Pediastrum Species Research Articles

Sedimentary Pediastrum record of middle–late Holocene temperature change and its impacts on early human culture in the desert-oasis area of northwestern China

Although the pattern of Holocene temperature variations in central Asia is complex, it is clear that temperature played a fundamental role in influencing humidity conditions and regional human activity. We reconstructed temperature changes using Pediastrum species data, verified by clumped isotopes (Δ47), in the carbonates of sediment cores recovered from Bosten Lake in Xinjiang Province, northwestern China. Combined with archaeological data, the results indicate an unusually warm climatic interval that peaked at ∼4.7–4.3 kyr and promoted human occupation of the Altai Mountains. The climate cooled during 4.2–4.1 kyr and 3.6–3.5 kyr, as indicated by the decrease or absence of Pediastrum simplex. These cold events may have triggered the southward human migration out of the Altai region, resulting in the widespread distribution of archaeological sites at lower latitudes, in the Tienshan Mountains, and in the desert-oasis areas of the Tarim Basin in southern Xinjiang. Our data support the notion that a series of cultural transitions across the monsoonal Loess Plateau and Tibetan Plateau of China may have been linked to temperature changes during the middle to late Holocene.

Morphology-based identification and classification of Pediastrum through AlexNet Convolution Neural Network

In general solutions and outcomes to an issue in image processing, a ton of trail and examination with an enormous assortment of test photographs is incorporated. Pediastrum, which comprises of pigments like carotene, xanthophyll, chlorophylls, and other nourishing elements like complex sugars, major and minor minerals, and protein, enzymes, fiber, is a minute coccal shaped colony forming green algae. In this research, an attempt was made to solve the problem of identifying and classifying different species of Pediastrum with the aid of CNN based deep learning model. The informational collection comprising of 12,000 algal pictures was being utilized by, AlexNet CNN (Convolution Neural Network) model for the training and validating purposes. The features like the presence of sporopollenin in the cell wall, the structures and the functions of the cells, and the structural properties of coenobia make the basis for automated classification by AlexNet deep learning model. The efficacy of the proposed approach is demonstrated by an experimental outcome of 99.54 percent classification accuracy with precision and Fl-score more than 0.98.

Pediastrum (Chlorophyceae) assemblages in surface lake sediments in China and western Mongolia and their environmental significance

Pediastrum Meyen is often well preserved in lake sediments and its abundance and species composition are very sensitive to changes in the aquatic environment. Previous studies have shown that changes in the composition or abundance of Pediastrum species have great potential for studying paleoenvironmental evolution. However, until now, very few studies have explored the environmental significance of Pediastrum and used it as a paleoclimatic or paleoenvironmental indicator. In this study, we investigated the occurrence of Pediastrum in 26 natural lakes and 17 reservoirs, with varying hydro-chemical and climatic gradients, in China and western Mongolia. 25 Pediastrum taxa (including species and varieties) were found in the surface sediments of 36 different water bodies, and the spatial distribution characteristics of Pediastrum species and the environmental factors determining the community composition were identified using both Canonical Correspondence Analysis (CCA) and extended Huisman-Olff-Fresco (eHOF) methods. The results demonstrate that mean annual temperature is the most significant environmental variable influencing modern Pediastrum species composition and abundance. Water salinity and trophic status are probably secondary factors that are responsible for the variations in the abundance of Pediastrum species, and they cannot survive in water bodies with total dissolved solids (TDS) higher than ~2–3 g L−1. Overall, our results indicate that Pediastrum assemblages have great potential for reconstructing environmental variables in the past, and therefore that they can be used for environmental monitoring in global warming research.

ResNeXt convolution neural network topology-based deep learning model for identification and classification of Pediastrum

For identification of different Pediastrum species in a sample, the determination of microscopic feature and colony morphology are the preliminary steps before sending them to the higher genomic and proteomic level. Great efforts with high expertise are required for the time-consuming manual process. In the present study, the first time an effort has been done to address the problem for identification and classification of Pediastrum species with the help of convolutional neural networks (CNNs). The modified ResNeXt CNN (Convolution Neural Network) model is used for training and validation of the data set consisting of 42,000 algal images. Modified ResNeXt CNN topology differentiates cells based on the formation of coenobia, cell arrangement and feature and particularly the sculptures on the outer sporopollenin cell-wall layers. An experimental result of 98.45% classification accuracy and F1-score more than 0.98 demonstrates the effectiveness of the proposed method. In the future, such time and cost-effective facilities can be used as promising sources for phycological studies.

The taxonomic composition, distribution and abundance of the phytoplankton flora of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Osun State, Nigeria

The study determined the abundance and distribution of phytoplankton flora of an impoundment in the Agricultural Teaching and Research Farm of ObafemiAwolowo University (O.A.U), Ile-Ife, Osun State, Nigeria. The study was carried out over an annual cycle from September 2006- August 2007, Phytoplankton and water samples were collected monthly from three sampling stations by filtering 50 litres of water through a phytoplankton net of 45μm mesh size to a concentrate volume of about 30ml preserved in 5% formalin solution. The phytoplankton were viewed under a compound light microscope at both scanning power (x40) and low power (x100), measured with an ocular micrometer drawn to scale, counted and later identified using various phytoplankton identification keys on Nigerian freshwaters.The results showed that one hundred and fifteen species of phytoplankton belonging to five divisions, seven classes, nineteen orders, forty seven families and eighty three genera were recorded. The predominant genera in terms of occurrence and abundance were members of the green algae (Division Chlorophyta) and included Tetradesmus, Ulotrix, Tetraspora, Protosiphon, Chlorella, Closteriopsis and Pediastrum. Phytoplankton occurrence and abundance were slightly higher in the rainy season (600±350) than in the dry season (533±186) (f= 0.918, p= 0.05). The highest values were recorded at the surface stations of the lake.It was concluded that the water body was comparatively rich in phytoplankton flora. Also the occurrence of some species in the water body such as scenedesmus, stauraastum, Tetradesmus, Ulotrix, Tetraspora and Pediastrum species suggested a high level of primary productivity and a non-polluted lake that was oligotrophic to moderately eutrophic.Keywords: Phytoplankton, composition, distribution, abundance

Pediastrum Meyen sensu lato (Chlorophyceae) in the phytoplankton of lowland and upland water bodies of Central Europe (Poland)

Thirteen species and thirteen varieties of microscopic green algae from the genus Pediastrum were found in thirty one localities scattered in lowland and upland water bodies in Poland. Seven groups of localities are distinguished with cluster analysis. The groups differ from each other in terms of Pediastrum communities and environmental variables (pH, conductivity, carbonate hardness, nitrate and orthophosphate concentrations). The most distinct group contains five coastal lakes, which have high pH values and chloride concentration. Because the lakes have a high number of taxa, including a few rarely occurring worldwide, they are considered a hot spot for Pediastrum. Redundancy analysis revealed that the environmental variables account for ca thirty per cent of the variability of Pediastrum occurrence. Conductivity and pH statistically significantly explain the taxonomical variation of Pediastrum species and varieties. The genus Pediastrum as a whole is most positively correlated with conductivity. Individual taxa are influenced by different variables, except for P. tetras which is indifferent to them. The environmental preferences of the taxa can make inference on conditions in both recent and past water bodies more reliable.

Vegetation and lake changes on the southern Taymyr peninsula, northern Siberia, during the last 300 years inferred from pollen and Pediastrum green algae records

Siberian arctic vegetation and lake water communities, known for their temperature dependence, are expected to be particularly impacted by recent climate change and high warming rates. However, decadal information on the nature and strength of recent vegetation change and its time lag to climate signals are rare. In this study, we present a 210Pb/137Cs dated pollen and Pediastrum species record from a unnamed lake in the south of the Taymyr peninsula covering the period from AD 1706 to 2011. Thirty-nine palynomorphs and 10 morphotypes of Pediastrum species were studied to assess changes in vegetation and lake conditions as probable responses to climate change. We compared the pollen record with Pediastrum species, which we consider to be important proxies of climate changes. Three pollen assemblage zones characterised by Betula nana, Alnus viridis and Larix gmelinii (1706–1808); herbs such as Cyperaceae, Artemisia or Senecio (1808–1879), and higher abundance of Larix pollen (1955–2011) are visible. Also, three Pediastrum assemblage zones show changes of aquatic conditions: higher abundances of Pediastrum boryanum var. brevicorne (1706–1802); medium abundances of P. kawraiskyi and P. integrum (1802–1840 and 1920–1980), indicating cooler conditions while less eutrophic conditions are indicated by P. boryanum, and a mainly balanced composition with only small changes of cold- and warm-adapted Pediastrum species (1965–2011). In general, compositional Pediastrum species turnover is slightly higher than that indicated by pollen data (0.54 vs 0.34 SD), but both are only minor for this treeline location. In conclusion, the relevance of differentiation of Pediastrum species is promising and can give further insights into the relationship between lakes and their surrounding vegetation transferred onto climatic conditions.

Response of Pediastrum in German floodplain lakes to Late Glacial climate changes

Subfossil remains of the Pediastrum-algae group (Fam. Hydrodictyaceae) are frequently found in lake sediments, but very few studies have used them as palaeoclimate and palaeolimnological indicators. This study explored the species composition of Pediastrum assemblages in shallow floodplain lakes in northern Germany during two transitional periods from cold to temperate climate conditions (GS-2/GI-1 and GI-1/Holocene). We identified Pediastrum taxa to subspecies level and used multivariate statistics (constrained clustering, principal component analysis and redundancy analysis) to show that shifts in taxonomic composition reflected the strong Late Glacial climate oscillations. The Pediastrum assemblages indicate that climate amelioration already begun shortly before the main GS-2/GI-1 summer-temperature transition. In contrast to previous studies that identified trophic state as the main driver of change in Pediastrum species composition, we identified climate shifts and related factors as the major drivers of community change. Water depth and trophic state probably acted as secondary factors that were responsible for differences in Pediastrum response between the first and second investigated climate transitions. During cold periods, Pediastrum algae composition was controlled mainly by environmental variables, whereas during warm periods, Pediastrum assemblages may have been influenced to a greater extent by intra- and intergeneric competition. This study contributes to knowledge about ecological niches of Pediastrum species. Size-measurements on Pediastrum coenobia reveal that one response of Pediastrum algae to climate shifts probably was size change. Coenobia of Pseudopediastrum boryanum var. boryanum were significantly smaller during cold climate periods than during temperate periods. The shifts in Pediastrum species composition and coenobium size suggest this algae group has great potential for enabling palaeoecological and palaeoclimate inferences.

Pediastrum species as potential indicators of lake-level change in tropical South America

We explored the potential for using Pediastrum (Meyen), a genus of green alga commonly found in palaeoecological studies, as a proxy for lake-level change in tropical South America. The study site, Laguna La Gaiba (LLG) (17°45′S, 57°40′W), is a broad, shallow lake located along the course of the Paraguay River in the Pantanal, a 135,000-km2 tropical wetland located mostly in western Brazil, but extending into eastern Bolivia. Fourteen surface sediment samples were taken from LLG across a range of lake depths (2–5.2 m) and analyzed for Pediastrum. We found seven species, of which P. musteri (Tell et Mataloni), P. argentiniense (Bourr. et Tell), and P. cf. angulosum (Ehrenb.) ex Menegh. were identified as potential indicators of lake level. Results of the modern dataset were applied to 31 fossil Pediastrum assemblages spanning the early Holocene (12.0 kyr BP) to present to infer past lake level changes qualitatively. Early Holocene (12.0–9.8 kyr BP) assemblages do not show a clear signal, though abundance of P. simplex (Meyen) suggests relatively high lake levels. Absence of P. musteri, characteristic of deep, open water, and abundance of macrophyte-associated taxa indicate lake levels were lowest from 9.8 to 3.0 kyr BP. A shift to wetter conditions began at 4.4 kyr BP, indicated by the appearance of P. musteri, though inferred lake levels did not reach modern values until 1.4 kyr BP. The Pediastrum-inferred mid-Holocene lowstand is consistent with lower precipitation, previously inferred using pollen from this site, and is also in agreement with evidence for widespread drought in the South American tropics during the middle Holocene. An inference for steadily increasing lake level from 4.4 kyr BP to present is consistent with diatom-inferred water level rise at Lake Titicaca, and demonstrates coherence with the broad pattern of increasing monsoon strength from the late Holocene until present in tropical South America.

Subfossil faunal and floral remains (Cladocera,Pediastrum) in two northernLobelialakes in Finland

The analysis of lake sediment cores have been long used as historical integrators of environmental changes. Nutrient poor isoetid lakes remain under studied in the north boreal region. Hence, the bottom sediments of two north boreal Lobelia lakes, located in NE Finland were analysed for the presence of Cladocera and Pediastrum remains. Sediment cores from the littoral zones were sampled, sectioned every centimetre and aged with 210 Pb. The number of taxa of both Cladocera and Pediastrum identified in the cores was high, while the number of individuals in each taxon was low. In Lake Kevojarvi, twenty five Cladocera species and eight Pediastrum species were found. Along with widely distributed species, typical for north boreal regions, species preferring more temperate environments occurred. In Lake Petajalampi, the species composition was similar. Twenty one Cladocera species and five Pediastrum species occurred there, however with a lower frequency of individuals in each taxon. In both Lobelia lakes, analyses of subfossil Cladocera and Pediastrum remains, from the sediments deposited within the last 30–40 years indicated a recent increase in trophic status.

Pediastrum algae from the classic late glacial Bølling Sø site, Denmark: Response of aquatic biota to climate change

The late glacial and the early Holocene sediments of the classic site Bølling Sø in Denmark are being reinvestigated by multi-proxy analyses. We present here the record of Pediastrum species and discuss the climate-mediated changes in the aquatic ecosystem, as reflected by aquatic proxies (e.g. aquatic plants and mosses, cladocerans, ostracods, bryozoan statoblasts), as well as a number of other proxies (organic content, biogenic silica, carbonates, terrestrial plant macrofossils). Climate had warmed to such an extent at c. 12,500 14C yrs BP that aquatic life could begin. Productivity was low and only very scarce indication of a warmer interval predating the Allerød chronozone was found. At the beginning of the Allerød chronozone climate ameliorated and productivity clearly increased. The cool climate of the Younger Dryas chronozone (YD) was more clearly reflected in the terrestrial ecosystem than in the aquatic ecosystem, where productivity appeared to remain rather high. The lake was very shallow and non-stratified during the YD, indicating low effective moisture. Probably it warmed throughout early in the open-water season and in that way enabled higher productivity, even if summer temperatures were rather low. It is also possible that the difference in July temperatures between the late part of the Allerød chronozone and the YD was not large in central Jutland. The amelioration of climate at the beginning of the Holocene is clearly reflected in all proxies. There is also evidence that the lake level rose. The lake probably remained alkaline during all of its history but some evidence suggests that pH was somewhat lowered during the YD chronozone. Pediastrum species appear to be relatively good indicators of environmental conditions; similarly, the concentrations may reflect productivity variations during changing climatic conditions.

The Fossil Record of Freshwater Micro-Algae Pediastrum Meyen (Chlorophyceae) in Southern South America

The fossil record of Pediastrum Meyen (Chlorophyceae) in southern South America is revised and 10 species/varieties are recognised within the genus. Previously published material is identified and new data are included. The oldest and most widespread variety for the region is P. boryanum var. boryanum, which appears in the Late Cretaceous age. P. tetras is recorded in the Early Eocene in Patagonia. P. boryanum var. brevicorne, P. boryanum var. longicorne, P. duplex, P. integrum, P. kawraiskyi, P. leonensis, P. mustersii and P. simplex are present in numerous Miocene assemblages. Assemblages of different species and mass production episodes are also detected in the fossil record. New examples of the value of Pediastrum species as paleoenvironmental markers are presented.

A Miocene algal assemblage dominated by Pediastrum leonensis n. sp. (Chlorophyceae) from Patagonia, Argentina: paleoenvironmental implications

Taxonomic identification of Pediastrum species in an Early Miocene assemblage from southeast Patagonia, Argentina, is used to assess paleoecological conditions. Pediastrum leonensis n. sp. is described based on unique features of the coenobia morphology. It belongs to the P. kawraiskyi–mustersii–patagonicum complex and has no known living counterpart. This group seems to have a long evolutionary history in the region. P. kawraiskyi and P. mustersii are recorded for the first time in pre-Quaternary deposits and their presence suggests a depositional environment represented by a cold stenothermal lake conditions, indicating a temperate to a cold-temperate climate.

Phylogenetic Relationships Among Pediastrum sPP. and Hydrodictyon sPP.

AbstractWithin the class Chlorophyceae, the family Hydrodictyaceae (order Sphaeropleales) consists of taxa that form flat or net‐like coenobia and reproduce asexually by way of biflagellated zoospores. Two taxa within this family, Pediastrum and Hydrodictyon, share many features during development, especially the manner of daughter colony formation. The colonies of Pediastrum differ from Hydrodictyon in that growth is planar resulting in two‐dimensional colonies, while three‐dimensional nets are formed in Hydrodictyon. Studies of the Chlorophyceae using morphological and ultrastructural data, as well as molecular sequence data, have supported the close relationship of Pediastrum and Hydrodictyon and they have remained in the family Hydrodictyaceae throughout major classification revisions. However, in these studies only single species of Pediastrum (P. duplex) and Hydrodictyon (H. reticulatum) were included, therefore the exact relationship of these two taxa could not be explored. Preliminary molecular data from a second species of Pediastrum, P. boryanum, indicate that Hydrodictyon may be derived from Pediastrum. In this analysis, H. reticulatum resolves as sister taxon to P. duplex with P. boryanum the ancestral taxon. Further molecular studies of the family Hydrodictyaceae allow exploration of the relationships between Pediastrum spp. and Hydrodictyon spp., and assist in determining whether they are monophyletic. Preliminary analyses include H. reticulatum and H. africanum and several species of Pediastrum, P. duplex, P. boryanum, P. tetras, P. biradiatum and P. simplex. An understanding of the phylogenetic relationships among the species of Pediastrum and Hydrodictyon will allow a more complete comparison of colony formation.

The coenobial morphology of Pediastrum privum (Printz) Hegewald

The eight-celled coenobia of Pediastrum privum differ from all other Pediastrum species by having an asymmetrical central cell with one or two protuberances, more or less pointing out from the coenobial plane.

<i>Pediastrum</i> in Lake Sediment and Its Mineralization

A lot of algae fossils were found in Cenozoic lake sediments, especially Pediastrum fossil sedimentary deposits in some places of China and also in some nearby seacoasts. For imitating Pediastrum mine ralization in lake sediments, several species of Pediastrum are cultured using BBM medium and sea water with 18% salt. By optical and electronic microscope observation and photosyntheic pigment analysis, we found that Pediastrum boryanum, P.duplex var clathratum and P.tetras , etc. cannot grow well in sea water. If cultured in saline medium, the specimen will die in a short period of time. We consider that probably the Pediastrum fossil that appeared in marine sediments were transported to the sea by river. In order to prove the mineralization condition of in living organism and fossils of Pediastrum, the following analysis is made. The fat soluble substances are high and they contain a small amount of alkane, alkene fatty acid and a great deal of plant pigments. Pediastrum has high H/C and low O/C (atom number ratio) value. Therefore, it is a good resource of oil formation. The products of oxidative degradation of the insoluble cell wall of Pediastrum are similar to the production obtained by kerogen, which is known to be of algal origin. So, the insolable materials of cell wall are probably a source of kerogen during the deposition.

Algal transformation of fluometuron and atrazine by N‐dealkylation

The potential for 14C‐fluometuron (N,N‐dimethyl‐N'‐[3‐(trifluoromethyl)‐phenylurea]) degradation in unialgal cultures of 15 strains of green algae and 2 species of cyanobacteria (blue‐green algae) was investigated. Eight of 15 algal strains (Ankistrodesmus, Chlorella, Pediastrum, Scenedesmus and Selenastrum species) metabolized fluometuron via N‐demethylation to desmethyl fluometuron. The highest fluometuron‐demethylation activity was observed in the genera Ankistrodesmus (A. falcatus and A. cf. nannoselene) and Selenastrum (S. capricormitum, S. gracile and S. mimitum) with complete sequential demethylation to trifluoromethylphenylurea observed in certain strains. Low levels of fluometuron‐demethylating activity in certain algal strains may be due to herbicide toxicity. Algal strains (Ankistrodesmus and Selenastrum sp.) that metabolize fluometuron via N‐demethylation also transform the herbicide atrazine (6‐chloro‐N‐ethyl‐N‘’‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) by N‐dealkylation to deethylatrazine, however this activity is several‐fold lower than fluometuron‐demethylation activity. Our study indicates that algae have the potential to contribute to herbicide transformations in aquatic environments via N‐dealkylation transformations.

Reduction of Molecular Motion of Polymethylene in Oil Shales by Mineral Matter

Kerogen from the Stuart deposit, Queensland, Australia has been isolated from its oil shale by a number of methods and studied by solid-state 13C nuclear magnetic resonance spectroscopy (NMR). The kerogen is unusual, since there is clear evidence of a resolved polymethylene peak in the NMR spectrum rather than the broad resonance at about the same chemical shift normally obtained for highly aliphatic kerogens with aromaticities less than 0.25. X-ray diffraction data also indicate some ordered material in the kerogen. This polymethylene peak is not present in the NMR spectrum of the original oil shale and is absent in spectra of both oil shales and kerogens of similar deposits (e.g., Condor, Queensland, Australia). The mineral-matter components of Stuart oil shale do not differ significantly from oil shales with conventional kerogen NMR spectra. It may be concluded that precursor biopolymers in Stuart kerogen are not as cross-linked as other aliphatic kerogens such as Condor. This could be due to a higher concentration of Pediastrum species in the kerogen-forming biomass.

Phyto‐ and Zooplankton Composition and Some Ecological Observations on a Man‐made Lake in Wadi el Majanin, Libya

AbstractThe small eutrophic man‐made lake in Wadi el Majanin, Libya has a well‐buffered hydrogen‐carbonate (98 … 160 mg/l CaCO3) system (pH = 7 … 7.8) and a poor Secchi visibility (21 … 35 cm). Conductivity data (272 … 480 μS/cm) fit the water‐body in class 2 (‘freshwater’ range) of Beadle. The annual surface water temperature cycle (before noon readings) showed strong seasonal variations from 12 °C in Jan. and Feb. 1986 to 28.5 °C in June, 1987. The lake sustains a good crop of plankton populations. The main phytoplankton were species of Pediastrum, Scenedesmus, Navicula, Amphora, Synedra, Gomphonema, Oscillatoria, Gomphosphaeria and from zooplankton these were Keratella, Polyarthra, Brachionus, Moina, Acanthocyclops and nauplii of copepods. The presence of euglenoids supports the enriched water status of the ecosystem. Planktonic algal flora appeared closer to the eutrophic chlorococcales‐diatom type (Hutchinson). Rotifers dominated the zooplankton community. A well established macrophytic vegetation was lacking.

Cytotoxic polyunsaturated fatty acid from Pediastrum

A polyunsaturated fatty acid isolated from a Pediastrum species was identified as (4 Z,7 Z,10 Z,13 Z)-hexadecatetraenoic acid. It inhibited the development of fertilized echinoderm eggs at a concentration of 25 μg/ml.