THE INFLUENCE OF FLUCTUATING LIGHT ON DIVERSITY AND SPECIES NUMBER OF NUTRIENT‐LIMITED PHYTOPLANKTON1

The influence of fluctuating light on diversity and species number of a natural phytoplankton assemblage competing for nutrients was investigated for 48 days under semicontinuous culture conditions. Light conditions were either changed periodically from high (65 μmol photons·m^?2·s^?1) to low intensity (15 μmol photons·m^?2·s^?1) at intervals of 1, 3, 6, and 12 days or fixed at constant light conditions of intermediate intensity (40 μmol photons·m^?2·s^?1). Fluctuating light at intervals of 1–12 days significantly affected phytoplankton diversity. The development of phytoplankton communities differed in treatments with different light regimes. In treatments with long light intervals, species abundance oscillated with the light phases. Differences in the temporal development of phytoplankton communities resulted in hump‐shaped relations between the interval length of the light phases and both species number and diversity index and can be explained by the intermediate disturbance hypothesis. Fluctuating light tends to sustain phytoplankton diversity under nutrient limitation if the light regime changes in the order of several days. This indicates that temporal changes in weather regime are important in preventing competitive exclusion of phytoplankton species in nature.     

Photosynthèse phytoplanctonique: Réponse à un stimulus simple,imitant les variations rapides de la lumière engendrées par les vagues

Experiments were conducted in order to assess the response of marine phytoplankton production to a simplified stimulus modelling rapid light fluctuations induced by sea surface waves. Studies were carried out in the St Lawrence Estuary, during three clear and absolutely calm days. The photosynthesis of artificially incubated samples was generally depressed in fluctuating light, when compared with that in constant light of the same average intensity. There is, however, a daily trend of increased energy utilization in varying light, at saturating intensities, while some unpredictable instances of higher photosynthesis were observed in fluctuating light, especially at low intensities. Results are interpreted in terms of changes in carboxylation pathways, and might be a function of the average fluctuating light intensity and of the sun adaptation by the phytoplankton. It follows that the use of fixed light ‘imitated in situ’ incubators should be viewed with some caution.     

An efficient leaf-disc culture method for the regeneration via somatic embryogenesis and transformation of grape (Vitis vinifera L.)

By manipulating hormone levels, light intensities and temperature, we have developed an efficient leaf-disc method for the regeneration of plants via embryogenesis and for transformation in four genotypes of Vitis vinifera L. In MS basal medium supplemented with 1 mg l^-1 6-benzylaminopurine (BAP) and 0.1 mg l^-1 2,4-dichlorophenoxyacetic acid, leaf discs cultured for 2 weeks under dark conditions produced calli in over 80% of the cultures. These subsequently differentiated into pro-embryos and embryos only if kept under conditions of low light intensity (15 µE m^-2 s^-1) for 2 weeks before being transferred to conditions of high light intensity (60 µE m^-2 s^-1). If the calli were directly transferred to high light intensity, the differentiation into embryos was blocked and the calli turned pink. The somatic embryos germinated at a frequency of about 10% on NN basal medium and about 32% on NN medium supplemented with 1 mg l^-1BAP and 0.1 mg l^-1 indole-3-butyric acid. The embryos, however, germinated when pre-exposed to a low temperature of 4°C for 2 weeks. If they were transferred directly to room temperature under conditions of high light intensity (60 µE m^-2 s^-1), shoot buds were produced, whereas under conditions of low light intensity (15 µE m^-2 s^-1) secondary embryogenesis was induced. About 90-95% of the in vitro grown plantlets could be successfully transferred to soil. The above method was also applicable for developing transgenic embryos whose transgenic nature was monitored using #-glucuronidase as a reporter gene.     

The Adaptation of Plankton Algae IV. Light Adaptation in Different Algal Species

Two types with regard to adaptation to different light intensities are described: tbe Chlorella type and the Cyclotella type. The Chlorella type is mostly found among the green algae, the Cyclotella type among the diatoms. The Chlorella type adapts to a new light intensity mainly by changing the pigment content. Therefore the cells adapted to a high light intensity have a lower chlorophyll a content per cell than cells adapted to a low light intensity. Light saturation is mostly rather low for cells adapted to low light intensities. The light-saturated rate of photosynthesisist mostly lower for cells adapted to a high light intensity than for cells adapted to a low light intensity. The actual photosynthesis is not much higher at a high light intensity than at a low one. The actual photosynthesis is the photosynthesis at the light intensity where the cells are grown. - The Cyclotella type adapts only by changing the light-saturated rate. The chlorophyll content is the same in cells grown at low and high light intensities. Light saturation for cells grown at a low light intensity is rather high. The light-saturated rate is much higher in the case examined at the high light intensity than at the low one. The actual photosynthesis is considerably higher for cells grown at the high light intensities than for cells grown at low light intensities.- The two adaptation types are not sharply separated since transition types occur.     

Effects of Light on Degradation of Chlorophyll and Proteins during Senescence of Detached Rice Leaves

Regulatory effects of light on senescence of rice leaves wereinvestigated by measuring degradation of chlorophyll and proteinsin leaf segments which had been kept in the dark or under illuminationwith light of different intensities and colors. When leaveshad been left in total darkness for three days at 30°C,there was an initial long lag that lasted for one whole dayand then chlorophyll was rapidly degraded in the second andthird days. Breakdown of chlorophyll was strongly retarded bycontinuous illumination with white light of intensity as lowas 0.5 µmol photons m^–2 s^–1 but the effectof light decreased at intensities above 10 µmol photonsm^–2 s^–2. The initial lag and subsequent degradationof chlorophyll in the dark were little affected by illuminationwith red or far red light at the beginning of dark treatment.However, a brief illumination with red light at the end of thefirst and/or second day significantly suppressed degradationof chlorophyll during subsequent dark periods and the effectof red light was nullified by a short irradiation with far redlight. Thus, degradation of chlorophyll is regulated by phytochrome.Thylakoid membrane proteins and soluble proteins were also largelydegraded during three days in the dark. Degradation of membraneproteins such as the apoproteins of light-harvesting chlorophylla/b proteins of photosystem II and chlorophyll a-binding proteinsof reaction center complexes showed a long lag and was stronglysuppressed by illumination with weak white light. Thus, theloss of chlorophyll can be correlated with degradation of chlorophyll-carryingmembrane proteins. By contrast, light had only a weak protectingeffect on soluble proteins and ribulose-1,5-bisphosphate carboxylase/oxygenaserapidly disappeared under illumination with weak white light.Thus, breakdown of thylakoid membrane and soluble proteins aredifferently regulated by light. Artifacts which would be introducedby detachment of leaves were also discussed. ¹ Present address: Department of Applied Biology, Faculty ofScience and Technology, Science University of Tokyo, Yamazaki,Noda-shi, Chiba, 278 Japan. ² Present address: Department of Life Science, Faculty of Science,Himeji Institute of Technology, Harima Science Park City, Hyogo,678-12 Japan.     

The Effects of Temperature and Light Intensity on Embryo Numbers in Wheat Doubled Haploid Production through WheatxMaize Crosses

Triticum aestivumxZea mayscrosses are now widely used in theproduction of wheat doubled haploids to produce homozygous lines.Seasonal effects are known to influence the number of haploidembryos produced through wheatxmaize crosses, but the effectsof temperature and light have not been quantified. This studyinvestigated the effect of temperature and light intensity onhaploid embryo production. New Zealand wheat cultivars weregrown in a glasshouse until booting when they were transferredto growth cabinets at three temperatures (day/night; 17/12,22/17 or 27/22 °C at an irradiance of 250 µmol m^-2s^-1PAR).In another experiment, wheat lines were transferred to a growthcabinet at one of three light intensities (300, 500 or 1000µmol m^-2s^-1PAR at 22/17 °C day/night, with a photoperiodof 16 h). The temperature and light intensity at which pollinationswere made and subsequent fertilisation and embryo developmentoccurred, significantly (P<0.01) influenced the frequencyof haploid embryo production. The optimal temperature for embryorecovery was 22/17 °C. The greatest number of embryos wasproduced at a light intensity of 1000 µmol m^-2s^-1. Thesefindings will result in improvements in the overall efficiencyof the wheatxmaize system for wheat doubled haploid production.Copyright1998 Annals of Botany Company Intergeneric crossing, temperature, light intensity,Triticum aestivum,wheat,Zea mays,maize.     

Regulation of CO2-fixation in Chlorella by light of varied wavelengths and intensities

1) The wavelength effects on ¹⁴CO₂-fixation by Chlorella cellswere studied, using monochromatic light of different light intensities. 2) Blue light (453 mµ) stimulated the incorporation of¹⁴C into aspartate, glutamate and malate. Red light (679 mµ),on the other hand, stimulated its incorporation into P-esters,free sugars and insoluble material. 3) The blue light effect was observed in the presence of CMUat concentrations completely suppressing ordinary photosyntheticCO₂-fixation. 4) The blue light effect in the presence of CMU was inducedat very low intensities. At 453 mµ, 300 erg cm^–2sec^–1 was sufficient for complete saturation. 5) Time courses of ¹⁴C-incorporation into individual compoundswere investigated. Irrespective of the wavelength of the illuminatinglight, the first stable CO₂-fixation product formed under weaklight (400–500 erg cm^–2 sec^–1) was citrulline.At higher light intensities (4,000–7,000 erg cm^–2sec^–1), PGA was the first stable CO₂-fixation product.The incorporation of ¹⁴C into citrulline was not inhibited byCMU. 6) Experimental results indicate that both blue light-inducedincorporation of ¹⁴C into amino and organic acids and the incorporationof ¹⁴C into citrulline induced by low intensity light are operatedby a mechanism(s) independent of ordinary photosynthetic CO₂-fixation.Possible effects of light regulating the carbon metabolism inalgal cells are discussed. (Received July 24, 1969; )     

Photosynthetic oxygen production and community respiration in the Indian sector of the Antarctic Ocean during austral summer

Photosynthetic oxygen production by phytoplankton and community respiration in the Indian sector of the Antarctic Ocean were estimated from changes in oxygen concentrations in light and dark bottles. Gross production varied between 0.1 and 5.1 µmol O₂ l^-1 day^-1. In the same water, community respiration (the sum of oxygen consumption by heterotrophs and phytoplankton) was 0.4-3.6 µmol O₂ l^-1 day^-1, which accounted for 47-343% of the gross production. Algal and heterotrophic respirations were distinguished using some assumptions. These estimates showed that heterotrophic respiration accounted for most of the community respiration (70-91% depending upon the assumptions), indicating that heterotrophic respiration plays an important role in the mineralization of phytoplankton production in the surveyed sea area. Gross production rate correlated with chlorophyll a concentration, showing that the photosynthetic production rate of oxygen depends on the abundance of phytoplankton. Moreover, there was a significant relationship between gross production and community respiration rates. These regression equations suggested that negative net production occurred under the usually low concentration of chlorophyll observed in the Indian sector of the Antarctic Ocean. Hence, the net exchange of carbon dioxide due to biological processes through the sea surface seemed to be not as large as expected in the Antarctic Ocean, although the number of data were limited at this stage.     

Effects of water-column mixing on bacteria,phytoplankton, and rotifers under different levels of herbivory in a shallow eutrophic lake

Water-column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, nutrient status and the plankton community structure, and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water-column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water-column mixing that provoked a substantial nutrient input into the euphotic zone led to a strong net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones because of the greater contribution of a few fast-growing species. After the second mixing event, at a high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged because enhanced growth of small fast-growing phytoplankton was prevented by zooplankton grazing. Bacterial abundance did not increase after the second mixing, when cladoceran biomass was high. Changes in rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water-column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community via enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacterial growth, but the effects on biomass may be damped by high levels of herbivory. Received: 3 May 1999 / Accepted: 13 April 2000     

Acclimation to low light intensity in photosynthesis and growth of Pseudo-nitzschia multiseris Hasle, a neurotoxigenic diatom

Pseudo-nitzschia multiseries, a neurotoxigenic diatom, was grownin batch culture at light intensities between 53 and 1100 µmolm^–2 s^–1. Cellular contents of carbon. nitrogen andchlorophyll a, and the relationship between photosynthesis andlight levels, were studied during exponential (day 4) and stationaryphases (day 12). In the stationary phase at low light, therewas an increase in cellular chlorophyll a and the initial slopeof P-I curves (^B), which permitted a photosynthetic assimilationof energy equivalent to that of cells grown at high light. Inpast incidents of domoic acid poisoning, this may have facilitateddomoic acid production at low light intensities.     

The annual patterns of photosynthesis in two large, freshwater, ultra-oligotrophic Antarctic lakes

The phytoplankton productivity and biomass of two large, freshwater Antarctic lakes (Vestfold Hills, eastern Antarctica) were investigated over a 12-month period. Crooked Lake was sampled at one site, while Lake Druzhby, a complex lake with two shallow and one deep basin, was subject to a more detailed investigation. Concentrations of chlorophyll a were usually below 1 µg l^-1, indicating ultra-oligotrophic conditions. Despite periodic low nutrient levels, low temperatures (range 0.4-2.8°C) and periodic poor light climate, some degree of photosynthesis was measurable throughout the year, including the dark winter phase. Snow cover had a pronounced impact on the light climate of the water column and inhibited photosynthesis. Mean rates of carbon fixation in the 0- to 15-m water column varied between 0 and 38.47 µg C l^-1 day^-1 in Crooked Lake and 0.24 and 37.68 µg C l^-1 day^-1 in Lake Druzhby. There were significant differences in the seasonal patterns of primary production between the basins of Lake Druzhby. The shallow basins had highest productivity in August, whereas the deep basin had highest rates in summer. Chlorophyll specific rates of photosynthesis or assimilation numbers [µg C (chl. a)^-1 h^-1] varied between 0.05 and 44.9, and photosynthetic efficiency [µg C (chl. a)^-1 h^-1 µmol m^-2 s^-1] between 0.02 and 5.19. The data suggest that the phytoplankton of these lakes is adapted to low irradiance levels, low temperatures and nutrient limitation.     

Action Potentials Evoked by Light in Traps of Dionaea muscipula Ellis

At low light intensities (less than 50 µmol m^–2s^–1) illumination evokes transient depolarization of membranepotential in mesophyll cells of the leaf-trap of Dionaea muscipulaEllis. Darkening causes hyperpolarization approximately symmetricto the response to illumination. The amplitude as well as therate of potential changes depend on light intensity. After exceedinga definite threshold (usually between 50 and 80 µmol m^–2s^–1)the depolarization plays the role of a generator potential andan all-or-none action potential (AP) is released. Switchinglight off in a depolarization phase of an AP does not changeits shape and the amplitude. When the light intensity is increasedto 80–150 µmol m^–2 s^–1 a single lightstimulus triggers two successive APs. The time interval betweenthe two APs decreases with increasing stimulus strength andreaches the minimum between 300 and 400 µmol m^–2s^–1. At higher light intensities the interval increasesagain, and finally only a single AP is triggered. It was shownthat the effect was evoked by light but not by temperature changeaccompanying illumination. An inhibitor of the photosyn-theticelectron transport chain, DCMU, blocked the generator potentialsmediating between light absorption and APs. Residual responsesto light stimuli in plants treated with DCMU had reverse polarityand strongly reduced the amplitudes. (Received September 16, 1997; Accepted January 16, 1998)     

Primary production, light and vertical mixing in Potter Cove, a shallow bay in the maritime Antarctic

Phytoplankton photosynthesis was measured during spring-summer 1991-1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quantified by means of the root-mean square expected vertical displacement depth of cells in the water column, Z_t. The light attenuation coefficient was used as a measure of the influence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious differences between photosynthetic capacity [P*_max; averages 2.6 and 0.6 µg C (µg chlorophyll-a)^-1 h^-1] and photosynthetic efficiency {!*; 0.073 and 0.0018 µg C (µg chlorophyll-a)^-1 h^-1 [(µmol m^-2 s^-1)^-1]} values were obtained for both sites during low mixing conditions (Z_t from 10 to 20 m), while no differences were found for high mixing situations (Z_t>20 m). This suggests different photoacclimation of phytoplankton responses, induced by modifications of the light field, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P*_max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.     

Chlorophyll a forms in mesophyll and bundle sheath chloroplasts of Zea mays leaves grown at low light intensity

Mesophyll and bundle sheath chloroplasts were prepared fromleaves of Zea mays grown at light intensities of 1.1 and 240µW/cm², respectively. The mesophyll chloroplasts thatdeveloped at the low intensity and bundle sheath chloroplatsthat developed at both low and high intensities showed higherratios of chlorophyll a/b and P700/chlorophylls compared withthe normal ratios found for the mesophyll chloroplasts thathad developed at the high intensity. Derivative absorption spectrophotometryat 77?K revealed that the low intensity mesophyll chloroplastscontained more of chlorophyll a forms with longer wavelengthred bands than high intensity mesophyll chloroplasts. More ofthe longer wavelength forms of chlorophyll a were also presentin the bundle sheath chloroplasts that had developed at lowand high intensities. All these four types of chloroplasts showedtwo peaks of fluorescence, one at 687 hra and the other at 733or 738 nm. In addition to these peaks, the high intensity mesophyllchloroplasts showed a shoulder at 697 nm, and the two typesof bundle sheath chloroplasts showed a shoulder at 680 nm. (Received June 17, 1974; )     

Physiological characteristics of picophytoplankton, isolated from Lake Kinneret: responses to light and temperature

Two different phylogenetic groups of picophytoplankton, namelypicocyanobacteria and picoeukaryotes, are represented in LakeKinneret. Three species were isolated from the lake and identifiedas the picoeukaryote Mychonastes homosphaera and two picocyanobacteria,Synechococcus sp. A and B. Picocyanobacterial and M. homosphaeracultures grew well at light intensities up to 330 and 700 µmolphotons m^-2 s^-1, respectively, but poorly below 10 µmolphotons m^-2 s^-1. Picocyanobacterial and M. homosphaera culturesphotoacclimated to low light by increasing their chlorophyllper cell through increase in photosynthetic unit (PSU) sizeand PSU numbers, respectively. Growth rates of SynechococcusA and B were higher at temperatures characteristic of summer–autumnin the epilimnion, when maximum abundances of picocyanobacteriaoccur. Growth rates of M. homosphaera were higher at 14°C,corresponding to lake water temperatures during their occurrencein winter–spring. Temperature is a dominant factor influencingthe seasonal dynamics of both picocyanobacteria and picoeukaryotesin Lake Kinneret, while the vertical distribution is controlledby acclimation to different light conditions. Differences intemperature tolerance and photoacclimation suggest that SynechococcusA belongs to picocyanobacteria found in summer below surfacewaters, while Synechococcus B represents picocyanobacteria foundthroughout the year at all depths. Photoacclimation to highlight as shown in M. homosphaera cultures, may account for therelatively high abundance of picoeukaryotes in surface watersin Lake Kinneret.     

Phytoplankton dynamics at the ice-edge zone of the Lazarev Sea (Southern Ocean) during the austral summer 1994/1995 drogue study

Phytoplankton dynamics in the open waters of the ice-edge zone of the Lazarev Sea were investigated over 12 consecutive days during a drogue study conducted in austral summer (December/January) 1994/1995. Throughout the study, the upper water column (<30 m) was stratified with a well-defined pycnocline evident. Although a subsurface intrusion of colder, more saline water into the region was recorded on days 5-9 of the experiment, its effect on the water column structure was negligible. Total surface chlorophyll a biomass doubled between days 1 and 5 (from 0.82 to 1.62 mg m^-3), and then showed a tendency to stabilise, while the depth-integrated chlorophyll a standing stock displayed an increasing trend during the entire experiment. All changes in biomass were associated with an increase in microphytoplankton. Flagellates and picoplankton dominated cell counts, while diatoms composed most of the phytoplankton biovolume. Results of the study indicate that, during the period of investigation, average cell abundance decreased. Coupled with this decrease was an increase in the biovolume and average size of the phytoplankton. Phytoplankton succession was observed in the ice edge during the drogue study. Typical ice-associated species of genera Haslea, Fragilariopsis and Chaetoceros, which dominated at the beginning of study, were replaced by open-water species of genera Corethron, Dactyliosolen and Rhizosolenia. The shift in phytoplankton species composition and size can likely be related to high light intensities and grazing by microzooplankton. The intrusion of colder, more saline water on day 5 appeared to modify the diatom succession, indicating extreme variability in phytoplankton dynamics in the near ice-edge zone of the Lazarev Sea.     

Population and community responses of phytoplankton to fluctuating light

Light is a major resource in aquatic ecosystems and has a complex pattern of spatio-temporal variability, yet the effects of dynamic light regimes on communities of phytoplankton are largely unexplored. I examined whether and how fluctuating light supply affects the structure and dynamics of phytoplankton communities. The effect of light fluctuations was tested at two average irradiances: low, 25 μmol quanta m⁻² s⁻¹ and high, 100 μmol quanta m⁻² s⁻¹ in 2- and 18-species communities of freshwater phytoplankton. Species diversity, and abundances of individual species and higher taxa, depended significantly on both the absolute level and the degree of variability in light supply, while total density, total biomass, and species richness responded only to light level. In the two-species assemblage, fluctuations increased diversity at both low and high average irradiances and in the multispecies community fluctuations increased diversity at high irradiance but decreased diversity at low average irradiance. Species richness was higher under low average irradiance and was not affected by the presence or absence of fluctuations. Diatom abundance was increased by fluctuations, especially at low average irradiance, where they became the dominant group, while cyanobacteria and green algae dominated low constant light and all high light treatments. Within each taxonomic group, however, there was no uniform pattern in species responses to light fluctuations: both the magnitude and direction of response were species-specific. The temporal regime of light supply had a significant effect on the growth rates of individual species grown in monocultures. Species responses to the regime of light supply in monocultures qualitatively agreed with their abundances in the community experiments. The results indicate that the temporal regime of light supply may influence structure of phytoplankton communities by differentially affecting growth rates and mediating species competition. Received: 24 September 1997 / Accepted: 8 July 1998     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

Primary production,light absorption and quantum yields of phytoplankton from the Bellingshausen and Amundsen Seas (Antarctica)

Chlorophyll concentration, light intensity, primary production, light absorption and quantum yield were measured between 12 January 1994 and 27 March 1994 in the Bellingshausen and Amundsen Seas. Primary production and quantum yield within Bellingshausen and Amundsen Seas were typical of the high-nutrient, low-chlorophyll area of the Southern Ocean while small variations were found as a result of local conditions. Chlorophyll a (chl a) concentrations were generally low (<1 μg l⁻¹) in the water column, while in cases of blooms it reached 7–8 μg l⁻¹. The light intensity at which photosynthesis approaches saturation varied between 59 and 105 μmol q m⁻² s⁻¹.The initial slope of the photosynthesis curve varied between 0.02 and 0.07 μg C (μg chl a)⁻¹ h⁻¹ (μmol q m⁻² s⁻¹)⁻¹. The maximal photosynthetic rate at light saturation ranged between 1.6 and 5.4 μg C (μg chl a)⁻¹ h⁻¹. Light limitation was found within the mixing depth, while no photoinhibition was observed when surface light was 500 μmol q m⁻² s⁻¹. The mean spectral absorption coefficients of phytoplankton ranged between 0.018 and 0.042 m² (mg chl a)⁻¹ depending on the phytoplankton taxonomy. The quantum yield of photosynthesis varied between 0.027 and 0.076 mol C mol q⁻¹. These high quantum yields are explained by the prevailing high nutrient concentrations in this area. Light intensity plays a major role as limiting factor, even in very shallow water. The phytoplankton close to the surface did not show photoinhibition but had higher UV absorption capabilities.