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1.
Studies were conducted over a 13 month period at four pelagicsites in eutrophic Lake Okeechobee, Florida (USA), in orderto quantify carbon (C) uptake rates by size-fractionated phytoplankton,and subsequent transfers of C to zooplankton. This was accomplishedusing laboratory 14C tracer methods and natural plankton assemblages.The annual biomass of picoplankton (<2 µm), nanoplankton(220 µm) and microplankton (<20 µm averaged60, 389 and 100 µg C 11 respectively, while correspondingrates of C uptake averaged 7, 51 and 13 µg C11h1. The biomass of microzooplankton (40200 µm)and macrozooplankton (<200 µm averaged 18 and 60 µgC 11, respectively, while C uptake rates by these herbivoregroups averaged 2 and 3 µg C 11 h1. Therewere no strong seasonal patterns in any of the plankton metrics.The ratio of zooplankton to phytoplankton C uptake averaged7% over the course of the study. This low value is typical ofthat observed in eutrophic temperate lakes with small zooplanktonand large inedible phytoplankton, and indicates ineffectiveC transfer in the grazing food chain. On a single occasion,there was a high density (<40 11) of Daphnia lumholrzii,a large-bodied exotic cladoceran. At that time, zooplanktoncommunity C uptake was <20 µg C 11 h1and the ratio of zooplankton to phytoplankton C uptake was near30%. If D.lumholrzii proliferates in Lake Okeechobee and theother Florida lakes where it has recently been observed, itmay substantially alter planktonic C dynamics. 相似文献
2.
Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya--Lakes Bogoria, Nakuru and Elmenteita 总被引:4,自引:0,他引:4
Ballot Andreas; Krienitz Lothar; Kotut Kiplagat; Wiegand Claudia; Metcalf James S.; Codd Geoffrey A.; Pflugmacher Stephan 《Journal of plankton research》2004,26(8):925-935
For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaiasminor Geoffroy) have been observed at alkaline-saline KenyanRift Valley lakes. To estimate the potential influence of toxiccyanobacteria on these mass deaths, the phytoplankton communitieswere investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterialtoxins were analyzed both in the phytoplankton from the threelakes and in isolated monocyanobacterial strains of Arthrospirafusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidiumterebriformis. Lake Bogoria was dominated by the cyanobacteriumA. fusiformis. In L. Nakuru and L. Elmenteita the phytoplanktonmainly consisted of A. fusiformis, A. abijatae and Anabaenopsisarnoldii, and in L. Nakuru an unknown Anabaena sp. was alsofound. Furthermore, this is the first time A. abijatae and theunknown Anabaena sp. have been found in Kenyan lakes. Phytoplanktonwet weight biomass was found to be high, reaching 777 mg L1in L. Bogoria, 104 mg L1 in L. Nakuru and 202 mg L1in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxinsmicrocystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-awere detected in phytoplankton samples from L. Bogoria and L.Nakuru. Total microcystin concentrations amounted to 155 µgmicrocystin-LR equivalents g1 DW in L. Bogoria, and 4593µg microcystin-LR equivalents g1 DW in L. Nakuru,with anatoxin-a concentrations at 9 µg g1 DW inL. Bogoria and 223 µg g1 DW in L. Nakuru. In L.Elmenteita phytoplankton, no cyanobacterial toxins were found.A. fusiformis was identified as one source of the toxins. Theisolated strain of A. fusiformis from L. Bogoria was found toproduce both microcystin-YR (15.0 µg g1 DW) andanatoxin-a (10.4 µg g1 DW), whilst the A. fusiformisstrain from L. Nakuru was found to produce anatoxin-a (0.14µg g1 DW). Since A. fusiformis mass developmentsare characteristic of alkaline-saline lakes, health risks towildlife, especially the Arthrospira-consuming Lesser Flamingo,may be expected. 相似文献
3.
Seasonal uptake and regeneration of inorganic nitrogen and phosphorus in a large oligotrophic lake: size-fractionation and antibiotic treatment 总被引:3,自引:0,他引:3
Uptake and regeneration of inorganic N and P in oligotrophicFlathead Lake (Montana) were measured with 15N and 32P incorporationand dilution experiments, six times over a seasonal cycle. Theannual mean molar N P uptake ratio at ambient concentrationswas 13 9 (range = 4 834.2); uptake of nitrate, ammoniumand phosphate were always below saturation indicating both Nand P deficiency Organisms >280 µm were responsiblefor 060% of ammonium and 040% of phosphate regeneration,40100% of the ammonium and 3498% of phosphateregeneration occurred in the <3 µm fraction The <3µm fraction accounted for 770% of the ammoniumand 664% of the phosphate uptake. Results from antibiotictreatments indicated that both prokaryotic and eukaryotic ammoniumuptake was important, and that eukaryotes accounted for 5398%of the ammonium regeneration. During thermal stratification,heterotrophic ammonium and phosphate regeneration by organisms>3 µm supplied much of the inorganic N and P in theepilimnion. Estimated rates of allochthonous and diffusive (i.enew) ammonium, nitrate and phosphate input were<5% of biotic regeneration. These results suggests that (i)both N and P dynamics should be considered when examining nutrientregulation of primary productivity of oligotrophic lakes, (ii)bacteria probably compete with phytoplankton for both ammoniumand phosphate, (iii) biotic regeneration is the main sourceof nutrients to the epilimnion during stratification, and (iv)crustacean zooplankton were relatively unimportant sources ofregenerated ammonium and phosphate. 相似文献
4.
Priscu John C.; Vincent Warwick F.; Howard-Williams Clive 《Journal of plankton research》1989,11(2):335-351
The isotope 15N was used to examine nitrogen dynamics in LakesFryxell and Vanda, two permanently ice-covered Antarctic lakes.Half-saturation constants for NH4+. uptake in the shallow watersof both lakes were <10 µg N l1; uptake kineticexperiments on populations forming the deep-chlorophyll layersof these lakes showed zero-order kinetics and could not be fittedwith the Michaelis-Menten equation. Elevated uptake within thefirst few minutes following pulses of NH4+. and NO3 occurredin both lakes. NH4+ regeneration, determined from isotope dilutionexperiments, exceeded uptake at 4.6 m in Lake Fryxell, was lessthan uptake at 9 m in Lake Fryxell and was equal to uptake at10 m in Lake Vanda under the experimental conditions. NO3uptake was suppressed by NH4+ levels as low as 2 µg NH4+-N l1 in Lake Fryxell; the suppression was strongestin the near-surface populations. Substrate-saturated C:N uptakeratios (g:g) in Lake Fryxell decreased from 8.4 near the surfaceto 1.8 at the bottom of the trophogenic zone. Overall, the nitrogendynamics in these lakes are similar to other lakes and the openocean in that biological productivity during the austral summeris supported by regenerated nutrients. 相似文献
5.
Annual pattern of micro- and mesozooplankton abundance and biomass in a subtropical estuary 总被引:7,自引:0,他引:7
The pattern of biomass and abundance of microzooplankton andmesozooplankton were studied over an annual cycle in the NuecesEstuary, Texas. Zooplankton samples and associated hydrographicdata were collected at four locations at biweekly intervalsfrom September 1987 through October 1988. This is a broad, shallowbay system with an average depth of 2.4 m. The concentrationof chlorophyll a in the surface waters averaged 7.4 µgl1with 85% passing through a 20 µ mesh. Microzooplankton(20200 µ in length) were extremely abundant throughoutthis study. Abundances of ciliates (including both aloricateciliates and tintinnids) ranged from 5000 to 400 000 l,with a mean of 38 000 l1 of seawater over the entirecourse of the study. Mesozooplankton (2002000 µmin length) abundance averaged 6100 m3 for samples collectedduring the day and 10 100 m3 for samples collected atnight. Mesozooplankton were dominated by Acartia tonsa whichmade up {small tilde}50% of the total. Biomass estimates formicrozooplankton (based on volume estimates) were often higherthan measured biomass of mesozooplankton. Given the shortergeneration times and higher metabolic rate of microzooplanktoncompared to mesozooplankton, microzooplankton should have agreater effect on the trophic dynamics of the Nueces Estuarythan mesozooplankton. 相似文献
6.
Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000 总被引:1,自引:0,他引:1
Jochem Frank J.; McCarthy Mark J.; Gardner Wayne S. 《Journal of plankton research》2004,26(11):1265-1275
Microbial potential uptake and regeneration rates of ammonium(NH4+) were studied along a salinity gradient (salinities 0.234.4)in the Mississippi River plume during an extreme drought inspring 2000. Chlorophyll concentrations up to 30 µg L1were highest in the low- and mid-salinity regions (salinities8.528.2) and comparable to records of other years butextended over smaller areas than during periods of normal riverflow. Bacterial biomass (5.128.3 µg C L1)was at the low end of the range observed in normal flow years,decreased with distance from the river mouth and did not peakwith chlorophyll. Heterotrophic nanoflagellate abundance (1.44.0µg C L1) did not reflect phytoplankton and bacterialspatial distribution but peaked at 9.2 µg C L1at salinity 8.5. Microbial NH4+ regeneration rates were estimatedby 15NH4+ isotope dilution experiments for the whole microbialcommunity, under light and dark conditions, and for the <2µm bacterium-dominated size fraction. Microbial NH4+ regenerationrates (0.0180.124 µmol N L1 h1) werelow relative to previous reports and peaked at salinity 28.Total NH4+ regeneration rates were higher than those in the<2 µm size fraction at only four stations, suggestingthat bacterial mineralization was a significant component ofNH4+ recycling in some parts of the river plume. Higher NH4+regeneration in whole-water samples versus <2 µm fractionsprovided evidence for microbial grazing in regions where chlorophylland regeneration rates peaked and at two full-salinity stations. 相似文献
7.
Annual variation in the abundance and size of heterotrophic nanoflagellates on the SW coast of Finland, the Baltic Sea 总被引:3,自引:0,他引:3
Annual variation and vertical distribution in the abundanceand cell volume of heterotrophic nanoflagellates (HNF) was studiedon the SW coast of Finland, the Baltic Sea. HNF cell numbersand mean cell volume varied annually from 90 to 104 cells ml1,and from 3 to 32 µm3, respectively, with maxima in earlysummer. The proportion of choanoflagellates in the HNF communitywas 023%. Statistical analysis revealed the verticaldifferences in HNF abundance to be insignificant, but verticaldifferences in the size structure of HNF communities were found,especially during thermal stratification. The majority (>80%)of HNF were small (maximum dimension 24 µm); theproportion of large (>7 µm) cells were only 24%of the HNF abundance. An empirical equation for the relationshipbetween HNF cell length and volume is presented, and the measurementof flagellate volume by epifluorescence microscopy is discussed. 相似文献
8.
Community structure, biomass and productivity of size-fractionated summer phytoplankton populations in lower Narragansett Bay, Rhode Island 总被引:1,自引:0,他引:1
Seventeen size-fractionation experiments were carried out duringthe summer of 1979 to compare biomass and productivity in the< 10, <8 and <5 µm size fractions with that ofthe total phytoplankton community in surface waters of NarragansettBay. Flagellates and non-motile ultra-plankton passing 8 µmpolycarbonate filters dominated early summer phytoplankton populations,while diatoms and dinoflagellates retained by 10 µm nylonnetting dominated during the late summer. A significant numberof small diatoms and dinoflagellates were found in the 108µm size fraction. The > 10 µm size fraction accountedfor 50% of the chlorophyll a standing crop and 38% of surfaceproduction. The <8 µm fraction accounted for 39 and18% of the surface biomass and production. Production by the< 8 µm fraction exceeded half of the total communityproduction only during a mid-summer bloom of microflagellates.Mean assimilation numbers and calculated carbon doubling ratesin the <8 µm (2.8 g C g Chl a1 h1; 0.9day1)and<5 µm(1.7 g C g Chl a1h1; 0.5day1)size fractions were consistently lower than those of the totalpopulation (4.8 g C g Chl a1 h1; 1.3 day1)and the <10 µm size fraction (5.8 g C g Chl a1h1; 1.4 day 1). The results indicate that smalldiatoms and dinoflagellates in fractionated phytoplankton populationscan influence productivity out of proportion to their numbersor biomass.
1Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia. 相似文献
9.
Microzooplankton herbivory and bacterivory in Newfoundland coastal waters during spring, summer and winter 总被引:8,自引:0,他引:8
Grazing by microzooplankton on autotrophic and heterotrophicpicoplankton as well as >0.7 µm phytoplankton (as measuredby chlorophyll a) was quantified during July, August, October,January and April in the surface layer of Logy Bay, Newfoundland(47°38'14'N, 52°39'36'W). Rates of growth and grazingmortality of bacteria, Synechococcus and >0.7 µm phytoplanktonwere measured using the sea water dilution technique. Microzooplanktoningested 83184, 96366 and 64118% of bacterial,Synechococcus and >0.7 µm phytoplankton daily potentialproduction, respectively and 34111, 2530 and 16131%of bacterial, Synechococcus and >0.7 µm phytoplanktonstanding stocks, respectively. The trends in prey net growthrates followed the seasonal cycles of prey biomass, suggestingthat microzooplankton are important grazers in Newfoundlandcoastal waters. Ingestion was lowest during January and October(~2 µg C l1 day1) and highest in August(~20 µg C l1 day1). Aside from April when>0.7 µm phytoplankton represented the majority (~80%)of carbon ingested, bacterioplankton and <1 µm phytoplanktonrepresented most of the carbon ingested (~40100%). Althoughmicrozooplankton have here-to-fore been unrecognized as an importantgrazer population in Newfoundland coastal waters, these resultssuggest that they play an important role in carbon flow withinthe pelagic food web, even at low temperatures in Logy Bay. 相似文献
10.
Park Yong C.; Carpenter Edward J.; Falkowski Paul G. 《Journal of plankton research》1986,8(3):489-503
In Great South Bay, nanoplankton, (<20 sµm) accountedfor the largest fraction (56%) of zooplankton glutamate dehydrogenase(GDH) activity over a one year period. Microzooplankton (20200µm) and macrozooplankton (>200 µm) accountedfor 20% and 24%, respectively. Total zooplankton ammonium regenerationin Great South Bay could account for 74% of the ammonium requirementby phytoplankton in winter, but in summer when phytoplanktondemand was greater, and zooplankton population was low, it suppliedless than 5%. This study suggests that the smallest zooplanktonfraction, less than 20 µm, can be the most important asregards nitrogen regeneration in estuarine environments. MacrozooplanktonGDH activity in Great South Bay ranged from 0.18 mg atoms NH+4-Nm3 d1 in winter to 3.34 mg atoms NH+4-N m3d1 in spring. Over an annual period, the averaged GDH/excretionratio was 20.4 3.5 (n = 10), and this ratio agrees well withobservations by other investigators. Observed macrozooplanktonexcretion rates showed a strong correlation with the excretionrates indirectly estimated from GDH activities. The GDH/excretionratio seems to vary depending on the internal physiologicalstates of zooplankton as well as food availability. 相似文献
11.
The siphons and mantle edge of Donax serra and D. sordidus possesstwo types of ciliated sensory receptor. Type 1 has > 7 ciliawith an exposed length of 0.72.4 µm. Type II hasfewer cilia (25) which are 26 µm long. Athird type (Type III) described from the tips of the tentaclesof the siphon and mantle edge of D. sordidus, possesses twotufts of cilia which are 12 µm long. All three receptortypes appear to be primary receptors. Estimates of abundanceshow that receptors are most numerous on the tips of the siphontentacles (9.75 x 103. mm2), and it is suggested thatthese receptors function as chemoreceptors. (Received 11 May 1983; 相似文献
12.
Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer 总被引:5,自引:0,他引:5
Nagata Toshi; Takai Kenji; Kawanobe Kyoko; Kim Dong-Sup; Nakazato Ryoji; Guselnikova Nina; Bondarenko Nina; Mologawaya Oliga; Kostrnova Tatyana; Drucker Valentine; Satoh Yasuhiro; Watanabe Yasunori 《Journal of plankton research》1994,16(8):945-959
Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 5001300 m) of southern Lake Baikal; maximum numberswere 2 x 106 cells ml1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 105 cells ml1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 1484 µg C l1and 3.621 µg N l1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer. 相似文献
13.
Nodule lipid, glyoxylate and ureide transformations associatedwith nitrogenase activity of Jack bean (Canavalia ensiformis(L.) DC.) were determined at anthesis, 72 day age from emergence(DAE), and with mature seed pod development at 149 DAE. Totalnodule lipid content decreased about 86% during seed development.Acylglycerides were dominant, 10.9 g kg1 nodule, withtriacyl content decreasing from 55% at anthesis to about 13%at full seed set. Phosphatidylcholine composed about 39% oftotal nodule glycerphosphatides, 9.03 g kg1 nodule atanthesis, decreasing to 16% at full seed set. Oleic was theprincipal unsaturated fatty acid, 33.0% at anthesis decreasingto 25.8% at full seed set. Nitrogenase activity decreased from617.8 nmol C2H4 plant1s1 at anthesis to 499.5nmol C2H4 plant1s1 at full seed set. Key glyox-ylatecycle enzymes changed significantly with increase of isocitratasefrom 4.59 katal?10-6 (µkat) kg1 to 18.36µkatkg1 nodule and decrease of malate synthetase from 32.47µkat kg1 to 4.25µkat kg1 nodule. Highlysignificant decreases occurred with purine catabolic enzymes;uricase decreased from 39.10µkat kg1 to 2.21 µkatkg1, allantoinase decreased from 4.08µkat kg1to 1.36µkat kg1 and allantoicase decreased from3.91 µkat kg1 to 0.85 µkat kg1 nodule.Ureide content decreased from 204.40 mMol kg1 to 33.03mMol kg1 nodule. (Received April 4, 1988; Accepted August 17, 1988) 相似文献
14.
Ephyra larvae and small medusae (1.795 mm diameter, 0.01350mg ash-free dry wt, AFDW) of the scyphozoan jellyfish Aureliaaurita were used in predation experiments with phytoplankton(the flagellate Isochrysis galbana, 4 µm diameter, {smalltilde}6 x 106 µg AFDW cell1), ciliates (theoligotrich Strombidium sulcatum, 28 µm diameter, {smalltilde}2 x 103 µg AFDW), rotifers (Synchaeta sp.,0.5 µg AFDW individual1) and mixed zooplankton(mainly copepods and cladocerans, 2.13.1 µg AFDWindividual1). Phytoplankton in natural concentrations(50200 µg C I1) were not utilized by largemedusae (4495 mm diameter). Ciliates in concentrationsfrom 0.5 to 50 individuals ml"1 were consumed by ephyra larvaeand small medusae (314 mm diameter) at a maximum predationrate of 171 prey day1, corresponding to a daily rationof 0.42%. The rotifer Synchaeta sp., offered in concentrationsof 100600 prey I1, resulted in daily rations ofephyra larvae (25 mm diameter) between 1 and 13%. Mixedzooplankton allowed the highest daily rations, usually in therange 540%. Large medusae (>45 mm diameter) consumedbetween 2000 and 3500 prey organisms day"1 in prey concentrationsexceeding 100 I1. Predation rate and daily ration werepositively correlated with prey abundance. Seen over a broadsize spectrum, the daily ration decreased with increased medusasize. The daily rations observed in high abundance of mixedzooplankton suggest a potential scope for growththat exceeds the growth rate observed in field populations,and this, in turn, suggests that the natural populations areusually food limited. The predicted predation rate at averageprey concentrations that are characteristic of neritic environmentscannot explain the maximum growth rates observed in field populations.It is therefore suggested that exploitation of patches of preyin high abundance is an important component in the trophodynamicsof this species.
1Present address: University of Bergen, Department of MarineBiology, N-5065 Blomsterdalen, Norway 相似文献
15.
Eudiaptomus gracilis makes up 3040 and 8090% ofthe zooplankton in Lake Balaton during the summer and the winterrespectively. More than half of the species population consistsof nauplii We studied feeding and size selectivity of naupliiin suspensions which contained polystyrol latex beads in a concentrationdose to the natural seston. Guts of NI nauplii were free ofboth beads and remnants of natural food Of NIINVI nauplii,6787% took in beads. Older animals consumed more andlarger particles. The maximum diameter of ingested beads reached29 µm On an average, NII nauplii took in 128 µm3of beads in 10 min, whereas older animals consumed 615900µm3. The clearance rate remained below 0 01 µl h1NII nauplii strongly preferred 1 2 µm particles Oldernauplii did not show any preference or selected only slightlyfor the smallest particles. Nauplii rejected 411 µmbeads. In some cases a weak positive selection could be observedtoward 12 µm or larger beads. 相似文献
16.
Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (45µm diameter) alone or in combination with Peridinium trochoideum(1618 µm diameter) at concentrations of 0.150.70mm3 x 11. Grazing rates (ml x zooid1 x 24 h 1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC1x 24 h1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (106 µm3x zooid1 x 24 h1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC1 x 24 h1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m3) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day.
1Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5 相似文献
17.
The nutritional value of different sized fractions of naturalplankton was investigated for the growth of Eodiaptomus japonicusBurckhardt by comparing the development of its naupliar andcopepodid stages fed on differentially fractionated planktonicassemblages of a eutrophic pond, at 20°C. Water filteredthrough a 0.8 µm Nuclepore filter, containing mainly smallcoccoid bacteria (0.450.6 µm in cell diameter),at a concentration of 82.7 µg C 11 could not supportthe development of E.japonicus. The 3 µm filtered water,containing bacteria and picoalgae. at a total concentrationof 259 µg C 11, supported development but not eggproduction. The 20 µm filtered water, containing bacteria,picoalgae and large algae, at a total concentration of 2600µg C 11, supported rapid development of the juvenilesand continuous egg production by the adults. The separated 320µm fraction, containing only large algae, could not supportthe development at concentrations of 131 and 196 µg C11. However, the same rapid development of the juvenilesand continuous egg production by adults occurred at all of thetested concentrations between 261 and 3920 µg C11of the large algae. The results suggest that E.japonicus favoursalgae larger than 3 µm during its complete lifespan, andthat the threshold food concentration for its development variesbetween 200 and 250 µg C 11. 相似文献
18.
Nitrogen dynamics in lower Narragansett Bay, Rhode Island. I. Uptake by size-fractionated phytoplankton populations 总被引:1,自引:0,他引:1
The contribution of nanoplankton (< 10 µm fraction)to winter spring (1977 78) and summer (1978,1979) phytoplankton nitrogen dynamics in lower NarragansettBay was estimated from ammonium, nitrate and urea uptake ratesmeasured by 15N tracer methods. During the winter spring,an average of 80% of chlorophyll a and nitrogen uptake was associatedwith phytoplankton retained by a 10 µm screen. In contrast,means of 51 58% of the summer chlorophyll a standingcrops and 64 70% of nitrogen uptake were associatedwith cells passing a 10 µm screen. Specific uptake ratesof winter spring nanoplankton populations were consistentlylower than those of the total population. Specific uptake ratesof fractionated and unfractionated summer populations were notsignificantly different. Ammonium uptake averaged between 50and 67% of the total nitrogen uptake for both the total populationand the < 10µm fraction. The total population and the10 µm fraction displayed similar preferences for individualnitrogen species. Though composed of smaller cells, flagellatedominated nanoplankton assemblages may not necessarily takeup nitrogen at faster rates than diatom dominated assemblagesof larger phytoplankters in natural populations.
1Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia 相似文献
19.
JONES RUSSELL S.; COE LAURA L.; MONTGOMERY LADONNA; MITCHELL CARY A. 《Annals of botany》1990,66(6):617-622
Physical agitation applied as periodic seismic stress (shaking)reduced stem clongation, leaf expansion, and biomass accumulationby vegetative soybeans. Level of photon flux (PPF) influencedthe type and extent of plant response to mechanical stress.Plant parts responded differently as PPF varied between 135and 592 µmol m2 S1. Stem length was significantlyreduced by seismic stress at 135 µmol m2 s1but this effect was insignificant at higher PPFs. Reduced stemlength resulted from an inhibition of internode elongation.Stem diameter was unaffected by stress at the PPFs tested. Incontrast to effects on stem elongation, leaf area was insensitiveto stress treatments at 135 µmol m2 S1 butwas progressively inhibited by stress as PPF increased. Statisticallysignificant reductions in shoot f. wt and d. wt by seismic stressoccurred only at 295 µmol m2 S1. Root biomassaccumulation was not affected by seismic stress at any PPF usedin this study. Glycine max (L.) Merr. cv. Century 84, mechanical stress, photosynthetic photon flux, seismic stress, soybean 相似文献
20.
The concentrations of dissolved organic nitrogen (DON) and dissolvedinorganic nitrogen (DIN) in the epilimnetic waters of Lake Kinneretdecreased from 371 to 152 µg N 11 and from 65 to13 µg N 11, respectively, during September-October1994, concomitantly with the outgrowth of the cyanobacteriumAphanizomenon ovalisporum. A mass balance estimate based onthe cyanobacterial standing stock indicates that the maximum,net N requirement of A.ovalisporum was between 106 and 245 µgN 11 These observations suggest that components of theDON pool were a major direct or indirect source of N for themicroplankton and that N fixation was not a significant factorin the development of A.ovalisporum. Further support for thisidea was given by experiments which showed that monoculturesof this organism grew well in mineral media supplemented withorganic N com pounds (urea, hypoxanthine, lysine, guanine, glucosamine).In general, it is proposed that the DON pool, which is oftenin relatively high concentrations compared to DIN, must be consideredan active participant in N recycling and may serve as an importantN source for phytoplankton in many aquatic environments. 相似文献