PIGMENT AND PHOTOSYNTHETIC RESPONSES OF OSCILLATORIA AGARDHII (CYANOPHYTA) TO PHOTON FLUX DENSITY AND SPECTRAL QUALITY1

The effects of photon flux density (PFD) and spectral quality on biomass, pigment content and composition, and the photosynthetic activity of Oscillatoria agardhii Gomont were investigated in steady-state populations. For alterations of PFD, chemostat populations were exposed to 50, 130 and 230 μmol photons·m^?2·s^?1 of photosynthetic active radiation (PAR). Decreases in biomass, chlorophyll a (Chl a) and c-phycocyanin (CPC) contents, and CPC: Chl a and CPC: carotenoid content was not altered. Increases in the relative abundances of myxoxanthophyll and zeaxanthin and deceases in the relative abundances of echinenone and β-carotene within the carotenoid pigments coincided with increasing PFD. Increases in Chl a-specific photosynthetic rates and maxima and decreases in biomass-specific photosynthetic rates and maxima with increasing PFD were attributed to increased light harvesting by carotenoids per unit Chl a and reduction in total pigment content, respectively. Responses to spectral quality were tested by exposing chemostat populations to a gradient of spectral transmissions at 50 μmol photons·m^?2·s^?1 PAR. Biomass differences among populations were likely attributable to the distinct absorption of the PAR spectrum by Chl a, CPC, and carotenoids. Although pigment contents were not altered by spectral quality, relative abundances of zeaxanthin and echinenone in the carotenoid pigments increased in populations exposed to high-wavelength PAR. The population adapted to green light possessed a greater photosynthetic maximum than populations adapted to other spectral qualities.     

SIMAZINE-INDUCED INHIBITION IN PHOTOACCLIMATED POPULATIONS OF ANABAENA CIRCINALIS (CYANOPHYTA)1

The effects of the triazine herbicide, simazine, on photosynthetic oxygen evolution and growth rate in photoacclimated populations of Anabaena circinalis Rabenhorst were investigated. Chemostat populations were acclimated to photon flux densities (PFDs) of 50, 130, and 230 μmol·m^?2·s^?1 of photosynthetic active radiation (PAR), Decreases in chlorophyll a (Chl a). c-phycocyanin (CPC), and total carotenoid (TCar) contents and CPC: Chl a and CPC: TCar ratios of populations coincided with increasing PFD, Polynomial regression models that characterize inhibition of photosynthesis for populations acclimated to 50 and 130 μmol photons·m^?2·s^?1 PAR were distinct from the model for populations acclimated to 230 μmol photons·m^?2·s^?1 PAR. Simazine concentrations that, depressed oxygen evolution 50% compared to controls decreased with increasing PFD. Increases and decreases in both biomass and growth rate coincided with increasing PFD and simazine concentration, respectively. Simazine concentrations that depressed growth rate 50% compared to controls increased with decreasing PFD. The differences in photosynthetic and growth inhibition among photoacclimated populations indicate that sensitivity to photosystem II inhibitors is affected by alterations in pigment contents.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER,MONTANA1

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer-early fall. Maximum uptake rates of ammonia-N and nitrate-N were 5935–6991 and 507–984 μg · g DW^?1· h^?1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L^?1. During November-December, when DIN was 72–376 μg · L^?1, maximum ammonia-N uptake was 1137–1633 μg · g DW^?1· h^?1 and maximum nitrate-N uptake was 0–196 μg · g DW^?1· h^?1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer-early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.     

DIEL PATTERNS IN LIGHT ABSORPTION AND ABSORPTION EFFICIENCY FACTORS OF ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE)1

The chl a specific absorption coefficients [a* (λ), m²·mg chl a ^{? 1}] were examined in chemostat culture of the Prymnesiophyceae Isochrysis galbana (Parke) under a 12:12‐h light:dark cycle at low light (75 μmol photons·m ^{? 2}·s ^{? 1}) and high light (500 μmol photons· m ^{? 2}·s ^{? 1}) conditions. Other associated measurements such as pigment composition, cell density, and diameter as the measure of cell size were also made at the two light regimes every 2 h for 2 days to confirm the periodicity. A distinct diel variability was observed for the a* (λ) with maxima near dawn and minima near dusk. The magnitude of diel variation in a* (440) was 15% at low light and 22% at high light. Pronounced diel patterns were observed for cell size with minima near dawn and maxima near dusk. The magnitude of diel variation in cell size was 9.3% at low light and 21% at high light. The absorption efficiency factors [Q _a (440)] were determined by reconstruction using intracellular concentrations of pigments and cell size. The Q _a (440) also showed a distinct diel variability, with minima near dawn and maxima near dusk. The diel variation in a* (λ) and Q _a (λ) was primarily caused by changes in cell size due to growth, although there was some influence from diel variations in the intracellular pigment concentrations. The results presented here indicated that diel variation in a* (λ) was an important component of the optical characterization of phytoplankton.     

GROWTH AND MORPHOLOGY OF YOUNG GAMETOPHYTES OF PORPHYRA ABBOTTAE (RHODOPHYTA): EFFECTS OF ENVIRONMENTAL FACTORS IN CULTURE1

Growth, blade shape and blade thickness of young gametophytes of Porphyra abbottae Krishnamurthy cultured from conchospores were determined at various combinations of temperature (8, 10, 12° C), photon flux density (17.5, 70, 140 μmol·m-^?2·S^?1), nutrient concentration (5, 25, 50, 100% f medium) and water motion (0, 50, 100, 150 rpm). Growth (as surface area) was light-saturated at 70 μmol· m^?2· S^?1, light-inhabited at 140 μmol·m^?2· S^?1, and nutrient-saturated an 25% f medium. Temperature had no significant effect on growth. Water motion and nutrients had an interactive effect on growth, with water motion having the greatest effect at the lowest nutrient concentrations. Water motion enhanced growth even at saturating nutrient concentrations. Blade length / width ratio was greater in low light (2.5) than in saturating light (1.9); with increasing water motion the ratio increased from 1.2 to 2.4. Blade thickness (53-88 μm) was greatest at the highest nutrient concentrations and at the lowest water motion levels. Temperature and light did not have a consistent effect on blade thickness.     

A SEASONAL COMPARISON OF CARBON,NITROGEN, AND PIGMENT CONTENT IN LAMINARIA SOLIDUNGULA AND L. SACCHARINA (PHAEOPHYTA) IN THE ALASKAN ARCTIC1

Laminaria solidungula and L. saccharina inhabit the Beaufort Sea in the Alaskan High Arctic. Laminaria solidungula is an Arctic endemic, whereas L. saccharina extends from north temperate Pacific and Atlantic waters to the Arctic. Previous studies have shown that the two species have different seasonal timing of growth, but little comparative physiological information exists. As a first step in characterizing these two species from a mixed Arctic population, we measured variations in carbon, nitrogen, and photosynthetic pigment content in blade tissue from plants collected under the fast ice in April and during the open water Period in late July, Both species exhibited seasonal differences in many measured variables; seasonal differences in L. solidungula were most pronounced in growing basal blades. For example, the molar CIN ratio of basal blades averaged 11 in April and 21 in July for L. solidungula and 11.5 in April and 28 in July for L. saccharina. Basal and mature second blades differed in pigment content in April but not in July: chlorophyll a + c in L. solidungula basal and mature second blades averaged 19 and 27 nmol.cm^?2 in April and 30 and 29 nmol. cm^?2 in July, respectively. The corresponding values for L. saccharina were 17 and 29 nmol.cm^?2 in April and 16 and 16 nmol.cm^?2 in July (95% confidence intervals approximately 1–3 nmol. cm ^?2). Carotenoids exhibited similar patterns. Species differences in pigments, carbon, and nitrogen were minor and were probably effects rather than causes of the different seasonal patterns of growth and development. The primary difference between the two species may be the ability of L. solidungula to retain multiple metabolically active blades and to fuel areal growth with stored carbohydrates during winter near-darkness, whereas L. saccharina growth is more closely tied to active photosynthesis in the growing basal blade. The cause of old blade retention in L. solidungula and the possibility of other physiological differences between the two species, including gametophytes, remain to be determined.     

PHYCOBILIN CONTENT OF THE CONCHOCELIS PHASE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES: RESPONSES TO ENVIRONMENTAL VARIABLES1

Variations of pigment content in the microscopic conchocelis stage of four Alaskan Porphyra species were investigated in response to environmental variables. Conchocelis filaments were cultured under varying conditions of irradiance and nutrient concentrations for up to 60 d at 11°C and 30 psu salinity. Results indicate that conchocelis filaments contain relatively high concentrations of phycobilins under optimal culture conditions. Phycobilin pigment production was significantly affected by irradiance, nutrient concentration, and culture duration. For Porphyra abbottiae V. Krishnam., Porphyra sp., and Porphyra torta V. Krishnam., maximal phycoerythrin (63.2–95.1 mg · g dwt^?1) and phycocyanin (28.8–64.8 mg · g dwt^?1) content generally occurred at 10 μmol photons · m^?2 · s^?1, f/4–f/2 nutrient concentration after 10–20 d of culture. Whereas for Porphyra hiberna S. C. Lindstrom et K. M. Cole, the highest phycoerythrin (73.3 mg · g dwt^?1) and phycocyanin (70.2 mg · g dwt^?1) content occurred at 10 μmol photons · m^?2 · s^?1, f nutrient concentration after 60 d in culture. Under similar conditions, the different species showed significant differences in pigment content. P. abbottiae had higher phycoerythrin content than the other three species, and P. hiberna had the highest phycocyanin content. P. torta had the lowest phycobilin content.     

Studies on nitrate reductase activity in Laminariadigitata (Huds.) Lamour. I. Longitudinal and transverse profiles of nitrate reductase activity within the thallus

The distribution of the enzyme nitrate reductase (NR) within the thallus of the brown alga Laminaria digitata (Huds.) Lamour is described for plants sampled from the east coast of Scotland in May and June when growth rates are at a maximum. Highest NR activities (≈ 0.2 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the mature blade. NR activities declined towards the basal meristematic region of the blade. Activities in the stipe and holdfast were also low, being between 0.05 and 0.07 μmol NO₃^? reduced·g^?1 wet wt·h^?1. The activities of the enzyme glutamine synthetase (GS), which is important in the assimilation of NH₄⁺, showed a similar distribution within the blade to those of NR.The transverse profile of NR activity in the stipe exhibited a decline from the outer to the inner tissues. Maximum activities (0.13 μmol NO₃^? reduced·g^?1 wet wt·h^?1) occurred in the meristoderm, while those of the cortex and medulla were 0.04 and 0.01 μmol NO₃^? reduced·g^?1 wet wt·h^?1 respectively.These data indicate that most of the NO₃^? assimilation occurs in the mature blade rather than in the meristematic tissue where there is a high nitrogen demand for growth. The data are consistent with the maintenance of meristematic growth by the internal transport of organic nitrogen from the mature blade.     

PHOTOSYNTHESIS-IRRADIANCE RELATIONSHIPS IN PHYTOPLANKTON FROM THE PHYSICALLY STABLE WATER COLUMN OF A PERENNIALLY ICE-COVERED LAKE (LAKE BONNEY,ANTARCTICA)1

The perennially ice-covered lakes of Antarctica have hydrodynamically stable water columns with a number of vertically distinct phytoplankton populations. We examined the photosynthesis-irradiance characteristics of phytoplankton from four depths of Lake Bonney to determine their physiological condition relative to vertical gradients in irradiance and temperature. All populations studied showed evidence of extreme shade adaptation, including low I_k values (15–45 μE · m^?2· s^?1) and extremely low maximal photosynthetic rates (P^B_m less than 0.3 μg C ·μg chl a^?1· h^?1). Photosynthetic rates were controlled by temperature as well as light variations with depth. Lake Bonney has an inverted temperature profile within the trophogenic zone that increased from 0° C at the ice-water interface to 6° C from 10 to 18 m. Deeper phytoplankton (10 m and 17 m) were found to have photosynthetic capacities (P^B_m) and efficiences (α) three to five times higher than those at the ice-water interface. However, Q₁₀ values were only ca. 2 for P^B_m (no temperature dependence was evident for α), suggesting that a simple temperature response cannot explain all the differences between populations. Lake Bonney phytoplankton (primarily cryptophytes and chlorophytes) had photosynthetic characteristics similar to diatoms from other physically stable environments (e.g. sea ice, benthos) and may be ecologically analogous to multiple deep chlorophyll maxima.     

Seasonal nitrate physiology of Macrocystis integrifolia Bory

Ambient sea-water nitrate and tissue nitrogen (ethanol soluble nitrate and amino acids, as well as total nitrogen) of Macrocystis integrifolia Bory were monitored over a 2-yr period in Bamfield, Vancouver Island, British Columbia. Sea-water nitrate varied from a high of 12 μmol · 1^?1 (individual values as high as 23 μmol · 1^?1 were recorded) in late winter to below detection limits for most of the summer. Tissue nitrate and total nitrogen paralleled the ambient nitrate levels and showed summer minima and winter maxima (from 0 to 70 μmol · g fresh wt^?1 for nitrate and from 0.8 to 2.9% of dry wt for total N). The nitrate uptake capacity was inversely proportional to tissue nitrate concentration and, furthermore, was much higher for subapical surface blades (60–70 nmol · cm^?2 · h^?1) than for older, deeper blades (5–10 nmol · cm^?2 · h^?1). Nitrate uptake by subapical blade disks in summer is apparently higher in dark (1.0–1.7 μmol · g fresh wt^?1 · h^?1) than in light (0.6–1.3 μmol · g fresh wt^?1 · h^?1) and the data obtained in 36–108 h experiments indicate nitrate pool sizes of 30–90 μmol · g fresh wt^?1. These pools are $\text{2}\text{3}$ to nearly full in winter. Ammonium does not inhibit nitrate uptake. It is taken up and apparently utilized much faster than nitrate and it may well be an important source of nitrogen for marine macrophytes.     

SPECTRAL LIGHT ABSORPTION BY INTACT BLADES OF PORPHYRA ABBOTTAE (RHODOPHYTA): EFFECTS OF ENVIRONMENTAL FACTORS IN CULTURE1

Whole thallus absorptance spectra were recorded for Porphyra abbottae Krishnamurthy gametophytes grown in batch culture at combinations of temperature (8, 10, 12° C), irradiance (17.5, 70, 140 μmol photons·m^?2·s^?1), nutrients (f/4, f/2, f media) and water motion (0, 50, 100, 150 rpm). Light, nutrients, water motion and the interaction of nutrients with water motion all significance affected broadband (400-700 nm) absorptance and absorptance by phycoerythrin (566 nm), phycocyanin (624 nm) and chlorophyll a (680 nm). Absorptances increased in low light, low water motion and high nutrient levels. Shifts in phycoerythrin: chlorophyll a absorptance ratios closely paralleled changes of absorptance by the major pigments, whereas the phycoerythrin: phycocyanin ratio decreased only with increasing nutrient supply Absorptance ratios were significantly correlated with growth rate. Absorptance increased asymptotically with blade thickness or pigment content. Based on previously determined growth rates, nutrient saturated P. abbottae can synthesize photosynthetic pigments in excess of immediate needs. Allocation is given preferentially to the phycobiliproteins, with highest preference for phycocyanin.     

PRODUCTIVITY OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYTA) IN SURREY LAKE,INDIANA1

Biomass, akinete numbers, net photosynthesis, and respiration of Pithophora oedogonia were monitored over two growing seasons in shallow Surrey Lake, Indiana. Low rates of photosynthesis occurred from late fall to early spring and increased to maximum levels in late spring to summer (29–39 mgO₂·g^?1 dry wt·h^?1). Areal biomass increased following the rise in photosynthesis and peaked in autumn (163–206g dry wt·m^?2). Photosynthetic rates were directly correlated with temperature, nitrogen, and phosphorus over the entire annual cycle and during the growing season. Differences in photosynthetic activity and biomass between the two growing seasons (1980 and 1981) were apparently related to higher, early spring temperatures and higher levels of NO₃-N and PO₄-P in 1981. Laboratory investigations of temperature and light effects on Pithophora photosynthesis and respiration indicated that these processes were severely inhibited below 15°C. The highest P_max value occurred at 35°C (0.602 μmol O₂·mg^?1 chl a·min^?1). Rates of dark respiration did not increase above 25°C thus contributing to a favorable balance of photosynthetic production to respiratory utilization at high temperatures. Light was most efficiently utilized at 15°C as indicated by minimum values of I_k(47 μE·m^?2·s^?1) and I_c (6 μE·m^?2·s^?1). Comparison of P. oedogonia and Cladophora glomerata indicated that the former was more tolerant of temperatures above 30°C. Pithophora's tolerance of high temperature and efficient use of low light intensity appear to be adaptive to conditions found within the dense, floating algal mats and the shallow littoral areas inhabited by this filamentous alga.     

PHYSIOLOGICAL ECOTYPES IN THE MARINE ALGA BOSTRYCHIA RADICANS (CERAMIALES,RHODOPHYTA) FROM THE EAST COAST OF THE U.S.A1

The comparative ecophysiology of nine culture isolates of the eulittoral red alga Bostrychia radicans (Montagne) Montague collected at sites from seven states along the east coast of the U.S.A. was investigated. The growth response in relation to different salinity and light conditions as well as photosynthesis-irradiance curves were studied. In addition, the effect of salt treatment on the content of the isomeric polyols d -sorbitol and d -dulcitol was also studied. All isolates grew between salinities of 5.3 and 70 ppt but with quite different optima and maxima. The isolates were all adapted to low light levels, i.e. growth was already recorded at 2.5 μmol photons·m^?2·s^?1, and growth rates peaked between 40 and 60 μmol photons·m^?2·s_-1. These low-light requirements were also reflected by the photosynthesis-irradiance curves: all plants had low light compensation points (2.5–9.7 μmol photons ·m^?2·^?1) and low photon fluence rates for initial saturation of photosynthesis (38.1–84.7 μmol photons·m^?2·s^?1, indicating that these isolates are “shade-adapted.” Isolates from Florida and Georgia synthesized and accumulated both the osmolytes d -sorbitol and d -dulcitol in increasing salinities, whereas only d -sorbitol was present in plants from North Carolina north to Connecticut. d -sorbitol was always strongly involved in osmotic acclimation. In various isolates from the same location in South Carolina, both polyol patterns were found, i.e. d -sorbitol plus d -dulcitol and d -sorbitol only. All data indicate that B. radicans exhibits a broad salinity tolerance and a low-light preference, which explain the successful colonization of this alga on various intertidal and shaded substrates. The data also clearly indicate intraspecific differences among the nine isolates, which is interpreted as development of different physiological ecotypes.     

LIPID CLASS,CAROTENOID, AND TOXIN DYNAMICS OF KARENIA BREVIS (DINOPHYCEAE) DURING DIEL VERTICAL MIGRATION1

The internal lipid, carotenoid, and toxin concentrations of Karenia brevis (C. C. Davis) Gert Hansen and Moestrup are influenced by its ability to use ambient light and nutrients for growth and reproduction. This study investigated changes in K. brevis toxicity, lipid class, and carotenoid concentrations in low‐light, nitrate‐replete (250 μmol quanta · m^?2 · s^?1, 80 μM NO₃); high‐light, nitrate‐replete (960 μmol quanta · m^?2 · s^?1, 80 μM NO₃); and high‐light, nitrate‐reduced (960 μmol quanta · m^?2 · s^?1, <5 μM NO₃) mesocosms. Reverse‐phase HPLC quantified the epoxidation state (EPS) of the xanthophyll‐cycle pigments diadinoxanthin and diatoxanthin, and a Chromarod Iatroscan thin layer chromatography/flame ionization detection (TLC/FID) system quantified changes in lipid class concentrations. EPS did not exceed 0.20 in the low‐light mesocosm, but increased to 0.65 in the high‐light mesocosms. Triacylglycerol and monogalactosyldiacylglycerol (MGDG) were the largest lipid classes consisting of 9.3% to 48.7% and 37.3% to 69.7% of total lipid, respectively. Both lipid classes also experienced the greatest concentration changes in high‐light experiments. K. brevis increased EPS and toxin concentrations while decreasing its lipid concentrations under high light. K. brevis may mobilize its toxins into the surrounding environment by reducing lipid concentrations, such as sterols, limiting competition, or toxins are released because lipids are decreased in high light, reducing any protective mechanism against their own toxins.     

RESPONSE OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) TO LIGHT OF DIFFERENT SPECTRAL QUALITIES AND IRRADIANCES: GROWTH AND PIGMENTATION1

Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m^?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m^?2· s^?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m^?2· s^?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m^?2· s^?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.     

PHYSIOLOGICAL RESPONSES OF ANABAENA VARIABILIS (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE1

Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m^?2·s^?1 to 35°C at 562 μE·m^?2·s^?1. The light saturation parameter, I_K, increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt.^?1·d^?1) occurred at 35°C and 564 μE·m^?2·s^?1. At 15°C, the maximum rate was 1.25 g C·g dry wt.^?1·d^?1 at 332 μE·m^?2·s^?1. The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light-saturation parameters a function of temperature.     

The Loch Eil project: Planktonic pigments in sediments from Loch Eil and the firth of Lorne

Photosynthetic pigments and their derivatives were measured in sediments in the fjordic Loch Eil and the Firth of Lome, Scotland, between November 1975 and November 1976. After acetone extraction from the top 10 mm of sediment cores, pigments were crudely separated, by fluorescence change on acidification, into (chlorophyll a + chlorophyllide a) and phaeopigments. The greatest pigment concentrations (mean 73 μg · g sediment dry wt^?1) were found in the most reducing sediments which also had a high average proportion (23%) of chlorophyll. The least mean pigment concentration (23 μg · g^?1) and proportion of chlorophyll (17%) were found in the most oxidizing sediments in the Firth of Lorne where there was a clear seasonal cycle, with a peak in sediment pigment concentration and chlorophyll proportion in May and June, just after the planktonic spring increase. The Loch Eil stations showed a less clear or no seasonal cycle; the station most affected by organic input was the most variable from month to month. It was concluded that redox status was the most obvious control of sediment pigment content, whereas the effect of sedimentation of phytoplankton was complex.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.