Coccal Green Algae Research Articles

Vegetation dynamics in a disturbed lacustrine record: The Eocene maar lake of Groß-Zimmern (Hesse, SW Germany)

Palynological studies of lacustrine sediments in Eocene maar craters on the Sprendlinger Horst (Hesse, SW Germany) are complemented by 26 core samples from Groß-Zimmern. In addition, diatoms have been studied to assess palaeolimnological conditions. The palynomorph assemblage proves a middle Eocene age more or less coeval to the upper part of the nearby lacustrine succession at Messel. The core includes 33 m of massive to finely laminated bituminous shale abruptly following the underlying breccia of the diatreme filling. The lacustrine deposits are characterised by frequent mass movements and redeposition probably due to tectonic activity in combination with syn- and postsedimentary subsidence in the lake basin. Together with a diatom assemblage characteristic for shallow to moderately deep water, this indicates that the core was drilled in the area of a marginal syncline rather than in the centre of the basin. Freshwater conditions with low nutrient levels were inferred for Lake Groß-Zimmern from diatoms and coccal green algae. Despite the strong disturbance of the sedimentary record, results of cluster analysis and non-metric multidimensional scaling (NMDS) of the palynomorph assemblages can be compared to the undisturbed succession from Messel. This includes successional stages of the azonal vegetation in the crater area during an initial and early recolonisation phase as well as in the zonal vegetation, which are related to the reoccupation of the crater area by a thermophilic forest. Furthermore, slight changes of the climate can be inferred.

Mychonastes dominates the photosynthetic picoeukaryotes in Lake Poyang, a river-connected lake.

Lake Poyang, which is connected to the Yangtze River, is the largest freshwater lake in China and experiences large and frequent changes in water levels. The seasonal diversity and composition of photosynthetic picoeukaryotes (PPEs) in Lake Poyang were investigated from flow-cytometry-sorted samples using MiSeq high-throughput sequencing. Flow cytometric counting indicated that PPEs accounted for 97% of the total picophytoplankton abundance in spring, reaching a maximum value of 6.30 × 104 cellsmL-1. PPEs in Lake Poyang showed lower diversity than those in other investigated lakes in the lower reaches of the Yangtze River and were dominated by one OTU (66.29%) affiliated with Mychonastes (Chlorophyceae). Other minor classes of PPEs were found to be sporadically abundant in specific seasons, i.e. Chrysophyceae prevailed in spring and summer, while Eustigmatophyceae was mainly present in winter. This study reports coccal green algae of Mychonastes in Lake Poyang; additionally, these algae are reportedly representative of the prominent plankton in this river-connected lake ecosystem but are often overlooked due to their lack of morphological features. Finally, the sequencing results from the sorted samples of Lake Poyang revealed that the proportion of PPEs was quite low, with an average of 36% of total reads. Many OTUs belonging to heterotrophic picoeukaryotes were also identified in the sorted samples, most of which were affiliated with terrestrial fungi, including Basidiomycota and Ascomycota. The spores of these fungi can disperse in the aquatic environment during the flood seasons, yet their effect on PPEs is still unclear.

Lichen photobiont diversity and selectivity at the southern limit of the maritime Antarctic region (Coal Nunatak, Alexander Island)

Antarctic ice-free inland sites provide a unique perspective on the strategies coevolving organisms have developed for survival at the limits of life. Here, we provide the first combined description of the ecological and genetic diversity of lichen photobionts colonising an isolated Antarctic inland site, Coal Nunatak, on south-east Alexander Island (Antarctic Peninsula). Photobionts of 14 lichen species (42 samples), all belonging to the group of coccal green algae, representing the entire lichen community of Coal Nunatak were investigated using the internal transcribed spacer region (ITS) of the nuclear ribosomal DNA. The study attempted to address the hypothesis that mycobiont selectivity for the photobiont partner is lower in more extreme environments. This hypothesis did not appear to hold true for the entire lichen community except one species. Another aspect focuses on the relevance of the reproduction modus concerning the distribution of photobiont haplotypes in the lichen community.

First Limnological Records of Highly Threatened Tropical High-Mountain Crater Lakes in Ethiopia

Lakes Dendi, Wonchi and Ziqualla are among the few remnants of undisturbed crater lakes in the central highlands of Ethiopia, and have never been investigated reliably owing to seclusion and inaccessibility. As the lakes offer a pristine environment in a beautiful landscape and are located in the vicinity of the capital city Addis Ababa, they are highly threatened by unsustainable tourism, shoreline and crater rim modifications, water abstraction and land grabbing. We provide a first limnological description to establish baseline data against which future environmental and biological changes can be monitored. The lakes are located above 2,800 m elevation with no surface outflow and generally show low concentrations of ions, displaying an equal distribution of readily soluble components like Na or K throughout the water column, but distinct oxygen depletion in greater depths linked to rising concentrations of Fe and Mn, which indicates subterranean springs. Based on nutrients, chlorophyll a, and water transparency, lakes Dendi and Wonchi are classified as oligotrophic and Ziqualla as oligo-mesotrophic. The phytoplankton community is dominated by coccal green algae, desmids and dinoflagellates in lakes Dendi and Wonchi, typical for unpolluted dilute waterbodies; whereas chlorococcales, in particular Botryococcus braunii and benthic diatoms, prevail in Ziqualla. The zooplankton fauna is depauperate, comprising a total of 11 rotifer taxa and 13 crustaceans. Copepods were the most abundant group and contributed over 60% to the total zooplankton abundance in all three lakes, followed by rotifers and cladocerans. The conservation significance of these lakes lies predominantly in their representation of dilute, nutrient–poor highland lake systems that support diverse biota assemblages like desmids and daphnids, which are highly sensitive to eutrophication.

Natural xenobiotics to prevent cyanobacterial and algal growth in freshwater: Contrasting efficacy of tannic acid, gallic acid, and gramine

Allelochemical action against planktonic phototrophs is one central issue in freshwater ecology and quality management. To determine some basic mechanisms of this toxic action, we exposed the coccal green alga, Desmodesmus armatus, and the coccal cyanobacterium, Microcystis aeruginosa, in a batch culture well-supplied with carbon dioxide to increasing concentrations of the polyphenols tannic acid and gallic acid and the alkaloid gramine. The phototrophs were checked after 2d and at the end of the culture for biomass-based growth rates, cell volume, maximum quantum yield of photosystem II (ΦPSIImax), chlorophyll a content (chla) after 2d and at the end of the culture, and lipid peroxidation only at the end of the culture. During the culture, the pH rose from 7.64 to 10.95, a pH characteristic of eutrophic freshwater bodies during nuisance algal blooms. All xenobiotics reduced the growth rate, ΦPSIImax, and chla during the first 2d with M. aeruginosa being more sensitive to the polyphenols than D. armatus. The efficacy of the polyphenols declined with increasing pH, indicating potential polymerization and corresponding reduced bioavailability of the polyphenols. In contrast to the polyphenols, gramine increased its toxic action over time, independent of the prevailing pH. All exposures caused slight to severe lipid peroxidation (LPO) in the phototrophs. Hence, one mechanism of growth inhibition may be oxidative stress-mediated reduction in photosynthesis. The presented results suggest that in successful field trials with leachate, the prevailing environmental conditions may inactivate polyphenols and xenobiotics other than polyphenols may be more effective.

Algal diets and natural xenobiotics impact energy allocation in cladocerans. II. Moina macrocopa and Moina micrura

In freshwater lakes, changing mineral and biochemical food qualities as well as exposure to natural xenobiotics, such as humic substances (HSs) are common challenges to life history traits of zooplankters. In this contribution, we tested the bottom-up effect of different food qualities alone and in concert with exposure to increasing HS concentrations in a clone of each Moina micrura (inhabitant of Brazilian coastal lagoons) and Moina macrocopa (invasive species). Carbon, nitrogen, and phosphorus contents, fatty acid (FA) and the amino acid (AA) patterns of three coccal green algae of the summer aspect in the lagoons were analyzed. All algae were deficient in P, differed in their content of α-linolenic acid (ALA), histidine, and arginine and were lacking long-chained polyunsaturated fatty acids (PUFAs >C18). M. micrura did not grow on Desmodesmus armatus . Maximal mean lifespan and total lifespan reproduction were achieved on Pseudokirchneriella subcapitata . M. macrocopa fed all algae offered. Multiple regressions showed that ALA triggered longevity and the P-content reproduction. Exposure to HSs revealed that M. micrura reduced either its lifespan on Monoraphidium minutum or its reproduction on P. subcapitata . Conversely in M. macrocopa , lifespan on M. minutum was extended by a factor of 1.7 and offspring numbers increased by 1.4 upon HS exposure. On D. armatus an originally very low reproductive output increased maximal by a factor 4.6. Relating HS-mediated lifespan and offspring modulations of the 1.08 mM exposure to food components, it appears that ALA controls lifespan modulation even under HS stress, whereas offspring modulation seems to be controlled by C and total AA content. This indicates that, upon HS exposure, the investment of energy in body maintenance or reproduction would depend at least partly on the biochemical composition of the food available. This also shows that even short-chained dietary PUFAs may play a major role in keeping lipid peroxidation low. A comparison of the two Moina species tested revealed that M. macrocopa has the capacity to outcompete M. micrura , since it had the greater clutch size, never reduced the reproductive output upon HS-exposure, and fed all diets offered.

Algal diets and natural xenobiotics impact energy allocation in cladocerans. I. Daphnia magna

Recently emerged indications imply that particular concentrations and qualities of dissolved organic carbon (DOC) have the potential to reduce species diversity in zooplankton. In this contribution, we tested the impact of a major component of DOC, the dissolved humic substances (HSs), on two life history traits of a clone of Daphnia magna , namely lifespan and reproduction. We chose reproduction as a variable since it guarantees the persistence of the population in its habitat, and lifespan was selected as the most integrative individual variable. We found that lifespan was extended by exposure to HSs, but lifetime reproduction was clearly reduced. On the other hand, the mineral and biochemical composition of food also significantly modulated these life history traits. By feeding coccal green algae that contained linolenic acid, arginine (Arg), and histidine (His), but that lacked polyunsaturated fatty acids (PUFAs) with C-back bones >18, we examined how short-chained PUFAs, either alone or in concert with Arg and His, are able to modulate life history traits. Our expectation was that the additional challenge by HSs would shift the energy allocation in favor of reproduction. We found that the carbon and amino acid content may account for longevity, even when challenged by HSs. Reproduction appeared to be triggered by the C:P and N:P ratios of the food, particularly given the rather low P-content, which was within the range of severe growth limitation. Consequently, exposure to HSs reduced offspring numbers. Resting eggs without males occurred only in Desmodesmus armatus fed Daphnia that were simultaneously exposed to HSs. Under these conditions, the total amino acid (AA) content seemed to trigger reproduction. In summary, exposure to HSs appeared to have the potential to change the competitive ability of zooplankters by modulating the energy allocation between body maintenance and reproduction.

Algae influence the hydrophysical parameters of a sandy soil

abstract Article history:Received 2 August 2011Received in revised form 31 January 2012Accepted 3 February 2012Available online xxxxKeywords:AlgaeBiological soil crustSoil water repellencySand duneSorptivityHydraulic conductivity Biological soil crusts have a major effect on water flow in soils. Two study sites, located at a pine-forest gladecovered with a biologicalsoil crust, formed the basis of our study. The sand soil atthe surface (Glade soil) wascompared to a control soil (Pure sand) with limited impact of vegetation or organic matter, occurring at50 cm depth beneath a glade area. To assess the influence ofalgae in the biological soil crust on the propertiesof pure sand, a coccal green alga (Choricystis minor), filamentous green alga (Klebsormidium subtile) and stra-menopile alga (Tribonema minus) were isolated from the top layer of glade soil and grown in the lab in Petridishes on sterile pure sand as monoalgal and bialgal (C. minor and K. subtile) crusts for 3, 5, 7, 9, 11, 13, 15, 17,19, and 21 days. Atthe end ofeach growth stage, the hydrophysicalparametersof crusted sand were estimat-ed after drying at 50 °C for 15 h (equivalent to a 3-day hot spell) and compared to the parameters of puresand. The hydrophysical parameters were substantially different between the two surfaces. The glade soilhad an index of water repellency about 18-times that of pure sand and the persistence of water repellencyalmost 54-times that of pure sand. Both sorptivity and hydraulic conductivity in the glade soil were about7% those of the pure sand, respectively. The growth of artificial algal crusts, characterized by an increase inorganic carbon content from 0.16% to 0.33%, resulted in an increase in water drop penetration time of thedried crusts up to 14-times that of the pure sand and a decrease in the water sorptivity of the dried crustsup to 10% that of the pure sand. Whereas K. subtile crusts (both monoalgal and bialgal with C. minor) hadup to a 9% decrease in hydraulic conductivity compared to pure sand, there was no impact of monoalgalC. minor and T. minus crusts on hydraulic conductivity. K. subtile was possibly limited to surface growth,whereas C. minor and T. minus penetrated to depth. Consequently, K. subtile may have clogged the toppores more effectively than the other two strains. The water repellency cessation time increased with anincrease in water drop penetration time for all the dried monoalgal and bialgal crusts used in this study. Agreater impact of K. subtile on the shifts in hydraulic behaviour could influence water capture and storage,potentially decreasing evaporation during dry periods, but enhancing overland flow diminishing leachingduring wet periods.© 2012 Elsevier B.V. All rights reserved.

Ettliella tetraspora (Chlorophyta, Chlorophyceae): life cycle and taxonomy.

The morphology and mode of reproduction in Ettiella tetraspora Hindak 1988, a green coenobial alga described from the Czech Republic and Finland, were studied from the plankton of the water reservoir Formitzspeicher in NE Bavaria, Germany. The morphology of cells and coenobia of the species in this population was in agreement with published data for the species, but its reproduction was not of the Oocystis - type as it has been declared in the relevant literature. The protoplast of mother cells does not divide simultaneously into 4 autospores as in many coccal green algae, but always in two autospores. The first division of the mother cell is perpendicular to the longitudinal axis of the cell and two walled daughter cells arise. Subsequently, the newly formed daughter cells divide again, but this time perpendicular to the new formed cell cross wall. Ultimately, in a new coenobium all four daughter cells are arranged in parallel. Daughter cells remain inside a slightly enlarged mother cell wall (well visible only near the cross wall) and are released by its gelatinisation. Such subsequent production of four autospores from the mother cell represents a special type of multiplication in the green coccal algae known also in some other species [e.g. Tetrastrum komarekii Hindak 1977, Willea irregularis (Wille) Schmidle 1900, Makinoella tosaensis Okada 1949].

Does quinone or phenol enrichment of humic substances alter the primary compound from a non-algicidal to an algicidal preparation?

Dissolved organic matter (DOM) has been shown to affect phytoplankton species directly. These interactions largely depend on the origin and molecular size of DOM and are different in prokaryotes and eukaryotes. In a preceding study, however, two humic substance preparations did not adversely affect coccal green algae or cyanobacterial growth even at high concentrations of dissolved organic carbon (DOC). These results contradicted previous findings, showing a clear, negative response of different phototrophs to much lower DOC concentrations. To test whether or not at least defined building blocks of humic substances (HSs) are effective algicidal structures, we enriched two humic preparations with hydroquinone and p-benzoquinone, respectively, and exposed two different green algae, Pseudokirchneriella subcapitata and Monoraphidium braunii, and two cyanobacterial species, Synechocystis sp. and Microcystis aeruginosa, to the unmodified and enriched HSs. As response variables, growth rates in terms of biomass increase, chlorophyll-a content, and photosynthetic yield were measured. The highest concentration (4.17mM DOC) of the modified HSs clearly inhibited growth; the cyanobacterial species were much more sensitive than the green algal species. However, realistic ecological concentrations did not adversely affect growth. Aerating the exposure solution for 24h strongly reduced the inhibitory effect of the modified HSs. The algicidal effect was obviously caused by monomers and not by polymerised high molecular weight HSs themselves. Furthermore, the maximum quantum yield (Φ PSII max) was stimulated in the green algal species by low and medium DOC concentrations, but reduced in the cyanobacterial species upon exposure to higher HS concentrations. The quinone- and phenol-enriched HSs only showed algicidal activity at high concentrations of 4.17mM DOC and lost their effects over time, presumably by oxidation and subsequent polymerisation. This study confirms that the applied humic substances themselves are not effective algicides even if enriched in effective structures.

Selected coccal green algae are not affected by the humic substance Huminfeed® in term of growth or photosynthetic performance

Humic substances (HSs) have been shown to influence growth, photophysiology, and redox homeostasis in phototrophs. However, many ecological studies deliver controversial results indicating inhibitory or stimulating effects depending on the kind of phototrophic organism or type of HSs applied. Here we analyzed the effect of Huminfeed® (HF), a preparation from leonardite associated with lignite deposits, on growth and photosynthetic performance of three different coccal green algae. Concentrations of HF in the range of 2–20 mg l−1 dissolved organic carbon (DOC) did neither affect the growth rate nor the light-adapted photosynthetic electron transport. Even photoinhibitory light intensities of 1,600 μmol photons m−2 s−1, representing the tenfold of growth light intensity, did not result in a decline of the maximal photosynthetic rate in HF-treated algae. In HF-grown algae, a very subtle decrease by about 10% could be observed in thermoluminescent light emission, a sensitive method to detect changes in photosystem II (PSII) chemistry. However, thermoluminescence (TL) represents only 3% of the light-induced charge separated states in PSII. Hence, rather small changes will not have significant effects on overall photosynthetic performance and growth. Therefore, the physiological effect of HSs on freshwater phototrophs has to be revisited.

Impact of two different humic substances on selected coccal green algae and cyanobacteria—changes in growth and photosynthetic performance

There is growing evidence to show that dissolved humic substances, HSs, can directly interact with freshwater organisms, such as phototrophic organisms, cladocerans, amphipods and fish. The responses are-at least in part-transcriptionally controlled. These interactions can lead to stress symptoms in the exposed organisms. In phototrophs, stress symptoms include a reduction in photosynthetic oxygen release and antioxidative stress. Besides the direct effects, HSs also cause indirect effects that provoke different physiological adaptations in the phototrophs. The HS-influenced photosynthetic performance and stress response of two different green algae, Pseudokirchneriella subcapitata (Koršikov) Hindák and Monoraphidium braunii (Nägeli in Kützing) Komárková-Legnerová, and two cyanobacterial species, Synechocystis sp. (PCC 6803, Institut Pasteur) and Microcystis aeruginosa (PCC 7806, Institut Pasteur), were tested. Two humic preparations were applied, the synthetic HS1500 and HuminFeed, HF, which had previously been proven effective in bioassays with invertebrates and a water mould. When the algae were grown near light saturation, most of the tested species were positively affected by HSs in growth rate or chlorophyll content. Cell sizes decreased with increasing HS concentrations for all eukaryotic phototrophs, except for the cyanobacteria. After 4 to 5 days of cultivation at the highest HS exposure, there was a decrease in total dry weight due to reduced cell sizes in contrast to an increase in cell numbers. With the exception of Synechocystis, the dry weight per cell ratio decreased with increasing HS concentration. The efficiency of utilizing absorbed light quanta increased with increasing HS concentrations; the maximum quantum yield of photosystem II (ΦPSIImax) was higher in all of the tested species, with the exception of M. aeruginosa, after exposure to HS. The applied humic preparations did not interact directly with PSII, but changed the physiological state of the algae, especially the photosynthetic performance. Neither the green algae nor the cyanobacteria were inhibited in growth or negatively affected in their photosynthetic performance. The exposure to lower concentrations of HS stimulated better growth of the phototrophs. The tested humic preparations obviously did not have the potency to act as xenobiotic stressors; furthermore, there was no sign of herbicide potency.

Rare Pediastrum species (Chlorophyceae) from Polish coastal lakes

An account is given of the occurrence of <em>Pediastrum</em> (<em>Chlorophyceae</em>, <em>Sphaeropleales</em>) in five eutrophic coastal lakes (Jamno, Bukowo, Gardno, Łebsko and Sarbsko) in northern Poland, together with morphological data of the species and more detailed taxonomic and ecological information for three taxa which appear to be rare world wide. These are <em>P. musterii</em>, <em>P. orientale</em> and <em>P. alternans</em>; the first is recorded for the first time from central Europe. <em>P. orientale</em> and <em>P. alternans</em> show considerable morphological variability under different environmental conditions, indicating the need for further studies. The studied lakes seem to be especially favourable for <em>Pediastrum</em>, with a total of eight species (15 taxa) in the phytoplankton noted during the summer. However, the relative frequency of the genus in the overall algal communities was low. The most frequent species were <em>P. boryanum</em>, <em>P. kawraiskyi</em> and <em>P. duplex</em> and these were accompanied by cyanobacteria, coccal green algae (<em>Chlorophyceae</em>, <em>Chlorococcales</em>) and diatoms (<em>Bacillariophyceae</em>). All the <em>Pediastrum</em> taxa were documented using LM and SEM.

Initial Events Associated with Virus PBCV-1 Infection of Chlorella NC64A.

Chlorella viruses (or chloroviruses) are very large, plaque-forming viruses. The viruses are multilayered structures containing a large double-stranded DNA genome, a lipid bilayered membrane, and an outer icosahedral capsid shell. The viruses replicate in certain isolates of the coccal green alga, Chlorella. Sequence analysis of the 330-kbp genome of Paramecium bursaria Chlorella virus 1 (PBCV-1), the prototype of the virus family Phycodnaviridae, reveals <365 protein-encoding genes and 11 tRNA genes. Products of about 40% of these genes resemble proteins of known function, including many that are unexpected for a virus. Among these is a virus-encoded protein, called Kcv, which forms a functional K(+) channel. This chapter focuses on the initial steps in virus infection and provides a plausible role for the function of the viral K(+) channel in lowering the turgor pressure of the host. This step appears to be a prerequisite for delivery of the viral genome into the host.

Diversity of subaerial algae and cyanobacteria on tree bark in tropical mountain habitats

AbstractWe report the species composition of subaerial epixylic algae and cyanobacteria from a South-East Asian mountain rainforest locality in Cibodas, West Java. Green algae (Trebouxiophyceae, Chlorophyceae, Trentepohliales) were dominant and Cyanobacteria were the second most frequent group. We specifically concentrated on the comparison of species composition of closed primary forest and open antropogenic spaces. Trentepohliales and Cyanobacteria dominated in open spaces with higher light intensities, whereas closed forest localities were dominated by trebouxiophycean coccal green algae. There was a significantly higher algal diversity in open spaces than in closed forest samples indicating the limiting effect of light on subaerial algal communities of closed tropical forests. A number of isolated strains and morphotypes probably represent undescribed taxa.

Seasonal variability of Holocene climate: a palaeolimnological study on varved sediments in Lake Jues (Harz Mountains, Germany)

Studies combining sedimentological and biological evidence to reconstruct Holocene climate beyond the major changes, and especially seasonality, are rare in Europe, and are nearly completely absent in Germany. The present study tries to reconstruct changes of seasonality from evidence of annual algal successions within the framework of well-established pollen zonation and 14C-AMS dates from terrestrial plants. Laminated Holocene sediments in Lake Jues (10°20.7′ E, 51°39.3′ N, 241 m a.s.l.), located at the SW margin of the Harz Mountains, central Germany, were studied for sediment characteristics, pollen, diatoms and coccal green algae. An age model is based on 21 calibrated AMS radiocarbon dates from terrestrial plants. The sedimentary record covers the entire Holocene period. Trophic status and circulation/stagnation patterns of the lake were inferred from algal assemblages, the subannual structure of varves and the physico-chemical properties of the sediment. During the Holocene, mixing conditions alternated between di-, oligo- and meromictic depending on length and variability of spring and fall periods, and the stability of winter and summer weather. The trophic state was controlled by nutrient input, circulation patterns and the temperature-dependent rates of organic production and mineralization. Climate shifts, mainly in phase with those recorded from other European regions, are inferred from changing limnological conditions and terrestrial vegetation. Significant changes occurred at 11,600 cal. yr. BP (Preboreal warming), between 10,600 and 10,100 cal. yr. BP (Boreal cooling), and between 8,400 and 4,550 cal. yr. BP (warm and dry interval of the Atlantic). Since 4,550 cal. yr. BP the climate became gradually cooler, wetter and more oceanic. This trend was interrupted by warmer and dryer phases between 3,440 and 2,850 cal. yr. BP and, likely, between 2,500 and 2,250 cal. yr. BP.

Coccal green algae (Chlorophyta) in shallow ponds in Veracruz, Mexico

Coccal green algae (Chlorophyta) in shallow ponds in Veracruz, Mexico

Differential Sensitivity of a Coccal Green Algal and a Cyanobacterial Species to Dissolved Natural Organic Matter (NOM) (8 pp)

and Aim. In non-eutrophicated freshwaters, humic substances (HS) pose chemical stresses on aquatic organisms and, hence, separating sensitive from less sensitive or even tolerant species. One of the stresses, identified so far, is the reduction of photosynthetic oxygen production and reduction in growth in freshwater macrophytes and algae. In a previous paper, it has been shown that even closely related coccal green algae responded differently upon identical stress by HS, which is consistent with the hypothesis above. Due to their much simpler cellular ultrastructure, cyanobacteria are supposed to be more sensitive to HS exposure than eukaryote should be. One coccal green algal species (Desmodesmus communis) and one cyanobacterium (Chroococcus minutus) were exposed to four natural organic matter (NOM) isolates. One NOM has been isolated from a brown water lake (Schwarzer See) in Brandenburg State; three were obtained from a comprehensive Scandinavian NOM research project and originated from Norway (Birkenes), Finland (Hietajärvi), and Sweden (Svartberget). Cultures of D. communis and C. minutus were obtained from the Culture Collection of Algae, Göttingen, and maintained in a common medium. The cultures were non-axenic. The algae and cyanobacteria were exposed under identical conditions to environmentally realistic NOM concentrations. Cell numbers were counted microscopically in Neugebauer cuvettes in triplicates. To avoid limitation by nutrient depletion, the experiments were terminated after 14 to 15 days. Until culture day 12, no growth limitation has been observed in the controls. All NOM isolates modulated the growth of the algae and cyanobacteria. During the early culture days, there was a slight growth promotion with the coccal green alga and to a much lesser degree with the cyanobacterium. Yet, the major effect were significant reductions in cell yield in both primary producer cultures. C. minutus was much more affected than D. communis. This applies particularly to the three tested Scandinavian NOM isolates, which were effective at concentrations even below 1 mg L-1 DOC. The growth promoting effect may be due to an increase in bioavailability of some trace nutrients in the presence of NOM, the release of some growth promoting substances by microbial or photochemical processing of the NOM, and/or a hormetic effect. The growth reducing effect can be explained as a herbicide-like mode of action that affects the photosystem II most prevalent by blocking the electron transport chain, absorption of electrons, or production of an internal oxidative stress after processing the bioconcentrated HS. Furthermore, it may be postulated that also photo-toxicity of these HS in the algal cells contributes to the overall toxicity; however, experimental evidence is lacking so far. Upon exposure to HS, cyanobacteria appear to be much more sensitive than coccal green algae and respond in growth reduction. This high sensitivity of cyanobacteria to HS may explain phytoplankton patterns in the field. Eutrophic, humic-rich lakes do not support the cyanobacterial blooms characteristic of eutrophic, but humic-poor lakes. In the humic-rich systems, raphidophytes or, less frequent, specific coccal greens are more common. Obviously, cyanobacteria appear to be unable to make advantage of their accessory pigments (phycocyanin) to exploit the reddish light prevailing in humic-rich lakes. . At present, no effective structure can be figured out which may be responsible for the adverse effect on the cyanobacterial species. It is reserved to future research whether or not HS may be applied more specifically (for instance, with elevated moieties of the effective structures) as a natural geochemical to combat cyanobacterial blooms.

Late Glacial and Holocene history of Plešné Lake and its surrounding landscape based on pollen and palaeoalgological analyses

Pollen analysis has been carried out on a 549 cm thick sediment profile from lake Plesne jezero (Plesne Lake) in the Bohemian Forest (Sumava, Czech Republic; 1090 m a.s.l.; 48°47′ N; 13°52′ E). Analyses of 67 samples characterise the development of the lake biotope and the surrounding landscape during the last ca. 14,000 years. The pollen diagram shows a very distinct transition between the Late Glacial and the Holocene biostratigraphic units at a depth of ca. 312 cm. In the surroundings of Plesne Lake the vegetation was treeless during the entire Late Glacial. The alpine tree limit, formed by Betula and Pinus with undergrowth of shrubs, might have been at ca. 500 m a.s.l. Pollen transported from long distances was significant due to the openness of the landscape, coming from southern Europe and even Africa, and including high numbers of Artemisia, Poaceae, Chenopodiaceae, and some other herbs and shrubs from steppe and forest-steppe areas in southern Europe or Africa (likely Ephedra, certainly Lygeum spartum). The expansion of shrubs, particularly Juniperus, preceded the expansion of trees near the end of the Late Glacial. Afforestation of the region by thin stands of Betula and Pinus occurred during the Preboreal. Significant warming in the Boreal resulted in the expansion of Corylus, Quercetum mixtum (QM) trees, and probably also Picea and Alnus. Picea as well as QM trees were further expanding during the Early Atlantic. Picea was the dominant tree during the Late Atlantic and Fagus started to spread towards its end. Abrupt expansion of Abies marks the Subboreal. A high degree of afforestation (Abies, Fagus, Picea) was characteristic for the Early Subatlantic. During Late Subatlantic, pollen of synanthropic plants appears. Phases of the lake biotope development were defined on the basis of coccal green algae and Isoetes.

Natural Organic Matter Differently Modulates Growth of Two Closely Related Coccal Green Algal Species (6 pp)

Humic substances (HS) comprise the majority of dead and living organic carbon, including organisms. In the environment, they are considered to be chemically inert or at least refractory. Recent papers, however, show that HS (including natural organic matter-NOM, isolated by reverse osmosis) are natural chemicals which interact with aquatic organisms. They are taken up and cause a variety of stress defense reactions which are well known from man-made chemicals. These reactions include chaperon activation, induction and modulation of biotrans-formation enzymes, or induction of antioxidant defense enzymes. One specific reaction with freshwater plants is the reduction of photosynthetic oxygen release. In this contribution, we compare the susceptibilities (cell yield) of two closely related coccal green algae, Monoraphidium convolutum and M. minutum, towards various NOM isolates. Cultures of M. convolutum and M. minutum were obtained from the algal collection of the Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, and from the Culture Collection of Algae, Göttingen, and maintained in a common medium. The cultures were non-axenic. The algae were exposed to 5 mg L(-1) DOC of each humic material, an environmentally realistic concentration. Cell numbers were counted microscopically in Neugebauer cuvettes in 5 replicates on days 1, 4, 7, 10, 14, and 21. Almost all NOM isolates modulated the growth of the algae. Only the NOM of a Norwegian raised peat bog lake did not reveal any significant effect with M. convolutuim. In general, the results with two algal species are by no means uniform. For instance, Suwannee River NOM causes a decrease in cell density with M. minutum, but temporarily stimulates the growth of M. convolutum. The opposite applies to Aurevann NOM: Growth increase in M. minutum, but a bi-phasic response in M. convolutum. Different responses of both Monoraphidium species must be attributed to intrinsic factors of the algae rather than only to chemical features of the exposed materials, because the exposures were identical with both algal species. The reduction in growth yields can be explained as a herbicide-like mode of action that affects the photosystem II most prevalently. The growth promoting effect remains somewhat obscure. It may be due to (1) an increase in bioavailability of some trace nutrients in the presence of HS, (2) the release of some growth promoting substances by microbial or photochemical processing of the humic materials, and (3) a hormetic effect upon the exposure of HS. Hormesis means stimulation of organisms or metabolic activities when exposed to noxes in low concentrations. However, it is still open to discussion why the growth promotion only applies to one or the other, but not simultaneously to both Monoraphidium species. Exposure of the closely related coccal green algal species to humic material changes their growth characteristics. Since the reactions are not consistent within the two species and the various humic materials, it seems that the less sensitive species is favored by HS exposure. The environmental relevance, however, is subject to future studies.