Genetic Determinism vs. Phenotypic Plasticity in Protist Morphology

Untangling the relationships between morphology and phylogeny is key to building a reliable taxonomy, but is especially challenging for protists, where the existence of cryptic or pseudocryptic species makes finding relevant discriminant traits difficult. Here we use Hyalosphenia papilio (a testate amoeba) as a model species to investigate the contribution of phylogeny and phenotypic plasticity in its morphology. We study the response of H. papilio morphology (shape and pores number) to environmental variables in (i) a manipulative experiment with controlled conditions (water level), (ii) an observational study of a within-site natural ecological gradient (water level), and (iii) an observational study across 37 European peatlands (climate). We showed that H. papilio morphology is correlated to environmental conditions (climate and water depth) as well as geography, while no relationship between morphology and phylogeny was brought to light. The relative contribution of genetic inheritance and phenotypic plasticity in shaping morphology varies depending on the taxonomic group and the trait under consideration. Thus, our data call for a reassessment of taxonomy based on morphology alone. This clearly calls for a substantial increase in taxonomic research on these globally still under-studied organisms leading to a reassessment of estimates of global microbial eukaryotic diversity.</p

Loss of testate amoeba functional diversity with increasing frost intensity across a continental gradient reduces microbial activity in peatlands

Soil microbial communities significantly contribute to global fluxes of nutrients and carbon. Their response to climate change, including winter warming, is expected to modify these processes through direct effects on microbial functions through osmotic stress, and changing temperature regimes. Using four European peatlands reflecting different frequencies of frost events, we show that peatland testate amoeba communities diverge among sites with different winter climates, and that this is reflected through contrasting functions. We found that exposure to harder soil frost promoted species β-diversity (species turnover) thus shifting the community composition of testate amoebae. In particular, we found that harder soil frost, and lower water-soluble phenolic compounds, induced functional turnover through the decrease of large species (-68%, > 80 μm) and the increase of small-bodied mixotrophic species (i.e. Archerella flavum; +79%). These results suggest that increased exposure to soil frost could be highly limiting for large species while smaller species are more resistant. Furthermore, we found that β-glucosidase enzymatic activity, in addition to soil temperature, strongly depended (R2 = 0.95, ANOVA) of the functional diversity of testate amoebae. Changing winter conditions can therefore strongly impact peatland decomposition process, though it remains unclear if these changes are carried–over to the growing season

Palaeoecology of testate amoebae in a tropical peatland.

We present the first detailed analysis of subfossil testate amoebae from a tropical peatland. Testate amoebae were analysed in a 4-m peat core from western Amazonia (Peru) and a transfer function developed from the site was applied to reconstruct changes in water table over the past ca. 8,000 years. Testate amoebae were in very low abundance in the core, especially in the lower 125cm, due to a combination of poor preservation and obscuration by other organic matter. A modified preparation method enabled at least 50 testate amoebae to be counted in each core sample. The most abundant taxa preserved include Centropyxis aculeata, Hyalosphenia subflava, Phryganella acropodia and Trigonopyxis arcula. Centropyxis aculeata, an unambiguous wet indicator, is variably present and indicates several phases of near-surface water table. Our work shows that even degraded, low-abundance assemblages of testate amoebae can provide useful information regarding the long-term ecohydrological developmental history of tropical peatlands

Potential implications of differential preservation of testate amoeba shells for paleoenvironmental reconstruction in peatlands

Testate amoebae are now commonly used in paleoenvironmental studies but little is known of their taphonomy. There is some experimental evidence for differential preservation of some testate amoeba shell types over others, but it is unclear what, if any impact this has on palaeoenvironmental reconstruction. To investigate this issue we looked at palaeoecological evidence for the preservation of different shell types. We then investigated the possible impact of selective preservation on quantitative palaeoenvironmental inference. We first used existing palaeoecological data sets to assess the vertical patterns of relative abundance in four testate amoeba shell types: (1) shells made of secreted biosilica plates (idiosomes, e.g. Euglypha), (2) idiosomes with thick organic coating (Assulina), (3) proteinaceous shells (e.g. Hyalosphenia), (4) shells built from recycled organic or mineral particles (xenosomes) (e.g. Difflugia, Centropyxis). In three diagrams a clear pattern of decay was only observed for the idiosome type. In order to assess the implications of differential preservation of testate amoeba taxa for paleoenvironmental reconstruction we then carried out simulations using three existing transfer functions and a wide range of scenarios, downweighting different test categories to represent the impact of selective test decomposition. Simulation results showed that downweighting generally reduced overall model performance. However downweighting a shell type only produced a consistent directional bias in inferred water table depth where that shell type is both dominant and shows a clear preference along the ecological gradient. Applying a scenario derived from previous experimental work did not lead to significant difference in inferred water table. Our results show that differential shell preservation has little impact on paleohydrological reconstruction from Sphagnum-dominated peatlands. By contrast, for the minerotrophic peatlands data-set loss of idiosome tests leads to consistent underestimation of water table depth. However there are few studies from fens and it is possible that idiosome tests are not always dominant, and/or that differential decomposition is less marked than in Sphagnum peatlands. Further work is clearly needed to assess the potential of testate amoebae for paleoecological studies of minerotrophic peatlands

Widespread drying of European peatlands in recent centuries

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this record Climate warming and human impacts are thought to be causing peatlands to dry,potentially converting them from sinks to sources of carbon. However, it is unclear whether the hydrological status of peatlands has moved beyond their natural envelope. Here we show that European peatlands have undergone substantial, widespread drying during the last ~300 years. We analyse testate amoeba-derived hydrological reconstructions from 31 peatlands across Britain, Ireland, Scandinavia and continental Europe to examine changes in peatland surface wetness during the last 2000 years. 60% of our study sites were drier during the period CE 1800-2000 than they have been for the last 600 years; 40% of sites were drier than they have been for 1000 years; and 24% of sites were drier than they have been for 2000 years. This marked recent transition in the hydrology of European peatlands is concurrent with compound pressures including climatic drying, warming and direct human impacts on peatlands, although these factors vary between regions and individual sites. Our results suggest that the wetness of many European peatlands may now be moving away from natural baselines. Our findings highlight the need for effective management and restoration of European peatlands.Natural Environment Research Council (NERC

Development and refinement of proxy-climate indicators from peats

Peat, especially from acidic mires (bogs), is a natural archive of past environmental change. Reconstructions of past climate from bogs commenced in the 19th Century through examination of visible peat stratigraphy, and later formed the basis for a postglacial climatic scheme widely used in Northwest Europe. Nevertheless, misconceptions as to how bogs grow led to a 50-year lacuna in peat-climate study, before the concept of "cyclic regeneration" in bogs was refuted. In recent decades, research using proxyclimate indicators from bogs has burgeoned. A range of proxies for past hydrological change has been developed, as well as use of pollen, bog oaks and pines and other data to reconstruct past temperatures. Most of this proxy-climate research has been carried out in Northern Europe, but peat-based research in parts of Asia and North America has increased, particularly during the last decade, while research has also been conducted in Australia, New Zealand and South America. This paper reviews developments in proxy-climate reconstructions from peatlands; chronicles use of a range of palaeo-proxies such as visible peat stratigraphy, plant macrofossils, peat humification, testate amoebae and non-pollen palynomorphs; and explains the use of wiggle-match radiocarbon dating and relationship to climate shifts. It details other techniques being used increasingly, such as biomarkers, stable-isotopes, inorganic geochemistry and estimation of dust flux; and points to new proxies under development. Although explicit protocols have been developed recently for research on ombrotrophic mires, it must be recognised that not all proxies and techniques have universal applicability, owing to differences in species assemblages, mire formation, topographic controls, and geochemical characteristics

Regional variability in peatland burning at mid- to high-latitudes during the Holocene

Acknowledgements This work developed from the PAGES (Past Global Changes) C-PEAT (Carbon in Peat on EArth through Time) working group. PAGES has been supported by the US National Science Foundation, Swiss National Science Foundation, Swiss Academy of Sciences and Chinese Academy of Sciences. We acknowledge the following financial support: UK Natural Environment Research Council Training Grants NE/L002574/1 (T.G.S.) and NE/S007458/1 (R.E.F.); Dutch Foundation for the Conservation of Irish Bogs, Quaternary Research Association and Leverhulme Trust RPG-2021-354 (G.T.S); the Academy of Finland (M.V); PAI/SIA 80002 and FONDECYT Iniciación 11220705 - ANID, Chile (C.A.M.); R20F0002 (PATSER) ANID Chile (R.D.M.); Swedish Strategic Research Area (SRA) MERGE (ModElling the Regional and Global Earth system) (M.J.G.); Polish National Science Centre Grant number NCN 2018/29/B/ST10/00120 (K.A.); Russian Science Foundation Grant No. 19-14-00102 (Y.A.M.); University of Latvia Grant No. AAp2016/B041/Zd2016/AZ03 and the Estonian Science Council grant PRG323 (TrackLag) (N.S. and A.M.); U.S. Geological Survey Land Change Science/Climate Research & Development Program (M.J., L.A., and D.W.); German Research Foundation (DFG), grant MA 8083/2-1 (P.M.) and grant BL 563/19-1 (K.H.K.); German Academic Exchange Service (DAAD), grant no. 57044554, Faculty of Geosciences, University of Münster, and Bavarian University Centre for Latin America (BAYLAT) (K.H.K). Records from the Global Charcoal Database supplemented this work and therefore we would like to thank the contributors and managers of this open-source resource. We also thank Annica Greisman, Jennifer Shiller, Fredrik Olsson and Simon van Bellen for contributing charcoal data to our analyses. Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government.Peer reviewedPostprin

Soil protistology rebooted: 30 fundamental questions to start with

Protists are the most diverse eukaryotes. These microbes are keystone organisms of soil ecosystems and regulate essential processes of soil fertility such as nutrient cycling and plant growth. Despite this, protists have received little scientific attention, especially compared to bacteria, fungi and nematodes in soil studies. Recent methodological advances, particularly in molecular biology techniques, have made the study of soil protists more accessible, and have created a resurgence of interest in soil protistology. This ongoing revolution now enables comprehensive investigations of the structure and functioning of soil protist communities, paving the way to a new era in soil biology. Instead of providing an exhaustive review, we provide a synthesis of research gaps that should be prioritized in future studies of soil protistology to guide this rapidly developing research area. Based on a synthesis of expert opinion we propose 30 key questions covering a broad range of topics including evolution, phylogenetics, functional ecology, macroecology, paleoecology, and methodologies. These questions highlight a diversity of topics that will establish soil protistology as a hub discipline connecting different fundamental and applied fields such as ecology, biogeography, evolution, plant-microbe interactions, agronomy, and conservation biology. We are convinced that soil protistology has the potential to be one of the most exciting frontiers in biology

Plant functional diversity drives niche-size-structure of dominant microbial consumers along a poor to extremely rich fen gradient

1. Plant community composition is recognized more and more for playing an important role in ecosystem processes, such as C cycling. In particular, plant functional type (PFT) composition seems to have a key regulatory role, yet the underlying mechanisms in the interaction between PFTs and ecosystem processes are still to be identified. 2. Here, we assess the link between PFTs and dominant microbial consumers along a calcareous poor to extremely rich fen gradient in western Poland. We particularly focussed on dominant microbial consumers (testate amoebae), which can exert large effects on the functioning of peatlands. Using moving-window analyses and path-relation networks subjected to structural equation modelling (SEM), we investigated linkages among abiotic factors, PFTs and testate amoebae. 3. We show that along the poor to extremely rich fen gradient, the dependence of testate amoebae to PFTs is higher than their dependence to abiotic factors. We also found that the link between testate amoebae and PFTs differs between size assemblages of testate amoebae. While large testate amoeba species (i.e. high trophic level) were highly linked to Sphagnum mosses cover, small species (i.e. low trophic level) were linked to brown mosses. Distinction between shallow-rooted and deep-rooted vascular plants also showed that shallow-rooted plants play a role on testate amoeba community structure at the 'poor' side of the gradient. 4. Our results further show a dominant role for calcium content and the structure of the bryophyte community on testate amoeba size assemblages at the poor to extremely rich fen scale, both for diversity and abundance of testate amoebae. 5. Synthesis. Variations in plant functional type composition drive niche-size-structure of testate amoebae along the (calcareous) poor to extremely rich fen gradient. Furthermore, strong relationships between moss types and testate amoeba size-structure suggest that mosses specifically influence testate amoeba development through autogenic effects. Therefore, moss cover composition is key to microbial consumers and may be the driving factor determining microbial network structure and associated ecosystem processes, such as carbon cycling