Photosynthesis-irradiance Curves Research Articles

A comparison of the physiological ecology of the seagrasses Halophila decipiens ostenfeld and H. Johnsonii eiseman from Florida

The allocation of proximate constituents in the two small seagrasses, Halophila decipiens Ostenfeld and H. johnsonii Eiseman, is similar to that reported for other seagrasses, including the concentration of soluble carbohydrate in the rhizome and roots. The photosynthesis-irradiance curves indicate that the deep water populations of H. decipiens are intolerant of irradiances above 1000 μE m −2s −1 and salinities below 35 ppt. Halophila johnsonii, an intertidal to shallow subtidal species, shows broad tolerances to higher irradiances, and to variations in salinity and temperature. The two species are compared with the larger, more widely distributed H. engelmannii Aschers.

Environmental forcing versus endogenous control of photosynthesis in intertidal epilithic microalgae

Photoadaptation and photosynthetic capacity of an intertidal epilithic microflora were measured hourly over a period of 8 d. The algae were photoadapted to the dim light intensities experienced when submerged and showed little resistance to the extreme irradiances received when exposed. During neap tide when the community was permanently submerged, the photosynthetic response of algae collected hourly in the field followed a circad~an cycle. The endogenous control of this cycle was demonstrated by isolation experiments. During spring tide, photosynthet~c processes were photoinactivated at low tide when extreme irradiances reached the algae. These results lead to the general hypothesis that short-term variability in the photosynthetic capacity of intertidal epilithic microalgae is controlled primarily by endogenous phasing at neap tide and tidal forclng a t spring tide. Time senes of in situ production were reconstructed from solar irradiance measurements and hourly estimates of the parameters of the Photosynthesis-Irradiance curve. Despite the additional stress of low tide exposure, average daily production was comparable between spring and neap tides.

SEASONAL PATTERN OF DIEL PERIODICITY IN PHOTOSYNTHESIS BY POLAR PHYTOPLANKTON: SPECIES-SPECIFIC RESPONSES

The diel patterns of light-saturated and light-limited photosynthesis were measured for three diatom species in McMurdo Sound, Antarctica during the transition from late austral winter to summer. Maximum photosynthetic capacity occurred around mid-day during September, when there was a well defined light/dark cycle, and progressively shifted to about midnight by late october when irradiance was continuous. There was a concomitant shift in minimum photosynthetic capacity from midnight to midday. Rates of light-saturated and -limited photosynthesis covaried, and the magnitude of seasonal and diel changes in photosynthetic characteristics were similar. The linear relationship between light-saturated and -limited photosynthesis suggests that the shapes of the photosynthesis-irradiance curves remained relatively constant over the day and througout the season. The unique diel patterns of photosynthesis of these polar phytoplankton appear to be a response to the persistently low, yet continuous irradiance of the polar summer.

Steady-State Effects of 2,5,2′,5′-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum

The steady-state effect of 2,5,2',5'-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 x 10 in steady-state cultures. At a cellular TCBP concentration of 12.2 x 10 ng . cell, growth rate was not affected. However, photosynthetic capacity (P(max)) was significantly enhanced by TCBP (56 x 10 mumol of C . cell . h versus 34 x 10 mumol of C . cell . h in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected.

Growth and Photosynthetic Responses to Manganese and Copper Deficiencies in Wheat (Triticum aestivum) and Barley Grass (Hordeum glaucum and H. leporinum)

Wheat and barley grass were raised as seedlings in aerated solution cultures under high-pressure sodium vapour lamps in a growth cabinet. Manganese and copper were provided over a wide span of concentrations to induce a range in deficiency symptom expression. Plant response was documented in terms of biomass gain, in vivo chlorophyll fluorescence, CO2-saturated O2 evolution by leaf slices, single leaf H2O/CO2 exchange and A(pI) curves (assimilation as a function of intercellular CO2 partial pressure) at saturating light. Photosynthetic dysfunction due to trace element deficiency lowered O2 evolution (both area and chlorophyll basis) and slowed down leaf gas exchange. Both initial slope and CO2-saturated phases of A(pi) curves were similarly affected in the two species under either Cu or Mn deficiency. Induction kinetics of in vivo chlorophyll fluorescence proved distinctive for both species. Mn deficiency was often manifest as increased constant-yield (Fo) in combination with much reduced variable fluorescence (Fv). Increased ratio of Fo/ Fv was confirmed as a useful index for early diagnosis of Mn deficiency regardless of leaf Cu status. Barley grass (both H. glaucum Steud. and H. leporinum Link) was more tolerant of low Mn and Cu status than wheat, especially in terms of growth and photosynthetic response to Mn deficiency. Wheat plants made little growth once Mn supply was reduced to 10% of control level whereas barley grass was only moderately constrained.

Photosynthetic parameters of northern gulf of California phytoplankton

At the end of autumn, 1981, and end of spring-beginning of summer, 1982, we generated photosynthesis-irradiance curves for phytoplankton from five locations, in each cruise, of the northern Gulf of California. In general, photosynthetic parameters, phytoplankton abundance and chlorophyll a had large vertical changes within the euphotic zone, even in cases where thermohaline vertical homogeneity indicated high instability. Nutrient concentrations were very high. The assimilation number ( P m B), in general, decreased with depth due to conditioning of phytoplankton to lower irradiances. Surface ( P m B) values had a range of 2–15 mg C ( mg Chla) −1h −1. Where the bottom of the euphotic zone was within the thermocline, P m B was 4–15% of the values for surface waters; and where it was within the mixed layer, P m B was 25–85% of the values for surface waters. This was due to greater residence time of phytoplankton at depth in the first case. Very strong turbulence by storm winds caused relatively low P m B values in a December station, possibly because of mixing of the near-surface phytoplankton with relatively deep populations conditioned to low irradiances. Our data indicate that in the Gulf moderate turbulence causes higher P m B values than strong turbulence or stratification.

Mesocosm studies of DCMU-enhanced fluorescence as a measure of phytoplankton photosynthesis

When measurements of in-vivo fluorescence are used to estimate photosynthesis in the field, the marked temporal and spatial variations in phytoplankton populations, and their nutrient and light histories, have produced varied results. Natural phytoplankton populations in large, flow-through mesocosms with different controlled nutrient and sewage sludge additions were sampled weekly from June to September 1984. Good correlations were observed between the increase in fluorescence upon the addition of DCMU (ΔF) and both in-situ production and the parameters (Pm and α) of the photosynthesis-irradiance curve for these phytoplankton populations. Good correlations were also obtained between DCMU-enhanced fluorescence (FDCMU) and chlorophyll a concentrations. The relationship between ΔF and in-situ14C production was consistent among mesocosms even in the face of major shifts from diatom-dominated to dinoflagellate-dominated populations. On the other hand, the FDCMU:Chl a relationship was significantly different between mesocosms and related to species composition. It was concluded that ΔF offers the possibility of rapidly and accurately indexing both in-situ production and the photosynthetic capacity of mixed phytoplankton populations.

The effects of light quality and intensity on photosynthesis and growth of marine eukaryotic and prokaryotic phytoplankton clones

The aim of this work was to assess the relative efficiency of different phytoplankton groups growing under various spectral light fields commonly found in the marine environment. Using neritic and oceanic clones of cyanobacteria (prokaryotic) of the genus Synechococcus and various sized eukaryotic algae representing diverse pigment groups, we compared absorption and fluorescence excitation/emission spectra. Colored filters and neutral density screens were used to simulate oceanic and coastal water-types and rates of photosynthesis and growth were measured under variable conditions of light intensity and quality. Relative photosynthetic efficiencies were determined by comparing light-limited slopes of photosynthesis-irradiance curves in green, blue, and blue-violet light with those in white light. The relative quantum efficiency for photosynthesis was related to both size and pigment composition of the phytoplankter. Independent of light color, smaller algal species were photosynthetically more efficient than larger algae from the same pigment group. In general, the ratio of in vivo cholorophyll intensity fluorescence at the red emission maximum induced by 530 nm excitation to that produced by 470 nm excitation was better than absorption spectra in predicting the ability of organisms from different pigment groups in using various light qualities. Within the ultraplankton size range, algae photosynthesized and grew most efficiently in low intensity blue-violet and blue light, while phycoerythrin-rich Synechococcus clones were most efficient in dim green light. Even though some ultraplankton algal clones, such as the diatom 13−1 and the cryptomonad ID2, contained large quantities of fucoxanthin and phycoerythrin, respectively, their photosynthetic and growth efficiencies in green light were much lower than those of phycoerythrin-rich Synechococcus clones. Moreover, the presence of phycourobilin chromophores in the phycoerythrin of some Synechococcus clones, apparently increased the ability of these cyanobacteria to photosynthesize in low intensity blue light. We conclude that Synechococcus clones containing phycourobilin chromophores could out-compete other Synechococcus clones at depth. However, oceanic ultraplanktonic algae may have a competitive advantage over larger algae and Synechococcus spp. at the base of the photic zone, because these small algae would be more efficient in using the available dim blue-violet light.

The Pluvinage method for alkali dimers. III. Potential energy curves for the excited states of Na2up to the (3p+3p) dissociation limit

A two-electron model together with a correlated orbital method are used to compute the Sigma , Pi and Delta potential curves of Na2 up to the states dissociating into Na(3p)+Na(3p). Crossings of the 'adiabatic' curves with the ground-state potential curve of the Na2+ ion occur for the 8 3 Sigma u+ and 11 Sigma u- states at the internuclear distances R=5 and 8.9 au respectively. The efficiency of the Pluvinage method for the treatment of excited states is discussed.

Effects of temperature on photosynthesis and growth of seagrasses

The effect of temperature on the photosynthesis and growth of seagrasses may be summarized by considering the ways in which temperature alters the characteristics of the photosynthesis-irradiance (P-I) curve of seagrasses. Within the limits of physiological tolerance (∼6–30°C) temperature has little effect on the initial slope of the P-I curve. At 35–40°C the photosynthetic capacity of seagrasses is reduced. Within the limits of physiological tolerance, the rate of photosynthesis at light saturation, the dark respiration rate and the light compensation point more than double as temperature increases. The optimum temperature for photosynthesis decreases from 25–35°C at light saturation to as low as 5°C as irradiance decreases. As a result of these effects of temperature on the P-I curve, growth of seagrasses in high(saturating) light environments increases with temperature, whereas growth of seagrasses in low (near the light compensation point) light environments decreases as temperature increases.

A system for measuring phytoplankton photosynthesis in a defined light field with an oxygen electrode

A system is described for the precise continuous measurement of oxygen consumption and photo-synthetic oxygen evolution in a well defined light field with a polarographic oxygen electrode. The procedure uses a parallel light beam to irradiate samples, a relatively short pathlength and temperature regulation. Maximal sensitivity of the O 2 -mcasurement is 1.4 μmol O 2 /mV at 20°C. The O 2 -chamber and the O 2 -amplifier are presented in full detail together with a typical recorder tracing of a photosynthesis-irradiance curve.

Phytoplankton production in two east coast estuaries: Photosynthesis-light functions and patterns of carbon assimilation in Chesapeake and Delaware Bays

Chesapeake Bay is a large and productive estuary that has received close scrutiny in recent years because of indications that its water quality and biota have been damaged by man's activities. Data on primary production for the estuary as a whole, however, are surprisingly sparse. We describe here the distribution of photosynthetic carbon assimilation by phytoplankton in Chesapeake Bay, and relate productivity patterns to hydrographic characteristics of the estuary. Between March 1982 and April 1983, a series of four cruises was conducted on Chesapeake Bay, and two cruises on the urbanized Delaware Bay for comparison. The upper Chesapeake and Delaware were highly turbid with high concentrations of suspended particulate matter and dissolved inorganic nutrients. Low chlorophyll concentrations were usually found in these areas of high turbidity, despite the abundance of nutrients, suggesting light limitation. Application of Wofsy's (1983) model of phytoplanton growth confirmed this suggestion. Chlorophyll and productivity maxima usually occurred seaward of the turbidity maxima where light penetration increased and suffient nutrients were present to support active phytoplankton growth. Further seaward of the chlorophyll maxima in the Chesapeake, the photic zone depth increased, concentrations of nutrients decreased, and phytoplankton biomass decreased, suggesting that nutrient availability, rather than light, controlled phytoplankton growth in the lower portion of the estuary. In contrast to the Chesapeake, Delaware Bay was more turbid, had generally higher nutrient concentrations, and was lower in phytoplankton productivity. The chlorophyll maxima and region of rapid phytoplankton growth occurred further toward the lower estuary and shelf regions in Delaware Bay because the high turbidity extended further seaward. Nutrients were never depleted at the shelf end of the estuary sufficiently to retard phytoplankton growth. Photosynthesis-irradiance (P-I) curves from simulated in situ and constant intensity incubations showed a strong correlation of the light-limited slope ( a B) with the light-saturated rate ( P m B ) on each cruise. Spatial variations in P m B corresponded to patterns of phytoplankton abundance, as did integral production (PP) and carbon-based growth rates ( μ C, μ m), and photosynthetic parameters varied significantly with temperature.

Evidence for Cyclic Electron Flow around Photosystem II in Chlorella pyrenoidosa

Electron flow around photosystem II was investigated in Chlorella pyrenoidosa. Using a bare platinum O(2) electrode, simultaneous measuremnts were made of steady-state photosynthesis in continuous light, the yield of oxygen (Y(o(2) )) produced by a superimposed saturating xenon flash, and the change in fluorescence yield of a weak flash triggered before and 70 microseconds after the saturating flash. Throughout most of the continuous photosynthesis-irradiance curve, normalized O(2) flash yields (Y(o(2) )/Y(o(2)max)) and normalized variable fluorescence yields (Deltaphi/Deltaphi') were linearly correlated with a slope of 1.0. As photosynthetic rates reached light saturation, however, the variable fluorescence yields remained relatively constant while O(2) flash yields decreased. These results strongly suggest that there is a cyclic electron flow around photosystem II in unpoisoned intact cells at light saturation and supraoptimal light intensities.

Intertidal microalgal production and the auxiliary energy of tides

We monitored the photosynthetic response of an estuarine epilithic microflora exposed to natural variations in water level and light intensity. The experimental community developed on an artificial substrate in the intertidal zone of the St. Lawrence estuary. Fragilaria striatula dominated the assemblage. Samples for the determination of the Photosynthesis-Irradiance curve were collected at intervals of 2 h over a period of 11 d. The initial slope of the curve (αB) and the maximum photosynthetic rate (P m B ) per unit Chl a were estimated. During spring tide, wave-induced turbulence reaching the experimental substrate at low tide eroded the arborescent stratum of the cell mat. The physiological condition of the remaining prostrate stratum was poor (low Chl a/ phaeopigment ratio). The photosynthetic response of the community was weak and showed little variability. During neap tide, the arborescent stratum of the permanently inundated community persisted. The community showed a stronger and more variable photosythetic response. During this period fluctuations in the magnitude of αB and P m B were dominated by a 24-h periodicity, but also presented a secondary semidiurnal rhythm. The ciradian periodicity in the photosynthetic response was best explained by postulating an endogenous control. Circatidal variations in P m B were perhaps related to tidal fluctuations in nutrient availability. The fortnightly renewal of space by the auxiliary energies of wind and tides apparently controlled the dynamics of the community.

Continued studies of high algal productivities in a shallow flume

Tetraselmis suecica was grown in outdoor shallow flume systems over a period from June to August, 1985, in an effort to test the reproducibility of results achieved in 1984, and to gain some understanding about the responses of the alga to changing conditions in the culture. Production results during 1985 were not significantly different from those achieved in 1984 when the cells were grown in a three-day dilution interval mode, and averaged 35±5 g ash-free dry weight m −2 day −1 over a total of 78 days during both years. Production on the third day of the growth cycle was significantly higher than on days one and two during both years. Statiscally significant changes were found in compositional characteristics and photosynthesis-irradiance curve parameters as a function of biomass and/or time during two, three and four-day growth cycles. These changes could not, however, explain why production was consistently higher when the cells were grown in a three-day dilution interval mode.

PHOTOSYNTHESIS AND RESPIRATION INTRIDACNA GIGASAS A FUNCTION OF IRRADIANCE AND SIZE

The effects of irradiance level and size on the rate of O2 evolution and consumption was examined in Tridacna gigas using an oxygen electrode. Seven photosynthesis-irradiance (P-I) curves were generated for intact clams ranging from 1 to 23 cm in shell length. Both alpha and Pmax decreased with increasing size of the clam. Oxygen evolution at 1000 µE·m–2·s–1 and consumption in the dark were measured for an additional 9 clams ranging up to 38 cm in shell length. Oxygen evolved per gram clam tissue in the light, dark respiration, and the number of zooxanthellae per gram all decreased with increasing clam size. The average amount of shading experienced by the zooxanthellae in the clam tissues was estimated by comparing the P-I curves of different-sized clams to the P-I curves of zooxanthellae freshly isolated from these clams. Estimates of shading increased from negligible levels in small clams to 80% in the largest clams investigated. Use of these results to chose optimum light intensities for the mariculture of T. gigas is discussed.

Observed and predicted measurements of photosynthesis in a phytoplankton culture exposed to natural irradiance

Photosynthesis-irradiance (P-I) curves were produced (using artificial illumination) from samples taken at one or more times per day from a continuous culture illuminated with sunlight. The continuous culture housed an oxygen electrode used to measure photosynthises semi-continuously. Rates of photosynthesis predicted from P-I curves agreed with photosynthises observed in the culture only for days of low irradiance. For sunny days or for days of variable irradiance, P-I curves predicted neither the morning photosynthesis maximum nor the afternoon depression. Daily integrals of predicted and observed photosynthesis, however, were probably within the possible errors of measurement.

Electron-polarised-photon coincidence study of the excitation of the C1Πustate in hydrogen and deuterium

The electron-polarised-photon coincidence technique has been used to study the X1 Sigma g+ to C1 Pi U to X1 Sigma g+ excitation/de-excitation process in H2 and D2. Polarisation correlations for integrated vibrational bands have been measured for electron scattering angles up to 25 degrees and incident electron energies up to 80 eV. It was found that the P(0) parameter displays a pronounced dip to zero at a scattering angle of theta c-12.5 degrees in H2, independent of the actual impact energy, and at theta c=10 degrees in D2. Characteristic features in the P(1/4 pi ) angular dependence are a negative value at a small scattering angle, P(1/4 pi )=-0.36 at theta c=10 degrees in hydrogen and P(1/4 pi )=-0.23 at theta e=7.5 degrees in deuterium, and a rapid variation of P(1/4 pi ) back to zero. The region of the steepest gradient in the P(1/4 pi ) curve was found to coincide with the dip in P(0). The decline in the level of coherence when going from H2 to D2 can be attributed to the more developed rotational envelope in deuterium. An attempt is made to relate the observed systematic trends in the data to the properties of the respective target molecule.

Adaptation of photosynthesis to irradiance and daylength in the red alga Acrosymphyton purpuriferum (J. Ag.) Sjöst. (Rhodophyceae, Cryptonemiales), a species from the deep sublittoral region

The crustose tetrasporophyte of the red alga Acrosymphyton purpuriferum (J. Ag.) Sjost. (Rhodophyceae, Cryptonemiales), a species from the deeper sublittoral region, was cultured at a series of daylength and irradiance conditions and the pigment content and photosynthetic rates were compared. Chlorophyll-a and phycobilin contents varied little over the wide range of conditions tested (daylengths: 4, 8, 12 and 16 h; photon flux densities: 2.5, 5, 20, 40 and 80 μmol m−2 s−1). Nevertheless, the irradiance and daylength history of the plants distinctly influenced the shape of the photosynthesis–irradiance curve (PI-curve). The irradiance history mainly influenced the maximum photo-synthetic capacity (Pmax, which was highest in plants grown at the higher irradiance. This suggests an increased capacity of the enzymatic processes of photosynthesis at high irradiance. The daylength history of the plants influenced the initial slope (α) of the curve as well as Pmax. Pmax was highest and α steepest for plants that had been grown in the shorter days. This suggests an influence of daylength on photosynthetic efficiency through changed photosynthetic energy transduction. From the PI-curves the actual photosynthetic rate and the daily photosynthetic production at the various culture conditions were calculated. The influence of daylength and irradiance on these photosynthetic parameters was compared with their influence on tetrasporogenesis and thus the role of photosynthesis in the irradiance-dependency of the short day response in tetrasporogenesis was evaluated.

Angular correlation between autoionisation electrons from Ne(2p43s2)1D and scattered ions in He++Ne collisions

Angular distributions of autoionisation electrons from Ne(2p43s2)1D due to He++Ne collisions at 2 keV were measured in coincidence with the scattered projectiles and compared with those of electrons from He(2p2)1D, measured by Kessel et al. (1979). A theoretical analysis of such angular electron correlations in terms of a density-matrix description is given. The authors find that the Ne excitation occurs in a nearly pure m=0 sublevel with respect to an axis in the scattering plane which coincides with the internuclear line of the collision partners on the outgoing part of the trajectory at a separation of R approximately=2.4a0. This is interpreted as being due to an excitation at small R by a radial coupling of two Sigma -potential curves, followed by a rotation of the quasimolecule as a whole up to R approximately=2.4a0. A quantitative estimate of the energy separations between Sigma , Pi and Delta potential curves correlating to He++Ne(2p43s2)1D indicates that a rotational coupling between these curves is responsible for the decoupling of electronic and nuclear motion at R approximately 2.4a0.