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1.
Occurrence of mycosporine-like amino acids in the red-tide dinoflagellate Alexandrium excavatum: UV-photoprotective compounds? 总被引:1,自引:0,他引:1
Carreto J.I.; Carignan M.O.; Daleo G.; Marco S.G.De 《Journal of plankton research》1990,12(5):909-921
Water extracts of the red-tide dinoflagellate Alexandrium excavatumgrown at high light intensity (200 µE m2s1) show a broad absorbance maximum in the UV regionof the spectrum (310360 nm). Using TLC and reverse-phaseHPLC a series of mycosporine-like amino acids have been characterized:mycosporine-glycine (max = 310 nm), palythine (max = 320 nm),asterina-330 (max = 330 nm), shinorine (max = 334 nm), porphyra-334(max= 334 nm), palythenic acid (max = 337 nm) and the isomericmixture of usujirene and palythene (max = 359 nm). From theobserved spectral changes during transference from low(20 µE m2 s1) to high (200µE m2 s1) light intensities and vice versa,the series of compounds are supposed to be biogenically relatedto one another. The presence of these compounds in A.excavatumis discussed in relation to their possible role in the photoprotectionto deleterious UV radiation. 相似文献
2.
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
3.
The Meaning of Matric Potential 总被引:6,自引:1,他引:5
The commonly used equation, = P - + , which describes thepartitioning of plant water potential, , into components ofhydrostatic pressure, P, osmotic pressure, , and matric potential,, is misleading. The term , which is supposed to show the influenceof a solid phase on , is zero if a consistent definition ofpressure is used in the standard thermodynamic derivation. However,it can be usefully defined by = + D, where D is the osmoticpressure of the equilibrium dialysate of the system. The practicaland theoretical significance of this definition is discussed. 相似文献
4.
In a series of experiments, the planktonic larvae of Marenzelleriaviridis (Verrill, 1873) were exposed to various combinationsof salinity (S = 0.6, 2.5, 5.0, 10 and 20) and temperature (T= 5, 10 and 20C) from the 1-setiger stage to the onset of metamorphosis(16- to 17-setiger stage). One-setiger larvae were unable tocomplete their development to metamorphosis at salinities below5. Metamorphosis was successful at salinities of 10 and 20,when the animals adopted a benthic life mode. Larval developmentwas more rapid at 10 than at 20, and was positively affectedby higher temperatures. Larvae exposed to a salinity of 3.5at the 4- to 5-setiger stage developed and completed metamorphosisto benthic juveniles despite the low salinity. These larvaedeveloped most rapidly at a temperature of 10C. The salinitytolerances (LC50) of M. viridis larvae (t = 48 h), juvenilesand adults (t = 72 h in each case) were determined at 10C.The results showed that all development stages can toleratesalmities <1 The importance of constraints on developmentand tolerance to low salinities for the successful colonizationof oligohaline regions is shown and discussed in connectionwith other brackish-water organisms. 相似文献
5.
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
6.
Water-relations parameters were measured on sections of secondaryphloem from red oak (Quercus borealis michx. f.) and white ash(Fraxinus americana var. biltmoreana [Beadle] J. Wright) usinga linear displacement transducer. Changes in tissue thicknessin response to changes in the osmotic pressure of the bathingsolution were used to calculate the volumetric elastic modulusplus osmotic pressure (v + ) of the tissue, and an applied forcemethod was used to estimate the time constant for water equilibration(T). The hydraulic conductivity of the cell membranes (Lp) wascalculated utilizing v + and r values. The time-dependent behaviour of the tissue was much more complexthan originally expected. A correction for a time-dependentprocess that we call drift was required to obtainnumbers for v + . Furthermore, v + was calculated on two assumptionsin order to relate changes in tissue dimensions to sieve elementparameters. In the first case, a lower limit for v + of thesieve elements was determined by attributing all changes intissue dimensions to these cells. For red oak the average v+ on this assumption is 72 bars. Assuming that all cell typeswere equally responsible for the changes in tissue dimensionsresulted in an v + value of 192 bars for oak. If v + and rare the same for all cells in the tissue, Lp for the sieve elementsof oak is 9.6 x 108 cm s1 bar1. Exudationfrom the sieve elements of white ash during excision of thephloem led to artificially high values of v + for that species. Quercus borealis michx. f., Fraxinus americana var, biltmoreana (Beadle) J. Wright, red oak, white ash, water relations, phloem, volumetric elastic modulus, membrane hydraulic conductivity 相似文献
7.
Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL 总被引:3,自引:0,他引:3
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 in1.2 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
8.
Carbon isotopic composition of Trichodesmium spp. colonies off Bermuda: effects of colony mass and season 总被引:1,自引:0,他引:1
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
9.
Wilting of leaves of Vicia faba L., which occurs when the pressurepotential (p) is zero, and the leaf-water potential () at wiltingboth depend entirely upon the solute potential at incipientplasmolysis (so) and not on soil-water status. Wilting in V.faba is acropetal; this is consistent with the hypothesis thatthere is a gradient of decreasing so up the plant and that wateris transferred from the lower to the upper leaves, hasteningthe overall water loss from the lower leaves to the point whenp is zero. The gradient in so up the plant is of the order of38 bar. It is proposed that wilting when p>0 (i.e. > so) shouldbe apparent wilting and that when p0 (i.e. so),true wilting. 相似文献
10.
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 23 and 26 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 26 sialylated glucoside. Competition experimentswith n-octyl lactoside and lactosylceramide and gangliosideGal1-3GalNAc1-4(NeuAc23)Gal14Glcbeeta11Cer(GM1) as acceptors for sialyltransferases suggested that SAT-I[NeuAc23Gal14Glc1-1Cer (GM3) synthase] was atleast in least in part responsible for the 23 sialylationof n-octyl lactoside. alkylgalactosides alkylglucosides alkyllactosides neoglycolipids sialytransferases 相似文献
11.
LOBODA T.; KLECZKOWSKI L. A.; TARLOWSKI J.; NALBORCZYK E. 《Journal of experimental botany》1988,39(12):1765-1770
The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (Pn, the CO2 compensation point (),post-lower illumination burst of CO2 (PLIB) and post-lower temperatureburst of CO2 (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m3),-HPMS initially stimulated Pn and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.055.0 mol m3. The effects of -HPMS onPn and were time-dependent and, after a few minutes, the Pnwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m 3), the transient effects of-HPMS were shorter () or not observed at all (Pn. Both PLIBand PLTB, when expressed in relation to Pn, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate Pn by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO2 compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis 相似文献
12.
An equation is derived expressing average turgor pressure ofa leaf (p) as a function of relative water content (RWC). Basedon this derivation, the relationships of the bulk elastic modulus(v) and both RWC and p, are formulated and discussed. The bulkelastic modulus (v) becomes zero for p = 0, that is at the turgorloss point for the leaf. At full water saturation the valueof ev is proportional to the water saturation turgor potentialp(max). The factor relating P and v (structure coefficient ,Burstrom, Uhrstr?m and Olausson, 1970) changes only very littlefor values of p, which are not too close to zero. An exampleis given for the calculation from experimental data of the turgorpressure function, the structure coefficient function, and thev function. Key words: Cell wall, Turgor pressure, Bulk elastic modulus 相似文献
13.
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
14.
Primary production was measured for 7 years, using the in situ14C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m3. The maximum volumetric rate of production(Amax) was 12->8800 mg C m3 h1 with areal productions(A) of 69->3300 mg C m2 h1 for euphotic zonedepths of <0.58.4 m. The intrinsic parameters of phytoplanktonproduction (, Amax/B, Ik) indicated that the phytoplankton populationwas adapted to high light levels. Both Amax/B and Ik were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm2 h1,while the measured rate was 2.5 g Cm2 h1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis. 相似文献
15.
The conformation of the heptasaccharide Man-1,6-(Man-1,3)(Xyl-ß1,2)-Man-ß,4-GlcNAc2-ß1,4-(L-Fuc-1,3)-GlcNAc1,the carbohydrate moiety of Erythrina corallodendron lectin (EcorL),the hexasaccharide Man-1,6-(Man-1,3) (GlcNAc-ß1,4)-Man-ß1,4-GlcNAc-ß1,4-GlcNAcand their disaccharide fragments have been studied by moleculardynamics (MD) simulations for 1000 ps with different initialconformations. In the isolated heptasaccharide, the most frequentlyaccessed conformation during MD has a value of 180° aroundMan-1,6-Man linkage. This conformation is stabilized by theformation of a hydrogen bond between the carbonyl oxygen ofGlcNAc2 with the O3/O4 hydroxyls of the 1,6-linked mannose residue.The conformation of the heptasaccharide found in the crystalstructure of the EcorL-lactose complex (Shaanan et al., Science,254, 862, 1991), that has a value of 76° around Man-1,6-Manlinkage, is accessed, although less frequently, during MD ofthe isolated oligosaccharide. The ,, = 58°,134°,60°conformation around Man-1,6-Man fragment observed in the crystalstructure of the Lathyrus ochnrs lectin complexed with a biantennaryoctasaccharide (Table I in Homans,S.W., Glycobiology, 3, 551,1993) has also been accessed in the present MD simulations.These values for the 1,6-linkage, which are observed in theprotein-carbohydrate crystal structures and are accessed inthe MD simulations, though occasionally, have not been predictedfrom NMR studies. Furthermore, these different values of leadto significantly different orientations of the 1,6-arm for thesame value of . This contrasts with the earlier predictionsthat only different values of can bring about significant changesin the orientation of the 1,6-arm. The MD simulations also showthat the effects of bisecting GlcNAc or ß1,2-xyloseare very similar on the 1,3-arm and slightly different on the1,6-arm. bisecting GlcNAc carbohydrates glycoprotein lectinsaccharide complex 相似文献
16.
Leaf diffusion resistance interpreted as stomatal resistance,leaf water potential (w), solute potential (s) and leaf turgorpotential (p) of the chilling sensitive species Phaseolus vulgariswere determined during chilling at 4 °C in the light. Bothchill-hardened and non-hardened plants were used. For comparison,the chilling resistant species Pisum sativum was also used. The results for chilled P. sativum were similar to those obtainedfor chill-hardened P. vulgaris plants receiving a chilling treatment.In both cases a reduction in stomatal aperture and the maintenanceof a positive leaf turgor were the responses to chilling. Leavesof chilled but non-hardened P. vulgaris plants were found tomaintain open stomata throughout the chilling treatment despitea severe wilt developing after 7 h at 4 °C. This was incontrast to the chill-resistant P. sativum. which showed a rapidclosing and subsequent re-opening of the stomata to a new reducedaperture. During the first 12 h of chilling wof P. vulgaris leaves changedfrom 0.47 MPa to 1.24 MPa. On more prolonged chillingw tended to return to pre-chilling values. In addition. p decreasedfrom 0.42 MPa to zero after only 9 h of chilling, and remainedat this value for the remainder of the chilling period, s, changedrapidly from 0.89 MPa to 1.35 MPa in the first7.5 h, and after 9 h. w and s, were equal, i.e. zero p. In contrast,the chilling resistant plant P. sativum maintained a positivep throughout the chilling period, and there was little differencebetween values of w, and s in control and chilled leaves. Key words: Chilling, Stomata, ater relations, Phaseolus vulgaris, Pisum sativum 相似文献
17.
The pressure-volume technique was employed to compare waterrelations and moisture stress-induced osmotic adjustment ofPeriwinkle (Catharanthus roseus) cv. Pink (PC), Oscillatus (REC)and White (WC). Leaf water potential (w), osmotic potential(s), turgor potential (p), bulk modulus of elasticity (), boundwater (RWCw) and leaf hydration (H), were estimated by exposingthe plants to a drying cycle during which well watered plantswere dehydrated to zero turgor, and then irrigated. Osmoticadjustment (w 100) was calculated by comparing a at full hydration(a 100) in stressed plants after recovery, with a 100 in controlplants. Values of 2100 were 0.76, 0.33 and 0.11 MPa in cv. PC,REC and WC, respectively. Maintenance of p at lower 3 and relativeleaf water content (RWC) in prestressed PC was attributableto a higher alkaloid content and greater leaf cell wall elasticity.RWCW was plotted against p to determine its contribution tohydration maintenance at lower p. Genotype PC showed greaterRWCw at lower p compared with REC and WC. The present studyhas demonstrated that there are cultivar differences in alkaloidaccumulation and water relations in acclimated plants and thatthe relative ranking for drought resistance within periwinkleappeared to correspond with the changes in osmotic properties. Medicinal plant, drought resistance, alkaloids, periwinkle [Catharanthus roseus (L.) G. Don] 相似文献
18.
Derivation of Pressure-Volume Curves by a Non-Linear Regression Procedure and Determination of Apoplastic Water 总被引:1,自引:0,他引:1
Data from pressure-volume (PV) analysis may be submitted totransformation I [i.e. leaf water potential (1) versus inverserelative water content (1/R)] or to transformation II (i.e.1/1 versus R). This may cause an essential distortion of theerror structure especially in transformation II due to the relativelylarge range which is to be covered by the 1/1 ratio. Similarly,logarithmic transformation of leaf turgor potential (P) whenderiving the sensitivity factor of elasticity (ß)by linear regression from values of In p and 1/R may distortthe error structure. In order to investigate the magnitude ofthe distortion effect on parameters derived from PV analysisby regression a non-linear regression procedure was comparedwith the common linear procedure when calculating p from ßin the turgid region and leaf osmotic potential (P) in boththe turgid and non-turgid region. As test plants we used fieldgrown species of spring barley (Hordeum distichum L., cvs Gunnarand Alis). The results show that transformations and applicationof linear regression procedures distort the error structureof p more than the error structure of ', which was only slightlyaffected. However, we recommend the use of the non-linear procedurein both cases. Furthermore, from PV analysis, obtained by thermocouple hygrometryon living and killed leaf tissue, respectively, we derived themathematical basis for calculating the apoplastic water fraction(Ra). Ra was 0.15 at R= 1 and decreased with dehydration. The equations describing the relation between and R and betweenp and R were extended to take into account the apoplastic waterfraction. Key words: Apoplastic water, distortion errors, non-linear regression, pressure-volume curves 相似文献
19.
Responses of Soybean Leaf Angle, Photosynthesis and Stomatal Conductance to Leaf and Soil Water Potential 总被引:2,自引:0,他引:2
The hypothesis that soil water potential (s) is better correlatedto heliotropic leaf orientation, photosaturated photosyntheticCO2 assimilation and stomatal conductance during periods oflimited water availability than is bulk leaf water potential(1) was examined in greenhouse-grown soybean (Glycine max) plants,submitted to a progressive drought. Paired plants were exposedto either 1000 or 100 µmol m2 s1 photonflux densities (PFD) for 4560 mins. The higher irradianceinduced short-term decreases in 1, due to increased transpiration,while l in the plant exposed to low PFD did not decrease. Thesechanges in 1 occurred independently of changes in soil waterstatus. Concurrent to the light treatments, a single attachedleaf from each of the two plants was isolated from the restof the plant by shading, and the pulvinus of its terminal leafletwas exposed to a perpendicular PFD of 500 µmol m2S1. Leaf movement of this leaflet was recorded in responseto this light, until a stable leaflet angle was achieved. Valuesof s and l (before and after light treatment), and photosaturatedrates of photosynthesis and stomatal conductance, were thenmeasured on these leaves. Leaflet angle and gas exchange werebetter correlated with s (r2 = 0.50, 0.50 and 0.57 for angle,photosynthesis and conductance, respectively) than with l especiallywhen l was the result of short-term, high-light induced changesin leaf water status (r2 = 0.36, 0.32 and 0.49, for the sameparameters). Leaflet angle was also correlated with stomatalconductance (r2 = 0.61) and photosynthetic rate (r2 = 0.60),suggesting a close association between leaf orientation, leafmetabolism and soil water availability. Glycine max (L.) Merr. cv. Essex, soybean, heliotropism, water potential, photosynthesis, stomatal conductance, solar tracking 相似文献
20.
Temporal and spatial variations in phytoplankton carbon isotopes in a polymictic subtropical lake 总被引:2,自引:0,他引:2
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