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C L (c + l)
Kinds of C L Selected AbstractsCalcium balance in Daphnia grown on diets differing in food quantity, phosphorus and calciumFRESHWATER BIOLOGY, Issue 11 2009XUE-JIA HE Summary 1.,The influences of dietary phosphorus (P) and food concentration on the calcium (Ca) balance in Daphnia magna were examined in this study at two different ambient Ca concentrations (0.5 and 10 mg Ca L,1). Daphnia were grown by feeding the young adults differentially under contrasting dietary P conditions [molar C : P ratio = c. 900 and c. 90 as low P (LP) and high P (HP), respectively], ambient Ca concentrations [0.5 mg and 10 mg Ca L,1 as low Ca (LCa) or high Ca (HCa), respectively] and food levels [0.15 or 1.5 mg C L,1 as low food (LF) or high food (HF), respectively] for 5 days. 2.,The specific Ca contents of daphniids (1.9,6.5% of dry weight,1) increased with increasing Ca concentration, food level and dietary P content, although the food level did not affect the Ca content in the HPHCa treatment. A radioactive tracer method showed that the food level did not affect the influx of Ca from the water under LP conditions, but the Ca influx under HP conditions doubled with a HF level. A LP condition also led to a decrease in Ca influx with a HF level. 3.,During the 3 days of efflux, generally only a small proportion of Ca (2.6,3.3%) was retained by the daphniids, but this retention increased (14,23%) under low ambient Ca concentrations and under P-limitation. Excretion was the most important pathway for Ca loss (accounting for 50,60% of body Ca), followed by moulting (20,47%), but the relative contribution of these two pathways (excretion and moulting) did not vary among all the different treatments. The absolute loss of Ca through excretion and moulting, on the contrary, differed with different ambient Ca concentrations and dietary P conditions. A HF level led to an increase in the loss rates in most cases. 4.,Our study strongly suggested that there is an interaction between an essential metal (Ca) and macronutrients (C and P) in freshwater crustaceans with HCa and P contents. The results imply that variation in environmental nutrient conditions may change the Ca budget in crustaceans and may affect the dynamics of Ca in the epilimnion of freshwaters. [source] Lability of organic carbon in lakes of different trophic statusFRESHWATER BIOLOGY, Issue 6 2009A. P. OSTAPENIA Summary 1. We used first-order kinetic parameters of biological oxygen demand (BOD), the constant of aerobic decomposition (k) and the asymptotic value of BOD (BODult), to characterise the lability of organic carbon pools in six lakes of different trophic state: L. Naroch, L. Miastro and L. Batorino (Belarus), L. Kinneret (Israel), L. Ladoga (Russia) and L. Mendota (U.S.A.). The relative contributions of labile and refractory organic carbon fractions to the pool of total organic carbon (TOC) in these lakes were quantified. We also determined the amounts of labile organic carbon within the dissolved and particulate TOC pools in the three Belarus lakes. 2. Mean annual chlorophyll concentrations (used as a proxy for lake trophic state) ranged from 2.3 to 50.6 ,g L,1, labile organic carbon (OCL = 0.3BODult) from 0.75 to 2.95 mg C L,1 and k from 0.044 to 0.14 day,1. 3. Our data showed that there were greater concentrations of OCL but lower k values in more productive lakes. 4. In all cases, the DOC fraction dominated the TOC pool. OCL was a minor component of the TOC pool averaging about 20%, irrespective of lake trophic state. 5. In all the lakes, most (c. 85%) of the DOC pool was refractory, corresponding with published data based on measurements of bacterial production and DOC depletion. In contrast, a larger fraction (27,55%) of the particulate organic carbon (POC) pool was labile. The relative amount of POC in the TOC pool tended to increase with increasing lake productivity. 6. Long-term BOD incubations can be valuable in quantifying the rates of breakdown of the combined particulate and dissolved organic carbon pools and in characterising the relative proportions of the labile and recalcitrant fractions of these pools. If verified from a larger number of lakes our results could have important general implications. [source] Periphyton as alternative food source for the filter-feeding cladoceran Daphnia magnaFRESHWATER BIOLOGY, Issue 1 2009SILVANA SIEHOFF Summary 1., Daphnia magna, a well-studied primary consumer, is mainly known as a filter feeder. In this study, we investigated the ability of D. magna to use periphyton as an alternative food source to phytoplankton. We examined the development of laboratory populations fed with different food sources (Desmodesmus subspicatus and/or periphyton or neither) over a period of 42 days, and observed the behaviour of the daphnids. 2.,The addition of periphyton to phytoplankton food led to an increase of daphnid population biomass. When fed with periphyton as the only food source, a small but stable D. magna population developed. 3.,The behaviour of daphnids fed with both food sources revealed a preference for feeding on D. subspicatus. Only below a concentration of D. subspicatus of approximately 0.05 mg C L,1 (0.4 × 107 cells L,1) did D. magna use periphyton as an alternative food source. 4.,Periphyton showed distinct reactions to grazing by D. magna. The thickness of the periphyton layer was reduced from about 4 to 1 mm and we observed a change in species composition due to grazing. 5.,The ability of D. magna to graze on periphyton could serve to stabilize its population density and reinforce its competitive advantage over other cladocerans. By switching between food sources, D. magna can act as a coupler between pelagic and benthic habitats and food webs. [source] Body size and food thresholds for zero growth in Dreissena polymorpha: a mechanism underlying intraspecific competitionFRESHWATER BIOLOGY, Issue 12 2008ALEXANDER WACKER Summary 1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low-food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size-related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C0) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C0 = 0.08 mg C L,1) is substantially lower than that for adults (C0 = 0.36 mg C L,1). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature. [source] Survival and development of five species of cyclopoid copepods in relation to food supply: experiments with algal food in a flow-through systemFRESHWATER BIOLOGY, Issue 9 2005ULRICH HOPP Summary 1. Cyclops spp. generally develop and grow during favourable food conditions in spring and undergo a diapause in summer, while Acanthocyclops robustus, Mesocyclops leuckarti and Thermocyclops crassus develop and grow in summer when they face poorer food conditions and more competition from Cladocera. Since nauplii are the bottleneck in copepod development, we tested the hypothesis that Cyclops abyssorum and C. vicinus nauplii have higher food requirements for survival and development than the nauplii of A. robustus, M. leuckarti and T. crassus. We also tested survivorship and development from hatching to adulthood. 2. Survivorship and development of the copepods was studied in a flow-through system using five concentrations of the phytoflagellate Chlamydomonas reinhardtii in the range from 1 × 104 to 4.5 × 105 cells mL,1 (approximately 0.5,22.5 mg C L,1). 3. Nauplii of both species of Cyclops died at intermediate to low (C. abyssorum) and low (C. vicinus) food concentrations, while nauplii of A. robustus, M. leuckarti and T. crassus survived at all concentrations. 4. The negative effects of low food concentration were also reflected in development. In C. abyssorum and C. vicinus, development duration increased at low food concentration while development was much less affected in A. robustus and T. crassus. Mesocyclops leuckarti was intermediate between Cyclops spp. and A. robustus/T. crassus, with an increase in development duration at the lowest food concentration. 5. Our results support the hypothesis that summer diapause in Cyclops spp. has developed as a strategy to avoid a food bottleneck for nauplii. [source] Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basinFRESHWATER BIOLOGY, Issue 11 2004María M. Castillo Summary 1. We examined the influence of hydrologic seasonality on temporal variation of planktonic bacterial production (BP) in relatively undisturbed lowland rivers of the middle Orinoco basin, Venezuela. We sampled two clearwater and two blackwater rivers over 2 years for dissolved organic carbon (DOC), chlorophyll, phosphorus and bacterial abundance to determine their relationship to temporal variation in BP. 2. Dissolved organic carbon concentration was greater in blackwater (543,664 ,m) than in clearwater rivers (184,240 ,m), and was generally higher during periods of rising and high water compared with low water. Chlorophyll concentration peaked (3 ,g L,1) during the first year of study when discharge was lowest, particularly in blackwater rivers. Soluble reactive phosphorus (SRP) was very low in the study rivers (<3.8 ,g L,1) and concentration increased during low water. 3. Average BP was higher in clearwater (0.20,0.26 ,g C L,1 h,1) than in blackwater rivers (0.14,0.17 ,g C L,1 h,1), although mean bacterial abundance was similar among rivers (0.6,0.8 × 106 cells mL,1). 4. Periods of higher chlorophyll a concentration (low water) or flushing of terrestrial organic material (rising water) were accompanied by higher BP, while low BP was observed during the period of high water. 5. Interannual variation in BP was influenced by variations in discharge related to El Niño Southern Oscillation events. 6. Seasonal variation in BP in the study rivers and other tropical systems was relatively small compared with seasonal variation in temperate rivers and lakes. In addition to the low seasonal variation of temperature in the tropics, low overall human disturbance could result in less variation in the inputs of nutrients and carbon to the study rivers compared with more disturbed temperate systems. [source] Humic acids crossinteractions with root and organic acidsANNALS OF APPLIED BIOLOGY, Issue 2 2008L.P. Canellas Abstract The apparent high molecular mass of humic acids (HAs) hardly seems compatible with their direct effects in plant physiology. However, previous evidence has indicated that HAs are non-covalent associations of relatively small molecules, which can be broken down by the action of organic acids. The aim of this work was to evaluate the effects of organic acids on the structure of HAs by spectroscopy and on their bioactivity by following the responses of maize root growth. Changes in the exudation of organic acids from maize seedlings treated with HAs at 50 mg C L,1 were evaluated by high-performance liquid chromatography. The results are in agreement with the concept that HAs are chemical aggregates that acquire characteristics typical of low-molecular-mass humic substances when exposed to organic acids exuded by the roots. Maize seedlings grown in solutions supplemented with HAs plus citric acid at 0.0005, 0.005 and 0.05 mM exhibited significant changes in their root area, primary root length, number of lateral roots and lateral root density and increases in plasma membrane H+ -ATPase activity. Furthermore, the root exudation profile of plants treated with HAs exhibited an increase in the efflux of oxalic and citric acids, with a concurrent decrease in malic and succinic acids. These data reveal a crosstalk between HAs and plants where the exudation of organic acids from the roots influences and is influenced by bioactive molecules released from HAs during root development. [source] Effect of Campsurus notatus on NH+4, DOC Fluxes, O2 Uptake and Bacterioplankton Production in Experimental Microcosms with Sediment-Water Interface of an Amazonian Lake Impacted by Bauxite TailingsINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2003João José Fonseca Leal Abstract The aim of this study was to evaluate the influence of Campusurus notatusEaton 1868 (Ephemeroptera: Polimitarciydae) and the impact of bauxite tailings on ammonium (NH4+) and dissolved organic carbon (DOC) fluxes, oxygen uptake and bacterioplankton production in the sediment-water interface of Lake Batata, a shallow Amazonian floodplain lake. Mesocosms were constructed from natural and impacted areas of Lake Batata, to reproduce the sediment-water interface. The cores were incubated with 0 to 2,388 ind m,2 of Campsurus notatus nymphs, and the changes in NH4+, DOC, O2 concentration and bacterioplankton production in the overlying water column were measured. Ammonium efflux (F = 9.8, p < 0.05, multiple regression) and oxygen uptake (F = 11.8, p < 0.05) showed a significant correlation with the density of C. notatus in the cores with natural sediment. No differences on DOC release were observed in cores with natural or impacted sediment. In the cores incubated with natural sediment and nymphs of C. notatus, a significant increase (Two-way ANOVA, p < 0.05) in bacterial production (0.44 ,g C l,1 h,1) was observed after 3 hours of incubation. In cores incubated with sediment impacted by bauxite tailings, there was no difference in bacterial production with and without C. notatus. We conclude that C. notatus is an important bioturbator in Lake Batata, increasing the turnover rate of nitrogen (NH4+) at the sediment-water interface and bacterial production in cores incubated with natural sediment. It is also clear that bauxite tailings reduce the nutrients turnover rates in impacted regions of Lake Batata and influence bacterial production. [source] Leptodora kindti and Flexible Foraging Behaviour of Fish , Factors behind the Delayed Biomass Peak of Cladocerans in Lake HiidenvesiINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2003Laura Uusitalo Abstract In the eutrophic L. Hiidenvesi, the spring biomass maximum of cladoceran zooplankton is missing and the highest biomass takes place in July,August. The factors behind the delayed biomass peak were studied in four different basins of the lake with concomitant data on cladocerans assemblages, density of the predatory cladoceran Leptodora kindti and food composition of fish. In all the basins, the abundance of Leptodora peaked in June, being highest (up to 800 ind. m,3) in the two most shallow basins (max depth < 4 m). The duration of the high population density was short and in July-August Leptodora density stayed below 200 ind. m,3, although the water temperature was still favourable. The collapse of the Leptodora population coincided with the change in the feeding habits of fish. In early summer, fish predation was targeted mainly on copepods and zoobenthos, while in high summer Leptodora was one of the main preys of perch, white bream and bleak. The biomass of herbivorous cladocerans was below 10 ,g C l,1 in June, and climbed to a maximum in August in the two most shallow basins (34 and 76 ,g C l,1), in July in the deepest basin (27 ,g C l,1), and in September in the intermediate basin (55 ,g C l,1). In the two most shallow basins, the death rate of the dominating cladoceran, Daphnia cristata, closely followed the food consumption rate by the Leptodora population. In the deeper basins, the agreement was not so close, smelts (Osmerus eperlanus) and chaoborids being important predators of herbivores. The duration of the period of high Leptodora density thus depended on the predation pressure by fish, while the increased fish predation on Leptodora in July,August allowed the elevation of the biomass of herbivorous cladocerans. [source] Utilization of oligo- and polysaccharides at microgram-per-litre levels in freshwater by Flavobacterium johnsoniaeJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2010E.L.W. Sack Abstract Aims:, To obtain a bacterial strain that can be used to quantify biodegradable polysaccharides at concentrations of a few micrograms per litre in freshwater. Methods and Results:,Flavobacterium johnsoniae strain A3 was isolated from tap water supplemented with laminarin, pectin or amylopectin at 100 ,g C l,1 and river Rhine water. The organism utilized 14 of 23 oligo- and polysaccharides, and 1 of 9 monosaccharides, but none of the sugar acids, sugar alcohols, carboxylic acids or aromatic acids tested at 10 ,g C l,1. Amino acids promoted growth of strain A3, but not in coculture with assimilable organic carbon (AOC) test strain Pseudomonas fluorescens P17, which utilized these compounds more rapidly than strain A3. Compounds released by strain P17 and AOC test strain Spirillum sp. NOX grown on acetate promoted the growth of strain A3 at Nmax values of , 2 × 105 CFU ml,1 of strain P17 and , 5 × 105 CFU ml,1 of strain NOX. Significant growth of strain A3 was observed in surface water and in tap water in the presence of strain P17 (Nmax P17 < 2 × 105 CFU ml,1). Conclusions:, Strain A3 utilizes oligo- and polysaccharides at microgram-per-litre levels. In surface water and in tap water, the organism was able to utilize compounds that were not utilized by strain P17. These compounds may include oligo- and/or polysaccharides. Significance and Impact of the Study:, Phytoplanktonic and bacterial polysaccharides can constitute an important biodegradable fraction of natural organic matter in water and may promote growth of heterotrophic bacteria during water treatment and drinking water distribution. Strain A3 can be used to quantify a group of compounds that includes oligo- and polysaccharides at microgram-per-litre levels in freshwater. [source] Ecological implications of biomass and morphotype variations of bacterioplankton: an example in a coastal zone of the Northern Adriatic Sea (Mediterranean)MARINE ECOLOGY, Issue 2 2005Rosabruna La Ferla Abstract This study had the objective of quantifying the variability in abundance, cell volume, morphology and C content of a natural bacterioplankton community in a coastal zone of the North Adriatic Sea during two periods (February and June) of two consequent years (1996 and 1997). We used epifluorescence microscopy with Acridine Orange staining procedures and a microphotographic technique. Low variability in bacterial abundance (range 0.3,3.1 × 105 cells ml,1) occurred between summer and winter periods. Conversely, the cell volume and the calculated carbon content changed greatly with warm and cold periods (ranges: 0.015,0.303 ,m3 and 5.83,42.17 fg C cell,1, respectively). Elongated bacteria were dominant while coccoid cells prevailed only in February 1997. Biomass showed high variability (range 0.12,10.21 ,g C l,1) whilst the abundance did not show noticeable differences among the sampling periods. As a consequence, quantification of bacterial biomass based solely on cell abundance must be considered with caution because the true biomass could depend on variability in cell volumes and morphotypes. [source] | ||||||||||