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1.
Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa 总被引:1,自引:0,他引:1
Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O2 and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O2 concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured
at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness
decreased the O2 concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell
surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O2 h−1 foraminifer−1. The net photosynthesis averaged 5.3 ± 2.7 nmol O2 h−1. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O2 h−1, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O2 h−1). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross
photosynthesis versus scalar irradiance curves (P vs E
o curves) showed light saturation irradiances (E
k) of 75 and 137 μmol photons m−2 s−1 in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m−2 s−1. The light compensation point of the symbiotic association was 50 μmol photons m−2 s−1. Radial profile measurements of scalar irradiance (E
o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E
d).
Received: 26 January 1998 / Accepted: 11 April 1998 相似文献
2.
Use of pulse amplitude modulated (PAM) fluorometry for in situ measurements of photosynthesis in two Red Sea faviid corals 总被引:7,自引:0,他引:7
Measurements of the photosynthetic activity of symbiotic zooxanthellae in corals under natural growth conditions has been limited until recently, and this is one of the first reports on utilising a newly developed underwater pulse amplitude modulated (PAM) fluorometer (the Diving-PAM, Walz Gmbh, Germany) for such studies in situ. Photosynthetic responses to irradiance (photosynthetic photon flux, PPF) of the two faviid corals Favia favus (Forskål) and Platygyra lamellina (Ehrenberg) were measured while snorkelling or SCUBA diving (in August 1997), and we report here the results in terms of effective quantum yields of photosystem II (Y?) and estimated rates of photosynthetic electron transport (ETR, calculated as Y?×?0.5?× PPF?×?FA, where FA is the estimated fraction of light absorbed by the photosymbiont-containing tissue). Both species showed a reduction in Y with increasing actinic irradiances produced by the instrument above 500?μmol photons m?2 s?1, and the corresponding ETR values yielded apparently typical photosynthesis versus irradiance (P-I?) curves, which saturated between 1500 and 2000?μmol photons m?2 s?1. It was found that 30?s irradiation at each PPF level was sufficient to give optimal ETR values and, therefore, each P-I curve could be obtained within a few minutes. In situ point measurements from various areas of colonies under ambient light showed average ETR values within the range expected from the P-I curves. In order to test the Diving-PAM in an eco-physiologically relevant experiment, photosynthetic ETR versus PPF was measured for three sections of a large P. lamellina, each section of which received different natural irradiance levels. The results clearly demonstrated adaptations to the ambient light field in that vertical and downward-facing portions of the colony showed gradually lower maximal ETRs, steeper initial slopes of the P-I curves and, accordingly, lower light saturation points than upward-facing areas receiving higher light levels. Based on these trials, some evaluations are given as to the applicability of the Diving-PAM for photosynthetic measurements when monitoring similar corals. 相似文献
3.
Short-term effects of temperature and irradiance on oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat were investigated with O2 microsensors in a laboratory. The effect of temperature on O2 fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons
m−2 s−1) in the temperature range from 15 to 45 °C. Areal rates of dark O2 consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol−1 and the corresponding Q
10 value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O2 consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of
net photosynthesis increased with temperature up to 40 °C and exhibited a Q
10 value (20 to 30 °C) of 2.8. Both O2 dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced
increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q
10 of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m−2 s−1) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated
with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E
k = 148 to 185 μmol photons m−2 s−1) estimated from P versus E
d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis
was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m−2 s−1, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation
irradiance increased with temperature, from 32 μmol photons m−2 s−1 at 25 °C to 77 μmol photons m−2 s−1 at 40 °C, due to increased rates of O2 consumption relative to gross photosynthesis. Areal rates of O2 consumption in the illuminated mat were higher than dark O2 consumption at corresponding temperatures, due to an increasing O2 consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O2 cycling within hypersaline cyanobacterial mats.
Received: 30 November 1999 / Accepted: 11 April 2000 相似文献
4.
In situ measurements of seagrass photosynthesis in relation to inorganic carbon (Ci) availability, increased pH and an inhibitor
of extracellular carbonic anhydrase were made using an underwater pulse amplitude modulated (PAM) fluorometer. By combining
the instrument with a specially designed Perspex chamber, we were able to alter the water surrounding a leaf without removing
it from the growing plant. Responses to Ci within the chamber showed that subtidal plants of the seagrasses Cymodocea serrulata and Halophila ovalis had photosynthetic rates that were limited by the ambient Ci concentration depending on the irradiance that was available
during short-term photosynthesis–irradiance trials. Relative electron transport rates (RETRs) at light saturation (up to 500 μ
mol photons m−2 s−1) increased by 66–100% when the Ci concentration was increased from ca. 2.2 to 6.2 mM. On the other hand, intertidal plants
of the same species exhibited a much lesser limitation of photosynthesis by Ci at any irradiance (up to 1500 μ mol photons
m−2 s−1). Both species were able to use HCO−
3 efficiently, and there was stronger evidence for direct uptake of HCO−
3 rather than extracellular dehydration of HCO−
3 to CO2 prior to Ci uptake. Subtidally, H. ovalis and C. serrulata grew to 10 and 12 m, respectively, where ambient irradiances were approximately 16 and 11% of those at the surface. Maximum
RETRs (at light saturation) were lower for these deep-growing plants than for the intertidally growing ones. For both species,
the onset of light saturation of photosynthesis (E
k) occurred at approximately 100 μ mol photons m−2 s−1 for the deep water populations, which was four and two times lower than for the shallow populations of C. serrulata and H. ovalis, respectively. This, and the differences in maximal photosynthetic rates (RETR
max), reflects an acclimation of the deep-growing populations to the lower light environment. The results presented here show
that photosynthesis, as measured in situ, was limited by the availability of Ci for the deeper growing plants in Zanzibar,
while the intertidally growing plants photosynthesised at close to Ci saturation. The latter result is contrary to previous
conclusions regarding Ci limitations for these intertidal plants, and, in general, our findings highlight the need for performing
similar experiments in situ rather than under laboratory conditions.
Received: 4 April 2000 / Accepted: 31 August 2000 相似文献
5.
In the Red Sea, the zooxanthellate sponge Cliona vastifica (Hancock) is mainly present at >15 m depth or in shaded areas. To test whether its scarcity in unshaded areas of shallower
waters is linked to the functional inefficiency of its photosymbionts at high irradiances, sponges were transferred from 30 m
to a six times higher light regime at 12 m depth, and then returned to their original location. During this time, photosynthetic
responses to irradiance were measured as rapid light curves (RLCs) in situ by pulse amplitude modulated (PAM) fluorometry
using a portable underwater device, and samples were taken for microscopic determinations of zooxanthellar abundance. The
zooxanthellae harboured by this sponge adapted to the higher irradiance at 12 m by increasing both their light saturation
points and relative photosynthetic electron transport rates (ETRs). The ETRs at light saturation increased almost fourfold
within 15–20 days of transfer to the shallower water, and decreased back to almost their original values after the sponges
were returned to 30 m depth. This, as well as the fact that the photosynthetic light responses within an individual sponge
were in accordance with the irradiance incident to specific surfaces, shows that these photosymbionts are highly adaptable
to various irradiances. There was no significant change in the number of zooxanthellae per sponge area throughout these experiments,
and the different photosynthetic responses were likely due to adaptations of the photosynthetic apparatus within each zooxanthella.
In conclusion, it seems that parameters other than the hypothesised inability of the photosymbionts to adapt adequately to
high light conditions are the cause of C. vastifica's rareness in unshaded shallow areas of the Red Sea.
Received: 25 April 2000 / Accepted: 13 October 2000 相似文献
6.
In situ seagrass photosynthesis measured using a submersible, pulse-amplitude modulated fluorometer 总被引:8,自引:0,他引:8
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 相似文献
7.
The effect of irradiance, prey concentration and pH on the growth and grazing responses of the mixotrophic prymnesiophyte
Chrysochromulina ericina under N-and P-replete conditions was studied using the pedinophyte Marsupiomonas pelliculata as prey. The two organisms were inoculated in monocultures and in mixed cultures at different predator: prey ratios at three
irradiances and allowed to grow for 4–7 days. All cultures were non-axenic. Algal densities and pH were monitored throughout
the experiments and growth and grazing rates were measured. An increase in growth of C. ericina cultures at irradiances of 25 and 70 μmol photons m−2 s−1 was observed after the addition of prey, while growth of C. ericina cultures at the high irradiance (150 μmol photons m−2 s−1) was unaffected by the addition of prey. However, although the growth of C. ericina increased at low irradiance (25 μmol photons m−2 s−1), it did not reach the same level as monocultures at the high irradiance (150 μmol photons m−2 s−1), suggesting that phagotrophy can only partly replace photosynthesis in C. ericina. Maximum growth rates of C. ericina at irradiances of 25 and 70 μmol photons m−2 s−1 were obtained at concentrations of > 0.15–0.3×105
M. pelliculata ml−1, corresponding to 50–100 μg C 1−1. Ingestion of M. pelliculata cells by C. ericina did not generally follow Michaelis—Menten kinetics. Deviation from the expected saturation kinetics was especially pronounced
at irradiances of 70 and 150 μmol photons m−2 s−1. At these irradiances ingestion of M. pelliculata cells by C. ericina decreased at high concentrations of M. pelliculata, indicating an increased uptake of bacterial prey in these cultures. The growth rate of C. ericina was affected in both monocultures and in mixed cultures when pH increased above 8.6, and growth stopped around pH 9. The
prey alga M. pelliculata tolerated high pH better and, consequently, took over in the mixed cultures when pH exceeded 9. The ecological significance
of mixotrophy in the genus Chrysochromulina is discussed.
Published online: 4 July 2002 相似文献
8.
A method was developed for measurement of active oxygen production in embryonic stages of the brown seaweed Fucus spiralis, using the label CM-DCFH-DA. Active oxygen species convert the label into the green fluorescent CM-DCF (exc/em 488/530 nm)
that is detected via confocal laserscan microscopy and quantitative image analysis. Loading of the label did not harm the
embryos; loading efficiency was age-independent, and the esterases needed for conversion to CM-DCFH were not inhibited by
the effective UV dose (2 W m−2) applied in the experiments. After correction for daily variation of the laser power, and calibration with DCF standard solutions,
this automated analysis of confocal images rendered active oxygen concentrations in fucoid embryos (μM DCF). An experiment
was designed for the assessment of active oxygen production following irradiance stress in the light-sensitive embryos. Dim-light-acclimated,
1-, 2- and 4-day-old embryos were transferred for 60 min to defined high-light conditions (4π-irradiance 300 μmol photons
m−2 s−1), optionally without UV radiation, including UVA, or including UVA plus UVB. PSII yield measurements (PAM fluorometer) were
carried out in order to assess the degree of photoinhibition under these light conditions. The imposed light stress initially
caused a rapid decrease of the PSII yields (ΦP). With increasing embryo age, minimum ΦP values attained under light stress remained higher. Consequently, electron transport rates (ETR) would increase with embryo
age, i.e., with the development of their photosynthetic apparatus. Active oxygen production increased with ETR, and when UVB
was included, relatively greater amounts of active oxygen were produced. A slow, second-phase decrease of ΦP under light stress that was proportional to active oxygen production indicated that some photooxidative damage was caused,
in particular during UVB exposure. Recovery from light stress was a rapid process in the absence of UVB; in such cases ΦP was almost restored to the initial values within 60 min. The relative state of recovery of ΦP was correlated with both the effective UV dose and active oxygen production rate (DCF). Recovery was slowest in embryos exposed
for 60 min to an experimental UVB dose, which was representative of a situation at low tide, on a sunny day. The results suggest
that active oxygen may cause an in situ inhibition of growth of the earliest life stages of F. spiralis.
Received: 26 January 2000 / Accepted: 4 September 2000 相似文献
9.
The physico-chemical microenvironment of larger benthic foraminifera was studied with microsensors for O2, CO2, pH, Ca2+ and scalar irradiance. Under saturating light conditions, the photosynthetic activity of the endosymbiotic algae increased
the O2 up to 183% air saturation and a pH of up to 8.6 was measured at the foraminiferal shell surface. The photosynthetic CO2 fixation decreased the CO2 at the shell down to 4.7 μM. In the dark, the respiration of host and symbionts decreased the O2 level to 91% air saturation and the CO2 concentration reached up to 12 μM. pH was lowered relative to the ambient seawater pH of 8.2. The endosymbionts responded immediately to changing light conditions,
resulting in dynamic changes of O2, CO2 and pH at the foraminiferal shell surface during experimentally imposed light–dark cycles. The dynamic concentration changes
demonstrated for the first time a fast exchange of metabolic gases through the perforate, hyaline shell of Amphistegina lobifera. A diffusive boundary layer (DBL) limited the solute exchange between the foraminifera and the surrounding water. The DBL
reached a thickness of 400–700 μm in stagnant water and was reduced to 100–300 μm under flow conditions. Gross photosynthesis
rates were significantly higher under flow conditions (4.7 nmol O2 cm−3 s−1) than in stagnant water (1.6 nmol O2 cm −3 s−1), whereas net photosynthesis rates were unaffected by flow conditions. The Ca2+ microprofiles demonstrated a spatial variation in sites of calcium uptake over the foraminiferal shells. Ca2+ gradients at the shell surface showed total Ca2+ uptake rates of 0.6 to 4.2 nmol cm−2 h−1 in A. lobifera and 1.7 to 3.6 nmol cm−2 h−1 in Marginopora vertebralis. The scattering and reflection of the foraminiferal calcite shell increased the scalar irradiance at the surface up to 205%
of the incident irradiance. Transmittance measurements across the calcite shell suggest that the symbionts are shielded from
higher light levels, receiving approximately 30% of the incident light for photosynthesis.
Received: 6 July 1999 / Accepted: 28 April 2000 相似文献
10.
Besides diatoms Demospongiae are the most important consumers of dissolved silica in the sea. They can play an important
role for the silica budget especially in the shallow water areas of the Baltic Sea. The dependence of the silica uptake rate
on the silica concentration of the seawater was measured for the sponge Halichondria panicea (Pallas, 1766). The sponges were collected in Kiel Bight. The uptake conformed to Michaelis–Menten kinetics with a half-saturation
constant of 46.41 μM and a saturated uptake rate of 19.33 μmol h−1 g−1 ( p < 0.01). In the red algae zone of Kiel Bight the sponges depend on silica supply from the surrounding waters and may be silica-limited
rather than food-limited in growth. Because of the much faster uptake of silica by diatoms and their lower saturation point,
as well as the difference in spatial distribution of the two main silica consumers, a competition for silica between sponges
and diatoms seems unlikely.
Received: 21 June 1997 / Accepted: 15 July 1997 相似文献
11.
We used microscopy, reflectance spectroscopy, pigment analysis, and photosynthesis-irradiance curves measured with variable
fluorescence techniques to characterise the endolithic communities of phototrophic microorganisms in the skeleton of three
massive corals from a shallow reef flat. Microscopic observations and reflectance spectra showed the presence of up to four
distinct bands of photosynthetic microorganisms at different depths within the coral skeleton. Endolithic communities closer
to the coral surface exhibited higher photosynthetic electron transport rates and a green zone dominated by Ostreobium quekettii nearest the surface had the greatest chlorophyll pigment concentration. However, Ostreobium was also present and photosynthetically active in the colourless band between the coral tissue and the green band. The spectral
properties and pigment density of the endolithic bands were also found to closely correlate to photosynthetic rates as assessed
by fluorometry. All endolithic communities were extremely shade-adapted, and photosynthesis was saturated at irradiances <7 μmol
photons m−2s−1. 相似文献
12.
A survey of the distribution and maximum depth of a continuous Fucus vesiculosus belt was carried out in the Gulf of Finland in 1991. F. vesiculosus is widely distributed throughout the Gulf of Finland, including the vicinity of Vyborg Bay, Russia in the east. The maximum
growth depth of F. vesiculosus in the Gulf of Finland reflects two different patterns according to the exposure to wave action. The most robust and continuous
F. vesiculosus belt is observed on exposed shores, where the maximum growth depth is 5 to 6 m, with the optimum at 2 to 3 m. On moderately
exposed shores the maximum growth depth is 3 m, with an optimum growth depth of <2 m. The maximum growth depth also varies
geographically, with a decreasing trend towards the east. Maximum growth depth of F. vesiculosus correlates with light intensity. The compensation point for F. vesiculosus photosynthesis is about 25 μmol m−2 s−1, and photosynthesis is saturated at a light intensity of 300 μmol m−2 s−1. Vertical irradiance attenuation measurements in situ in summer revealed that for F. vesiculosus photosynthesis the quantity of light is optimal (200 to 300 μmol m−2 s−1) at <3 m depth. At depths >5 m the quantity of light is near or below the photosynthesis compensation point and insufficient
for growth. These depth limits of light penetration coincide with measured growth depths of F. vesiculosus in the Gulf of Finland.
Received: 7 May 1999 / Accepted: 18 November 1999 相似文献
13.
We investigated heterogeneity of light acclimation of photosynthesis in sun- and shade-adapted coenosarc and polyp tissues of Pocillopora damicornis. The zooxanthellar community within P. damicornis colonies at Heron Island is genetically uniform, yet they showed a large degree of plasticity in their photo-physiological acclimation linked to light microclimates characterised by fibre-optic microprobes. Microscale scalar irradiance measurements showed higher absorption in polyp than coenosarc tissues and higher absorption in the more densely pigmented shade-adapted polyps than in sun-adapted polyps. The combination of an O2 microelectrode with a fibre-optic microprobe (combined sensor diameter 50–100 μm) enabled parallel measurements of O2 concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface under steady-state conditions as a function of increasing irradiances. Lower O2 levels at the tissue surface and higher compensation irradiance indicated a higher respiration activity in sun-adapted polyp tissue as compared to shade-adapted polyps. Shade-adapted coenosarc and polyp tissues exhibited lower maxima of relative electron transport rates (rETRmax) (84±15 and 41±10, respectively) than sun-adapted coenosarc and polyp tissues (136±14 and 77±13, respectively). Shade-adapted tissues showed stronger decrease of rETR at high scalar irradiances as compared to sun-adapted tissues. The relationship between the relative PSII electron transport and the rate of gross photosynthesis, as well as O2 concentration, was non-linear in sun-adapted tissues over the entire irradiance range, whereas for shade-adapted tissues the relationship became non-linear at medium to high scalar irradiances >200 μmol photons m−2 s−1. This suggests that rETR measurements should be used with caution in corals as a proxy for photosynthesis rates. The apparently high rates of photosynthesis (oxygen evolution rates) suggest that there must be a considerable electron transport rate through the photosystems that is not observed by the rETR measurements. This may be accounted for by vertical heterogeneity of zooxanthellae in the tissue and the operation of an alternative electron pathway such as cyclic electron flow around PSII. 相似文献
14.
Changes in male guppy courting distance in response to a fluctuating light environment 总被引:1,自引:0,他引:1
In the guppy (Poecilia reticulata), effective courting by a male requires visual contact with the female. Therefore, environmental light intensity may affect
male display behavior, particularly initial courtship distance. We found that male guppies courted at exact and predictable
distances from the female given a particular light level, both in field and laboratory studies. In lower light levels (<0.1 μmol m−2 s−1), for example at dawn, dusk, or under heavy canopy, males court females at closer and less variable distances (<3 cm). At
higher light levels, which occur during most of the day and with less canopy cover, males often court from twice or three
times further out. Light levels over guppy streams change over relatively short time periods and ranges, correlating with
variation in courtship distances. Laboratory manipulations of irradiance confirmed that courtship distance depends on illumination.
Hence, courtship distances may be set by the effect of lighting on signal efficiency, minimization of energy or time expenditures,
or predation risk.
Received: 16 December 1997 / Accepted after revision: 8 August 1998 相似文献
15.
Miriam Schutter Sander Kranenbarg René H. Wijffels Johan Verreth Ronald Osinga 《Marine Biology》2011,158(4):769-777
In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing
irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis.
Four series of nine nubbins of G. fascicularis were grown at either high (600 μE m−2 s−1) or intermediate (300 μE m−2 s−1) irradiance in combination with either high (15–25 cm s−1) or low (5–10 cm s−1) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific
experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was
determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and
water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating
that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth
with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective
mechanisms at low flow regimes could explain the differences in growth with flow. 相似文献
16.
Corals harbouring genetically mixed communities of endosymbiotic algae (Symbiodinium) often show distribution patterns in accordance with differences in light climate across an individual colony. However, the
physiology of these genetically characterised communities is not well understood. Single stranded conformation polymorphism
(SSCP) and real time quantitative polymerase chain reaction (qPCR) analyses were used to examine the genetic diversity of
the Symbiodinium community in hospite across an individual colony of Acropora valida at the spatial scale of single polyps. The physiological characteristics of the polyps were examined prior to sampling with
a combined O2 microelectrode with a fibre-optic microprobe (combined sensor diameter 50–100 μm) enabling simultaneous measurements of O2 concentration, gross photosynthesis rate and photosystem II (PSII) quantum yield at the coral surface as a function of increasing
irradiances. Both sun- and shade-adapted polyps were found to harbour either Symbiodinium clade C types alone or clades A and C simultaneously. Polyps were grouped in two categories according to (1) their orientation
towardps light, or (2) their symbiont community composition. Physiological differences were not detected between sun- and
shade-adapted polyps, but O2 concentration at 1,100 μmol photons m−2 s−1 was higher in polyps that harboured both clades A and C symbionts than in polyps that harboured clade C only. These results
suggest that the acclimatisation of zooxanthellae of individual polyps of an A. valida colony to ambient light levels may not be the only determinant of the photosynthetic capacity of zooxanthellae. Here, we
found that photosynthetic capacity is also likely to have a strong genetic basis and differs between genetically distinct
Symbiodinium types. 相似文献
17.
To determine how fertilisation varied with sperm concentration for two species of scallop, Chlamys (Equichlamys) bifrons (Lamarck) and C. asperrima (Lamarck), we performed a simple series of sperm dilution experiments, and measured egg size and sperm swimming speeds. C. bifrons eggs were much larger (average diam=116.5 μm), and sperm swimming speeds faster (209.8 μm s−1), than C. asperrima (71.2 μm, 166.0 μm s−1). In both species, maximum fertilisation occurred at an ambient sperm concentration of around 100 sperm μl−1; the maximum proportion of eggs fertilised was less than 0.70 in the C. bifrons experiments, but nearer 1.0 with C. asperrima. At high sperm concentrations (>100 sperm μl−1), fertilisation decreased (presumably due to polyspermy) with increasing sperm concentration, but decreased more rapidly
in C. bifrons than C. asperrima. A polyspermy-adjusted fertilisation kinetics model could be fitted to the experimental data, but unique parameter estimates
could not be determined.
Received: 7 October 1999 / Accepted: 8 July 2000 相似文献
18.
Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations
remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and
12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue
weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium
(N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 108 cell clam−1, N = 6.6 · 108 cell clam−1, P = 5.7 · 108 cell clam−1, N + P = 5.7 · 108 cell clam−1; and C = 4.1 · 108 cell clam−1, N = 5.1 · 108 cell clam−1, P = 4.7 · 108 cell clam−1, N + P = 4.5 · 108 cell clam−1, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index
of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam−1, N = 13.1 mg chl a clam−1, P = 12.9 mg chl a clam−1, N + P = 11.8 mg chl a clam−1; and C = 8.8 mg chl a clam−1, N = 12.8 mg chl a clam−1; P = 11.2 mg chl a clam−1, N + P = 11.3 mg chl a clam−1, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment
was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association.
Received: 2 June 1997 / Accepted: 9 June 1997 相似文献
19.
The photosynthetic adaptive features of non-dormant seeds in Posidonia oceanica were studied in order to evaluate the effects of light on germination success. Transmission electron micrographs showed the
presence of chloroplasts in the epidermal cells, close to the nucleus at the periphery of the cytoplasm. The well-developed
thylakoid membranes and the presence of starch granules indicated that the chloroplasts were photosynthetically active. The
relationship between photosynthesis versus irradiance in P. oceanica seeds incubated at 15 and 21°C was analysed. The net photosynthesis in the non-dormant seed of P. oceanica was positive and compensated its respiration demand (90 μmol quanta m−2 s−1) at both temperatures. Net photosynthesis was negative at the other irradiance values. To test the effects of light on germination
success, seeds were placed both in dark and light conditions. Germination success was significantly higher in light rather
than in dark condition. The characteristics observed in the photosynthesis in P. oceanica seed could be a mechanism to guarantee seedling survival in temperate waters, demonstrating though the specialized nature
of this species. 相似文献
20.
The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile
shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg−1, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and
epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC50s ranged from 32.9 μg l−1 (Zoeae 2) to 10.7 μg l−1 (Mysis 3), and from 3.9 μg l−1 (Zoeae 3) to 2.0 μg l−1 (Mysis 3), respectively; 48 and 96 h LC50s in postlarvae (PL) at the same salinity ranged from 1.8 μg l−1 (PL1) to 0.6 μg l−1 (PL5), and from 0.3 μg l−1 (PL7) to 0.4 μg l−1 (PL15). In juveniles, 96 h LC50s were 0.8 μg l−1 in seawater and 1.5 μg l−1 in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed
by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept
in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph
osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time-
and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC50. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC
in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to
the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations
of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal
and sublethal concentrations of fenitrothion.
Received: 7 October 1996 / Accepted: 13 November 1996 相似文献