophorum, due to enhanced lignin and soluble phenols concentrations in the initial litter, and reduced litter-driven losses of starch and enhanced litter-driven losses of soluble phenols. While decomposition indices based on initial litter quality provide a broad explanation of quantitative and qualitative decomposition, they can only be taken as first approximations. Indeed, the microbial ATP activity, the litter N loss and resulting litter quality, were strongly altered irrespective of the compounds'' initial concentration and by means of processes that occurred independently of the initial litter-qualitative changes. The experimental design was valuable to assess litter- and ecosystem-driven decomposition pathways simultaneously or independently. The ability to separate these two drivers makes it possible to attest the presence of litter-qualitative changes even without any litter biochemical determinations, and shows the screening potential of this approach for future experiments dealing with multiple plant species. [Copyright &y& Elsevier]

Testate amoebae (TA) are a common and diverse group of protists and are especially abundant in peatlands. The structure of peatland TA communities is well correlated to surface moisture and water table depth (WTD). For that reason, TA are widely used as proxy indicators in ecological and palaeoecological studies. Peatlands are abundant across Asia, but the diversity and ecology of the TA that inhabit these systems are poorly documented. It is therefore unclear whether TA can be used as palaeohydrological indicators in the manner in which they commonly are in Europe and North-America. There is particular uncertainty as to the efficacy of this approach in the lower latitudes. We compiled existing and new data on testate amoebae from 1124 Sphagnum -dominated samples from 42 individual peatlands covering broad latitudinal (25°–66° N) and longitudinal (68°–129° E) ranges. Using a consensus taxonomic framework, we built a checklist of TA and developed TA-based hydrological transfer functions for Asian peatlands. The results showed that three models, weighted averaging (WA), weighted average partial least squares (WA-PLS), and maximum likelihood (ML), predicted similar WTD values for full samples, while the modern analogue technique (MAT) produced the strongest (R2 boot = 0.58) relationship between observed and estimated water-table depths (WTDs). Removing outlier samples improved the R2 values of observed vs. estimated WTDs, with ML then demonstrating the strongest predictive power (R2 boot = 0.68, RMSEP boot = 8.98 cm). The predictive capability of the developed WTD transfer function is comparable to equivalent models for Europe and North America and thus can be used for palaeohydrological reconstructions for boreal to subtropical peatlands in Asia. • A testate amoebae taxonomic checklist was compiled from Asian peatlands. • We developed continental scale testate amoeba-based hydrological transfer functions. • The water-table depth transfer functions can be used for paleohydrological reconstructions. [ABSTRACT FROM AUTHOR]