Viera Straskrábová

Academy of Sciences of the Czech Republic, Praha, Praha, Czech Republic

Are you Viera Straskrábová?

Claim your profile

Publications (8)15.33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The quantitative distribution and relationships of picocyanobacteria and viruses were studied in the mesotrophic Sheksna and mesoeutrophic Rybinsk reservoirs belonging to the system of the Volga-Baltic Waterway. The share of picocyanobacteria in the sum biomass and production of phytoplankton decreased along with increase in the productivity in the waterbody. However, the abundance of virioplankton increased in such conditions. The extent of infection by phages and virus-induced mortality of picocyanobacteria were two times higher on average in the mesoeutrophic reservoir compared to the mesotrophic one: 14 and 7% of the number of picocyanobacteria, 21 and 11% of daily production of picocyanobacteria, respectively. Mortality in picocyanobacteria resulted from lysis by viruses increased (up to 52% of daily production of picocyanobacteria) at the local parts where water was blooming with phytoplankton and at the parts affected by communal pollution.
    Izvestiia Akademii nauk. Seriia biologicheskaia / Rossiiskaia akademiia nauk 01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: As part of a comprehensive evaluation of the status of remote mountain lake ecosystems throughout Europe, the response of key organisms in mountain lakes to variations in environmental gradients due to geography and climate, pollution and catchment characteristics in Scotland was examined. Samples were taken from the pelagic (zooplankton, bacteria and chlorophyll a) and littoral (benthic invertebrates and epilithic diatoms) zones. Surface sediment samples were taken for analysis of sub-fossil cladocera, chironomids, diatoms and pigments. Concentrations of trace metals, persistent organic pollutants and spheroidal carbonaceous particles were also measured. This paper describes the variation in species composition and environmental characteristics of upland lochs across northern Scotland and examines how the former may be related to the latter. Multivariate techniques were employed to examine patterns and relationships within and among the multivariate species and environmental datasets. Results show that in remote mountain lakes in Scotland, biological assemblages of key organisms groups are driven by a number of environmental gradients, in particular organic content and acid-base status. It appears that these systems can broadly be divided, on the basis of their species composition. into two main types. Low alkalinity lochs with sparse soil coverage at higher altitudes have distinctly different biological communities compared with lochs with high organic levels and high proportions of peaty soils in the catchments.
    Fundamental and Applied Limnology - Advances in Limnology. 01/2009; 62:379-417.
  • Advances in Limnology 01/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The relationship between flow cytometry data and epifluorescence microscopy measurements was assessed in bacterioplankton samples from 80 lakes to estimate bacterial biovolume and cell size distribution. The total counts of 4',6'-diamidino-2-phenylindole-stained cells estimated by both methods were significantly related, and the slope of their linear regression was not significantly different from 1, indicating that both methods produce very similar estimates of bacterial abundance. The relationships between side scatter (SSC) and 4',6'-diamidino-2-phenylindole fluorescence and cell volume (microscopy values) were improved by binning of the data in three frequency classes for each, but further increases in the number of classes did not improve these relationships. Side scatter was the best cell volume predictor, and significant relationships were observed between the SSC classes and the smallest (R2 = 0.545, P < 0.001, n = 80) and the largest (R2 = 0.544, P < 0.001, n = 80) microscopy bacterial-size classes. Based on these relationships, a reliable bacterial biomass estimation was obtained from the SSC frequency classes. Our study indicates that flow cytometry can be used to properly estimate bacterioplankton biovolume, with an accuracy similar to those of more time-consuming microscopy methods.
    Applied and Environmental Microbiology 07/2007; 73(14):4508-14. · 3.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated net growth rates of distinct bacterioplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus availability by analysing eight in situ manipulation experiments, conducted between 1997 and 2003, in the canyon-shaped Rímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phosphorus limitation (range of soluble reactive phosphorus concentrations--SRP, 0.7-96 microg l-1). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate constants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betaproteobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabilities for possible life strategies of different bacterial phylogenetic lineages are discussed.
    Environmental Microbiology 10/2006; 8(9):1613-24. · 6.24 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In diversity research, the use of survey data appears to have declined in favour of experimental or modeling approaches because direct relationships are difficult to demonstrate. Here we show that use of field data can yield information concerning the mechanisms governing diversity. First, we establish that tintinnids display a global latitudinal pattern of diversity similar to other pelagic organisms; species numbers appear to peak between 20� and 30� north or south. This common large scale spatial trend has been attributed to the gradient in water column structure across the global ocean. We then examine the generality of a relationship between planktonic diversity and water column structure by considering data from the Mediterranean Sea, in which water column structure changes seasonally. Among populations of foraminifera, tintinnids, and the dinoflagellates of the genus Ceratium, we compare data from trans-Mediterranean sampling conducted at different times and monthly changes in species richness at single sites. We find that water column structure alone appears to be a poor predictor of temporal changes in diversity. Lastly, we present an example of temporal changes in tintinnid diversity based on data from an oceanographic sampling station in the N. W. Mediterranean where resources, as chlorophyll, appear distinctly unrelated to changes in water column structure. We show that short-tem temporal changes in diversity (week to week shifts) can be related to changes in chlorophyll concentration. We conclude that in tintinnids diversity can be directly linked to characteristics of food resources.
    Hydrobiologia 01/2006; 555:143-157. · 1.99 Impact Factor
  • Source
    V. Straskrábová, K. Simek
    [Show abstract] [Hide abstract]
    ABSTRACT: Los embalses difieren de los lagos principalmente en tres aspectos: (i) el tiempo de residencia del agua no suele ser superior a varios meses, (ii) la heterogeneidad horizontal inducida por la entrada de agua fluvial es más marcada, y (iii) son históricamente mucho más jóvenes que los lagos. Como consecuencia de todo ello, las dinámicas estacional y a largo plazo de las redes tróficas pelágicas reflejan los cambios en la cuenca y las variaciones hidrológicas más significativamente que en los lagos, y el envejecimiento y "madurez" tjel ecosistema del embalse podría afectar a la biomasa pelágica incluso varias décadas después de su llenado. Mediante el análisis de largas series de datos sobre la biomasa de componentes pelágicos en embalses con sección en forma de cañón y diferentes tiempos de residencia,. se discuten los siguientes aspectos: (1) cambios en las abundancias de bacterias-fitoplancton-zooplancton pelágicos durante el envejecimiento del embalse, así como cambios longitudinales desde la entrada de los ríos hasta la zona lacustre del embalse, (2) cambios a largo plazo en las abundancias de bacterias-fitoplancton-zooplancton pelágicos y cambios estacionalesdel bucle microbiano en dos embalses con diferentes tiempos de residencia. Se detectaron períodos con un predominio relativo de la biomasa bacteriana sobre la biomasa de zooqlancton, coincidiendo principalmente con (o justamente después de) los períodos con bajas relaciones fitoplancton/ zooplancton.
    Limnetica, ISSN 0213-8409, Vol. 24, Nº. 1-2, 2005 (Ejemplar dedicado a: XI Congreso de la Asociación Española de Limnología y III Congreso Ibérico de Limnología), pags. 9-19. 01/2005;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Three years of regular weekly/biweekly monitoring of seasonal changes in temperature, transparency, chlorophyll a (CHL) and bacteria [erythrosine-stained microscopic counts and cultivable colony forming units (CFUs)] at the vertical profile in the South basin of Lake Baikal (51°54′195″N, 105°04′235″E, depth 800 m) were evaluated. In more detail, the structure and function of phytoplankton and the microbial loop in the euphotic layer at the same site were investigated during the late-winter–early-spring period under the ice. The depth of euphotic zone (up to 1% of surface irradiation) was 35 to 40 m. Primary production was measured three times a week with the 14C method in 2, 10, 20, 30 and 40 m. Maximum production was found in 10 m, with lower values towards the surface (light inhibition) and towards the lower layers. The total production in cells larger than 1 μm in the column (0–40 m) was 204–240 mg C d−1 m−2, 30–40% of it being in cells 1–3 μm (mostly picocyanobacteria), which represented roughly 9% of the total chlorophyll a (estimated from pigment analyses). A major part of phytoplankton biomass was formed by diatoms (Synedra acus Hust., Asterionella formosa Hass. and Stephanodiscus meyerii Genkal & Popovskaya). Total production (including extracellular, dissolved organic matter) was 235–387 mg C day−1 m−2, and the exudates were readily used by bacteria (particles 0.2–1 μm). This part amounted to 1–5% of cellular production in 2 to 20 m and 11–77% of cellular production in 20–40 m, i.e., in light-limited layers. From 0 to 30 m, chlorophyll a concentration was 0.8 to 1.3 μg l−1, wherefrom it decreased rapidly to 0.1 μg l−1 towards the depth of 40 m. Bacteria (DAPI-stained microscopic counts) reached 0.5–1.4×106 ml−1; their cell volumes measured via image analysis were small (average 0.05 μm−3), often not well countable when erythrosine stain was used. Bacterial biomasses were in the range of 6–21 μg C l−1. Numbers of colony forming units (CFUs) on nutrient fish-agar were c. 3–4 orders lower than DAPI counts. The amounts of heterotrophic protists were low, whereby flagellates reached 6 to 87 ml−1 and ciliates, 0.2–1.2 ml−1 (mostly Oligotrichida). Bacterial production was measured in the same depths as primary production using 3H-thymidine (Thy) and 14C-leucine (Leu) uptake. Consistently, bacterial abundances, biomasses, thymidine and leucine production were higher by 30–50% in layers 2, 10 and 20 m compared with that in the deeper 30 and 40 m, where cellular primary production was negligible. Leucine uptake in the deeper layers was even three times lower than in the upper ones. From the comparison of primary and bacterial production, bacteria roughly use 20–40% of primary production during 24 h in the layers 2 to 20 m.
    Global and Planetary Change 01/2004; · 3.16 Impact Factor