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1.
The 15N values of micronekton collected from Sagami Bay rangedfrom 9.4 to 14.2%. The 15N values of the micronekton, Gonostomagracile, increased with growth (9.4 to 12.6%) and it seems thatmales, before sex reversal, and females consume different foodorganisms.  相似文献   

2.
The 15N of marine mesozooplankton species was measured on fouroccasions. Significant differences were found between copepodsand meroplanktonic larvae, yet not between holoplanktonic species.On average, mesozooplankton was enriched by 3.4 ± 0.9relative to selected seston size fractions. Despite suggestingsmall differences (0.5 to 1) in the 15N of different phytoplanktontaxa on one occasion, the size fractionation procedure generallyproved inadequate in separating major taxonomic groups composingseston. This circumstance, and phase-shifts in the transmissionof rapid changes (>2) in seston 15N to mesozooplankton complicatethe calculation of mesozooplankton trophic levels.  相似文献   

3.
Colonies of Trichodesmium spp. are conspicuous, macroscopiccomponents of the life in tropical and subtropical oceans. Thelarge size and the morphology of the colony raise questionsregarding the mechanism of carbon supply for photosynthesis.Constraints on these mechanisms may be indicated by the stablecarbon isotopic composition (13C) that reflects the balancebetween carbon supply and speciation, as well as the growthrate and colony size. The 13C of Trichodesmium off Bermuda measuredhere revealed a strong correlation between size of individualcolonies and season. The smallest colonies, 2–7 µgC colony–1, showed the lightest 13C composition (–19),increasing to asymptotic values of –12 above 7 µgC colony–1. The average 13C of the colonies was lightestimmediately after the onset of stratification in the SargassoSea, gradually increasing by 4 to heavier values during thesummer. We propose that the mass effect is due to increaseduse of HCO3 by the larger colonies, whereas the seasonalinfluence may be related to changes in irradiance and pCO2 affectingthe internal carbon cycling.  相似文献   

4.
A factorial experiment shows highly significant effects of temperature(12 5–22.5°C) and salinity (17.8–34 S) on thegrowth rate of Gyrodinium aureolum, with a significant temperature-salinityinteraction. The maximum growth rate of G aureolum is measuredto 0.61 div. day–1 at 20°C and 22.3 S. Gyrodiniumaureolum does not grow at temperatures :10 °C or 25°Cand at salinities 12 S. The cellular content of carbon (C) andnitrogen (N) and the elemental ratios N/C, P/C and N/P are significantlyaffected by the temperature The cellular content of phosphorus(P) and the elemental ratios P/C and N/P vary significantlywith salinity Significant temperature-salinity interactionsare found for the cellular content of carbon, nitrogen and phosphorus.Variations in the N/P ratio indicate that G.aureolum has a largestorage capacity for phosphorus It is suggested that temperatureis one important limiting factor in the initiation of bloomsof G.aureolum in north European waters.  相似文献   

5.
Laboratory-hatched larvae of this estuarine crab were rearedat 25°C in seawater of 25 salinity for 18 days coveringzoeal Stages I to IV and a megalops. Three-day periods betweenzoeal stages represent intermolt stages of circadean metecdysis,diecdysis, and proecdysis.Larvae were exposed to either a seriesof seawater salinities from 5-40 in 5 increments or of 10-40in 10 increments for one hour during each day of their development.The osmoconcentrations of 20-80 nanoliter hemolymph samplesfrom each of four larvae were measured separately by determinationsof freezing point depression. Eyestalkless larvae in metecdysis of zoeal Stage II were exposedto the same osmoconcentrations as unoperated controls to testfor osmoregulation by eyestalk nerve tissue. Larvae tend to be isosmotic with seawater of 30-40 salinity(S) and to hyperregulate in more dilute media except for larvaein their first diecdysis which remain isosmotic. Larvae in thelast few hours of proecdysis hyperregulate against 40 S as well,presumably to insure inflow of water to establish a greaterbody volume during hardening of the exoskeleton. They are consequentlyisosmotic in the very early metecdysis. The presence of eyestalks at the first metecdysis (Stage II)keeps zoeas hyperosmotic to 5-30 S, but prevents them from hyperregulationagainst 40 S. Eyestalkless zoeas become isosmotic with 5-30S and hyperregulate against 40 S like late proecdysal larvae.Lack of eyestalks makes diecdysal animals hyperregulate againsta medium with which normal animals are isosmotic. The eyestalkinfluence affects second metecdysal (Stage III) larvae in away similar to those in first metecdysis except that it apparentlyalso prevents a curious tendency to hyporegulate in 5-30 S.Similarly, in this stage, the eyestalks prevent hyperosmosityin 40 S seawater as they do during the first day of zoeal StageII. Eyestalk nerve tissue reduces the degree to which diecdysallarvae of this stage remain hyperosmotic to media of 10 S and20 S and apparently causes larvae to be hypoosmotic at 40 S. Preliminary data indicate that removal of eyestalks has littleeffect on proecdysal larval osmoregulation or on regulationof Stage IV zoeas. In other experiments ablation of eyestalks caused Stage II larvaeto lose the ability to osmoregulate against 10-30 S seawaterwithin two hours after the operation. The same zoeas did nothyperregulate against 40 seawater until four hours after removalof eyestalks.  相似文献   

6.
The stable carbon isotope composition of particulate organicmatter expressed as 13C was measured in cultures of 13 speciesof marine microalgae in different phylogenetic groups. The effectsof salinity variations and changes in photoperiod were alsoassayed for three of them (i.e. Skeletonema costatum, Amphidiniumopercularum and Isochrysis galbana); the effect of nature ofnitrogen supply (nitrate. ammonium) was studied for one (S.costatum).These environmental parameters were chosen because of theirvariability in the ocean and their possible effects on 13C valuesof phytoplankton organic carbon. Batch culture conditions andsampling time after inoculum were strongly controlled in orderto provide cells in good physiological state which were comparablefrom one culture to the other. In the same way, sampling waslimited to the first 2 days of exponential growth, in orderto avoid a possible dissolved inorganic carbon (DIC) limitation.Carboxylase activities [of the enzyme ribulose 1,5-bisphosphatecarboxylase oxygenase (Rubisco), and the three ß carboxylases:phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvatecarboxykinase (PEPCK) and pyruvate carboxylase (PC)] and totalchlorophyll a concentrations were assayed simultaneously. The13C values observed were between –30.2 and –12.7i.e. comparable to those observed in the world's oceans. Theisotopic composition of phytoplankton organic carbon was shownto be under the influence of the parameters tested but 13C variationsare specific to the species considered. The nature of ßcarboxylase found in each species, or systematic position, couldnot be linked to the isotopic composition of organic carbon.No linear or single correlation between 13C variations and environmentalmodifications were observed and there is no evidence for a simpleand universal relation between 13C of phytoplankters and theirenvironment. In monospecific cultures as in the field, 13C fractionationby Rubisco (and eventually by PEPCK) may be counterbalancedby other mechanisms.  相似文献   

7.
In nature, large concentrations of the toxic bloom-forming dinoflagellate,Gonyaulax tamarensis, are frequently observed in the vicinityof the pycnocline. In the absence of a pycnocline the organismis usually recorded near the surface, where light levels aremore advantageous for photosynthesis. In this paper we examinethe swimming behaviour of G.tamarensis when exposed to varyingdegrees of stratification and investigate whether the maintenanceof a subsurface (pycnocline) population is the result of retentionof the algae by a physical barrier or active accumulation ofthe organisms at a density interface. The study indicates thatG.tamarensis cells presented with a halocline of S<{smalltilde}6–7 (occurring over a few centimeters) cross thissalinity barrier and accumulate at the highest available photonflux density ({small tilde}100 µmol m–2 s–1).Cells exposed to a gradient of S>{small tilde}7remain atthe halocline (pfd={small tilde}40 µmol m–2 s–1).However, when light above the pycnocline is attenuated by theaddition of food colour to the medium, the cells cross a haloclineof S=10 and accumulate at the highest available photon fluxdensity. In the absence of added nutrients (inorganic N andP) the organism fails to exhibit a phototactic response. Thus,the presence of a strong halocline does not represent an inpenetrablephysical barrier for G.tamarensis and the development of pycnoclinepopulations of this organism is a function of density, lightand nutrient climate.  相似文献   

8.
Natural abundance values of plant 15N give an indication asto the source of nitrogen. In particular, carnivorous plantsare expected to be relatively enriched due to trophic enrichmentof their prey. Values of 15N for adultRoridula gorgonias(mean+3.02)are 4–9 greater than co-occurring non-carnivorous plantspecies and 5.24 greater than juvenileR. gorgoniasplants. Theyare also 3.5–4.26 greater than co-occurringDroseraspecieswhich, being sundews, are considered to be carnivorous. Thesehigh levels of 15N in adult plants are best explained as beingdue to access to trophically enriched N from insects. As isthe case for other carnivorous plants, leaves and stems ofR.gorgoniasare highly ultraviolet reflective and are thereforeprobably attractive to potential insect prey. This is furthersupport for this plant species being insectivorous.Copyright1998 Annals of Botany Company Nitrogen isotopes, carnivorous plants, insectivorous plant, ultraviolet,Roridula gorgoniasL.  相似文献   

9.
Measurements of 13C, 15N, and C/N for a variety of Antarcticpeninsula fauna and flora were used to quantify the importanceof benthic brown algae to resident organisms and determine foodweb relationships among this diverse littoral fauna. 13C valuesranged from–16.8 for benthic algal herbivores (limpets)to –29.8 for the krill, Euphausia superba; the averagepooled value for brown macroalgae, including their attachedfilamentous diatoms, was–20.6. There was no correlationbetween biomass 13C or 15N with C/N content, and consequentlyboth 13C and 15N values were useful in evaluating trophic relationships.15N values of the fauna ranged from 3.1 to 12.5, with lowestvalues recorded in suspension feeders (e.g., bryozoans) andhighest values in Adelie penguins (12.5) collected in 1989.The comparatively lower 15N value for a Chinstrap penguin (6.9)collected in 1997 is attributed to the different dietary foodsources consumed by these species as reflected in their respective13C values. Significant amounts of benthic macroalgal carbonis incorporated into the tissues of invertebrates and fishesthat occupy up to four trophic levels. For many benthic andepibenthic species, including various crustaceans and molluscs,assimilation of benthic algal carbon through detrital pathwaysranges from 30 to 100%. Consequently, the trophic importanceof benthic brown algae may well extend to many pelagic organismsthat are key prey species for birds, fishes, and marine mammals.These data support the hypothesis that benthic seaweeeds, togetherwith their associated epiphytic diatoms, provide an importantcarbon source that is readily incorporated into Antarctic peninsulafood webs.  相似文献   

10.
Gecarcinus lateralis can take moisture from a clamp substratumin amounts adequate for the needs of the entire intermolt cycle.It can also rehydrate in this way, even after severe dehydration. This crab is able to survive for many months when free waterof a wide range of salinities (0.30; = parts per thousand)is made available in a shallow dish. The crab dies within sevenweeks when the salinity of this water is 35. During proecdysisthe pericardial sacs of eyestalkless crabs become most swollenwhen the salinity of the available water is 15 or 23, and survivalduring and after ecdysis is greatest with water of 15. A crab in proecdysis shows no increase in the rate at whichwater enters following dehydration. Yet large amounts of waterare retained, particularly at the intermediate salinities. Maximalswelling of the pericardial sacs just prior to ecdysis is essentiallyequivalent in crabs with eyestalks, in eyestalkless crabs, andin eyestalkless crabs that have received an implant of centralnervous tissue. Hence, we conclude that a hormone causing theretention of water exists, but not in the eyestalks, in thebrain, or in the thoracic ganglionic mass. At ecdysis eyestalkless crabs show large increases in the dimensionsof the carapace, while crabs with eyestalks and eyestalklesscrabs that have received an implant of certain central nervoustissues show much less increase and may even show a decrease.Thus, we conclude that a hormone causing a release of waterat ecdysis is produced in the central nervous system. The advantages to the crab of a dual hormonal control of itswater balance are discussed.  相似文献   

11.
On filament width in oceanic plankton distributions   总被引:1,自引:0,他引:1  
A plankton patch deformed by diffusion, straining flow and biologicalgrowth is demonstrated to have a minimum width, /, which ispurely a function of the effective diffusivity, , and the strainrate, .  相似文献   

12.
Sixteen legumes were grown in N-free media so that N was suppliedentirely by symbiotic N2 fixation. The plant tissues were analyzedfor natural 15N abundance (expressed as 15N per mil relativeto air N2) with a ratio mass spectrometer. The nodules of desmodium,centro, siratro, soybean and winged bean showed high enrichmentin 15N (+9), while red clover showed slight enrichment (+2).The nodules of 9 other forage legumes (Townsville stylo, whiteclover, alsike clover, common vetch, Chinese milk vetch, senna,alfalfa, ladino clover, and hairy vetch) showed little enrichmentin 15N. In all the legumes investigated, particularly in the ureide-transportingplants such as desmodium, centro, siratro, soybean, winged beanand field bean, the 15N value of the shoots was negative (–3.2).The 15N value of the shoots in winged bean and field bean variedby about 1 depending on the Rhizobium strains used. The isotopicmass balance of 13 legumes indicated that isotopic fractionationoccurs during N2 fixation by the legume-rhizobia symbiosis witha preference for 14N over 15N, resulting in a 15N value of –0.2to –2 in the whole plant. The results indicate that 15N/14N isotopic discrimination witha preference for the lighter atom may occur in both N2 fixationand export of fixed N from nodules. 1Present address: Department of Soils and Fertilizers, NationalAgriculture Research Center, Kannondai, Tsukuba, Ibaraki 305,Japan. (Received October 8, 1985; Accepted April 7, 1986)  相似文献   

13.
Stable carbon isotopes (13C) were determined for phytoplanktonand dissolved inorganic carbon (DIC) from Lake Apopka, a shallow,polymictic and hypereutrophic lake in Florida, USA. Bulk planktondominated by pico- and nanqanobacteria were enriched in 13(–13.1± 1.1%) as a result of assimilation of extremely 13C-richDIC (13C = 9.6 ± 3.0%). Diatoms (Aulacoseira spp.) hada 13C of –14.3 ± 0.6% that was slightly more negativethan that of small cyanobacteria. Meroplanktonic diatoms hada 13C (–13.6 ± 1.8%), similar to their planktoniccounterparts. The 13C of a colonial cyanobacterium (Microcystisincerta) was exceptionally heavy (–3.0 ± 1.0%)and attributed to localized carbon limitation. Seasonal variationin 13C of bulk plankton was small (4%) relative to reports forother lacustrine systems No difference in the 13C of bulk planktonhorn surface water between stratified and non-stratified periodswas found. No measurable changes in 13C of bulk plankton wereindicated in light and dark incubation experiments Frequentwind mixing of the water column, high DIC concentration, andconsistently high lake productivity were used to explain thetemporal and spatial isotope consistency of phytoplankton inthis lake.  相似文献   

14.
A strain of the marine rotifer Synchaeta cecilia valentina,n. subsp., isolated from the Hondo of Elche Spanish Mediterraneancoastal lagoon at 22 salinity, was cultured in the laboratoryin 20 ml test tubes and fed with the alga Tetrasemis suecica.The effect of two temperatures (20 and 24°C), four salinities(20,25,30 and 37) and two food levels (15 000 and 25000 cellsml–1) on the life history traits of this rotifer werestudied in life tables performed with replicated individualcultures. Temperature and salinity had a significant negativeeffect (P < 0.001) on the average lifespan (LS) and on thenumber of offspring per female (R0) The effect of food levelon LS is unclear, whereas R0 is greater at 20°C with thelower concentration of algae and at 24°C with the higheralgal concentration. The maximum values of LS and R0, 5.6 daysand 9.2 offspring per female, respectively, were recorded at20°C, 25o salinity and low food concentration. There isalso a clear negative effect on the intrinsic growth rate (r)due to salinity. The effect of temperature depends on the foodlevel and, as occurs with R0 the maximum values of r occur withthe lower algal concentration at 20°C, whereas at 24°Cthey are obtained with the higher algal concentration. Theser values, from 1.04 to 1.10 day–1, were reached at 24°C,salinities of 20–25 and with high food concentration.  相似文献   

15.
The percent of light absorbed by algae, estimated from a regressionof attenuation of downwelling photosynthetic photon flux densityon chlorophyll a concentration, was used in conjunction withmeasurements of phytoplankton photosynthesis to estimate quantumyields () of Castle Lake phytoplankton populations during the1980 ice-free season. The maximum values occurred during mid-summerin the deep hypolimnion (<1% of surface photon flux) andwere {small tilde} 78% of the theoretical maximum. However,later in the season (September) the deep-water values decreasedsignificantly to {small tilde}27% of the theoretical maximumin conjunction with a decrease in quantum flux density to thesewaters. The values for epilimnetic phytoplankton populationswere never >15% of the theoretical maximum. The presenceof relatively high concentrations of peridinin and chlorophyllc in the deep-water algae enabled these organisms to absorbthe predominantly green light in this region of the lake which(i) allowed the use of a single extinction value per unit ofchlorophyll (kc) at all depths when calculating , and (ii) increasedthe of the deep-water algae, relative to those in the near-surfacewaters. These data indicate that the deep-water algae in CastleLake were able to utilize their ambient light field, particularlyin the early summer, and suggest that the deep-chlorophyll layerin this lake is maintained primarily by in situ algal growthrather than sinking and accumulation of organisms from nearsurface waters.  相似文献   

16.
KUMAR  A; ELSTON  J 《Annals of botany》1992,70(1):3-9
Various kinds of measurement of tissue water status were madeseveral times during water stress and recovery in Brassica juncea(cv Canadian Black) and B napus (cv Drakkar) Unstressed plantsof the two species had similar leaf water potentials (w), solute(s) and turgor potentials (p) Values of relative water content(RWC) and the slope of the linear relationship between p andRWC (p/RWC) were greater in B napus than in B juncea Statistical correlations of pooled data for the watered andstressed treatments differentiated the relationships among RWC,w and its components in the two species The major statisticaldifference was that p/RWC was related to RWC in B napus andto w and s in B juncea A decline in p/RWC with decreasing sin B juncea may be a mechanism for maintaining p at low soilwater potentials through maintenance of more elastic cell walls. Brassica juncea, Brassica napus, osmotic adjustment, tissue elasticity, water relations  相似文献   

17.
Integrated likelihood functions for non-Bayesian inference   总被引:1,自引:0,他引:1  
Severini  Thomas A. 《Biometrika》2007,94(3):529-542
Consider a model with parameter = (, ), where is the parameterof interest, and let L(, ) denote the likelihood function. Oneapproach to likelihood inference for is to use an integratedlikelihood function, in which is eliminated from L(, ) by integratingwith respect to a density function (|). The goal of this paperis to consider the problem of selecting (|) so that the resultingintegrated likelihood function is useful for non-Bayesian likelihoodinference. The desirable properties of an integrated likelihoodfunction are analyzed and these suggest that (|) should be chosenby finding a nuisance parameter that is unrelated to and thentaking the prior density for to be independent of . Such anunrelated parameter is constructed and the resulting integratedlikelihood is shown to be closely related to the modified profilelikelihood.  相似文献   

18.
An error occurs in the calibration of xylem pressure potential() against leaf-water potential () when the calibration is madeusing plant material in which the water stress has been inducedartificially after excision. The impostion of water stress afterexcision affects the determination more than it affects , consequentlythe relationship between these two indices of water stress isaltered. Care should be exercised to ensure that identical proceduresare adopted during . calibrations and during susbsequent fieldmeasurements of with the pressure-chamber apparatus.  相似文献   

19.
nAlkyl - and -lactosides, galactosides and glucosides with differentalkyl chain lengths (C2, C8, C14, and C20) were synthesizedand used as acceptors for sialyltransferases from rat liverGolgi vesicles. The -galactosides, -glucosides, and both - and-lactosides, were sialylated. Keeping the acceptor concentrationconstant, sialylation rates reached a maximum for the n-octyl- and -lactosides, n-Octyl -galactoside and noctyl -glucoside,respectively. noctyl -glucoside, respectivwly. n-Octyl -galactosideand n-octyl -glucoside were not sialylated. The reaction productswere characterized by TLC. With n-octyl lactoside and galactosideas acceptors, two major sialylation products were formed. Thjeycould be separated by preparative TLC, and their structureswere identified as 2–3 and 2–6 sialylated acceptors,respectively, by a combination of periodated oxidation, NaBD4reduction,permethylation and subsequent analysis by fast atombombardment mass spectrometry (FAB-MS). The structure of thesingle product obtained from n-ictyl -glucoside was determinedto be the 2–6 sialylated glucoside. Competition experimentswith n-octyl lactoside and lactosylceramide and gangliosideGal1-3GalNAc1-4(NeuAc2–3)Gal1–4Glcbeeta1–1Cer(GM1) as acceptors for sialyltransferases suggested that SAT-I[NeuAc2–3Gal1–4Glc1-1Cer (GM3) synthase] was atleast in least in part responsible for the 2–3 sialylationof n-octyl lactoside. alkylgalactosides alkylglucosides alkyllactosides neoglycolipids sialytransferases  相似文献   

20.
Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (b(g)), and a ‘hydrotime constant’(H) indicating the rate of progress toward germination per MPa.h.The distribution of b(g) determined by probit analysis was characterizedby a mean base (b) and the standard deviation in b among seeds(b). The three derived parameters, b, b) and H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (tg())can be normalized to be equivalent to that observed in water(tg(0)) according to the equation tg(0)=[l–(/b(g))]tg().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower b and a smaller H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller H. Seed priming (6 d in–1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >b(g), but did not lower theminimum allowing germination; i.e. priming reduced H withoutlowering b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in b during the incubation of cut seeds at low inthe test solutions. The difference in b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo b ceased at < –0.6 MPa, while the reductionin H associated with priming proceeded down to at least –1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation  相似文献   

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