Bibby, TS, Nield, J, Chen, M, Larkum, AWD & Barber, J 2003, 'Structure of a photosystem II supercomplex isolated from Prochloron didemni retaining its chlorophyll a/b light-harvesting system', Proceedings of the National Academy of Sciences, vol. 100, no. 15, pp. 9050-9054.
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Prochlorophytes are a class of cyanobacteria that do not use phycobiliproteins as light-harvesting systems, but contain chlorophyll (Chl) a / b -binding Pcb proteins. Recently it was shown that Pcb proteins form an 18-subunit light-harvesting antenna ring around the photosystem I (PSI) trimeric reaction center complex of the prochlorophyte Prochlorococcus marinus SS120. Here we have investigated whether the symbiotic prochlorophyte Prochloron didemni also contains the same supermolecular complex. Using cells isolated directly from its ascidian host, we found no evidence for the presence of the Pcb–PSI supercomplex. Instead we have identified and characterized a supercomplex composed of photosystem II (PSII) and Pcb proteins. We show that 10-Pcb subunits associate with the PSII dimeric reaction center core to form a giant complex having an estimated M r of 1,500 kDa with dimensions of 210 × 290 Å. Five-Pcb subunits flank each long side of the dimer and assuming each binds 13 Chl molecules, increase the antenna size of PSII by ≈200%. Fluorescence emission studies indicate that energy transfer occurs efficiently from the Pcb antenna. Modeling using the x-ray structure of cyanobacterial PSII suggests that energy transfer to the PSII reaction center is via the Chls bound to the CP47 and CP43 proteins.
Choinski, JS, Ralph, P & Eamus, D 2003, 'Changes in photosynthesis during leaf expansion in Corymbia gummifera', AUSTRALIAN JOURNAL OF BOTANY, vol. 51, no. 1, pp. 111-118.
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Growth, pigment levels and various photosynthesis parameters were measured in expanding leaves of Corymbia gummifera (Solander ex Gaertner) Hochreutiner. C. gummifera trees were studied growing in sandstone plateau woodland communities in Royal National Park, New South Wales, in a recently burned open habitat. Young leaves (horizontally oriented to maximise light exposure) were found to be conspicuously red until they reached approximately 75% of their full size. As the leaves expanded, anthocyanin content declined and chlorophyll levels proportionately increased. Young red leaves showed net negative carbon assimilation rates, although CO2 assimilation rate, transpiration rate, stomatal conductance, actual quantum yield of PSII (ΦPSII) and apparent electron transport rate (ETR) all increased in a similar pattern as the leaves expanded. Measurements of maximum quantum yield of dark-adapted leaves (Fv/Fm) were also correlated with leaf area. Younger leaves had lower Fv/Fm ratios than did mature leaves, whether measured at midday or 2 h after sunset, indicating that young leaves exhibited some degree of chronic photoinhibition. It is concluded that C. gummifera exhibits a transient red pattern of anthocyanin expression and that photosynthesis is limited in young leaves because of low stomatal conductance, low chlorophyll content, immature chloroplasts and an attenuation of light caused by anthocyanins.
Davey, MS, Suggett, DJ, Geider, RJ & Taylor, AR 2003, 'PHYTOPLANKTON PLASMA MEMBRANE REDOX ACTIVITY: EFFECT OF IRON LIMITATION AND INTERACTION WITH PHOTOSYNTHESIS1', Journal of Phycology, vol. 39, no. 6, pp. 1132-1144.
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Phytoplankton plasma membrane electron transport activity was determined by monitoring the reduction of the impermeant artificial electron acceptor ferricyanide in a range of diatoms. The results revealed that constitutive plasma membrane electron transport activity of marine diatoms is high compared with chlorophytes and higher plant cells. Diatom plasma membrane electron transport activity was not significantly increased by iron limitation. This lack of induction on iron limitation indicates that diatoms have an iron acquisition strategy that is distinct from chlorophytes and the dicotyledon higher plants that exhibit marked increases in plasma membrane ferricyanide reductase activity on iron limitation. The interaction of the constitutive plasma membrane electron transport with photosynthesis was also investigated. We found that 1) ferricyanide reduction at the plasma membrane was progressively inhibited in response to increasing irradiances; 2) the presence of extracellular ferricyanide, but not the reduced couple ferrocyanide, caused a marked inhibition of carbon fixation at high irradiance; and 3) extracellular electron acceptors ferricyanide and hexachloroiridate (but not ferrocyanide) induced an immediate and reversible decrease in fluorescence yields (Fo and Fm). The extent to which extracellular electron acceptors affected CO2 fixation, Fo, and Fm was related to the level of constitutive ferricyanide reductase activity, the species with highest ferricyanide reduction rates being most sensitive. The data suggest that consumption of electrons and/or reductant at the plasma membrane by external acceptors may compete directly with CO2 fixation for electrons, alter cytosolic‐chloroplast redox poise, and/or induce a redox‐signaling cascade that alters photosynthetic metabolism.
Gilmore, AM, Larkum, AWD, Salih, A, Itoh, S, Shibata, Y, Bena, C, Yamasaki, H, Papina, M & Van Woesik, R 2003, 'Simultaneous Time Resolution of the Emission Spectra of Fluorescent Proteins and Zooxanthellar Chlorophyll in Reef-building Corals ¶†', Photochemistry and Photobiology, vol. 77, no. 5, pp. 515-523.
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Light is absorbed by photosynthetic algal symbionts (i.e. zooxanthellae) and by chromophoric fluorescent proteins (FP) in reef-building coral tissue. We used a streak-camera spectrograph equipped with a pulsed, blue laser diode (50 ps, 405 nm) to simultaneously resolve the fluorescence spectra and kinetics for both the FP and the zooxanthellae. Shallow water (<9 m)-dwelling Acropora spp. and Plesiastrea versipora specimens were collected from Okinawa, Japan, and Sydney, Australia, respectively. The main FP emitted light in the blue, blue-green and green emission regions with each species exhibiting distinct color morphs and spectra. All corals showed rapidly decaying species and reciprocal rises in greener emission components indicating Förster resonance energy transfer (FRET) between FP populations. The energy transfer modes were around 250 ps, and the main decay modes of the acceptor FP were typically 1900-2800 ps. All zooxanthellae emitted similar spectra and kinetics with peak emission (∼683 nm) mainly from photosystem II (PSII) chlorophyll (chl) a. Compared with the FP, the PSII emission exhibited similar rise times but much faster decay times, typically around 640-760 ps. The fluorescence kinetics and excitation versus emission mapping indicated that the FP emission played only a minor role, if any, in chl excitation. We thus suggest the FP could only indirectly act to absorb, screen and scatter light to protect PSII and underlying and surrounding animal tissue from excess visible and UV light. We conclude that our time-resolved spectral analysis and simulation revealed new FP emission components that would not be easily resolved at steady state because of their relatively rapid decays due to efficient FRET. We believe the methods show promise for future studies of coral bleaching and for potentially identifying FP species for use as genetic markers and FRET partners, like the related green FP from Aequorea spp.
Helfrich, M, Bommer, B, Oster, U, Klement, H, Mayer, K, Larkum, AWD & Rüdiger, W 2003, 'Chlorophylls of the c family: absolute configuration and inhibition of NADPH:protochlorophyllide oxidoreductase', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 1605, no. 1-3, pp. 97-103.
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Using circular dichroism (CD) spectroscopy, the stereochemistry at C-132 of members of the chlorophyll (Chl) c family, namely Chls c1, c2, c3 and [8-vinyl]-protochlorophyllide a (Pchlide a) was determined. By comparison with spectra of known enantiomers, all Chl c members turned out to have the (R) configuration, which is in agreement with considerations drawn from chlorophyll biosynthesis. Except for a double bond in the side chain at C-17, the chemical structure of Chl c1 is identical with Pchlide a, the natural substrate of the light-dependent NADPH:protochlorophyllide oxidoreductase (POR). Thus, lack of binding to the active site due to the wrong configuration at C-132, which had been proposed previously, cannot be an explanation for inactivity of Chl c in this enzymic reaction. Our results show rather that Chl c1 is a competitive inhibitor for this enzyme, tested with Pchlide a and Zn-protopheophorbide a (Zn-Ppheide a) as substrates. © 2003 Elsevier B.V. All rights reserved.
Hohnberg, D, Ralph, PJ & Jones, H 2003, 'Toxicity of the herbicide atrazine at environmental concentrations to Vallisneria Gigantea, assessed using chlorophyll fluorescence', Australasian Journal of Ecotoxicology, vol. 9, pp. 93-100.
Jermiin, LS, Ho, SYW, Ababneh, F, Robinson, J & Larkum, AWD 2003, 'Hetero: a program to simulate the evolution of DNA on a four-taxon tree.', Appl Bioinformatics, vol. 2, no. 3, pp. 159-163.
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We present a computer program to simulate the evolution of a nucleotide sequence on a phylogenetic tree with four tips. The program, Hetero, allows users to assign lineage-specific differences in the rate matrices used to describe the evolutionary process. It has a simple user interface and output, making it equally useful in the teaching and research of phylogenetics.
Larkum, A, Koch, EW & Kuhl, M 2003, 'Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs', Marine Biology, vol. 142, no. 5, pp. 1073-1082.
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The effects of mass transfer resistance due to the presence of a diffusive boundary layer on the photosynthesis of the epilithic algal community (EAC) of a coral reef were studied. Photosynthesis and respiration of the EAC of dead coral surfaces were investigated for samples from two locations: the Gulf of Aqaba, Eilat (Israel), and One Tree Reef on the Great Barrier Reef (Australia). Microsensors were used to measure O2 and pH at the EAC surface and above. Oxygen profiles in the light and dark indicated a diffusive boundary layer (DBL) thickness of 180590 ?m under moderate flow (~0.08 m s-1) and >2,000 ?m under quasi-stagnant conditions. Under light saturation the oxygen concentration at the EAC surface rose within a few minutes to 200550% air saturation levels under moderate flow and to 600700% under quasi-stagnant conditions. High maximal rates of net photosynthesis of 825 mmol O2 m-2 h-1 were calculated from measured O2 concentration gradients, and dark respiration was 1.33.3 mmol O2 m-2 h-1. From lightdark shifts, the maximal rates of gross photosynthesis at the EAC surface were calculated to be 16.5 nmol O2 cm-3 s-1. Irradiance at the onset of saturation of photosynthesis, Ek, was <100 µmol photons m-2 s-1, indicating that the EAC is a shade-adapted community. The pH increased from 8.2 in the bulk seawater to 8.9 at the EAC surface, suggesting that very little carbon in the form of CO2 occurs at the EAC surface. Thus the major source of dissolved inorganic carbon (DIC) must be in the form of HCO3-. Estimates of DIC fluxes across the DBL indicate that, throughout most of the daytime under in situ conditions, DIC is likely to be a major limiting factor for photosynthesis and therefore also for primary production and growth of the EAC.
Larkum, AWD 2003, 'Contributions of henrik lundegårdh.', Photosynthesis Research, vol. 76, no. 1/3, pp. 105-110.
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Henrik Lundegårdh made major contributions in the field of ecology and plant physiology from 1912 to 1969. His early work at Hallands Väderö in the Kattegat pioneered quantitative approaches to plant ecology and laid the understanding of carbon dioxide exchange in natural communities which is still useful today in global carbon accounting. Very early on in this work he invented the flame photometer. In trying to understand salt respiration of plants, he started to formulate hypotheses for the relationship between respiration and ion movement, including protons, hypotheses that were forerunners to the Chemiosmotic Hypothesis of Peter Mitchell. Necessarily, this involved work on plant cytochromes. He invented several early recording spectrophotometers and made many early discoveries in the field of plant cytochromes, including the photo-oxidation of cytochrome f in photosynthesis.
Larkum, AWD, Koch, EMW & Kuhl, M 2003, 'Diffusive boundary layers and photosynthesis of the epilithic algal community of coral reefs', MARINE BIOLOGY, vol. 142, no. 6, pp. 1073-1082.
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Macinnis-Ng, CMO & Ralph, PJ 2003, 'In situ impact of petrochemicals on the photosynthesis of the seagrass Zostera capricorni', MARINE POLLUTION BULLETIN, vol. 46, no. 11, pp. 1395-1407.
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We used photosynthetic activity (measured as chlorophyll a fluorescence) and photosynthetic pigment concentrations to assess the effect of pulsed exposures of aged crude oil (Champion Crude), dispersant (VDC) and an oil+dispersant mixture on the seagrass Zostera capricorni Aschers in laboratory and field experiments, using custom-made chambers. Samples were exposed for 10 h to 0.25% and 0.1% concentrations of aged crude oil and dispersant as well as mixtures of 0.25% oil+0.05% dispersant and 0.1% oil+0.02% dispersant. During this time and for the subsequent four day recovery period, the maximum and effective quantum yields of photosystem II (Fv/Fm and ΔF/Fm ′ respectively) were measured. In the laboratory experiments, both values declined in response to oil exposure and remained low during the recovery period. Dispersant exposure caused a decline in both values during the recovery period, while the mixture of aged crude oil+dispersant had little impact on both quantum yields. In situ samples were less sensitive than laboratory samples, showing no photosynthetic impact due to dispersant and oil+dispersant mixture. Despite an initial decline in ΔF/Fm ′, in situ oil-exposed samples recovered by the end of the experiment. Chlorophyll pigment analysis showed only limited ongoing impact in both laboratory and field situations. This study suggests that laboratory experiments may overestimate the ongoing impact of petrochemicals on seagrass whilst the dispersant VDC can reduce the impact of oil on seagrass photosynthesis. © 2003 Elsevier Ltd. All rights reserved.
Macinnis-Ng, CMO & Ralph, PJ 2003, 'Short-term response and recovery of Zostera capricorni photosynthesis after herbicide exposure', AQUATIC BOTANY, vol. 76, no. 1, pp. 1-15.
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We used photosynthetic activity (measured as chlorophyll a fluorescence) and photosynthetic pigment concentrations to assess the effect of pulsed exposure to catastrophic levels of the herbicides Atrazine, Diuron and Irgarol 1051 on the seagrass Zostera capricorni Aschers. in laboratory and field experiments. Custom-made in situ chambers were developed so seagrasses could be dosed within the meadow. Zostera capricorni was exposed to 10 and 100 μg l-1 herbicide solutions for 10 h. During this time and for the subsequent 4-day recovery period, chlorophyll a fluorescence parameters (maximum quantum yield: Fv/Fm and effective quantum yield: ΔF′m) were measured. Laboratory samples exposed to these herbicides were severely impacted during the exposure period and most treatments did not recover fully. ΔF/F′m was a more sensitive indicator of herbicide impact than Fv/Fm. In situ samples were also severely impacted by Irgarol and Diuron exposure whereas samples recovered completely after exposure to Atrazine at the same concentrations as the laboratory experiments. Total chlorophyll concentrations showed only limited impact in both laboratory and field situations. This study suggests that laboratory experiments may overestimate the on-going impact of herbicides on seagrass. © 2003 Elsevier Science B.V. All rights reserved.
Mi, D, Chen, M, Lin, S, Lince, M, Larkum, AWD & Blankenship, RE 2003, 'Excitation Dynamics in the Core Antenna in the Photosystem I Reaction Center of the Chlorophyll d-Containing Photosynthetic Prokaryote Acaryochloris marina', The Journal of Physical Chemistry B, vol. 107, no. 6, pp. 1452-1457.
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Transient absorption difference spectroscopy on the picosecond time scale was used to study the ultrafast excitation dynamics in the photosystem I core antenna in Acaryochloris marina, a newly discovered marine oxygenic photosynthetic prokaryote that contains chlorophyll d as its major photopigment. Photosystem I particles were isolated using a detergent treatment of the thylakoid membranes and sucrose gradient ultracentrifugation. Steady-state fluorescence measurements at both room temperature and 77 K as well as ultrafast transient absorbance and fluorescence measurements were carried out on photosystem I. For ultrafast transient absorbance measurements, the sample was excited at 720, 740, and 75 nm with either high or low excitation energy. In each case, after a rapid (subpicosecond) energy transfer, the excitation energy resided on pigments absorbing at 710 nm. A kinetic component of about 40 ps and a nondecaying component on the order of nanoseconds were resolved. The 40-ps component was assigned to the trapping of excitation energy into the reaction center. The trapping time was confirmed by time-resolved fluorescence measurements. The 40-ps trapping time, because of the formation of a charge-separated state in the reaction center, is nearly excitation wavelength-independent. Narrow spectral-band excitations (5-nm fwhm) at 690, 720, 730, and 740 nm were used to excite different pools of the photosystem I core antenna selectivity. The initial special changes show a strong excitation wavelength dependence. An exceptionally broad, prompt bleaching, spanning from 700 to 740 nm, was induced when excitation was directly into the primary electron donor, P740, suggesting the existence of an excitonic coupling between a group of pigments, most likely the reaction center cofactors. A 2-3-ps energy equilibration process was also observed, similar to that observed in other cyanobacterial photosystem I. No evidence was found for a pool of long-wavelength antenna pigment...
Moore, CM, Suggett, D, Holligan, PM, Sharples, J, Abraham, ER, Lucas, MI, Rippeth, TP, Fisher, NR, Simpson, JH & Hydes, DJ 2003, 'Physical controls on phytoplankton physiology and production at a shelf sea front: a fast repetition-rate fluorometer based field study', Marine Ecology Progress Series, vol. 259, pp. 29-45.
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Observations of phytoplankton physiology collected using a fast repetition-rate fluorometer (FRRF) in the vicinity of a shelf-sea tidal-mixing front are presented. These data are combined with more traditional 14C-based measurements and observations of environmental parameters, including estimates of turbulent dissipation rates, in order to investigate the influence of physical forcing on the productivity of the system. Low nutrient concentrations on the stratified side of the front result in a reduction of photosynthetic efficiency. Conversely, the high degree of vertical mixing on the mixed side of the front constrains the ability of phytoplankton to adjust their photosynthetic apparatus to the ambient irradiance field. Redistribution of phytoplankton biomass and variations in physiological parameters also result from the spring-neap tidal cycle. FRRF- and 14C-derived physiological measurements are compared in the context of environmental gradients in the region. A strong correlation was found between independently measured functional absorption cross-sections (sPSII) and maximal photosynthetic rates (P*max). Such a relationship was unlikely to have been causative and may have resulted from shifts in the balance between light-harvesting and carbon fixation across the front. The association of changes in P*max with variations in sPSII provided the basis for the development of an empirical model, specific to the system and time of study, which utilised FRRF data to extrapolate between primary productivity rates measured at fixed sites. When applied to high resolution cross-frontal data, the model suggested small-scale variations in productivity related to both spatial and temporal physical forcing including the spring-neap cycle.
Nieuwenburg, P, Clarke, RJ, Cai, ZL, Chen, M, Larkum, AWD, Cabral, NM, Ghiggino, KP & Reimers, JR 2003, 'Examination of the photophysical processes of chlorophyll d leading to a clarification of proposed uphill energy transfer processes in cells of Acaryochloris marina', PHOTOCHEMISTRY AND PHOTOBIOLOGY, vol. 77, no. 6, pp. 628-637.
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Purkerson, DG, Doblin, MA, Bollens, SM, Luoma, SN & Cutter, GA 2003, 'Selenium in San Francisco Bay zooplankton: Potential effects of hydrodynamics and food web interactions', ESTUARIES, vol. 26, no. 4A, pp. 956-969.
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The potential toxicity of elevated selenium (Se) concentrations in aquatic ecosystems has stimulated efforts to measure Se concentrations in benthos, nekton, and waterfowl in San Francisco Bay (SF Bay). In September 1998, we initiated a 14 mo field study to determine the concentration of Se in SF Bay zooplankton, which play a major role in the Bay food web, but which have not previously been studied with respect to Se. Monthly vertical plankton tows were collected at several stations throughout SF Bay, and zooplankton were separated into two operationally defined size classes for Se analyses: 73-2,000 μm, and ≥2,000 μm. Selenium values ranged 1.02-6.07 μg Se g-1 dry weight. No spatial differences in zooplankton Se concentrations were found. However, there were inter- and intra-annual differences. Zooplankton Se concentrations were enriched in the North Bay in Fall 1999 when compared to other seasons and locations within and outside SF Bay. The abundance and biovolume of the zooplankton community varied spatially between stations, but not seasonally within each station. Smaller herbivorous-omnivorous zooplankton had higher Se concentrations than larger omnivorous-carnivorous zooplankton. Selenium concentrations in zooplankton were negatively correlated with the proportion of total copepod biovolume comprising the large carnivorous copepod Tortanus dextrilobatus, but positively correlated with the proportion of copepod biovolume comprising smaller copepods of the family Oithonidae, suggesting an important role of trophic level and size in regulating zooplankton Se concentrations.
Runcie, JW, Ritchie, RJ & Larkum, AWD 2003, 'Uptake kinetics and assimilation of inorganic nitrogen by Catenella nipae and Ulva lactuca', Aquatic Botany, vol. 76, no. 2, pp. 155-174.
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The kinetics of NH4+, the assimilation of NH4+ and nitrate uptake by Catenella nipae (Rhodophyta) were compared with Ulva lactuca (Chlorophyta). Both algal species demonstrated saturable NH4+ and nitrate uptake kinetics. Uptake of NH3 by simple diffusion across the plasmalemma could not account for the observed saturation uptake kinetics of ammonia-N (NH3 + NH4+), so NH4+ was the chemical form being taken up by the transport systems of the cells. Although the Vmax of NH4+ uptake by C. nipae and U. lactuca was high (≈550 and 450 μmol g-1 DW h-1, respectively), the Km for U. lactuca (≈85 μM) was much lower than that for C. nipae (≈692 μM). The Km and Vmax values for nitrate uptake were much lower than for NH4+ for both C. nipae (Km ≈ 5 μM; Vmax ≈ 8.3 μmol g-1 DW h-1) and U. lactuca (Km ≈ 34 μM; Vmax ≈ 116 -mol g-1 DW h-1). Over the incubation times used (up to 28 min) there was no apparent induction of nitrate transport in either species. There was no evidence for induction of NH4+ transport in C. nipae but incubation time did affect the kinetics of NH4+ uptake in U. lactuca. At high concentrations of NH4+, U. lactuca rapidly assimilated it into organic N with limited build-up of intracellular NH4+ whereas C. nipae accumulated large amounts of NH4+ because uptake of NH4+ overtook the rate of assimilation. The effects of species-specific differences and experimental design on uptake-kinetic estimates are discussed in the light of the results of this other comparable studies. C. nipae is promising as a bioindicator species of the N-status of estuaries but U. lactuca changes its N-status too quickly for it to be a useful bioindicator of environmental conditions. © 2003 Elsevier Science B.V. All rights reserved.
Suggett, DJ, Oxborough, K, Baker, NR, MacIntyre, HL, Kana, TM & Geider, RJ 2003, 'Fast repetition rate and pulse amplitude modulation chlorophyllafluorescence measurements for assessment of photosynthetic electron transport in marine phytoplankton', European Journal of Phycology, vol. 38, no. 4, pp. 371-384.
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Pulse amplitude modulation (PAM) and fast repetition rate (FRR) fluorescence are currently used to estimate photosynthetic quantum yields and photosynthetic rates in aquatic systems. Here we compare simultaneous measurements of the photochemical efficien
Waters, RL, Mitchell, JG & Seymour, J 2003, 'Geostatistical characterisation of centimetre-scale spatial structure of in vivo fluorescence', Marine Ecology Progress Series, vol. 251, pp. 49-58.
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