摘要:

AbstractA brief overview of the state‐of‐the‐art of freshwater autotrophic picoplankton (APP) is given as an introduction to this special issue ofInternationale Revue der gesamten Hydrobiologie. Some questions that have arisen from research over the past decade are re‐evaluated in light of new information reported here. These include: 1.) what is the average abundance of autotrophic picoplankters along a nutrient gradient in freshwater?; 2.) how diverse and what are the major components of the APP community in freshwater?; 3.) what is the origin of colonial forms of picoplankton?; 4.) what is the significance of prokaryotic and eukaryotic picoplankton in pelagic systems?; and 5.) how important is grazing in APP population regulation? New questions are proposed and an outlook for possible future research is offered.“Creating a theory … is rather like climbing a mountain, gaining new and wider views, discovering unexpected connections between our starting point and its rich environment. But the point from which we started still exists and can be seen, although it appears smaller and forms a tiny part of our broad view gained by mastery of the obstacles on our adventu

ISSN:0020-9309    

DOI:10.1002/iroh.19910760402

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractThe seasonal distribution of autotrophic picoplankton in Lake Constance was investigated over four consecutive years. Cell numbers varied seasonally and vertically over four orders of magnitude (102to 106cells ml−1). A horizontal variation by a factor of 3 in abundance and biomass across the different parts of the lake was found during summer stratification. Picoplankton peaks occurred during the phytoplankton spring bloom and in late summer. Low values were characteristic for the clear‐water phase in early summer and for autumn‐winter. This seasonal pattern differed from that of larger phytoplankton in Lake Constance and from the seasonal distribution of picoplankton known from other lakes and marine environments. Picoplankton was predominated by chroococcoid cyanobacteria of about 0.6 μ3biovolume. The average cell size increased from winter until early summer. Using HPLC pigment analysis, we identified zeaxanthin and β‐carotene as typical picoplankton pigments. Results of the pigment analyses suggest that algae others than picocyano‐bacteria may be more prominent in the picoplankton size class than derived from routine epifluorescen

ISSN:0020-9309    

DOI:10.1002/iroh.19910760403

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractThe seasonal development of autotrophic picoplankton was investigated in seven Danish lakes representing a eutrophication gradient. Highest cell abundance between 1.5 to 6 × 105cells ml−1were found in mid‐summer. Minor peaks were observed in spring. In winter, densities were below 103ml−1. The highest relative picoplankton contribution to total autotrophic biomass also occurred in mid‐summer. In the eutrophic lakes and one humic lake the average seasonal contribution of picoplankton to total chlorophyll was below 1% increasing to 5‐8% in the meso‐ and oligotrophic clear water lakes. During short periods the proportion of picoplankton did reach 25%. The higher relative importance of picoplankton in less productive lakes was not due to higher actual chlorophyll concentrations, but due to a much more pronounced response by larger algae at higher nutrient loading. Both cyanobacteria and eukaryote organisms were present as picoplankton. Only eukaryotes were found in one eutrophic lake and an acidic, humic lake. In the eutrophic lakes eukaryote picoplankton was dominant; both with respect to cell densities and biovolume, whereas cyanobacteria dominated the two meso‐oligotrophic lakes. Autotrophic picoplankton were present in all lake types, however their importance seemed to be less in most eutrophic lakes than in less productive, meso‐ol

ISSN:0020-9309    

DOI:10.1002/iroh.19910760404

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractThe abundance of picoplankton (0.2‐2 μm) was measured seasonally in the surface waters of six New Zealand lakes that represent a range of trophic states. The lakes were: Wakatipu, Te Anau, Manapouri, Hayes, Mahinerangi and Ross Creek Reservoir. Among the lakes, picoplankton abundance was associated positively with temperature; picoplankton were most abundant in summer and autumn when they attained densities of 108,000‐270,000 cells/ml in the oligotrophic lakes. In these lakes, prokaryotic picoplankton was generally an order of magnitude more abundant than eukaryotic picoplankton. Consistent with the hypothesis that picoplankton are more important in oligotrophic than eutrophic ecosystems, there was a weak negative correlation between the density of prokaryotic picoplankton in the lakes and the level of chlorophylla. The presence of large numbers of chroococcoid cyanobacteria in the guts ofCeriodaphnia dubiaandBosmina meridionalisimplies that prokaryotic picoplankton are collected, but not digested, by these spe

ISSN:0020-9309    

DOI:10.1002/iroh.19910760405

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractChroococcoid cyanobacteria, (mean size = 0.79 μm, likelySynchetocystis limneticaPopovsk) and total eubacteria (mean size = 0.33 μm), from Lake Baikal, USSR, were enumerated using epifluorescence microscopy and sized with image analysis. Bacterial densities ranged from 0.44 · 106cells ml−1at 250 m to 2.3 · 106cells ml−1at the surface. Mean eubacterial abundance was 1.3 · 106cells ml−1. Cyanobacterial densities were more variable, ranging from 0.42 · 104cells ml−1at 250 m to 9.8 · 104cells ml−1at the surface, with a mean abundance of 2.7 · 104cells ml−1. The cyanobacteria, in particular, occurred in clusters resembling “marine snow”. Our results indicate that Lake Baikal picoplankton size and density are similar to other large lakes but may have a more diverse community structure than in other l

ISSN:0020-9309    

DOI:10.1002/iroh.19910760406

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractKey features of photosynthetic picoplankton populations were compared during 1988 in ten lakes in northern England ranging from oligotrophic to slightly eutrophic; two of the three eutrophic lakes were shallow and lacked a thermocline. Measurements were made at 0.5 m depth of temperature, total chlorophylla, chlorophyll‐containing picoplankton cell density, mean picoplankton cell volume and percentage of phycoerythrin‐rich cells in the total picoplankton population. All lakes showed maxima for total chlorophyll concentration and picoplankton cell density in mid‐ to late summer. The maximum value for picoplankton density ranged from 3.4 × 103(Esthwaite Water) to 1.3 × 106cells ml−1(Ennerdale Water).There was a significant negative relationship (p<0.05) between log10of maximum picoplankton cell density and maximum total chlorophyll, the latter being taken as an indicator of lake trophic status. The ratio of maximum to minimum picoplankton density during the year in a particular lake ranged from 39 to 2360 and showed no obvious relationship to lake type. Overall, the seasonal range in picoplankton density was about one order of magnitude greater than the range in total chlorophylla, but there were considerable differences between lakes.Phycoerythrin‐rich picoplankton as a percentage of total picoplankton reached a maximum in summer in all lakes. Values were always very low (<5%) in the two shallow eutrophic lakes, but reached 97% and over in the four most oligotrophic lakes. In two of the oligotrophic lakes, Wast‐water and Ennerdale Water, phycoerythrin‐rich picoplankton was a major component of the summer phytop

ISSN:0020-9309    

DOI:10.1002/iroh.19910760407

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractIn Lake Kinneret, we have been monitoring the numbers and depth distributions of bacteria and picocyanobacteria since early 1988. Picocyanobacteria were found throughout the year at all depths, at concentrations ranging from<103to 105cells·ml−1. Highest abundances were recorded during summer and fall in the epilimnion. The lowest areal standing stocks occurred from March to May, the period which corresponds to the peak of the annual dinoflagellate bloom. Bacterial numbers ranged from about 105to 107cells·ml−1. The picocyanobacteria were evenly distributed in the water column during the mixed period. With the onset of thermal stratification and the end of the dinoflagellate bloom the numbers of picocyanobacteria increased rapidly in the epili

ISSN:0020-9309    

DOI:10.1002/iroh.19910760408

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractThe seasonal abundance and composition of photosynthetic picoplankton (0.2‐2 μm) was compared among five oligotrophic to mesotrophic lakes in Ontario. Epilimnetic picocyanobacteria abundance followed a similar pattern in all lakes; maximum abundance (2‐4 × 105cells · ml−1) occurred in late summer following a period of rapid, often exponential increase after epilimnetic temperatures reached 20 °C. In half of the lakes picocyanobacteria abundance was significantly correlated with temperature, while in other lakes the presence of a small spring peak resulted in a poor correlation with temperature. In all lakes there was a significant correlation between epilimnetic abundance and day of the year. Correlations with water chemistry parameters (soluble reactive phosphorus, total phosphorus, particulate C: P and C: N) were generally weaker or insignificant. However, in the three lakes with the highest spring nitrate concentrations, a significant negative correlation with nitrate was observed. During summer stratification, picocyanobacteria abundance reached a maximum within the metalimnion and at or above the euphotic zone (1% of incident light) in all lakes. These peaks were not related to nutrient gradients.The average total phytoplankton biomass ranged from 0.5 g m−3(wet weight) in the most oligotrophic lake to 1.4 g m−3for the most mesotrophic with picoplankton biomass ranging from 0.01 g m−3to 0.3 g m−3. Picocyanobacteria biomass comprised 1 to 9 % of total phytoplankton biomass in late summer, but in one year for one lake represented a maximum of 56%. Other photosynthetic picoplankton (unidentified eukaryotes,Chlorellaspp.Nannochlorisspp.), although less abundant (103cells · ml−1) than picocyanobacteria, represented biomass equal or greater than that of the picocyanobacteria in spring and early summer. On average, half of the photosynthetic picoplankton biomass was eukaryotic in the more coloured lakes, while in the clear lakes less than 20% was eukaryotic. Among the lakes there was a significant positive correlation between the average light extinction coefficient and the proportion of eukaryotic biomass of the picoplankton.In mesotrophic Jack's Lake, the contribution of picoplankton to the maximum photosynthetic rate ranged from 10 to 47% with the highest values in the spring (47%) and late summer (33%), as a result of eukaryotic picoplankton and picocyanobacteria respectively. Picocyanobacteria cell specific growth rates were high during July (0.6‐0.8 day−1) and losses were close to 80% of the growth rate. Thus, despite low biomass, photosynthetic picoplankton populations appeared to turn over rapidly and potentially contributed significantly to planktonic food webs in earl

ISSN:0020-9309    

DOI:10.1002/iroh.19910760409

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractAutotrophic picoplankton communities were examined in eleven oligotrophic lakes from a broad geographic region of western Canada, representing a variety of physico‐chemical and biological conditions. During our study, several of the lakes were treated with additions of inorganic nitrogen and phosphorus fertilizers. Picoplankton communities in most lakes were dominated (>70%) by unicellular or colonial coccoid cyanobacteria, provisionally identified by morphological and autofluorescence properties asSynechococcus. Also common in some lakes were red‐fluorescing cyanobacteria andChlorella‐like eucaryotes. Autotrophic picoplankters contributed from 36‐63% to total chlorophyll, from>2‐26% to total phytoplankton carbon, and from 29–53% to total photosynthesis. Average populations ranged from>5‐10,000 cells·ml−1in winter and early spring to 65‐75,000 cells · ml−1in summer and fall. Peak densities in most lakes occurred in August‐September and most populations were within the epilimnion or metalimnion/hypolimnion boundary. Subsurface peaks were prevalent only in untreated, strongly stratified lakes. Eucaryotic picoplankters became dominant in acidic (pH2x) and the elimination of subsurface peaks. Nutrients were considered to be one of the major factors controlling population abundance in these oligotrophic la

ISSN:0020-9309    

DOI:10.1002/iroh.19910760410

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY

摘要:

AbstractEpifluorescence microscopy, flow cytometry, and transmission electron microscopy were used to characterize the community of red fluorescing (emission>665 nm when excited with blue light) phototrophic picoplankton (RFPP) in lakes Huron and Michigan. A population of coccoid to ovate eukaryotic cells with a mean size of 1.2 μm dominated the RFPP community in both surface and deep water samples. Abundant prochlorophyte populations were not found in any samples. Comparisons of counts with epifluorescence microscopy and flow cytometry, revealed that RFPP were adequately enumerated with standard epifluorescence microscopy. These RFPP were significant contributors to total phototrophic picoplankton abundance in both lakes Michigan (24%) and Huron (18%), with maximum seasonal abundance during the May‐June period (surface mixing layer temperatures, 3‐9 °C). During thermal stratification, maximum vertical abundance was found in the metalimnion/hypolimnion at the 1‐5% isolumes. RFPP were only minor contributors (1‐7%) to total primary production. Growth rates of RFPP measured with dilution and small inocula growth experiments ranged from 0.05‐1.0 d−1. Microzooplankton grazing rates on RFPP measured with dilution experiments were similar to estimated growth rates, accounting for 52‐280% of growth on

ISSN:0020-9309    

DOI:10.1002/iroh.19910760411

出版商:Akademie Verlag, Berlin    

年代:1991

数据来源: WILEY