We studied the diversity of
using reverse line blot hybridization with
lineage-specific probes in the freshwater canyon-shaped Římov reservoir (Czech Republic). To examine the succession of distinct ...lineages, we performed (i) a study of an intensive spring sampling program at the lacustrine part of the Římov reservoir (from ice melt through a phytoplankton peak to the clear-water phase), and (ii) a seasonal study (April to November) when the occurrence of distinct
lineages was related to the inherent longitudinal heterogeneity of the reservoir. Significant spatiotemporal changes in the compositions of distinct
lineages allowed for the identification of "generalists" that were always present throughout the whole season as well as "specialists" that appeared in the reservoir only for limited periods of time or irregularly. Our results indicate that some phytoplankton groups, such as cryptophytes or cyanobacteria, and zooplankton composition were the major factors modulating the distribution and dynamics of distinct
lineages. The highest
diversity was observed during the spring algal bloom, whereas the lowest was during the summer cyanobacterial bloom. The microdiversity also markedly increased upstream in the reservoir, being highest at the inflow, and thus likely reflecting strong influences of the watershed.
The genus
is a typical freshwater bacterioplankton and is believed to play a significant role in inland freshwater habitats. This work is unique in detecting and tracing different closely related lineages of this bacterial genus in its natural conditions using the semiquantitative reverse line blot hybridization method and in discovering the factors influencing the microdiversity, subtype alternations, and seasonality.
Small lakes and ponds occupy an enormous surface area of inland freshwater and represent an important terrestrial-water interface. Disturbances caused by extreme weather events can have substantial ...effects on these ecosystems. Here, we analysed the dynamics of nutrients and the entire plankton community in two flood events and afterwards, when quasi-stable conditions were established, to investigate the effect of such disturbances on a small forest pond. We show that floodings result in repeated washout of resident organisms and hundredfold increases in nutrient load. Despite this, the microbial community recovers to a predisturbance state within two weeks of flooding through four well-defined succession phases. Reassembly of phytoplankton and especially zooplankton takes up to two times longer and features repetitive and adaptive patterns. Release of dissolved nutrients from the pond is associated with inflow rates and community recovery, and returns to predisturbance levels before microbial compositions recover. Our findings shed light on the mechanisms underlying functional resilience of small waterbodies and are relevant to global change-induced increases in weather extremes.
Summary
The ecological relevance and factors shaping dynamics of Limnohabitans sp. have been largely studied by fluorescence in situ hybridization with a 16S rRNA probe targeting the R‐BT group ...(lineages LimBCDE), but not lineage LimA. Consequently, ecology and distribution of LimA remained unknown. We developed a double hybridization strategy using a novel 23S rRNA probe specifically targeting LimA and LimE that in combination with the existing R‐BT probe can discriminate LimA populations. This technique was applied for more than 1000 samples from 46 freshwater sites including long‐term data sets from oligo‐mesotrophic Lake Zurich, CH and meso‐eutrophic Římov reservoir, CZ. LimA was ubiquitously distributed and highly abundant. Observed ecological preferences of LimA in Lake Zurich were in general similar to already reported for Limnohabitans with highest numbers in surface waters during growing seasons. Three times higher densities of LimA were detected in Římov reservoir, where they were significantly more abundant at the riverine zone especially after flood events that introduced fresh terrestrial DOM (dissolved organic matter). Moreover, statistical analyses of biological and physicochemical parameters obtained from small dynamic water bodies confirmed a correspondence between LimA and allochthonous DOM, in opposite to R‐BT that was more related to algal primary production.
Quillworts (Isoëtes) represent highly specialized flora of softwater lakes, that is, freshwater ecosystems potentially sensitive to acidification. In this paper, we combine a review of previous ...studies and our new results to address unrecognized reproduction strategies of quillworts to overcome long‐term environmental stresses. These strategies play an important role in the plant's ability to overcome atmospheric acidification of freshwaters, protecting the plants until their environment can recover. Environmental drivers of recovery of Isoëtes echinospora and I. lacustris were studied in two acidified lakes in the Bohemian Forest (Central Europe). Both populations survived more than 50 years of severe acidification, although they failed to recruit new sporelings. Their survival depended entirely on the resistance of long‐living adult plants because the quillworts do not grow clonally. During the past two decades, a renewal of I. echinospora population inhabiting Plešné Lake has been observed, while no such renewal of I. lacustris, dwelling in Černé Lake, was evident, despite similar changes in water composition occurring in both lakes undergoing advanced recovery from acidification. Our in vitro experiments revealed that the threshold acidity and toxic aluminium concentrations for sporeling survival and recruitment success differed between I. echinospora (pH ≤ 4.0 and ≥300 μg L−1 Al at pH 5) and I. lacustris (pH ≤ 5.0 and ≥100 μg L−1Al at pH 5). The higher sensitivity of I. lacustris to both stressors likely stems from its year‐long germination period and underlines the risk of exposure to chronic or episodic acidification in recovering lakes. By contrast, the shorter germination period of I. echinospora (2–3 months) enables its faster and deeper rooting, protecting this quillwort from periodic acidification during the next snowmelt. Our study brings novel insights into widely discussed environmental issues related to the long‐term degradation of softwater lakes, which represent important hotspots of pan‐European biodiversity and conservation efforts.
Isoëtes echinospora and I. lacustris, the survivors in acidified lakes, have in fact suffered and their recruitment of new plants failed over decades. Stress‐tolerant life strategies of the quillworts, however, remain successful in Anthropocene.
Extracellular phosphatase activity (PA) has been used as an overall indicator of P depletion in lake phytoplankton. However, detailed insights into the mechanisms of PA regulation are still limited, ...especially in the case of acid phosphatases. The novel substrate ELF97 phosphate allows for tagging PA on single cells in an epifluorescence microscope. This fluorescence-labeled enzyme activity (FLEA) assay enables for autecological studies in natural phytoplankton and algal cultures. We combined the FLEA assay with image analysis to measure cell-specific acid PA in two closely related species of the genus
(Trebouxiophyceae, Chlorophyta) isolated from two acidic lakes with distinct P availability. The strains were cultured in a mineral medium supplied with organic (beta-glycerol phosphate) or inorganic (orthophosphate) P at three concentrations. Both strains responded to experimental conditions in a similar way, suggesting that acid extracellular phosphatases were regulated irrespectively of the origin and history of the strains. We found an increase in cell-specific PA at low P concentration and the cultures grown with organic P produced significantly higher (ca. 10-fold) PA than those cultured with the same concentrations of inorganic P. The cell-specific PA measured in the cultures grown with the lowest organic P concentration roughly corresponded to those of the original
population from an acidic lake with impaired P availability. The ability of
strains to produce extracellular phosphatases, together with tolerance for both low pH and metals can be one of the factors enabling the dominance of the genus in extreme conditions of acidic lakes. The analysis of frequency distribution of the single-cell PA documented that simple visual counting of 'active' (labeled) and 'non-active' (non-labeled) cells can lead to biased conclusions regarding algal P status because the actual PA of the 'active' cells can vary from negligible to very high values. The FLEA assay using image cytometry offers a strong tool in plankton ecology for exploring P metabolism.
Man-made reservoirs are common across the world and provide a wide range of ecological services. Environmental conditions in riverine reservoirs are affected by the changing climate, catchment-wide ...processes and manipulations with the water level, and water abstraction from the reservoir. Long-term trends of environmental conditions in reservoirs thus reflect a wider range of drivers in comparison to lakes, which makes the understanding of reservoir dynamics more challenging. We analysed a 32-year time series of 36 environmental variables characterising weather, land use in the catchment, reservoir hydrochemistry, hydrology and light availability in the small, canyon-shaped Římov Reservoir in the Czech Republic to detect underlying trends, trend reversals and regime shifts. To do so, we fitted linear and piecewise linear regression and a regime shift model to the time series of mean annual values of each variable and to principal components produced by Principal Component Analysis. Models were weighted and ranked using Akaike information criterion and the model selection approach. Most environmental variables exhibited temporal changes that included time-varying trends and trend reversals. For instance, dissolved organic carbon showed a linear increasing trend while nitrate concentration or conductivity exemplified trend reversal. All trend reversals and cessations of temporal trends in reservoir hydrochemistry (except total phosphorus concentrations) occurred in the late 1980s and during 1990s as a consequence of dramatic socioeconomic changes. After a series of heavy rains in the late 1990s, an administrative decision to increase the flood-retention volume of the reservoir resulted in a significant regime shift in reservoir hydraulic conditions in 1999. Our analyses also highlight the utility of the model selection framework, based on relatively simple extensions of linear regression, to describe temporal trends in reservoir characteristics. This approach can provide a solid basis for a better understanding of processes in freshwater reservoirs.
Display omitted
•Several competeing models were used to identify trends in reservoir time series.•Numerous contrasting trends and trend reversals were found.•Trend reversals in hydrochemistry resulted from dramatic socioeconomic changes•Decrease in the water level resulted in a regime shift in reservoir hydrodynamics•Our analyses highlight the utility of the model selection to describe temporal trends.
Summary
Diatoms are one of the most important phytoplankton groups. As they grow, diatoms use silicon to produce a siliceous frustule, which protects the cell. During April–November 2011, at 1–3 week ...intervals, we estimated diatom silicification rates at two distinct sites along the longitudinal profile of the canyon‐shaped eutrophic Římov Reservoir (Czech Republic): (i) a nutrient‐depleted lacustrine zone near the dam and (ii) a nutrient‐rich transition zone upstream near the river inflow.
Diatom silicification was estimated using the 24‐h in situ incubation of natural phytoplankton assemblage with a fluorophore 2‐(4‐pyridyl)‐5‐{4‐(2‐dimethylaminoethyl‐aminocarbamoyl)methoxyphenyl}oxazole (PDMPO) which fluorescently stains the newly synthesised diatom frustules.
Diatoms contributed an average c. 40% to the total phytoplankton biovolume in the lacustrine zone, but only c. 20% in the transition zone where a cyanobacterial bloom developed during summer. Asterionella formosa and Fragilaria crotonensis were the most abundant diatom species, while Aulacoseira italica, Nitzschia acicularis, Synedra acus and Stephanodiscus sp. were less important. Silicification rates of all diatom species were significantly higher in the transition zone than at the dam.
The intensity of PDMPO fluorescence per diatom cell was tightly related to the growth rates of three diatom species calculated from changes in cell counts during the incubation. The PDMPO technique can thus be used as a proxy for diatom growth.
Growth rates of the two most abundant diatom species were positively correlated with daily light exposure but not with nutrient concentrations.
•Acidic, aluminium-rich lake water damages sporeling absorptive organs in the sediment surface.•Threshold dose-response relationships were found for sporeling rhizoids and the first root.•Quillwort ...sporelings in vitro and in situ readily accumulate aluminium in their tissues.•Lake acidification did not impair deeply rooted adults, which have survived for five decades.
The aquatic quillwort Isoëtes lacustris L. survived five decades of severe acidification in Černé Lake (Bohemian Forest, central Europe), but failed to reproduce. To detect which ontogenetic stage is more affected by water acidification and to identify water chemistry thresholds for successful recruitment, experiments were carried out on quillwort sporelings grown in the laboratory, using different pH (4–8) and aluminium (Al) concentrations (0–1000 μg/L). Growth-related symptoms and Al accumulations in tissues were compared with those observed in sporelings collected in the lake. In the laboratory, the threshold Al concentrations ≥100 μg/L and pH ≤ 5.0 reduced absorptive organs (macrogametophyte rhizoids, roots, and root hairs), so that the ratio of below-ground to above-ground sporeling biomass decreased to <1. Nonetheless, stimulatory growth was demonstrated that affected the dose-response relationships of both absorptive and assimilative organs as well as sporeling growth restoration. The sporelings exposed to Al concentrations ≥100 μg/L accumulated high amounts of Al in their macrogametophytes and roots, but not in leaves. The lake sporelings had markedly longer roots, lower Al accumulations, but more reduced rhizoids and root hairs than those at 100 μg/L of Al in the laboratory. Even though water acidification was harmful to the shallow-rooted early ontogenetic stages, the in situ population survived due to the resistance and long life span of the deep-rooted adults. The effects of water acidification on sympatric congeneric quillworts as well as the other isoetids and competitive macrophytes in acid-sensitive softwater lakes are discussed, taking into account the influence of exposure to threshold acidity and Al toxicity and also the likelihood of such exposure.
The anoxygenic phototrophic bacteria (APB) are an active component of aquatic microbial communities. While DNA-based studies have delivered a detailed picture of APB diversity, they cannot provide ...any information on the activity of individual species. Therefore, we focused on the expression of a photosynthetic gene by APB communities in two freshwater lakes (Cep lake and the Římov Reservoir) in the Czech Republic. First, we analyzed expression levels of pufM during the diel cycle using RT-qPCR. The transcription underwent a strong diel cycle and was inhibited during the day in both lakes. Then, we compared DNA- (total) and RNA-based (active) community composition by sequencing pufM amplicon libraries. We observed large differences in expression activity among different APB phylogroups. While the total APB community in the Římov Reservoir was dominated by Betaproteobacteria, Alphaproteobacteria prevailed in the active library. A different situation was encountered in the oligotrophic lake Cep where Betaproteobacteria (order Burkholderiales) dominated both the DNA and RNA libraries. Interestingly, in Cep lake we found smaller amounts of highly active uncultured phototrophic Chloroflexi, as well as phototrophic Gemmatimonadetes. Despite the large diversity of APB communities, light repression of pufM expression seems to be a common feature of all aerobic APB present in the studied lakes.
Despite the global importance of phytoplankton primary production, the ecological role of cell death as an important loss process in phytoplankton is poorly understood. To assess the significance of ...cell death in phytoplankton, we studied cell viability of dominant species in the canyon-shaped eutrophic Římov Reservoir (Czech Republic) at weekly and biweekly intervals from April to October 2011. Surface samples were taken from the lacustrine zone (near the dam, low nutrient level) and transition zone (near the river inflow, high nutrient level) of the reservoir. Moreover, samples from euphotic depth (1% of surface irradiance) were taken from the lacustrine zone. We used the membrane-impermeant nucleic acid dye SYTOX Green to examine seasonal and spatial differences in phytoplankton cell viability. Three species (diatoms Asterionella formosa, Fragilaria crotonensis, and cyanobacterium Aphanizomenon flos-aquae) were studied in detail. There was no difference in Asterionella cell viability among sampling sites. In the lacustrine zone, Fragilaria and Aphanizomenon exhibited lower viability than in the transition zone. In addition, Aphanizomenon viability was significantly lower at the euphotic depth. Nutrient levels were revealed as a factor influencing Fragilaria viability, while light availability was more important for Aphanizomenon. Our results evidenced that the importance of cell death, in particular phytoplankton taxa, varies both spatially and temporally. Moreover, our study indicates that coexisting taxa may differ in their capacity to cope with different environmental stressors.
PDF
