Yangmin Qin

Testate amoebae and δ13C of Sphagnum as surface-moisture proxies in Alaskan peatlands

Testate amoebae and stable isotopes have been used as surface-moisture proxies in peatlands. However, adequate modern calibration is critical to successful application and interpretation. Testate amoebae, δ13C of Sphagnum, and environmental conditions were examined at 126 sites within 12 peatlands of south-central and central Alaska to assess the potential of testate amoebae and δ 13C as surface-moisture proxies. Results indicate that water-table depth and pH were both correlated with testate amoeba community composition. However, the relative importance of these two variables varied, with pH more important in wetter habitats and water-table depth more important in drier habitats. Cross-validation of transfer functions indicated that water-table depth and pH can be inferred from testate amoeba communities with mean errors of ~8 cm and ~0.4 pH units, respectively, an improvement over previous calibration work in the region. However, application of these transfer functions should consider potential temporal variability in the relative importance of pH and water-table depth, and we applied our calibration data set to a subfossil testate amoeba record to highlight how knowledge of changes in the relative importance of these environmental variables can inform interpretation. In contrast with testate amoebae, δ13C of Sphagnum was found to be a relatively weak indicator of water-table depth. Variable carbon sources for Sphagnum photosynthesis, such as CO2 released by methanotrophic bacteria, likely complicate the relationship between δ 13C and moisture. Although more work is needed before δ13C of Sphagnum can be used as a proxy for water-table depth, testate amoebae should be useful in paleoenvironmental studies of peatlands in Alaska.

Diversity, distribution and biogeography of testate amoebae in China: Implications for ecological studies in Asia

Testate amoebae are a group of shelled protozoa that occur in high density populations in wet environments. More than 1900 testate amoebae species or subspecies have been reported in published literature over the last 200 years, from many regions of the world. Testate amoebae are classified as Lobosea or Filosea respectively, according to the presence of lobose or filiform pseudopodia. Testate amoebae have proved an interesting group of indicator organisms in palaeoenvironmental studies and have also been used as bioindicators of human impact on ecosystems. Until recently, the testate amoebae of China were unknown to most western scientists, but our knowledge has improved greatly over the past 20 years. This paper summarizes the testate amoebae research in China along with relevant data from other countries in Asia, and provides the necessary context for future research.

Testate amoebae as indicators of 20th century environmental change in Lake Zhangdu, China

We investigated the response of lacustrine testate amoeba communities to 20 th century environmental changes in Lake Zhangdu, China. The lake and surrounding region have undergone dramatic changes in the past century, including the expansion of agricultural and industrial activities, and associated hydrological modifications that led to the isolation of the lake from Yangtze River. We assessed the potential effects of these activities on testate amoeba communities of the lake by examining subfossil assemblages in contiguous samples along a 35-cm long, 210 Pb dated sediment core. A total of 25 testate amoeba taxa belonging to 4 genera (Difflugia, Centropyxis, Neztelia, and Pentagonia) were encountered in the core. The largest change in the composition of testate amoeba communities occurred in the 1960s, coincident with the expansion of human activities in the watershed. Testate amoeba communities shifted from species characteristic of relatively oligotrophic lakes (e.g. Difflugia biwae, D. tuberspinifera and D. pristis) to species more common to mesotrophic and eutrophic systems (e.g. Difflugia oblonga, D. corona, D. smilion and D. lanceolata). Our results provide valuable baseline data on testate amoebae and water conditions before and after major 20 th century human impact on the lake ecosystem. Lake Zhangdu was recently reconnected with the Yangtze River as part of ongoing conservation efforts, and future monitoring of testate amoeba communities could be used to inform management and assess restoration success.

Ecology of testate amoebae in Dajiuhu peatland of Shennongjia Mountains, China, in relation to hydrology

This study investigates the testate amoeba communities of a large peatland in Central China. The ecology and seasonal variability of testate amoeba communities were studied during 2009–2010. Investigation of environmental controls using ordination showed that the relationship between testate amoeba communities and depth to water table (DWT) and pH are extremely weak. The small proportion of variance explained by water table depth here (only 1.9% in the full data) shows that the hydrological control is weaker than we expected in this peatland, and weaker than any study we are aware of using a similar methodology. Attempts to develop species-environment (transfer function) models or identify indicator species for future palaeoecological studies were unsuccessful. Previous large-scale studies of peatland testate amoeba ecology have been largely restricted to Europe and North America and results have been relatively consistent among studies. Our results contrast with this consensus and suggest that at least in minerotrophic peatlands in China testate amoeba communities may be primarily controlled by different environmental variables. In China, testate amoebae have been relatively little studied but may prove to be valuable for a variety of applications in palaeoecology and biomonitoring and much further work is required.

Pentagonia zhangduensis nov. spec. (Lobosea, Arcellinida), a new freshwater species from China

The morphology of a new testate amoeba Pentagonia zhangduensis nov. spec. was investigated using light and scanning electron microscopy. The new species was discovered in the sediments of Lake Zhangdu, Hubei Province, China. The low coefficients of variation and normal size frequency distribution suggest that P. zhangduensis is a size-monomorphic species. P. zhangduensis differs from the one other species in this genus (P. maroccana), by its larger size and its quadrangular cross section with two parallel longitudinal ridges on each of the two flattened sides of the test.

Relationships between testate amoeba communities and water quality in Lake Donghu, a large alkaline lake in Wuhan, China

The middle Yangtze Reach is one of the most developed regions of China. As a result, most lakes in this area have suffered from eutrophication and serious environmental pollution during recent decades. The aquatic biodiversity in the lakes of the area is thus currently under significant threat from continuous human activities. Testate amoebae (TA) are benthic (rarely planktonic) microorganisms characterized by an agglutinated or autogenous shell. Owing to their high abundance, preservation potential in lacustrine sediments, and distinct response to environmental stress, they are increasingly used as indicators for monitoring water quality and reconstructing palaeoenvironmental changes. However this approach has not yet been developed in China. This study presents an initial assessment of benthic TA assemblages in eight lakes of Lake Donghu in the region of Wuhan, China. Testate amoeba community structure was most strongly correlated to water pH. In more alkaline conditions, communities were dominated by Centropyxis aculeata, Difflugia oblonga, Pontigulasia compressa, Pon. elisa and Lesquereusia modesta. These results are consistent with previous studies and show that TA could be useful for reconstructing past water pH fluctuations in China. To achieve this, the next step will be to expand the database and build transfer function models.

Testate amoebae as indicators of water quality and contamination in shallow lakes of the Middle and Lower Yangtze Plain

Testate amoebae are micro-organisms characterized by an agglutinated or autogenous shell enclosing the cytoplasm. Testate amoebae have been widely proposed as valuable bioindicators in a range of ecosystems (such as soils, peatlands and lakes). The use of testate amoebae as bioindicators of water quality in aquatic ecosystems is much less developed than for other microorganisms and previous research is geographically restricted. We investigated a large range of environmental variables and their relations to testate amoeba communities from 37 shallow lakes in the middle and lower Yangtze River Plain of China. Multiple factor analysis, redundancy analysis (RDA) and a forward-selection approach were used to explore the overall community structure and the links between the environmental variables and testate amoeba composition. Results showed that testate amoebae are widely distributed in most of the lakes despite often high levels of pollution. Our data highlight some links between water quality variables and testate amoeba communities. In particular, our results suggest that heavy metals have a role in shaping testate amoeba assemblage structure, although correlations are comparatively weak, perhaps due to lagged responses. Our results support previous suggestions that testate amoebae may be useful bioindicators in aquatic ecosystems but emphasize the need for an improved mechanistic understanding.

Latitudinal Diversity Gradients in Free-living Microorganisms – Hoogenraadia a Key Genus in Testate Amoebae Biogeography

The extent to which free-living microorganisms show cosmopolitan distributions has been a contentious aspect of microbial ecology over the last few decades. Testate amoebae are a group of free living protists that can provide important evidence for the nature of the biogeography of microorganisms because there are relatively good data on the distribution of their morpho-species (compared to many other microbial groups). Many testate amoebae appear to exhibit ubiquitous distributions, while some taxa have proven to be endemic to limited regions. The genus Hoogenraadia (Gauthier-Lievre and Thomas 1958) is of particular interest in this context as it appears to be restricted to relatively low latitudes. There are six described species of the genus: H. africana Gauthier-Lievre and Thomas 1958, H. asiatica Wang and Min 1987, H. cryptostoma Gauthier-Lievre and Thomas 1958, H. humicola Bonnet 1976, H. ovata Bonnet 1976, and H. sylvatica Vucetich 1974. However, information on these taxa is scattered through a number of different papers – here we provide a summary of what is known about the taxonomy and ecology of this genus. We also reinterpret recent new records of putative H. africana from China (suggesting this identification is not reliable). As an example of a protist taxon largely restricted to the tropics this genus is of particular interest in microbial biogeography and this paper discusses its morphology, ecology and distribution in this context.

Moss-dwelling testate amoebae and their community in Dajiuhu peatland of Shennongjia Mountains, China

Testate amoebae from a large fen peatland of China were investigated in August 2009. Thirty-six testate amoebae species belonging to 16 genera and one rotifer were identified. Three relatively drier indicator species, Assulina muscorum, Assulina seminulum, and Trinema-corythion type, were the dominate species, comprising 54% of total amoebae shells. Non-metric multidimensional scaling (NMS) ordination divided the testate amoebae assemblages into two groups – a drier group including A. muscorum, A. seminulum, Euglypha rotunda type, Trinema-corythion type, and Plagiopyxis callida and a wetter group including Centropysis cassis, Cyphoderia ampulla, Difflugia oblonga, Difflugia lanceolata, Euglypha strigosa type, Nebela galeata, Nebela lageniformis, and Quadruella symmetrica. Pearson correlations showed that most testate amoebae species between the two groups are negatively correlated, reflecting the possible influence of a moisture gradient. However, the ubiquitous distributions of other testate amoebae in the two-dimensional NMS ordination map suggested that factors other than moisture are also influencing the testate amoebae community in the fen.

Possible El Niño–Southern Oscillation-related lacustrine facies developed in southern Lake Poyang during the late Holocene: Evidence from spore-pollen records:

In order to explore the impacts of past climate changes on the origin and evolution of Lake Poyang, the biggest freshwater lake in China, eight periods of palaeoenvironmental changes were constructed to depict the history of climate change over the past 3500 years based on the palynological records and carbon isotopic excursions. The climate regime was associated with the presence of a deciduous and evergreen broad-leaved forest/a mixed needle broad-leaved forest and strong/weak solar variability. Palaeohydrology change reconstructed by the percentage of aquatics and stable carbon isotopes demonstrated that the wet episode was associated with the developed lacustrine facies and enhanced El Niño–Southern Oscillation (ENSO) activities. The presence of the united open lake (Lake Poyang) during 2000–1200 cal. a BP was linked to a long wet period caused by the strong ENSO activities. At the decadal-centennial timescales, climate changes together with the ENSO activities might have played a great role on the regional hydrological condition and sedimentary evolution in southern Lake Poyang. The correlations of the palaeotemperature and palaeohydrology with the multi-proxy data from the Northern Hemisphere all suggest that palaeotemperature change with the monsoon intensity is linked to the solar variations, but palaeohydrology change has a striking consistency with the ENSO activities. The distinct hydrothermal diversification (warm-wet, warm-dry, cold-wet, cold-dry) revealed by the palaeotemperature and palaeohydrology changes will provide important clues about the origin and evolution of Lake Poyang in the Holocene and a better understanding of the interactions between solar radiation, ENSO activity and lake deposition in the middle Yangtze River Valley.