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1.
The population abundances and rates of biomass production ofheterotrophic nanoplankton (HNAN) in Georgia coastal waterswere evaluated by epifluorescence microscopy. HNAN populations(mostly non-pigmented microflagellates <10 µm in diameter)ranged from 0.3 x 103 cells ml1 in shelf waters 15 kmoffshore to 6.3 x 103 cells ml1 in waters 0.25 km fromthe coast. There was a strong correlation (r = 0.83) betweenHNAN and free bacterioplankton population abundances, but noapparent relation (r = 0.38) between HNAN and phototrophic nanopLankton(PNAN) abundances. HNAN biomass production in estuarine andnearshore shelf waters, as estimated from increases in HNANpopulations during laboratory incubations of natural water samples,ranged from 0.10 to 0.79 mg C m3 h3, with populationgeneration times of 9.7 to 26.5 h. There was a significant linearrelation (r = 0.95) between HNAN biomass and HNAN productivity.We calculated that HNAN may graze at least 30% to 50% of dailybacterioplankton production in Georgia coastal waters. 相似文献
2.
Nutrient cycling through phytoplankton, bacteria and protozoa, in selectively filtered Lake Vechten water 总被引:2,自引:0,他引:2
Bloem Jaap; Albert Claudia; Bar-Gillissen Marie-Jose B.; Berman Thomas; Cappenberg Thomas E. 《Journal of plankton research》1989,11(1):119-131
The breakdown of organic carbon of dead Synechococcus cell walls,added to selectively filtered Lake Vechten water, was not acceleratedby protozoa. During 4 weeks of incubation at 15°C no significantdecrease of total organic carbon was observed. However, heterotrophicnanoflagel-lates (HNAN) and ciliates strongly increased theremineralization of N and especially P, from both cell wallsand cell extract. Bacterioplankton growth did not result innet P mineralization but in P uptake. P was remineralized onlyin the presence of protozoan grazers. Both HNAN and ciliatesgrazed on bacteria, with ingestion rates estimated at 2796bad HNAN1 h1 and 129 bact ciliate1 h1respectively. Grazers increased N mineralization too, althoughN was also mineralized in the absence of protozoa. The phytoplanktoncell walls yielded less P but more N remineralization than thecell extract. Thus, protozoa can strongly accelerate cyclingof specific nutrients through plankton. Nuclepore filters werefound to cause artificial DOC release during selective filtration. 相似文献
3.
The dynamics of heterotrophic nanoflagellates and bacterioplankton in a large ultra-oligotrophic Antarctic lake 总被引:4,自引:0,他引:4
Laybourn-Parry Johanna; Bayliss Peter; Ellis-Evans J.Cynan 《Journal of plankton research》1995,17(9):1835-1850
The abundance of both heterotrophic nanoflagellates (HNAN) andbacterioplankton in a large (9km2) ultraoligotrophic Antarcticlake (Crooked Lake) were investigated from December 1992 untilNovember 1993. HNAN abundance peaked in spring, summer and autumn,falling to lowest numbers during the winter. Numbers rangedbetween 0 and 50.9x104 l1. Bacterioplankton abundancewas highest during the late summer and then fell progressivelytowards winter and autumn (range 1.194.46x106 l1)In contrast to numbers, mean cell volumes (MCV) of the bacteriareached their highest in spring, and consequently highest bacterialbiomass occurred at this time. MCV ranged between 0.052 and0.224µm3. Bacterial production measurements followingthe incorporation of [3H] thymidine into DNA and [14C] leucineinto protein using a doubling-labelling procedure were undertakenin January, June, August, October and November. Rates variedbetween 2.8 and 52 ng C l1 h1. On occasions, a significant differencein production rates based on the uptake of leucine and thymidinewas observed, suggesting unbalanced growth. Highest rates ofproduction coincided with times of high dissolved organic carbonlevels in the water column and lowest production with low levelsof DOC. HNAN grazing rates were measured by following the uptakeof fluorescently labelled bacteria and averaged 4.8 bacterialcells individual1 day1 at 2 and 4°C. Specific growth rates(h1) ranged around 0.000700.00077 in both the field andlaboratory, giving doubling times of 37.3 and 41.0 days, respectively.These low rates of grazing and growth indicate that there isno adaptation to low temperatures in these freshwater protists.Based on these data, the gross production efficiency is 24%.HNAN removed between 0.1 and 9.7% of bacterial production perday. 相似文献
4.
Laybourn-Parry Johanna; Ellis-Evans J.Cynan; Butler Helen 《Journal of plankton research》1996,18(4):495-511
The dynamics of bacterioplankton and protozooplankton in twomaritime Antarctic lakes (Heywood Lake and Sombre Lake, SignyIsland, South Orkneys) were studied during the phase of icebreak-out (December and early January 1994/95). The lakes aresuffering animal-induced (fur seal) eutrophication, though HeywoodLake is most severely affected. Both lakes had morphologicallydiverse bacterial communities which increased during the studyperiod, reaching maxima of 80 x 108 l1 in Heywood Lakeand 31.8 x 108 l1 in Sombre Lake. Heterotrophic nanoflagellates(HNAN) reached a peak in late December with maxima of 40.6 x108 l1 in Sombre Lake and 174 x 105 l1 in HeywoodLake. Phototrophic nanoflagellates (PNAN) peaked in late Decemberafter ice loss in Heywood Lake (63 x 105 l1), which coincidedwith a peak in a bloom of Chroomonas acuta which reached abundancesof 1.0 x 108 l1. In Sombre Lake, ice persisted for alonger period and here PNAN reached their highest density atthe end of the study period (around 70.0 x 105 l1). Ciliateabundance reached high levels in Heywood Lake (>600011),while in Sombre Lake maximum abundance was 568l1. Protozooplanktondiversity was greater in the less-enriched Sombre Lake. Grazingrates of ciliates averaged 70.6 bacteria indiv.1 h1in Heywood Lake and 119.3 bacteria indiv.1 h1in Sombre Lake. The difference was a reflection of the differenttaxonomic make-up of the community in the lakes. HNAN grazingrates varied between 0.51 and 0.83 bacteria indiv.1 h1in Sombre and Heywood Lakes, respectively. Specific growth rates(r) h1 in Sombre Lake were 0.028 for ciliates and 0.013for HNAN, and in Heywood Lake 0.010 for ciliates and HNAN 0.012.These growth rates result in doubling times ranging between38 and 69 h for ciliates and around 55 h for HNAN.HNAN grazingon bacteria was curtailed in Heywood Lake in early January asa result of predation by microcrustacean larvae feeding on theplankton. Thus, for a short phase top-down control was apparentin the dynamics of Heywood Lake, a feature uncommon in Antarcticlake ecosystems. The impact of natural eutrophication on thesesystems is discussed in relation to other unaffected Antarcticlakes. 相似文献
5.
Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method 总被引:1,自引:0,他引:1
Vanderploeg Henry A.; Laird Gwenyth A.; Liebig James R.; Gardner Wayne S. 《Journal of plankton research》1986,8(2):341-352
The maximum excretion rate of NH4 (39 nmol mg dry wt1h1) was directly measured for Daphnia pulex by measuringNH4 accumulation in bottles containing D. pulex and dense, satiatingsuspensions of heat-killed algae. Ammonium release rates inthe algal suspensions were compared to those of individual animalsremoved from the suspension and placed in flow cells. Ammoniumrelease rate, R (nmol mg dry wt1 h1). in the flowcell decreased very rapidly with time, t (min), after removalaccording to the relation R = 26 + 25e0.16t. Ammoniumexcretion obtained by the flow cell method after extrapolationto time zero was not significantly different from that obtainedin the bottles. The considerable experiment-to-experiment variationin NH4 excretion was in large part correlated (r2 = 0.73) withthe feeding rate on the algae. 相似文献
6.
The contribution of ammonia excreted by zooplankton to phytoplankton production in Narragansett Bay 总被引:1,自引:0,他引:1
Ammonia excreted by mixed zooplankton populations over an annual(19721973) cycle in Narragansett Bay varied from 0.04to 3.21 µg at NH3-N dry wt1 day1, exclusiveof two exceptional rates measured one year apart: 11.74 and18.39 µg at NH3-N mg dry wt1 day1. Grossphytoplankton production integrated over the year (19721973)averaged 151 mg C m3 day1 for an 8 m water column;peaks of 332 and 905 mg C m3 day1 occurred duringthe winter-spring and summer blooms, respectively. Excretedammonia, integrated seasonally and annually, contributed only0.2% and 4.9% of the nitrogen required for observed gross productionduring the winter-spring and summer blooms, respectively, and4.4% annually. However, excreted ammonia may be an importantsource of the nitrogen required by Skeletonema costatum, thedominant diatom in Narragansett Bay, during the post-bloom periodwhen 186% of the nitrogen required for its net production wasmet by ammonia excretion. A combination of zooplankton ammoniaexcretion and benthic ammonia flux contributed 22% of the nitrogenrequired for the annual gross production (440 g C m2)while 51% of the nitrogen required for the net production ofSkeletonema was accounted for by regenerated nitrogen.
1This research was supported by NSF grant GA 31319X awardedto Dr.T.J.Smayda. 相似文献
7.
Malinsky-Rushansky Nechama Z.; Berman T.; Dubinsky Z. 《Journal of plankton research》1997,19(8):979-993
Autotrophic picoplankton populations in Lake Kinneret are composedof picocyanobacteria and picoeukaryotes. Overall, the ratesof photosynthetic carbon fixed by autotrophic picoplankton duringthis study were low (0.011.5 mg Cm3 h1).The highest chlorophyll photosynthetic activity of the <3µm cell-size fraction was found in spring, when picoeukaryotespredominated and in addition small nanoplankton passed throughthe filters. The maximum cell-specific photosynthetic rate ofcarbon fixation by picocyanobacteria and picoeukaryotes was2.5 and 63 fg C cell1 h1, respectively. The highestspecific carbon fixation rate of autotrophic picoplankton was11 µg C µg1 Chl h1 The proportionalcontribution of autotrophic picoplankton to total photosynthesisusually increased with depth. Picocyanobacteria collected fromthe dark, anaerobic hypolimnion were viable and capable of activephotosynthesis when incubated at water depths within the euphoticzone. Maximum rates of photosynthesis (Pmax) for picocyanobacteriaranged from 5.4 to 31.4 fg C cell1 h1 with thehighest values in hypolimnetic samples exposed to irradiance.Photosynthetic efficiency ( 相似文献
8.
The uptake of bacteria and picoplankton sized fluorescentlylabelled beads was measured off the west coast of the SouthIsland of New Zealand in winter. Phytoflagellates and heterotrophicflagellates showed similar grazing rates on 0.49 µm beads,with mean clearance rates of 1.1 and 1.8 nl ind.1 h1,respectively. Clearance rates for 1.09 µm beads were 0.9nl ind.1 h1 for heterotrophic flagellates and0.5 nl ind.1 h1 for phytoflagellates. Non-loricateciliates had clearance rates of 1.5 µl ind.1 h1for the picoplankton sized particles. The heterotrophic flagellatesshowed no significant difference between clearance rates of0.49 and 1.09 µm particles. Phytoflagellates, however,showed an apparent preference for the smaller particles. Themeasurement of significant grazing by phytoflagellate populationsin the marine environment is important and indicates that weneed to reassess our concepts of food web structure. 相似文献
9.
Conspicuous Peak of Oligotrichous Ciliates Following Winter Stratification in a Bog Lake 总被引:2,自引:0,他引:2
We analysed early spring protozooplankton peaks following winterstratification in two different basins (northeast, NE; southwest,SW) of an artificially-divided bog lake Große Fuchskuhle(Brandenburg,Germany). The maximum ciliate biomass and numbers (660 and 990µg l1 of organic carbon, and 290 and 260 cellsml1 in NE and SW, respectively) were reached in the surfacelayer during the ice melting and then continuously decreased.The surface layers were numerically dominated by species ofthe genus Urotricha, while in the ciliate biomass during thefirst part of the study, a mixotrophic oligotrich, Pelagostrombidiummirabile prevailed (Corg up to 940 µg l1). We observeda conspicuous ciliate peak that could not be related to thefeeding activity of the dominant ciliate species upon picoplankton.Seemingly, the peak was related to the specific conditions resultingfrom the ice melting where these ciliates could be concentrated.Additionally, the mixotrophy of oligo-trichous species allowedthem to penetrate below the oxycline, although feeding on nanoplanktonsuch as flagellates was also very likely. Our direct measurementsof uptake rates of bacteria showed that the abundant strombidiidswere not nutritionally dependent on bacterivory. However, theciliate uptake rate (up to 670 bacteria ciliate1 h1)contributed significantly to the overall bacteria mortalityrate. The maximum (community average) cell-specific ciliatefeeding rate of over 200 bacteria ciliates1 h1was reached, along with an increasing contribution of scuticociliates,paralleled by a drop in large oligotrichs. 相似文献
10.
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
11.
Bacterial secondary production and rates of bacterivory weredetermined from samples collected from mesotrophic Lake Arlington.Bacterial production and losses were determined by comparingthe growth of natural bacterial assemblages in the presenceof predators (unfiltered samples) to growth in the absence ofpredators (water filtered through 1.0 (im porosity filters).Growth rates of heterotrophic nanoflagellates (HNF) were estimatedfrom growth in the absence of predators (water filtered through5.0 µm porojity filters). Bacterial growth rates rangedbetween 0.002 and 0.069 h1 and averaged 0.026 h1.HNF grew at rates ranging between 0.003 and 0.107 h1and averaged 0.028 h Grazing rates ranged between 0.002and 0.043 h1, and averaged 0.018 h. The annual averagerate of bacterial biomass synthesis was 3.2 g Clh1 and {small tilde}69% of this production was grazed.Temporal changes in growth and grazing rates suggest a tightlycoupled predator-prey linkage in this lake.
1Present address: Hydrobiological Institute, Czech Academy ofSciences, Na sddkach 7, 370 05 teski Budjovice, Czech Republic 相似文献
12.
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
13.
Ecological studies on the phytoplankton of Boknafjorden, western Norway. II. Environmental control of photosynthesis 总被引:2,自引:0,他引:2
Both predicted (incubator) and measured (in situ) 14C-assimilationrates were studied from February to November 1981 at three stationsin Boknafjorden, a deep silled fjord of western Norway. Sampleswere taken from different light depths within the euphotic zone.A high degree of conformity was found between the two approaches.Daily values of carbon assimilation integrated over the euphoticzone varied between 0.05 and 1.4 g C m2. Yearly primaryproduction varied between stations from 82 to 112 g C m2(120148 g C m2 when based on average light conditions).The light-saturation curve parameters B and PBmax ranged from0.0056 to 0.0537 mg C mg Chla1 h1 µE1m2 and from 0.7 to 8.5 mg C mg Chla1 h2 (in situassimilation numbers ranged from 0.9 to 9.3 mg C mg Chla1h1) respectively, which compare well with those publishedfrom the northwestern side of the Atlantic. The overall importanceof light in controlling photosynthesis throughout the year wasrevealed by the light utilization index , estimated to be 0.43mg C mg Chla1 E1 m2. The maximum quantum yieldwas encountered on August 17, with 0.089 mol CE1. Chla/Cratios above and below 0.010 were found to be typical for shade-and light-adapted cells respectively. Assimilation numbers andgrowth rates were linearly related only when considering light-adaptedcells. Consistent with the findings of this study, the applicabilityof IK, B and PBmax as indicators of light-shade adaptation propertiesshould be questioned. Maximum growth rates were encounteredduring an autumn bloom of the dinoflagellate Gyrodinium aureolum(1.0 doublings day1), while 0.70.8 doublings day1were found for a winter bloom (water temperature of 2°C)of the diatom Skeletonema costatum. No unambiguous temperatureeffect on assimilation number and growth of phytoplankton couldbe recognized in Boknafjorden. A tendency towards increasedassimilation numbers coinciding with increased water columnstability was revealed. The highest PBmax values were oftenencountered at almost undetectable nutrient concentrations.At least during summer this could be attributed to recyclingof nutrients by macro- and/or microzooplankton, responsiblefor a greater part of the primary production now being grazeddown. This study supports the convention that the depth of theeuphotic zone may extend considerably below the 1% light depth. 相似文献
14.
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
15.
An investigation of the diurnal variation in contributions toproduction of the autotrophic and heterotrophic components ofthe picoplankton community was carried out during August andSeptember in Llyn Padarn, a mesotrophic upland lake in NorthWales. The picoplankton was separated using 1 µm pore-sizedfilters into the smaller cell sized fraction (<1 µm),the majority of the bacteria and the larger cell sized picoalgae(<3>1 µm), together with some bacteria. The distributionof bacterial heterotrophic activity between these two fractionsof picoplankton was assessed by uptake of [14C]glucose and differentialfiltration. Thus, the absolute autotrophic production by picoalgaeand the heterotrophic contribution by bacteria to picoplanktoncommunity production via uptake of extracellular organic carbon(EOC) were determined. Rates of picoplankton community productionexhibited diurnal variation with maximum rates of 19.1 mg Cm3 h1 recorded at 18.00 h at 4 m depth in September.The bacterial contribution to picoplankton community productionincreased markedly between 15.00 and 18.00 h. Rates of absoluteautotrophic production varied less over 24 h than rates of accumulationin bacteria of 14C-labelled EOC released from the entire phytoplanktoncommunity. Bacteria contributed up to 8698% of the neworganic carbon within the picoplankton community at the endof the day. The maximum rate of absolute autotrophic productionin the picoplankton was 1.6 mg C m3 h1 at 18.00h at 1 m in August, and the maximum rate of bacterial accumulationof new organic carbon was 18.5 mg C m3 h1 at 18.00h in September at 4 m depth. The diurnal pattern of picoplanktoncommunity production involved increasing rates during the daywith a maximum at 18.00 h. Autotrophic processes were dominantin the first 36 h of the light cycle and heterotrophicuptake of 14C-labelled EOC was the major component from 15.00h onwards. Bacterial uptake of newly released EOC by phytoplanktonwas rapid, comprised the majority of picoplankton production,particularly later in the day, and contributed a maximum of60% of the total pariculate primary production in plankton between15.00 and 18.00 h at 4 m in September with a mean contributionof between 6 and 26% over 24 h in these investigations. Theimportance of autotrophic processes in picoplankton communityproduction has been overestimated in previous investigations.Bacteria play a major role in transferring newly produced EOCrapidly from phytoplankton to the picoplankton community. Atthe end of the day, the majority of newly produced organic carbonis in bacterial cells and this production is significant inthe dynamics of carbon production within the entire planktoniccommunity. 相似文献
16.
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
17.
Particulate and dissolved phytoplankton production of the Patos Lagoon estuary, southern Brazil: comparison of methods and influencing factors 总被引:3,自引:0,他引:3
Abreu Paulo C.; Odebrecht Clarisse; Gonzlez Adriana 《Journal of plankton research》1994,16(7):737-753
Uptake rates of 14C (filtration and the acidification-bubblingmethodABM) were measured weekly in a shallow region ofthe Patos Lagoon estuary (3207'S, 5206'W) between March 1989and March 1990. Phytoplankton production varied seasonally,the lowest values occurring in the austral winter (JuneAugust1989) and the highest rates during spring and summer (March1989; September 1989March 1990). Particulate carbon productionvaried between 0.65 and 70.6 mg C m3 h1 and wasmostly associated with organisms <20 µm (mean = 73.4%).Dissolved organic carbon (DOC) released by phytoplankton variedbetween 0.1 and 89.3 mg C m3 h1 representing 相似文献
18.
The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass 总被引:5,自引:0,他引:5
Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.J. exp. Bot.37: 919927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added 15N-labelled nitrate were exposed,in chambers, for 40 d to NH3 in the air at concentrations of16, 118 and 520 µg m3. At the highest concentrationof NH3, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg1 dry soil) and 35?2% with the higher rate (200mgN kg1 dry soil) At the intermediate concentration ofNH3, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH3, they were 5?1% and 32%. Most of the N derived from theNH3 remained in the leaves, but some was transported to theroots. The amount of N derived from the NH3 that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH3 per unit leaf area ranged from 1?7 µg dm2h1 at a concentration of 16 µg m3 to 29?0µg dm2 h1 at a concentration of 520 µgm3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH3 per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH3 in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum 相似文献
19.
Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day1 and 630 mg.day1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO2.g totalbody mass1.h1 at 15°C, when the snails wereactive, and 11.27 µlO2.g total body mass1.h1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990) 相似文献
20.
Fonda Umani S.; Beran A.; Parlato S.; Virgilio D.; Zollet T.; De Olazabal A.; Lazzarini B.; Cabrini M. 《Journal of plankton research》2004,26(5):545-561
The first bloom of Noctiluca scintillans in theNorthern Adriatic Sea was recorded in 1977. The organism causedseveral red tides in the whole basin during the late 1970s,a period characterized by increasing nutrient loads. Duringthe 1980s and early 1990s, there was no red tide,but the species was an almost constant summer presence, associatedwith high temperatures. Noctiluca scintillans was almost completelyabsent from 1994 until May 1997, concurrent with a general planktondecrease. From summer 1997, N. scintillans was recorded againin the whole basin, although there was no other signal of increasingeutrophication. In contrast to all previous observations, duringwinter 20022003, N. scintillans was continuously sampledin the Gulf of Trieste. We estimated experimentally growth andgrazing rates of the dinoflagellate at 910°C in cultureand consuming the natural assemblage. Noctiluca scintillanswas able to reproduce actively at low temperatures, showingsimilar growth rates in both experiments (k = 0.2 day1).The values found were close to those reported in the literaturefor higher temperatures. The natural diet was mainly composedof phytoplankton (ingestion = 0.008 µg C Noctiluca 1day1), microzooplankton (ingestion = 0.008 µg CNoctiluca 1 day1) and bacteria (ingestion = 0.005µg C Noctiluca 1 day1) with an average carboncontent of 0.138 ± 0.020 µg C Noctiluca cell1. 相似文献