The seasonal productivity of phytoplankton in a hypertrophic, gravel-pit lake

The seasonal time course of phytoplankton primary productivitywas studied weekly in a hypertrophic, gravel-pit lake closeto Madrid, Spain. Chlorophyll a ranged 22–445 mg m^–2.Gross primary productivity attained 0.28±0.14 g C m^–2h^–1 (range: 0.06–0.60), its yearly value being 900g C m^–2, but the shallow euphotic depths and the highplankton respiration ensured that net productivity was generallylow. Respiration losses amounted to 0.31±0.24 g O₂ m^–2h^–1, with phytoplankton respiration roughly attainingone-half of overall plankton respiration. Areal phytoplanktonproductivity and plankton respiration followed a seasonal trendbut this was not the case for photosynthetic capacity. Surfacephotoinhibition was evenly distributed throughout the study.Quantum yields showed an increasing depth trend, but no seasonaltrend. Both P_max and I_k were both temperature- and irradiance-dependent.As compared with lakes of lesser trophic degree, phytoplanktonprimary production in hypertrophic lakes might be increasednot only by higher nutrient contents but also by low chlorophyll-specificattenuation coefficients and low background, non-algal attenuation,thereby allowing for higher areal chlorophyll contents and hencehigher areal productivity. Our study suggests that physical(irradiance and water column stability) as well as chemicalfeatures (dissolved inorganic carbon and soluble reactive phosphorus)may control seasonality of phytoplankton primary productionin this lake despite recent claims that only physical factorsare of significance in hypertrophic lakes. However, this doesnot explain all the variability observed and so a food web controlis also likely to be operating.     

Diurnal changes in buoyancy and vertical distribution in populations of Microcystisin two shallow lakes

Changes in the buoyancy of Microcystis populations were followedover 24 h periods in two shallow well-mixed lakes, Lake Vinkeveen(area 0 6 km²) and Lake IJsselmeer (1190 km²), in the NetherlandsThe Microcystis colonies collected from the surface layers inboth lakes showed a buoyancy decrease during the day and anincrease at night The buoyant colonies, and especially the faster-movinglarge ones, became concentrated by flotation into the surfacemixed layers As a result the mean position of the cyanobacterialpopulation became located nearer the surface than that of othernon-buoyant phytoplankton, such as Scencdesmus. The cyanobacteriawould, therefore, have received a higher average irradianceThe Microcystis in these shallow lakes had weaker gas vesiclesthan those found previously in deeper lakes but it was demonstratedthat the loss of buoyancy, which occurred at high irradiances,resulted from an increase in carbohydrate ballast rather thanthrough turgoi-driven gas vesicle collapse     

Effects of macronutrients upon buoyancy regulation by metalimnetic Oscillatoria agardhii in Deming Lake, Minnesota

Gas-vacuolate filaments of Oscillatoria agardhii form a metalimneticlayer in Oeming Lake, Minnesota. The environmental factors whichaffect buoyancy and the physiological processes which mediatechanges in buoyancy were determined. Buoyant filaments losttheir buoyancy in a few hours when incubated at light intensitiesabove those found in situ ({small tilde}15 µnol photonsm^–2 s^–1, or 1% of the surface value). The rate ofbuoyancy loss was accelerated by the addition of 10 µMphosphate at irradiances >200mol photons m^–2 s^–1.The effect of nutrient additions on buoyancy was also investigatedover a longer time period by incubating metalimnetic samplesin situ. The samples were deployed for 6 days at a depth wherethe irradiance was 8% of the surface value. As found in short-termexperiments, the addition of phosphate resulted in the largestdecrease in buoyancy. However, the addition of ammonia in additionto phosphate attenuated the buoyancy loss on day 2, and on day6 the filaments in these treatments were almost completely buoyant.The physiological status of the filaments in these treatmentswas assayed by analysis of elemental ratios of C, N and P, andby measurement of cellular chlorophyll, polysaccharide and protein.In addition, the cellular content of gas vesicles was determined.The construction of ballast balance sheets from these data indicatedthat changes in buoyancy were primarily due to differences inthe amount of polysaccharide ballast in the cells. However,in another set of in situ experiments, the increase in measuredballast molecules did not explain the observed loss of buoyancy.We hypothesized that another, undetected ballast-providing moleculehad accumulated in the cells.     

Vertical migration, entrainment and photosynthesis of the freshwater dinoflagellate Peridinium cinctum in a shallow urban lake

Vertical migration, entrainment and photosynthesis of Peridiniumcinctum were investigated in the Torrens Lake, South Australia.Cell distribution was a function of swimming speed, shear velocityand the surface mixed layer depth. During the morning, whenthe wind speed was low, cells migrated upwards, at a velocityof 2.35 x10^-4 m s^-1 and accumulated at 0.7 m (827 µmolm^-2 s^-1 at 13:00 h). After 13:00 h, cells migrated downwardsto 3.3–3.6 m at 1.85 x 10^-4 m s^-1. As wind speed increasedin the afternoon, the shear velocity of the surface mixed layerexceeded the swimming speed, leading to a homogeneous cell distributionwithin the surface mixed layer. Below the surface mixed layer,a deep chlorophyll maximum persisted. The observations werefound to fit in an entrainment function (), where if > 1,cells are disentrained, and if < 1, cells are entrained.The maximum effective quantum yield of photosystem II (F'_v/F'_m)was used as an index to monitor the photosynthetic performanceof P. cinctum and the ratio of bottle (fixed depth) to lakeF'_v/F'_m indicated whether or not migration or mixing was enhancingphotosynthesis or preventing photoinhibition. A small (0.1–0.2units) but significant depression in F'_v/F'_m was observed inP. cinctum in bottle and lake surface samples during stratifiedconditions. However, this recovered to initial values laterin the day. The ratio of bottle to lake F'_v/F'_m was consistentwith P. cinctum migration patterns. A comparison between modelleddaily photosynthetic rates of the observed migrating and a theoreticalhomogeneous population revealed that migration would not increasephotosynthetic rates within the Torrens Lake. The net ratesof O₂ production in the water column from dawn to dusk for themigrating and evenly distributed cell populations were 2574and 3120 mg m^-2, respectively.     

Sinking rates of heterogeneous, temperate phytoplankton populations

Throughout the summer of 1978, the sinking rates of phytoplanktonwithin the Controlled Experimental Ecosystems (CEE's) were monitoredusing a technique based upon measurement of the transit timeof radioactively (¹⁴C) labeled cells. The experimental frameworkof FOODWEB 1 offered an unprecedented opportunity to documentthe sinking rates of heterogeneous phytoplankton of diversetaxonomic composition, growing under a variety of nutrient regimes;the absence of advective exchange in the CEE's provided knowledgeof the preconditioning history of the phytoplankton sampledat any given time. Sinking rates of whole phytoplankton assemblages (not size-fractioned)ranged from 0.32 – 1.69 m·day^–1; the averagerate (± s.d.) observed was 0.64 ± 0.31 m·day^–1.The most notable deviations from the mean value occurred whenthe population size distribution and taxonomic composition shifteddue to blooms. The relationship between phytoplankton sinkingand ambient nutrient levels was studied by following the ratesof a given size fraction (8–53 µm) for ten daysfollowing nutrient enrichment of a CEE. Over this time sinkingrates ranged from 1.08– 1.53 m·day^–1; decreasedrates occurred after nutrification, yet over the course of theentire trial sinking rates were not significantly (p >0.05)correlated to the ambient levels of any single nutrient species. The sinking rate implications of spore formation were also studied,and showed that sinking rates of Chaetoceros constrictus andC. socialis spores (2.75 ± 0.61 m·day^–1)were ca 5-fold greater than rates measured when the vegetativestages of these species dominated the population, reflectingthe influence of physiological mechanisms in controlling phytoplanktonbuoyancy. An example of the potential influence of colony formation uponbuoyancy was noted in observations of C. socialis which occasionallywas found to exist in large spherical configurations made ofcoiled cell chains and having low (0.40 m·day^–1)sinking rates. A hydrodynamic rationale is presented to showhow such a colony together with enveloped water may behave asa unit particle having lower excess density, and therefore lowobserved sinking rate, despite its conspicuously large size. Overall, sinking rates were not significantly correlated withany of the measured nutrient or photic parameters. There were,however, trials and comparisons which showed evidence for: (1)higher sinking rates in populations dominated by large cells,(2) decreased sinking rates after nutrient enrichment, and (3)buoyancy response to light levels. It is suggested that correlationof sinking rates with synoptic environmental measurements atany given time is not explicit because the associations mayinvoke lag times of physiological response. The interpretationmade from these findings is that the preconditioning historyof the population, rather than the prevailing conditions atthe time of a given measurement, is most closely associatedwith population buoyancy modifications.     

The critical pressures of gas vesicles in Planktorhrix rubescens in relation tothe depth of winter mixing in Lake Zrich, Switzerland

The vertical distribution of the cyanobacterium Planktothrir(Oscillazoria) rubescens in Lake Zrich was investigated fromMarch 1993 to June 1995 by collecting filaments on filters andmeasuring them by epifluorescence microscopy and computer imageanalysis. The initial population, which began to stratify inApril, decreased by up to 99% by June. During the summer, thepopulation peaked at depths of 8–15 m; it reached a maximumareal filament-volume concentration of -60 cm ^–3 of lakesurface in early September and was then entrained in the deepeningsurface layer. It became mixed progressively deeper, to thelake bottom in the cold winter of 1993–94, but less completelyin the milder winter of 1994–95. Most of the filamentsremained viable during the winter. At the end of the mild winterof 1994–5, 70% of filaments in the water column retainedbuoyancy, but after the cold winter of 1996–7 only 22%were buoyant. Few remained buoyant below 80 m, where the hydrostaticpressure caused gas vesicle collapse. The proportion that remainbuoyant decreases with the depth and duration of winter mixing,and increases with the critical collapse pressure (P_c) of thegas vesicles, which provide buoyancy. Strains of P.rubescensisolated from Lake Zrich differed in mean (P_c) of their gasvesicles, from 0.9 to 1.1 MPa, the highest values in freshwatercyanobacteria. Allowing for a turgor pressure of 0.2 MPa. thesestrains would remain buoyant at depths down to 70 and 90 m,respectively. Natural selection for gas vesicles of high (P_c)will operate by increasing the proportion of filaments thatremain buoyant in the upper parts of the water column aftercirculation to various depths during the winter because onlybuoyant filaments will form the inoculum for the following season.     

Diurnal mixed layers and the long-term dominance of Microcystis aeruginosa

The population dynamics of the cyanobacterium Microcystis aeruginosain a hypertrophic, subtropical lake (Hartbeespoort Dam, SouthAfrica) were followed over 4.5 years. We examined the hypothesisthat M.aeruginosa dominated (>80% by volume) the phytoplanktonpopulation up to 10 months of each year because it maintaineditself within shallow diurnal mixed layers and was thus ensuredaccess to light, the major limiting resource. Wind speeds overHartbeespoort Dam were strong enough to mix the entire epilimnionthrough Langmuir circulations only 12% of the time. At othertimes solar heating led to the formation of diurnal mixed layers(z₁) that were shallower (<2 m) than the euphotic zone (z_cu;mean = 3.5 m, range: 0.45–8.4 m) while the seasonal mixedlayer (z_m) was always deeper than z_cu (range: 7–18 m).By means of its buoyancy mechanism M.aeruginosa maintained thebulk of its population within z₁, while non-buoyant speciessank into dark layers. Adaptation to strong light intensitywas implicated from low cellular chlorophyll a content (0.132µg/106 cells) and high I_k (up to 1230 µE m^–2s^–1). Ensured access to light, the post-maximum summerpopulations persisted throughout autumn and winter, despitesuboptimal temperatures, by sustaining low losses. Increasedsedimentation losses caused a sharp decline of the populationat the end of winter each year, and a short (2–3 months)successional episode followed, but by late spring M.aeruginosawas again dominant. The data from Hartbeespoort Dam point outthe importance of distinguishing between z_m and z₁, and showthe profound effect that the daily pattern of z₁ as opposedto the seasonal pattern of z_m, can have on phytoplankton populationspecies composition.     

Annual Variation of Environmental Variables, Phytoplankton Species Composition and Photosynthetic Parameters in a Coastal Lagoon

Physical–chemical variables, phytoplankton biomass, speciescomposition and photosynthesis–irradiance (P-I) parameterswere analysed during 1 year in the Santo André Lagoon,SouthwestPortugal – a land-locked coastal ecosystem withtemporary connections with the sea. When the lagoon stayed closedthe observed phytoplankton blooms were mainly caused by Prorocentrumminimum, a potentially toxic dinoflagellate. It was dominantduring most of the year but the seawater inflow to the lagoontriggered a decrease in phytoplankton biomass and an abruptshift in species composition. The maximum photosynthetic rate(P_max) ranged from 2.0 to 22.5 mg C (mg chlorophyll a)^–1h^–1 and the light saturation index (I_k), ranged from 5.2to 335.0 µE m^–2 s^–1, with winter minima andsummer maxima. P_max and I_k were both positively correlated totemperature. Abundance ofP. minimum was associated with highnitrate concentrations whereas diatoms appear when ammonium,salinity and wind velocity are high. A mathematical model todescribe photosynthetic rate as a function of irradiance andtemperature [P (I, t)] was applied to the samples in which P.minimum was the dominant species     

Uptake of 13C and 15N (ammonium, nitrate and urea) by Microcystis in Lake Kasumigaura

The uptake rate of carbon and nitrogen (ammonium, nitrate andurea) by the Microcystis predominating among phytoplankton wasinvestigated in the summer of 1984 in Takahamaira Bay of LakeKasumigaura. The V_max values of Microcystis for nitrate (0.025–0.046h^–1) and ammonium (0.15–0.17 h^–1) were considerablyhigher than other natural phytoplankton. The ammonium, nitrateand urea uptake by Microcystis was light dependent and was notinhibited with nigh light intensity. The K₁ values were farlower than the I_k values. The carbon uptake was not influencedby nitrogen enrichment. Microcystis accelerated the uptake rateby changing V_max/K _s value when nitrogen versus carbon contentin cells declined. Nitrate was scarcely existent in TakahamairiBay during the summer, when Microcystis usually used ammoniumas the nitrogen source. However, the standing stock of ammoniumin the water was far lower than the daily ammonium uptake rates.Therefore, the ammonium in this water had to be supplied becauseof its rapid turn-over time (–0.7–2.6 h).     

Dynamics of inorganic phosphorus in pelagic communities of the Sea of Okhotsk

Inorganic phosphorus uptake and regeneration in the OkhotskSea waters were investigated in July–August 1994 withthe use of radioisotopic techniques. The rates of PO₄-P uptakeby microplankton in the upper mixed layer were between 1.5 and6.6 µg P l^-1 day^-1 (average 2.75) in areas of diatom dominance,and between 0.68 and 1.68 µg P l^-1 day^-1 (average 1.16)in areas of intense warming and summer phytoplankton minimum.The residence time of PO₄-P standing stock in water at differentstations varied between 1.5 and 24 days (mean 9 days). The shareof bacterioplankton contributing to total PO₄-P uptake was 50%in areas of the summer phytoplankton minimum and 20–30%in areas of diatom dominance. The PO₄-P regeneration rate wasmeasured first time experimentally in the temperate sea. Itsrates varied from 0.30 to 1.65 µg P l^-1 day^-1. In areasof diatom dominance, it compensated with 30–60% of PO₄-Puptake. In zones of summer phytoplankton minimum and in thelayers of deep chlorophyll maxima at 10–25 m depths, thePO₄-P regeneration rate often exceeded its uptake. Primary phytoplanktonproduction correlated well with PO₄-P uptake values in the uppermixed layer, while no correlation was found between primaryproduction and the ambient PO₄-P content in water.     

Photoinhibition and the diurnal variation of phytoplankton photosynthesis--I. Development of a photosynthesis--irradiance model from studies of in situ responses

Diurnal series of fluorescence and photosynthesis assays wereconducted in high altitude (3803 m), tropical (16°), LakeTiticaca (Peru/Bolivia). Near-surface diurnal thermoclines formedon typical days of high photon flux density (PFD, {small tilde}2000 µE m^–2 s^–1). In the depth range of diurnalstratification profiles of in vivo fluorescence, both without(F_a and with (F_b DCMU, exhibited a mean decrease of 64% frommorning to mid-day, but little change (mean increase of 1.5%)through the afternoon. Three times during the day surface, mid-depth(3–5 m) and deep (15–20 m) phytoplankton sampleswere incubated with H¹⁴CO₃^– under short (<2 h) exposuresto a range of in situ PFDs. Comparison of phytoplankton in differentsamples (ANOVA) showed identical photosynthetic response insunrise (isothermal) samples but a significant drop in surfaceand mid-depth photosynthesis at all PFDs during times of diurnalstratification. Similarly, both low-light () and light-saturated(P² _max photosynthetic parameters were lower in mid-day surfacesamples compared to deep samples. In addition, previously photoinhibitedsamples had a higher threshold intensity for photoinhibition,I_T. These results, together with diurnal time series of fluorescencefrom in situ incubations, demonstrate that recovery from extendedepisodes of photoinhibition during diurnal stratification isslower than suggested by previous observations in vitro. Photosynthesisby near-surface phytoplankton is different in light increasingup to I_T than light decreasing from I_T. This effect can be modeledby reducing and P_max as a function of the maximum photoinhibitingPFD in the diurnal light history. ¹Present address: Division of Molecular Plant Biology, Universityof California, Berkeley, Berkeley, CA 94720, USA     

Effects of Preillumination on Dark Nitrogen Fixation and Respiration by Anabaena Cylindrica

In whole filaments of Anabaena cylindrica dark nitrogen-fixingactivity (measured as acetylene reduction) and respiration increasedwith the light intensity of a fixed period of preillumination,saturating at ca. 10,000 lux. With saturating light during preillumination,the amount and duration of dark nitrogen-fixing activity increasedwith length of preillumination, but respiration declined rapidlyin the dark. At dark respiration rates below 250 nmol O₂ uptake mg protein^–1?h^–1(State 1) no significant nitrogen-fixing activity is observed.From 250 to 550 nmol O₂ uptake?mg protein^–1?h^–1(State 2), nitrogen-fixing activity depends on O₂ uptake whileabove 550 nmol O₂ uptake?mg protein^–1?h^–1 (State3), nitrogen-fixing activity no longer increases with furtherincrease in O₂ uptake rate. (Received June 18, 1983; Accepted November 10, 1983)     

Carbon and nitrogen uptake response to light by phytoplankton during an upwelling event

The interactions between phytoplankton nutrition and the responseof carbon (C) and nitrogen (N) uptake to irradiance relationshipswere examined during September 1993 in Monterey Bay, California,an eastern boundary current upwelling regime. Measurements ofN uptake and C assimilation rates versus irradiance (V:I andP:I) experiments were performed using trace-level additionsof ¹⁵N-labeled NO₃^– and NH₄⁺, and ¹⁴C-labeled bicarbonateto water collected from a depth of {small tilde}30% of surfacephotosynthetic photon flux density (PPFD). An upwelled watermass was sampled consecutively, with hydrographic stations locatedat the upwelling site, 48 h later down the horizontal axis ofthe upwelling plume, and a final time (24 h later) with watersconsisting of a mixture of 5–6 day aged upwelled waterand warmer surface water from outside the plume. As the wateraged, a pro gressive shift in the rates of C and N utilizationoccurred, with C assimilation increasing while N uptake ratesdecreased. At the same time, NH₄⁺ dominated the nitrogenousnutrition in older upwelled water, even in the presence of highconcentrations of ambient NO₃^–. Dark-uptake rates forall substrates were uniformly low at all stations; NH₄⁺ uptakedemonstrated the least dependence on PPFD. The results of thisstudy demonstrate dramatic changes in the light-mediated responseof C and N uptake, resulting in assimilation ratios considerablydifferent from predicted values assuming phytoplankton C:N uptakerates will be proportional to Redfield C:N composition. Thesedata provide clear evidence of physiological changes in thenatural planktonic assemblage of this evolving upwelling ecosystem.     

Factors controlling primary production in a hypertrophic lake (Hartbeespoort Dam, South Africa)

The physical factors controlling algal primary production weredemonstrated from data collected for a hypertrophic lake. A_maxranged between 12.4 and 5916 mg C m^–3 h^–1. Arealrates (A) varied between 46.9 and 3381 mg C m^–2 h^–1.The factors permitting and controlling production were subjectivelyseparated into two categories. In category 1, nutrients (N +P), which were in overabundance, permitted large standing cropsof Microcystis aeruginosa to develop (>1000 µg chla 1^–1). Wind patterns determined the dramatic spatialand temporal changes in algal standing crop which could dropto 2.7 µg chl a 1^–1. In category 2 were the factorswhich affected the rate processes. The buoyancy mechanism ofMicrocystis usually kept the alga in the euphotic zone. A powerrelationship (r = 0.92, n = 54) between A and A_max/_min showedthat with increasing phytoplankton vertical stratification,A_max was increasingly important in the integral. The saturationparameter I_K and photosynthetic capacity were temperature dependent.Variations of A were significantly related to changes in watercolumn stability (g cm cm^–2) because both axes of thephotosynthesis depth-profile were affected by stability changes.     

Microbial ammonium cycling in the Mississippi River plume during the drought spring of 2000

Microbial potential uptake and regeneration rates of ammonium(NH₄⁺) were studied along a salinity gradient (salinities 0.2–34.4)in the Mississippi River plume during an extreme drought inspring 2000. Chlorophyll concentrations up to 30 µg L^–1were highest in the low- and mid-salinity regions (salinities8.5–28.2) and comparable to records of other years butextended over smaller areas than during periods of normal riverflow. Bacterial biomass (5.1–28.3 µg C L^–1)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 (1.4–4.0µg C L^–1) did not reflect phytoplankton and bacterialspatial distribution but peaked at 9.2 µg C L^–1at 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 (0.018–0.124 µmol N L^–1 h^–1) 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.     

Ammonium excretion and glutamate dehydrogenase activity of zooplankton in Great South Bay, New York

In Great South Bay, nanoplankton, (<20 sµm) accountedfor the largest fraction (56%) of zooplankton glutamate dehydrogenase(GDH) activity over a one year period. Microzooplankton (20–200µm) 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-Nm^–3 d^–1 in winter to 3.34 mg atoms NH⁺₄-N m^–3d^–1 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.     

Light absorption by phytoplankton: development of a matching parameter for algal photosynthesis under different spectral regimes

A spectral matching parameter (absorption efficiency, A_e) wasdeveloped to quantify the relationship between the light absorptionspectra of phytoplankton communities and the spectral irradianceof their ambient light field. A_e was defined as the ratio betweenthe amount of radiation absorbed by the phytoplankton in situand the amount absorbed in a spectrally flat light regime. Thisapproach was applied to our measurements of spectral absorptionfor the phytoplankton communities in six lakes in High ArcticCanada that spanned a range of bio-optical conditions. A_e valueswere calculated for the light spectrum down through the watercolumn and for 11 types of artificial light source. Spectralmatching varied among lakes and with depth. There was a significantlinear relationship between the relative change in A_e with depthand the diffuse attenuation coefficient K_d (r² = 0.52, P = 0.012for K_d for the 400–700 nm waveband; r² = 0.78, P = 0.0003for K_d at 440 nm). The tabulated values for the matching parameterA_e allow the comparison of photosynthesis versus irradiance(P versus E) curves among studies using different light sources.A_e estimates also facilitate the evaluation of chromatic adaptationin natural waters, and the calculation of spectrally adjusted,in situ primary production down through a water column fromP versus E relationships under a single spectral regime.     

Influence of Cadmium on Growth and Nitrogen Metabolism of Anabaena cylindrica Lemm

A study was made of the effects of cadmium on the Cyanobacterium(blue-green alga) Anabaena cylindrica Lemm. as part of the paddy-fieldecosystem. A simple culture vessel has been designed, which allows periodicalmeasurement of growth (optical density) and nitrogenase activity(C₂H₂-C₂H₄ method). The influence of medium renewal was checked:the renewal of the medium maintained a higher growth rate andhigher nitrogen fixation ability. The cadmium effects were studied using six concentration levelsranging from 0 (control) to 2 parts 10^–6 with renewedmedia (10% every day). No significant differences could be seen up to 1 part 10^–6for nitrogenase activity and relative percentage of heterocysts(decreasing as a function of time from ±4% to ±1.5%). Inhibition of growth (OD and dry weight) was weak at 1 part10^–6 but important at 2 parts 10^–6; at this concentrationcadmium induced morphological and physiological effects: chlorosis,cellular malformations and destruction, and increase in heterocystfrequency (up to 7.72% ±0.19). The cadmium concentration factors were much lower than thosereported for other plants like Chlorella and water pests     

The effects of Cu on the adenylate energy charge of open ocean phytoplankton

The effects of short-term, acute Cu exposure (6 h) on the adenylateenergy charge (EC_A) of open-ocean phytoplankton populations(northeastern equatorial Pacific) were investigated. Energycharge remained at {small tilde}0.77 over the range of Cu additions(0.025 – 5.µg l^–1), even though ¹⁴C uptakeand total adenylate levels (ATP + ADP + AMP) were reduced byas much as 60%. These findings suggest that EC_A alone is nota sensitive indicator of acute sublethal metal effects on phytoplankton. ¹This research was supported by the NSF Biological OceanographyProgram grant #OCE 81-17286.     

Transport and Fixation of Inorganic Carbon during Photosynthesis in the Cells of Anabaena Grown under Ordinary Air. II. Effect of Sodium Concentration during Growth on the Induction of Active Trasport System for IC

The requirement of sodium for growth of Anabaena variabilisM3 was investigated under low (0.04%) and high (1.5 or 5%) CO₂conditions. The growth rates under both conditions were stronglyaffected by NaCl concentrations up to 0.5 mM in the medium.In the presence of 40 µM NaCl, the cells were not ableto grow under a low CO₂ condition, but were able to grow undera high CO₂ condition. The sodium requirement for growth wasdependent on pH: in the Na⁺-deficient condition, cells couldgrow at pH6.8, while no growth occurred at pH 8.2, suggestingthat the requirement of Na⁺ for growth observed in the low CO₂condition can be substituted for by a lower pH. In the presence of 20 mM NaCl at pH 7.8, ¹⁴CO₂ as well as H¹⁴CO₃^–were actively transported into the cells which had been grownin air. In contrast, the transport of both of these inorganiccarbon (IC) species was suppressed under the Na⁺-deficient condition.These results suggest that sodium is required for the stimulationof transport of IC during photosynthesis. This is one of thereasons why Na⁺ is required for the growth of Anabaena underordinary air and alkaline conditions. (Received September 27, 1986; Accepted March 26, 1987)