Chl-a Fluorescence Research Articles

Combined dynamics of the 500–600 nm leaf absorption and chlorophyll fluorescence changes in vivo: Evidence for the multifunctional energy quenching role of xanthophylls

Carotenoids (Cars) regulate the energy flow towards the reaction centres in a versatile way whereby the switch between energy harvesting and dissipation is strongly modulated by the operation of the xanthophyll cycles. However, the cascade of molecular mechanisms during the change from light harvesting to energy dissipation remains spectrally poorly understood. By characterizing the in vivo absorbance changes (ΔA) of leaves from four species in the 500–600 nm range through a Gaussian decomposition, while measuring passively simultaneous Chla fluorescence (F) changes, we present a direct observation of the quick antenna adjustments during a 3-min dark-to-high-light induction. Underlying spectral behaviours of the 500–600 nm ΔA feature can be characterized by a minimum set of three Gaussians distinguishing very quick dynamics during the first minute. Our results show the parallel trend of two Gaussian components and the prompt Chla F quenching. Further, we observe similar quick kinetics between the relative behaviour of these components and the in vivo formations of antheraxanthin (Ant) and zeaxanthin (Zea), in parallel with the dynamic quenching of singlet excited chlorophyll a (1Chla*) states. After these simultaneous quick kinetical behaviours of ΔA and F during the first minute, the 500–600 nm feature continues to increase, indicating a further enhanced absorption driven by the centrally located Gaussian until 3 min after sudden light exposure. Observing these precise underlying kinetic trends of the spectral behaviour in the 500–600 nm region shows the large potential of in vivo leaf spectroscopy to bring new insights on the quick redistribution and relaxation of excitation energy, indicating a key role for both Ant and Zea.

Effects of temperature on the photosynthetic performance in mature thalli of the red alga Gelidium amansii (Gelidiaceae)

Gelidium amansii, a commercial marine red alga, yields agar of excellent quality, but thus far its cultivation has been unsuccessful. Effects of temperature, especially high temperature, on the photosynthetic performance of this alga are poorly understood. The responses of net O2 evolution and pigment content in mature thalli exposed to various temperatures of 14, 18, 22, 26, and 30 °C for 2 days were studied. Fast Chl-a fluorescence kinetics and RuBPCase activity of plants exposed to 30 °C for 6, 12, 24, and 48 h were also determined. The results showed that 14–26 °C favored the net O2 evolution of G. amansii, which ranged from 0.50 to 1.53 μmol O2∙g−1∙min−1. High temperature (30 °C) decreases the contents of Chl-a and carotenoids. Phycobiliproteins increased in the thalli treated for 12 h and longer at 30 °C, suggesting that phycobiliproteins might play an important role in alleviation of oxidative damage caused by high temperature. In addition, the carbon assimilation process, light harvesting pigments, PSII reaction centers, and PSII acceptor side of G. amansii were damaged under 30 °C at 12 h; however, the PSII acceptor side was relatively stable during the initial 24 h treatment. At 30 °C both PSII photochemistry and carbon assimilation were negatively affected and impacted the photosynthetic response of G. amansii. RuBPCase activity showed a stronger positive correlation with photosynthetic oxygen release than the photochemistry. The results of this study confirm that the optimal temperature for G. amansii photosynthesis is between 22 °C to 26 °C and high temperatures of 30 °C and above limit G. amansii growth in near-shore waters.

Impact of “The Blob” and “El Niño” in the SW Baja California Peninsula: Plankton and Environmental Variability of Bahia Magdalena

Bahia Magdalena is a coastal lagoon located in the Pacific coast of Baja California, a transitional zone between tropical and temperate regions. Its biological and fishing richness is enormous. The objective of this work was to determine the impact of the unusual and consecutive warming events knows as The Blob (TB2013-2015) and 2015-2016 El Nino on the hydrological characteristics and plankton communities, the lower levels of the trophic web. The changes we observed strongly suggested that the warming caused by those phenomena did affect the hydrology and phyto and zooplankton communities. This study included analyses of environmental and biological variables measured in situ and with MODIS-Aqua satellite images, from January 2015 to December 2017. In 2015, the air temperature was very high, upwelling strength decreased and temperature, salinity and water density showed the tropical influence. Additionally, the percentage of oxygen saturation and the nutrients and chlorophyll-a (Chl-a) concentrations were low and showed intra-annual variations different to usual. By April 2015, the chain-forming diatom Eucampia zodiacus bloomed, and we did not record an autumn bloom, but Chl-a fluorescence suggested that smaller phytoplankton fractions were predominant in that season. Zooplankton biomass (ZB) was lower since the second semester of 2015 and showed a negative trend until 2017. Relatively low percentages of dead zooplankton (%ZD) were also recorded. In 2016, when El Nino declined, and the ENSO cold phase (La Nina) started, there were an enhancing of upwellings, nutrients, and Chl-a concentrations. Blooms of diatoms occurred in spring and autumn (Guinardia/Rhizosolenia), whereas the ZB remained low, but %ZD was very high. La Nina finished in 2017, and in contrast to previous years, the upwelling's phenology was close to 1967-2010 average, and upwelling strength increased. Therefore, its rich-nutrients waters input caused several diatoms blooms, whereas ZB remained scarce.

Particle fluxes induced by benthic storms during the 2012 dense shelf water cascading and open sea convection period in the northwestern Mediterranean basin

The effects of deep dense shelf water cascading and open sea convection on the sediment dynamics of the northwestern Mediterranean basin were studied by near-bottom moored instruments recording trapped particle fluxes, suspended particle fluxes, water properties and hydrodynamics from November 2011 to July 2012. During this period, near-bottom currents induced by winter dense water formation generated benthic storms that caused resuspension at 2450 m water depth, increasing by more than one order of magnitude the ambient suspended sediment concentrations, the trapped particle fluxes and the suspended sediment fluxes. During the preconditioning phase of the open sea convection, from December 2011 to mid-February 2012, currents (1–10 cm s−1), suspended sediment concentrations (<0.1 mg l−1), Chl-a fluorescence values (<0.063 μg l−1), trapped total mass fluxes (10–50 mg m−2 d−1) and trapped organic carbon fluxes (1–4 mg m−2 d−1) were low, and organic matter was mainly undegraded and of marine origin. Open sea convection was observed at the study site in mid-February, at the beginning of the violent mixing phase, increasing current velocities up to 26 cm s−1 and Chl-a fluorescence values up to 0.074 μg l−1, supplying particles with fresh marine organic matter content. During the last fortnight of February, two major dense shelf water cascading pulses generated Chl-a fluorescence increases (up to 0.116 μg l−1) and large suspended sediment concentration peaks (up to19 mg l−1), suspended sediment fluxes (up to 6500 mg m−2 d−1) and trapped total mass flux increases (up to 22,900 mg m−2 d−1), which were associated with benthic storms resuspension. During this phase, trapped organic carbon flux increased almost two orders of magnitude (up to 260 mg m−2 d−1), with pulses of both marine and terrestrial organic matter. The sinking and spreading phase occurred from early March to mid-June. The signal of deep dense shelf water cascading lasted past early April, and the spreading of the newly formed dense water maintained maximum currents of up to 25 cm s−1 and trapped particle fluxes of up to 2000 mg m−2 d−1 until mid-June. At the beginning of this phase, organic matter was terrestrial and several turbidity peaks occurred during current speed increases generated by benthic storms. At the end of this phase, the organic matter became less terrestrial, trapped organic carbon fluxes decreased from about 190 to 10 mg m−2 d−1 and turbidity peaks occurred with low current velocities indicating the arrival of storm tails at the mooring site. The large particle fluxes of fresh or relatively undegraded organic carbon induced by deep dense water formation during winter 2012, contributed to the “fertilization” of the northwestern Mediterranean deep benthic ecosystems.

Effects of carotenoids on the absorption and fluorescence spectral properties and fluorescence quenching of Chlorophyll a

Fluorescence and absorption characteristics of Chlorophyll a (Chl-a) were modulated by the carotenoids (Cars) with different numbers of conjugated carbon‑carbon double bonds in solutions. The Chl-a absorption appears the redshift phenomenon with the effective conjugated of Cars increasing. The absorption of Chl-a and Cars are linearly dependent on intrinsic factors, namely effective conjugate length and functional groups, and on environmental factors, such as the polarizability of the solvent. Cars can be able to quench the Chl-a fluorescence by producing the non-emitting exciplex intermediate. The effective conjugated length of Cars is one of the reasons that effect the fluorescence quenching of Chl-a. According to the Stern-Volmer plots, the Chl-a fluorescence quenching should be predominantly dynamic rather than static.

The distribution of methylated sulfur compounds, DMS and DMSP, in Canadian subarctic and Arctic marine waters during summer 2015

Abstract. We present seawater concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) measured across a transect from the Labrador Sea to the Canadian Arctic Archipelago during summer 2015. Using an automated ship-board gas chromatography system and a membrane-inlet mass spectrometer, we measured a wide range of DMS (∼ 1 to 18 nM) and DMSP (∼ 1 to 150 nM) concentrations. The highest DMS and DMSP concentrations occurred in a localized region of Baffin Bay, where surface waters were characterized by high chlorophyll a (chl a) fluorescence, indicative of elevated phytoplankton biomass. Across the full sampling transect, there were only weak relationships between DMS(P), chl a fluorescence and other measured variables, including positive relationships between DMSP : chl a ratios and several taxonomic marker pigments, and elevated DMS(P) concentrations in partially ice-covered areas. Our high spatial resolution measurements allowed us to examine DMS variability over small scales (&lt; 1 km), documenting strong DMS concentration gradients across surface hydrographic frontal features. Our new observations fill in an important observational gap in the Arctic Ocean and provide additional information on sea–air DMS fluxes from this ocean region. In addition, this study constitutes a significant contribution to the existing Arctic DMS(P) dataset and provides a baseline for future measurements in the region.

Chlorophyll-a fluorescence evaluation of PEG-induced osmotic stress on PSII activity in Arabidopsis plants expressing SIP1

In this study, we evaluated the effect of osmotic stress on photosynthetic machinery of Arabidopsis plants expressing a gene encoding small basic intrinsic protein (SIP1) isolated from Solanum tuberosum. Intact leaves of SIP Arabidopsis plants were exposed to 15% polyethylene glycol (PEG) solution and fast Chlorophyll-a (Chl-a) fluorescence induction kinetics was measured. Photosynthetic parameters like ratio of variable and maximum fluorescence (FV/FM), absorbance of photons per active reaction center (ABS/RC), trapping of photons per active reaction center (TRo/RC), electron transport per active reaction center (ETo/RC), and performance index (PI) were measured. Furthermore, the energy pipeline model was deduced in response to PEG stress. The membrane model includes a visualization of the average “antenna size”, which follows the value of the ABS/RC. Analysis of SIP Arabidopsis plants under PEG stress through fast Chl-a fluorescence transient showed that the damage caused due to PEG is more prominent at the donor side rather than the acceptor side of PSII. Higher PI in SIP plants under PEG stress indicated a better vitality than control plants. Overall, these results indicate that constitutive expression of SIP1 in Arabidopsis plants induces significant changes in the photosynthetic machinery under PEG-induced osmotic stress.

Selective Inhibition of Rice Straw Extract on Growth of Cyanobacteria and Chlorophyta

Rice straw is supposed to be an environment-friendly biomaterial for inhibiting the growth of harmful blooms of the cyanobacterium Microcystis aeruginosa. The effects of rice straw extract(RSE) on algal growth, morphologic parameters(cell size), and physiological parameters(in vivo Chl-a fluorescence) were investigated using flow cytometry. We examined the selective inhibitory potential of rice straw on four cyanobacterial strains(toxic and non-toxic Microcystis aeruginosa, toxic Anabaena flos-aquae, and Microcystis ichthyoblabe), in comparison with inhibitory effects on three common freshwater green algae(Selenastrum capricornutum, Chlorella pyrenoidosa, and Scenedesmus obliqnus). Concentrations from 2.0 to 10.0 g·L-1 of RSE were found to efficiently inhibit the growth of cyanobacteria in a dose-dependent manner, simultaneously modifying the in vivo Chl-a fluorescence and cell size. The 50% growth-inhibition concentration(7 d) of A. flos-aquae, M. ichthyoblabe, M. aeruginosa(toxic strain), M. aeruginosa(non-toxic strain) was 1.72, 2.21, 2.92 and 5.72 g·L-1, respectively. Interestingly, the growth and cell size of C. pyrenoidosa and S. obliqnus increased with the addition of RSE and colony formation was observed. In the case of S. capricornutum, the inhibitory effect of RSE on growth and in vivo Chl-a fluorescence occurred at 1.0-4.0 g·L-1, while RSE induced a stimulatory effect on algal growth at 8.0-10.0 g·L-1. Taken together, the sensitivity of cyanobacteria to RSE was significantly higher than that of S. capricornutum, C. pyrenoidosa and S. obliqnus. The higher sensitivity of PSⅡ reaction center of cyanobacteria and the ability to form colonies of green algae may have important implications for the species-specific allelopathic antialgal activity of rice straw.

Are fluorescence-based chlorophyll quantification methods suitable for algae toxicity assessment of carbon nanomaterials?

Using a multiwalled carbon nanotube (MWCNT) and graphene oxide (GO) as representative test materials, we evaluated the applicability of in vivo and in vitro chlorophyll-a (Chl-a) fluorescence quantification methods, which are used in standard algae ecotoxicity tests such as OECD 201 and ISO 8692. In vivo quantification of Chl-a from Raphidocelis subcapitata indicated a significant reduction in Chl-a fluorescence in the presence of MWCNTs due to shading, but a significant autofluorescence from GO caused an overestimation of Chl-a concentration. In vitro Chl-a quantification methods employing a modified acetone and an ethanol extraction protocol reduced the influence of shading and autofluorescence, but both resulted in a significant loss of fluorescence signal in the presence of 100 mgL−1 MWCNTs (99–100%) and GO (21–52%). Chl-a reduction was dose dependent for both tested carbon-based MNMs (CNMs), but effects were more pronounced for MWCNT, which caused a significant fluorescence reduction (16 ± 0.3%) already at 1 mgL−1. Further study of the CNM–algae–Chl-a interaction processes revealed that CNM can not only interact with live algae, but also efficiently adsorb extracted Chl-a. Our results showed that within 10 min, 95–100% of Chl-a extracted from two algae concentrations were adsorbed to MWCNT, while 35–60% of Chl-a was adsorbed to the GO. This study shows that Chl-a quantification by fluorescence determination is not a suitable method for ecotoxicity testing of CNM. However, a quick screening test for individual MNMs is recommended to determine whether Chl-a adsorption is a significant process prior to selection of a quantification method.

A New Glider-Compatible Optical Sensor for Dissolved Organic Matter Measurements: Test Case from the NW Mediterranean Sea

The MiniFluo-UV is a new glider-compatible optical sensor for measurements of dissolved organic matter (DOM) in natural waters. The working principle, sensor design and challenges faced during the validation phase are reported. The first in situ application of the sensor during three glider deployments in the NW Mediterranean sea (spring, summer, and fall) are also presented. For these campaigns, the two channels of the sensor were adjusted to target Tryptophan-like (excitation/emission wavelengths λEx/λEm: 275/340 nm) and Phenanthrene-like (λEx/λEm: 255/360 nm) fluorescence. These were chosen because they represent fluorophores of interest commonly found in seawater. While Tryptophan (an amino-acid believed to be a by-product of biological activity) is naturally found in the ocean, Phenanthrene (a polycyclic aromatic hydrocarbon) is mainly introduced in the environment by human activities. The addition of these variables to more common physical and biogeochemical glider measurements reveals new features of DOM dynamics in the Mediterranean Sea. For example, the temporal and spatial decoupling between Tryptophan-like and Chl-a fluorescence suggests that the former is not only a marker of phytoplankton activity, but could also give more subtle information on the microbial processes occurring. The identification of a Phenanthrene-like layer just below the pycnocline at all seasons also raises questions on the mechanisms driving its presence in the Mediterranean. Knowing that the role of ocean DOM on atmospheric carbon sequestration is becoming clearer, the high spatio-temporal resolution possible with this new sampling strategy may represents a key step toward our deep understanding of DOM dynamics and its role on the biological pump.

The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis.

The carnivorous sundew plant (Drosera capensis) captures prey using sticky tentacles. We investigated the tentacle and trap reactions in response to the electrical and jasmonate signalling evoked by different stimuli to reveal how carnivorous sundews recognize digestible captured prey in their traps. We measured the electrical signals, phytohormone concentration, enzyme activities and Chla fluorescence in response to mechanical stimulation, wounding or insect feeding in local and systemic traps. Seven new proteins in the digestive fluid were identified using mass spectrometry. Mechanical stimuli and live prey induced a fast, localized tentacle-bending reaction and enzyme secretion at the place of application. By contrast, repeated wounding induced a nonlocalized convulsive tentacle movement and enzyme secretion in local but also in distant systemic traps. These differences can be explained in terms of the electrical signal propagation and jasmonate accumulation, which also had a significant impact on the photosynthesis in the traps. The electrical signals generated in response to wounding could partially mimic a mechanical stimulation of struggling prey and might trigger a false alarm, confirming that the botanical carnivory and plant defence mechanisms are related. To trigger the full enzyme activity, the traps must detect chemical stimuli from the captured prey.

Chlorophyll a fluorescence changes in response to short and long term high light stress in rice seedlings

Investigations were carried out to study the high light stress effects on photosystem (PS) II efficiency in intact leaves of four rice (Oryza sativa L.) cultivars, viz., Jyothi, Aiswarya, Swarnaprabha and Kanchana. Rice seedlings were exposed to high light stress of 2000 µmol m−2 s−1, and the photochemistry of the four rice cultivars was studied by analyzing chlorophyll-a (Chla) fluorescence at 0 (control), 2 and 8 h. The results showed that Fv/Fo, performance index, area above the flourescence curve, Φo/(1 − Φo), ΦDo, ΦEo, Vj and DIo/CSo were found to be more reliable for exploring the effect of changes in PSII activity after high light stress application for short term (2 h), which can aid in distinguishing the tolerant and sensitive rice cultivars. Some Chla fluorescence parameters (Fm, SFI, Fv/Fm, Ψo/(1 − Ψo), ETo/CSo, ABS/CSo) were modified only after exposing the plants to high light stress for 8 h. The order of high light stress tolerance of these cultivars according to the analysis of Chla fluorescence parameters was Jyothi > Aiswarya > Swarnaprabha > Kanchana.

South-Eastern Bay of Biscay eddy-induced anomalies and their effect on chlorophyll distribution

The analysis of deep-water glider hydrographic and fluorescence data, together with satellite measurements provides a new insight into eddy-induced anomalies within the South-Eastern Bay of Biscay, during summer. Two cyclonic eddies and a SWODDY have been observed in different glider transects and by means of different sources of satellite data. Vertical profiles reveal complex structures (characteristic of the second baroclinic mode): upward/downward displacement of the seasonal/permanent thermocline in the case of X13 and the opposite thermocline displacements in the case of the cyclones. This is a typical behaviour of mode-water and “cyclonic thinny” eddies. A qualitative analysis of the vertical velocities in the anticyclone indicates that though geostrophy dominates the main water column, depressing the isopycnals, near the sea-surface the eddy-wind interaction affects the vertical currents, favouring Ekman pumping and upwelling. The analysis of the Θ-S properties corroborates that inside cyclones and between the 26 and 27 isopycnals, net downwelling occurs. These two types of intra-thermocline lenses appear to deeply impact the Chl-a fluorescence profiles, since the maximum Chl-a fluorescence is located just below the seasonal thermocline. The mean Chl-a fluorescence was higher in the anticyclone than within the cyclones and the mean for the entire study period; the highest values were observed in the centre of the anticyclone. These results are in agreement with previous findings concerning the SWODDY F90 and surrounding cyclones, located in the South-Western Bay of Biscay. Significant differences in the Θ-S properties of the two cyclonic mesoscale structures have been observed: higher temperatures and lower salinity in the easternmost cyclone. Finally, time variation of the salinity content of the shallowest water masses of the anticyclone (salinity decreasing over time), probably indicates advective mixing processes occurred during the mission.

Effects of Dracontomelon duperreanum defoliation extract on Microcystis aeruginosa: physiological and morphological aspects.

Harmful cyanobacteria bloom contributes to economic loss as well as the threat to human health. Agricultural waste products, particularly straw, have been used to control bloom while arbor plant is the potential candidate for limiting antialgal activity. This study investigated the use of Dracontomelon duperreanum defoliation extract (DDDE) to inhibit the activity of Microcystis aeruginosa. The primary goal of the research was to explore the solution to control cyanobacterial bloom. The photosynthetic activity, cell morphology, membrane integrity, and esterase activity of M. aeruginosa were determined using phytoplankton analyzer pulse amplitude modulation (Phyto-PAM) and flow cytometry before and after exposure to DDDE. The inhibitory rate of M. aeruginosa was about 99.6% on day 15 when exposed to 2.0gL(-1). A reduction of chlorophyll a (Chl-a) activity and changes in cell membrane suggested the algistatic property of DDDE. Inhibition of photosynthetic activity was reflected by changing mean Chl-a fluorescence intensity (MFI) which was about 52.5% on day 15 when exposed to 2.0gL(-1) DDDE as well as relative electron transport rates (rETRs) of algal cell. These changes might contribute to the suppression of M. aeruginosa. Algal cell exposed to DDDE may lead to cell volume reduction or slow growth. This resulted in a decreased proportion of normal or swollen granular cells after DDDE treatment.

Investigating primary sites of damage in photosystem II in response to high temperature

The quick and non-invasive technique of Chlorophyll-a (Chl-a) fluorescence was used to investigate the primary site of damage in photosystem II in response to high temperature stress. Based on the changes observed in several parameters deduced from Chl-a fluorescence curves after giving heat treatment at 40 °C for 2–30 min it was observed that the sequence of events in PS II under heat stress was as follows: inhibition of OEC—decrease in electron donation capacity—increase in thermal dissipation—increase in number of inactive RC—dissociation of LHCII—decrease in the efficiency of primary charge separation, ultimately leading to inhibition of primary photochemistry. Further it was concluded that at 40 °C, the acceptor side of PSII [1–Vj and PHI(Eo)] showed insignificant changes, which indicated that acceptor side of PSII is not a major target site of heat stress.

Hydrodynamic effect of a large offshore mussel suspended aquaculture farm

Hydrodynamic effect of a mussel suspended aquaculture farm on tidal currents off Gouqi Island, outside the Changjiang Estuary, China, was examined using observational data. The surface friction induced by suspended mussel aquaculture facilities in the top 3.5m was much stronger than bottom friction. As a result, tidal current velocity was reduced by 75–90% in the top layer and by about 45% at the bottom. The mean surface hydraulic roughness z0s̅ and surface drag coefficient C500̅, were estimated to be around 1.392–1.890m and 0.0875–0.1694, respectively. On the contrary, the mean bottom hydraulic roughness z0b̅ and bottom drag coefficient C100̅ within the farm, were estimated to be around 0.093–0.098m and 0.0226–0.0252, respectively. The observed surface friction velocity u⁎s have the same order of magnitude with the bottom friction velocity u⁎b. However, the surface hydraulic roughness z0s is about 20 times greater than that at the bottom. The local surface drag coefficient C500̅ is 3.5–7.5 times of that at the local bottom. The aquaculture facilities not only inhibited the horizontal tidal currents, but also appeared to have induced downwelling, which was shown by the vertical profiles of salinity, temperature, and chlorophyll-a (chl-a) fluorescence. Surface chl-a fluorescence was depleted to below 1.0μgL−1 inside the farm area, which was 80% less than the outside. The reduction of horizontal velocity and the presence of downwelling can significantly decrease food supply for filter-feeding mussels.

A Poisson-Pareto model of Chl-a fluorescence signals in marine environments

Because of its central role in the global carbon cycle, quantifying the biomass of photosynthetic microalgae in the oceans is crucial to our ability to estimate the oceans’ carbon drawdown. Many traditional methods of primary production assessment have proven to be extremely time consuming and, consequently, have handled only very small sample sizes. The recent advent of in situ bio-optical sensors, such as the water quality monitor (WQM), is now providing lower cost and higher throughput data on these crucial biological communities. These WQMs, however, only quantify the total fluorescence of all individual cells within their optical sample windows, irrespective of size. In this paper, we further develop an established model, based on Pareto random variables, of the size structure of the microalgae community to understand the effect of the WQMs’ sampling and data pooling on their estimates of algal biomass. Unfortunately, evaluating sums of Pareto variables is a notoriously difficult problem. Here, we utilize an approximation for the right-tail of the resulting distribution to derive parameter estimates for the underlying size structure of the microalgae community. doi:10.1017/S1446181115000073

The effects of graphene oxide on green algae Raphidocelis subcapitata

Graphene represents a new class of nanomaterials that has attracted great interest due to its unique electrical, thermal, and mechanical properties. Once disposed in the environment, graphene can interact with biological systems and is expected to exhibit toxicological effects. The ecotoxicity of graphene and its derivatives, viz.: graphene oxide (GO) depends on their physicochemical properties, including purity, diameter, length, surface charge, functionalization and aggregation state. In this study we evaluated the effects of graphene oxide (GO) on green algae Raphidocelis subcapitata. The algae were exposed to different concentrations of GO pre-equilibrated for 24h with oligotrophic freshwater medium (20ml) during incubation in a growth chamber under controlled conditions: 120μEm−2s−1 illumination; 12:12h light dark cycle and constant temperature of 22±2°C. Algal growth was monitored daily for 96h by direct cell counting. Reactive oxygen species level (ROS), membrane damage (cell viability) and autofluorescence (chl-a fluorescence) were evaluated using fluorescent staining and further analyzed by flow cytometry. The toxic effects from GO, as observed in algal density and autofluorescence, started at concentrations from 20 and 10μgmL−1, respectively. Such toxicity is probably the result of ROS generation and membrane damage (cell viability). The shading effect caused by GO agglomeration in culture medium may also contribute to reduce algal density. The results reported here provide knowledge regarding the GO toxicity on green algae, contributing to a better understanding of its environmental behavior and impacts.

A pseudo-Lagrangian method for remapping ocean biogeochemical tracer data: Calculation of net Chl-a growth rates

A key goal in understanding the ocean's biogeochemical state is estimation of rates of change of critical tracers, particularly components of the planktonic ecosystem. Unfortunately, because ship survey data are not synoptic, it is difficult to obtain spatially resolved estimates of the rates of change of tracers sampled in a moving fluid. Here we present a pseudo-Lagrangian transformation to remap data from underway surveys to a pseudo-synoptic view. The method utilizes geostrophic velocities to back advect and relocate sampling positions, removing advection aliasing. This algorithm produces a map of true relative sampling locations, and allows for determination of the relative locations of observations acquired along streamlines, as well as a corrected view of the tracer's spatial gradients. We then use a forward advection scheme to estimate the tracer's relative change along streamlines, and use these to calculate spatially resolved, net specific rates of change. Application of this technique to Chlorophyll-a (Chl-a) fluorescence data around an ocean front is presented. We obtain 156 individual estimates of Chl-a fluorescence net specific rate of change, covering ∼1200 km2. After incorporating a diffusion-like model to estimate error, the method shows that the majority of observations (64%) were significantly negative. This pseudo-Lagrangian approach generates more accurate spatial maps than raw survey data, and allows spatially resolved estimates of net rates of tracer change. Such estimates can be used as a rate budget constraint that, in conjunction with standard rate measurements, will better determine biogeochemical fluxes.

Effects of Fructus ligustri lucidi on the growth, cell integrity, and metabolic activity of the Microcystis aeruginosa.

Agricultural waste has been used in the treatment of cyanobacterial bloom because of its environmental friendly and cost-efficient characteristics. In this work, the effects of Fructus ligustri lucidi (FLL) on the growth inhibition, physiological properties, algicidal property, and cell ultrastructure of Microcystis aeruginosa were investigated for the first time. The alga was efficiently inhibited by FLL at the dosages from 0.25 to 4.0gL(-1), and the Chl-a fluorescence and metabolic activity of cells also declined gradually. During 25days incubation time, the inhibition ratio of 0.25gL(-1) dosage increased from 8 to 68%, the percentage of intact cells decreased from 94.4 to 59.8%, the inhibition ratio of 2.0 and 4.0gL(-1) dosages was nearly 100%, and the cell membranes were completely broken. The results of Chl-a, propidium iodide (PI) staining, fluorescein diacetate (FDA) staining, and transmission electron microscopy (TEM) assays were consistent with that of growth inhibition tests. The new medium test with the PI staining test suggested that FLL may act as an algicidal agent which can inhibit the growth of M. aeruginosa in the acute time. Consequently, FLL could be an excellent choice in the treatment of eutrophic water.