Chlorophyll a fluorescence,an alternative method for estimating primary production

The in vivo chlorophyll a fluorescence index (F_+DCMU-F_-DCMU/F_+DCMU) of natural waters was compared to the ¹⁴C-determined primary production, and the fluorescence intensity in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (F_+DCMU) was studied as a function of extracted and spectrophotometrically determined chlorophyll concentrations. Samples were taken every second week from May through October, 1979, at the station Systrarna situated in a coastal area of the Bottnian Sea. In addition, samples from the Archipelago Sea of the Baltic were collected on board the Finnish research vessel R/S Aranda during the September cruise 1979. The correlations between the fluorescence index and the ¹⁴C-determined primary production and between F_+DCMU and total chlorophyll concentration were good when samples taken over short time intervals were compared. The shortcomings of both the fluorescence and the ¹⁴C methods are discussed. It is concluded that the fluorescence method is useful if it is desirable to follow with high time resolution any changes in the potential for photosynthesis (or primary production) in a water mass over relatively short time periods; e.g. during an algal bloom. The fluorescence method can furthermore be technically developed for automatic monitoring with a high time resolution. Efforts are being made in our laboratory to develop the method further to give information about the in situ rates of photosynthesis rather than the potential for photosynthesis in a photoplankton population.     

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 (F) and both in-situ production and the parameters (P_m and ) of the photosynthesis-irradiance curve for these phytoplankton populations. Good correlations were also obtained between DCMU-enhanced fluorescence (F_DCMU) and chlorophyll a concentrations. The relationship between F and in-situ ¹⁴C production was consistent among mesocosms even in the face of major shifts from diatom-dominated to dinoflagellate-dominated populations. On the other hand, the F_DCMU:Chl a relationship was significantly different between mesocosms and related to species composition. It was concluded that F offers the possibility of rapidly and accurately indexing both in-situ production and the photosynthetic capacity of mixed phytoplankton populations.This study was supported by EPA cooperative agreement 810265-03 and NOAA grant NA-83-ABD-00008     

Chlorophyll a fluorescence in marine centric diatoms: Responses of chloroplasts to light and nutrient stress

Observations at sea of large variations in the cellular fluorescence of phytoplankton prompted a study of the fluorescence responses in marine diatoms to light and nutrient stress. When older cultures of Lauderia borealis were exposed to intense light, the in vivo fluorescence of chlorophyll a declined within the first 2 min of exposure. This initial response to light stress appeared to be correlated with a contraction of the chloroplasts. Continued exposure led to a second decline in fluorescence, which required 30 to 60 min for completion. A movement of chloroplasts to the valvar ends of the cell caused this secondary response. Both the contraction and intracellular movement of chloroplasts appeared to be related to both photoinhibition of photosynthesis and diel fluctuations in cellular fluorescence. An investigation of continuous cultures of Cyclotella nana showed that in vivo chlorophyll a fluoresced more strongly in nitrogen-starved cells than in enriched ones. Photoinhibition of cellular fluorescence also increased with the cell's state of nitrogen deficiency.     

Effects of diurnal variations in phytoplankton photosynthesis obtained from natural fluorescence

Effects of diurnal variation in phytoplankton photosynthesis on estimating daily primary production (DPP) were examined using field data from Sagami Bay, Japan. DPP at 5 m depth was calculated from the continuous data of chlorophyll a (Chl a) and light intensity monitored by a natural fluorescence sensor with and without considering time-dependent changes in the photosynthesis–irradiance (P–E) relationship. Chl a could be estimated from natural fluorescence examining the variations in the quantum yield of fluorescence (φ _f) and Chl a-specific light absorption coefficient (a*_ph), and relating them to Chl a. The P–E relationship was determined by water sampling three times daily. A distinct diurnal pattern was observed for the maximum photosynthetic rate (P*_max), being maximal at noon, while periodicity of the maximum light utilization coefficient (α*) was less obvious. The actual DPP was calculated by interpolating the P–E parameters from those obtained at dawn, noon, and dusk. For comparison, DPP was calculated by fixing the P–E parameters as the constants measured at dawn, noon or dusk for a day. The difference from the actual DPP was small when the P–E parameters measured at dawn (3% on average) and noon (5%) were used as the constants for a day. The difference was largest when the values at dusk were used (−43%). The medium values of P*_max at dawn, its low values at dusk, and the fact that a major part of the DPP was produced around noon were responsible for these results. The present study demonstrates that measurement of the P–E parameters at dawn or noon can give a good estimation of DPP from natural fluorescence.     

Light absorption by a marine diatom: experimental observations and theoretical calculations of the package effect in a small Thalassiosira species

The relationship between in vivo light absorption efficiency of whole cells and in vitro absorption efficiency of algal pigments has been examined experimentally in the marine diatom Thalassiosira sp. In vitro absorption spectra were obtained for cells disrupted by either ultrasonic treatment or high-pressure shearing stress in a low-temperature (-40°C) pressure cell. A dimensionless measure of the magnitude of the package effect (Q _a ^*), calculated from the ratio of whole-cell to disrupted-cell absorption, ranged from about 0.5 at the blue absorption peak of chlorophyll a (λ=435 nm) to 0.7 at the red chlorophyll a peak (λ=670 nm) to 1.0 at the absorption minimum (λ=600 nm). Cell diameter was found to be an inappropriate measure of size for assessing the magnitude of the package effect. Instead, the effective optical diameter for calculation of intracellular self-shading was found to be less than the cell diameter. This observation is consistent with the fact that most algal pigments are contained within chloroplasts, and that chloroplast volume is necessarily smaller than cell volume.     

UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350–700 nm). UV absorption was high; chlorophyll-specific absorption, a ^* _ph, at 330 nm ranged from 0.06 to 0.41 m²/mg chlorophyll a. Values of a ^* _ph (330) were 4–13 times greater than a ^* _ph (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine are responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll a or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher irradiances. The relative fluorescence yield for chlorophyll a was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll a in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light. Received: 31 March 1999 / Accepted: 13 July 2000     

Photosynthesis and growth of red and green morphotypes of Kappaphycus alvarezii (Rhodophyta) from the Philippines

The effect of photosynthetic available radiation (PAR) levels, light quality, ultraviolet (UV) radiation, and temperature on photosynthesis, growth, and chlorophyll fluorescence was evaluated in red and green morphotypes of the rhodophyte Kappaphycus alvarezii (Doty) Doty under controlled conditions. Chlorophyll a and phycoerythrin (PE) levels were similar in the red and green morphotypes cultured under the same conditions, but phycocyanin (PC) and allophycocyanin (APC) levels were 2-fold greater in the green than in the red morphotype. Pigment characterization indicated that the overexpression of PC and APC masked the red pigmentation in the green morphotype. Maximum photosynthesis and photosynthetic efficiency were similar between the two morphotypes assayed at a wide temperature range, which was reflected in the similar growth rates observed in outdoor culture systems. In the green morphotype, photosynthetic efficiency increased 2-fold relative to the red morphotype when assayed with red light (λ > 600 nm), indicating that photosynthetic characteristics are modified as a result of pigment variation in these morphotypes. Such increase in photosynthetic efficiency in the green morphotype, however, did not result in greater growth rates when cultured under white light. Short exposure to high levels of solar radiation (UV-A + UV-B + PAR), and filtered solar radiation (UV-A + PAR or PAR) decreased effective quantum yield (ΔF/F _m′) in both morphotypes. The reduction of ΔF/F _m′ values in the red and green morphotypes was accounted for by high levels of PAR and not by the UV-A + UV-B + PAR and UV-A + PAR treatments. Photoinhibition caused by UV-A, UV-B, or PAR was completely reversed within 30 h after incubations. Recovery rates from photoinhibition, however, were significantly reduced in the green morphotype when incubated with UV-B radiation. The results here suggest that the overexpression of pigments do not necessarily increase photosynthesis and growth in these morphotypes. Received: 19 June 2000 / Accepted: 28 November 2000     

Changes in the acitivy of fucoxanthin-excited photosynthesis in the marine diatom Phaeodactylum tricornutum grown under different culture conditions

Variations in the photosynthetic activity under monochromatic light was studied in Phaeodactulum tricornutum grown under various culture conditions, with special reference to the composition of photosynthetic pigments. Photosynthetic activity, under light-limiting conditions, was reduced when the cells were grown under strong light. The reduction was more extensive in activity resulting from fucoxanthin-excitation than in that from chlorophyll a-excitation. The diminution in activity for fucoxanthin-excited photosynthesis did not correlate with variations in the pigment content. A similar diminution was observed with chlorophyll a fluorescence upon excitation of fucoxanthin. The change was accelerated by lowering the culture temperature, or limiting the supply of nitrogen source. The results were interpreted in terms of a nitrogen-deficient state for algal cells induced by strong light, low temperature or a limited supply of nitrogen. This leads to a modification of the physicochemical state of in vivo fucoxanthin, so that the excitation energy of fucoxanthin is less efficiently transferred to chlorophyll a. The significance of the phenomenon in the oceanic primary production is discussed.     

Evaluation of chlorophyll fluorescence, in vivo spectrophotometric pigment absorption and ion leakage as biomarkers of UV-B exposure in marine macroalgae

The photosynthetic fluorescence ratio F_v:F_m, in vivo absorption spectra and ion leakage were evaluated as biomarkers of ambient and elevated UV-B (280 to 320 nm) exposure of the intertidal alga Enteromorpha intestinalis (Chlorophyta) and the sublittoral alga Palmaria palmata (Rhodophyta). Measurements of thallus growth were also used to assess adverse biological effects. Ambient and elevated UV-B significantly inhibited photosynthesis in both species. It was shown that the F_v:F_m ratio is a sensitive, non-specific general biomarker of UV-B exposure in both species. Moreover, the in vivo absorption of what was tentatively identified as chlorophylls a and b as well as phycoerythrin and/or carotenoids, phycoerythrobilin and phycocyanin decreased in a dose-response dependent manner and was associated with a decrease in growth rate in P. palmata. The intertidal alga E. intestinalis showed a greater degree of tolerance to UV-B exposure. These results indicate that changes in the F_v:F_m ratio together with reductions in in vivo pigment absorption could provide an early quantitative warning of the detrimental effects of UV-B in marine macroalgae. Received: 16 May 1997 / Accepted: 16 July 1997     

Availability of ammonium influences photosynthesis and the accumulation of mycosporine-like amino acids in two<Emphasis Type="Italic"> Porphyra</Emphasis> species (Bangiales,Rhodophyta)

The effect of ammonium concentration on photosynthetic activity estimated as in vivo chlorophyll fluorescence, i.e. maximal quantum yield (F_v/F_m) and electron transport rate (ETR) and on the accumulation of mycosporine-like amino acids (MAAs), chlorophyll a (chl a), biliproteins (BP) and soluble proteins (SP) in the red algae Porphyra leucosticta Thuret in Le Jolis collected from Lagos (Málaga, Spain) and Porphyra umbilicalis (Linnaeus) J. Agardh from Helgoland (Germany) was evaluated. Discs of both species were incubated with three ammonium concentrations (0, 100 and 300 µM) under artificial PAR and UV radiation for 7 days. Photosynthetic activity decreased under the culture conditions due to UV radiation and ammonium availability. The decrease of both F_v/F_m and maximal ETR was related to ammonium supply, i.e. the lowest decrease occurred in algae growing with the highest concentration of ammonium. In both species, after 7 days of culture, the content of chl a, BP and SP was higher under 300 µM than that under 0 and 100 µM ammonium. In both species, the content of MAAs was increased under 300 µM ammonium compared to the initial value, whereas a decrease under 0 and 100 µM ammonium was observed only in P. leucosticta. The content of MAAs in P. umbilicalis did not present significant differences compared to the initial value, probably because of the high initial content of MAAs. In both Porphyra species, four MAAs were identified: shinorine, porphyra-334, palythine and asterina-330. However, P. leucosticta modified its MAA pattern during the incubation time, reaching the same percentages found for P. umbilicalis, which did not show any change during the experimental period. P. leucosticta exhibited a decrease in BP/SP and BP/chl a ratios through the incubation time and an increase in MAAs/BP. The ratio MAAs/chl a did not show any variation with time or treatment, as was also true for all ratios in P. umbilicalis. In summary, ammonium supply diminished the decrease of F_v/F_m, increased the content of photosynthetic pigments (chlorophyll and biliprotein) and soluble protein, and stimulated of the accumulation of MAAs in the red algae P. leucosticta and P. umbilicalis.Communicated by O. Kinne, Oldendorf/Luhe     

Effects of light exposure on the retention of kleptoplastic photosynthetic activity in the sacoglossan mollusc <Emphasis Type="Italic">Elysia viridis</Emphasis>

The effects of light exposure on the photosynthetic activity of kleptoplasts were studied in the sacoglossan mollusc Elysia viridis. The photosynthetic activity of ingested chloroplasts was assessed in vivo by non-destructively measuring photophysiological parameters using pulse amplitude modulation (PAM) fluorometry. Animals kept under starvation were exposed to two contrasting light conditions, 30 μmol photons m⁻² s⁻¹ (low light, LL), and 140 μmol photons m⁻² s⁻¹ (high light, HL), and changes in photosynthetic activity were monitored by measuring the maximum quantum yield of photosystem II (PSII), F _v/F _m, the minimum fluorescence, F _o, related to chlorophyll a content, and by measuring rapid light-response curves (RLC) of relative electron transport rate (rETR). RLCs were characterised by the initial slope of the curve, α_RLC, related to efficiency of light capture, and the maximum rETR level, rETR_m,RLC, determined by the carbon-fixation metabolism. Starvation induced the decrease of all photophysiological parameters. However, the retention of photosynthetic activity (number of days for F _v/F _m > 0), as well as the rate and the patterns of its decrease over time, varied markedly with light exposure. Under HL conditions, a rapid, exponential decrease was observed for F _v/F _m, α_RLC and rETR_m,RLC, F _o not showing any consistent trend of variation, and retention times ranged between 6 and 15 days. These results suggested that the retention of chloroplast functionality is limited by photoinactivation of PSII reaction center protein D1. In contrast, under LL conditions, a slower decrease in all parameters was found, with retention times varying from 15 to 57 days. F _v/F _m, α_RLC and rETR_m,RLC exhibited a bi-phasic pattern composed by a long phase of slow decrease in values followed by a rapid decline, whilst F _o decayed exponentially. These results were interpreted as resulting from lower rates of D1 photoinactivation under low light and from the gradual decrease in carbon provided by photosynthesis due to reduction of functional photosynthetic units.     

Age-specific responses to elevated salinity in the coastal marsh plant black needlerush (Juncus roemerianus Scheele) as determined through polyphasic chlorophyll a fluorescence transients (OJIP)

This study employed polyphasic chlorophyll a fluorescence transients (OJIP), a non-invasive marker of environmental stress in plants, to evaluate salt tolerance in three different Juncus roemerianus age classifications (6-, 24-, and 60-months). Following exposure to elevated salts (30 psu), the younger plants sustained growth, which was comparable to freshwater controls. While older (60-month) plants receiving only freshwater also grew over the 8-week study, the older salt-treated plants did not increase in size. Similarly, there were significant declines in variable chlorophyll a fluorescence parameters (F _v/F _m and F _v/F _o), electron transport flux per reaction center (ET_o/RC), and photosystem II performance index (PI_ABS) for 60-month J. roemerianus following salt treatment. These responses were not evident in the two younger salt-treated age classifications. Our results suggest that older J. roemerianus are less tolerant to rapid and sudden increases in salinity relative to younger plants and that this age-specific response may help explain observed discrepancies in salt tolerance in J. roemerianus.     

In situ seagrass photosynthesis measured using a submersible, pulse-amplitude modulated fluorometer

Assessments of photosynthetic activity in marine plants can now be made in situ using a newly developed, submersible, pulse-amplitude modulated (PAM) fluorometer: Diving-PAM. PAM fluorometry provides a measure of chlorophyll a fluorescence using rapid-light curves in which the electron-transport rate can be determined for plants exposed to ambient light conditions. This technique was used to compare the photosynthetic responses of seagrasses near Rottnest Island, Western Australia. Several fluorescence parameters were measured as a function of time of day and water depth; electron-transport rate (ETR), quantum yield, photochemical quenching and non-photochemical quenching and Photosystem II (PSII) photochemical efficiency (F _v :F _m ratio) were measured. Results indicate that recent light-history plays a crucial role in seagrass photosynthetic responses. Maximum ETR of Posidonia australis, Amphibolis antarctica and Halophila ovalis is influenced by the irradiance during the diurnal cycle, with low rates at dawn and dusk (<10 μmol electron m⁻² s⁻¹), highest rates in late morning (40 to 60 μmol electron m⁻² s⁻¹) and a mid-day depression. Maximum ETR and PSII photochemical efficiency varied widely between seagrass species and were not correlated. A comparison of photochemical to non-photochemical quenching indicated that seagrasses in shallow water receiving high light have a high capacity for non-photochemical quenching (e.g. light protection) compared to seagrasses in deep water. These results indicate that in situ measurements of photosynthesis will provide new insights into the mechanisms and adaptive responses of marine plants. Received: 26 May 1997 / Accepted: 27 May 1998     

Influence of light on algal symbionts of the deep water coral Leptoseris fragilis

Photoadaptations of zooxanthellae living within the deep water coral Leptoseris fragilis taken from the Gulf of Aqaba (Red Sea) were studied. Specimens-collected in summer 1988 between 110 and 120 m depth —were transplanted to 70 and 160 m. At each depth individuals were exposed in their natural growth position (oral side facing the surface) or in a reverse growth position (oral side facing the bottom). After 1 yr of exposure the corals were collected and the zooxanthellae were isolated. As a function of the availability of light with depth and growth position several algal parameters showed changes which are related to photoadaptations. The relatively low density of zooxanthellae of 0.15x10⁶ cellsxcm^-2 at a natural growth depth of 116 m decreased to 0.0034x10⁶ cellsxcm^-2 (2%) at 160 m in specimens growing with a natural orientation. In corals with a downward-facing oral surface at the same depth (160 m) only degenerated algae could be observed. With respect to depth dependence the volume of the algae decreased from 728 m³ at 116 m to 406 m³ at a depth of 160 m and the content of pigments increased. The augmentation of peridinin per cell was low (two times at 160 m compared to 116 m). Chlorophyll a and in particular chlorophyll c ₂ concentrations per cell were enhanced. Compared to natural amounts at 116 m, chl a was five times and chl c ₂ eight times higher at 160 m. At all depths the chl c ₂ content per cell was higher than for chl a. The formation of chl a/chl c ₂ complexes as light harvestor is discussed. Light harvesting, with chl c ₂ prevailing may be explained as a special type of chromatic adaptation of L. fragilis in a double sense: (1) in the habitat light short wavelengths predominate. This light can be directly absorbed with pigments such as chl a and chl c ₂. (2) Host pigments absorb visible violet light and transform these wavelengths, less suitable for photosynthesis, into longer ones by means of autofluorescence. The emitted longer wavelengths fit the absorption maxima of the algal pigments. Thus the host supports photosynthesis of his symbionts. Corals exposed at 160 m depth with a downward facing oral surface were alive after 1 yr and the host wavelength transforming pigment system was still present, but zooxanthellae were absent or degenerated. The light field at 160 m seems therefore to be critical: the combined photoadaptations of host and symbionts, allowing photosynthesis under barren light conditions, seem to be exhausted. In L. fragilis the photoadaptive strategies of host and symbionts cooperate harmoniously. In addition, the adaptations are interlocked with the particular light situation of the habitat with respect to light quantity and quality. The cooperation of physical and organismic parameters examplifies how evolution and, in particular, coevolution has led to optimal fitness.     

Humic substances. Part II†: Photophysical,photochemical and free radical characteristics

The effects of mercury (HgCl₂) on cell population, chlorophyll a concentration and rates of photosynthesis and excretion were investigated in the phytoplanktonic species Dunaliella minuta in laboratory cultures. Mercury, above 25ppb inhibited both cell population and chlorophyll a concentration approximately to the same extent, whereas the photosynthetic rate was inhibited to a significantly lesser degree. Although, the total photosynthetic rate of the tested organism was reduced, above a threshold concentration, the photosynthetic activity was not reduced under these conditions, but it was in fact significantly greater than that in the control culture. This may suggest that in D. minuta the inhibitory effect of mercury is primarily on cell division rather than cellular photosynthesis, which is enhanced by the fact mercury caused a significant increase of the mean cell volume. Mercury, also, decreased the growth rate and final cell yield. The excretory rate was markedly increased at concentrations ≥ 250 ppb of mercury, but at lower concentrations it tended to depend more on the physiological state of cells than on mercury concentration. In the different cultures, the photosynthetic activity showed variations which occurred without major changes in the chlorophyll a content per cell, which remained almost constant and independent of variations in cell size and growth conditions.     

Seasonal study of phytoplankton pigments and species at a coastal station off Sydney: Importance of diatoms and the nanoplankton

Phytoplankton pigments and species were studied at a coastal station off Sydney (New South Wales, Australia) over one annual cycle. Sudden increases in chlorophyll a (up to 280 mg m^-2), due to short-lived diatom blooms, were found in May, July, September, January and February. These were superimposed upon background levels of chlorophyll a (20 to 50 mg m^-2), due mostly to nanoplankton flagellates, which occurred throughout the year. The nanoplankton (<15 m) accounted for 50 to 80% of the total phytoplankton chlorophyll, except when the diatom peaks occurred (10 to 20%). The annual cycle of populations of 16 dominant species-groups was followed. Possible explanations as to alternation of diatom-dominated and nanoplankton-dominated floras are discussed. Thin-layer chromatography of phytoplankton pigments was used to determine the distribution of algal types, grazing activity, and phytoplankton senescence in the water column. Chlorophyll c and fucoxanthin (diatoms and coccolithophorids) and chlorophyll b (green flagellates) were the major accessory pigments throughout the year, with peridinin (photosynthetic dinoflagellates) being less important. Grazing activity by salps and copepods was apparent from the abundance of the chlorophyll degradation products pheophytin a (20 to 45% of the total chlorophyll a) and pheophorbide a (10 to 30%). Chlorophyllide a (20 to 45%) was associated with blooms of Skeletonema costatum and Chaetoceros spp. Small amounts of other unidentified chlorophyll a derivatives (5 to 20%) were frequently observed.     

Diel changes in phytoplankton photosynthetic efficiency in Brackish waters

From 18 to 23 September 1974, investigations on the diel changes in phytoplankton were carried out in the Baltic Sea. Every 4 h, water samples were collected from 2 and 15 m, and PO₄, chlorophyll a, temperature, salinity, pH, phytoplankton composition and phytoplankton light photosynthesis relationship were determined. Continuous measurements of surface irradiance and some estimations of zooplankton were also made. P ^B (photosynthesis per unit chlorophyll a at low light levels of 2·10^-2 cal cm^-2 min^-1) revealed only random variation during the sampling period, i.e., 1.0 to 1.6 mg C (mg chlorophyll a)^-1 h^-1. P _m ^B (Light-saturated photosynthesis per unit of chlorophyll a) displayed pronounced diel fluctuations with the highest value of about 6 mg C (mg chlorophyll a)^-1 h^-1 around noon, and the lowest value of about 2.5 mg C (mg chlorophyll a)^-1 h^-1 during the night, during which latter period the value of P _m ^B was more or less constant. Reasons for the diel fluctuations are discussed, and an equation which describes these fluctuations is proposed. Using this equation, the daily phytoplankton production estimated in incubators by a previously described method can be corrected for the time of day at which samples are collected.     

Profiles of photosynthetic pigments in the ocean using thin-layer chromatography

Phytoplankton pigments at a coastal station off Sydney, Australia, were studied by cellulose thinlayer chromatography. The chromatographic procedure distinguished chlorophylls a, b and c, chlorophyllide a, pheophytin a and pheophorbide a, and the major carotenoids carotene, astaxanthin, fucoxanthin, peridinin, diadinoxanthin and neoxanthin. Chlorophyllide a and pheophorbide a were the most significant chlorophyll-a degradation products in the water column, chlorophyllide a coming from chlorophyllase activity of senescent diatoms, and pheophorbide a from faecal pellets of copepods. Chlorophyll c occurred in every sample, even where there was no trace of chlorophyll a. Because of the greater chemical and biological stability of chlorophyll c compared to chlorophyll a, high chlorophyll c:a ratios result from a large proportion of senescent or detrital material in the samples. Determining the position of patches of copepods, diatoms, green algae and dinoflagellates in the water column was easily done by noting the presence of definitive pigments on the chromatograms.     

Fluorescence properties of natural phytoplankton populations

The cellular fluorescence of chlorophyll a in natural phytoplankton was measured during vertical profiling in marine coastal waters. The ratio of in situ fluorescence to chlorophyll a concentration, which was considered as an index of cellular fluorescence, varied over a wide range, with large changes occurring both within the water column and between profiling sites. The variations were caused in part by an inhibition in the fluorescence of cells exposed to intense sunlight. The inhibition, which occurred at irradiances exceeding 0.15 langley (ly)/min, led to diel fluctuations in the fluorescence of those phytoplankton near the sea surface. The remaining variations were independent of changes in temperature, but were unexplained. Both light-dependent and light-independent variations in cellular fluorescence will affect the accuracy of the continuous, fluorometric measurement of in vivo chlorophyll.     

The use of nondestructive methods to assess a physiological status and conservation perspectives of <Emphasis Type="Italic">Eryngium maritimum</Emphasis> L.

Eryngium maritimum is a perennial species growing exclusively in a coastal littoral zone both on sand dunes and shingle beach and indicated as declining in Northern Europe. The objective of the present study was to prove the use of nondestructive physiological measurement methods to access physiological status of endangered plants, using E. maritimum as a model species. Plants from two Latvian sites were studied in comparison with other populations in Northern Europe (Estonia, Lithuania, Poland, United Kingdom) to find out if local differences in environmental factors affect vitality of E. maritimum individuals. Noninvasive chlorophyll analysis and chlorophyll a fluorescence measurements were used as indicators of plant physiological status through characterization of various aspects of photochemistry of photosystem II activity. Dynamics and morphology of individuals were investigated for evaluation of clonal growth potential of E. maritimum in natural conditions. Highly fluctuating trend of dynamics of individuals (within 40 groups at two Latvian sites) was established for E. maritimum in natural conditions over a five-year period. Disturbance of individuals lead to formation of new shoots from nodal root meristems. An exponential regression between fluorescence parameters F_V/F_M and Performance Index and summary monthly precipitation was found indicating that E. maritimum plants had significant tolerance to water shortage together with susceptibility to increased precipitation. Negative correlation between leaf chlorophyll content and more northern localization of individuals was found (r = 0.95 and r = 0.94, for generative and vegetative shoots, respectively). Northern populations of E. maritimum are endangered by high precipitation in conditions of low air temperature, leading to decrease of photosynthetic productivity and overall physiological status. High developmental plasticity at the root level leads to clonal growth and an efficient survival and relatively long life span of E. maritimum individuals. Chlorophyll a fluorescence is a useful method to search for the effect of suboptimal conditions on physiological status of endangered plant species without elimination and disturbance of individuals.