Salt pollution reduces turbidity, dissolved organic matter, and cyanobacteria in experimental vernal pool communities.

Anthropogenic activities such as the over-application of road deicers are causing an increase in the concentration of salts in historically fresh waters. Experimental and field investigations demonstrate that freshwater salinization disrupts ecosystem functions and services, causing the death of freshwater organisms and changes to nutrient conditions. Wetland habitats are one system negatively affected by salt pollution, including ephemeral wetlands (vernal pools) that fill with salt-polluted water after snowmelt. In urbanized areas, the degradation of these ecosystems could result in irreversible ecological damage including reduced water quality and a reduction in biodiversity. To investigate the effects of freshwater salinization on vernal pool communities, we exposed soils from vernal pools to water containing no salt (control), or four concentrations of three salts standardized by chloride concentration (50 mg Cl- L-1, 100 mg Cl- L-1, 200 mg Cl- L-1, and 400 mg Cl- L-1; magnesium chloride, calcium chloride, and sodium chloride). The results of this experiment suggest that emerging zooplankton communities in vernal pools are sensitive to low concentrations of salt pollution, and that alternative salts such as magnesium chloride and calcium chloride are more toxic than sodium chloride. We did not find positive or negative changes in the abundance of eukaryotic phytoplankton but did find negative effects of salt on cyanobacteria abundance, possibly due to corresponding reductions in turbidity which might be needed as a fixation site for cyanobacteria to form heterocysts. Finally, we found that salt pollution likely caused flocculation of Dissolved Organic Matter (DOM), resulting in reduced concentrations of DOM which could alter the buffering capacity of freshwater systems, light attenuation, and the populations of planktonic heterotrophs.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton.

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Responses of plankton community to threshold metal concentrations of cadmium and lead in a mesocosm experiment at Bay of Bengal.

Metals are essential at trace levels to aquatic organisms for the function of many physiological and biological processes. But their elevated levels are toxic to the ecosystem and even brings about shifts in the plankton population. Threshold limits such as Predicted No Effect Concentration (PNEC - 0.6 µg/l of Cd; 2.7 µg/l of Pb), Criterion Continuous Concentration (CCC - 3.0 µg/l of Cd; 4.5 µg/l of Pb) and Criterion Maximum Concentration (CMC - 23 µg/l of Cd; 130 µg/l of Pb) prescribed for Indian coastal waters were used for the study. Short-term mesocosm experiments (96 h) were conducted in coastal waters of Visakhapatnam to evaluate responses of the planktonic community on exposure to threshold concentrations of cadmium and lead for the first time. Four individual experimental bags of 2500 L capacity (Control, PNEC, CCC & CMC) were used for the deployment and ambient water samples were analysed simultaneously to evaluate the impacts of the threshold levels in the natural waters. Chaetoceros sp. were dominant group in the control system whereas, Prorocentrum sp. Ceratium sp. Tintinopsis sp. Chaetoceros sp. and Skeletonema sp. were major groups in the test bags. Throughout the experiment the phytoplankton community did not show any significant differences with increased nutrients and plankton biomass (Chl-a <8.64 mg/m3). Positive response of plankton community was observed in the experimental bags. High abundance of diatoms were observed in PNEC, CCC & CMC bags at 48 h and the abundance decreased with shift in the species at 72-96 h. The catalase activity in phytoplankton (5.99 nmol/min/ml) and the zooplankton (4.77 nmol/min/ml) showed induction after exposure to PNEC. The present mesocosm study is confirmed that short-term exposure to threshold metal concentration did not affects the phytoplankton community structure in PNEC, but CCC and CMC affects the community structure beyond 24 h. The insights from this study will serve as a baseline information and help develop environmental management tools. We believe that long-term mesocosm experiments would unravel metal detoxification mechanisms at the cellular level and metal transfer rate at higher trophic levels in real-world environment.

Using single-species and algal communities to determine long-term adverse effects of silver nanoparticles on freshwater phytoplankton.

The physical and chemical properties of silver nanoparticles (AgNPs) have led to their increasing use in various fields such as medicine, food, and industry. Evidence has proven that AgNPs cause adverse effects in aquatic ecosystems, especially when the release of Ag is prolonged in time. Several studies have shown short-term adverse effects of AgNPs on freshwater phytoplankton, but few studies have analysed the impact of long-term exposures on these populations. Our studies were carried out to assess the effects of AgNPs on growth rate, photosynthesis activity, and reactive oxygen species (ROS) generation on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa, and additionally on microcystin (MC-LR) generation from these cyanobacteria. The tests were conducted both in single-species cultures and in phytoplanktonic communities exposed to 1 ngL-1 AgNPs for 28 days. The results showed that cell growth rate of both single-species cultures decreased significantly at the beginning and progressively reached control-like values at 28 days post-exposure. This effect was similar for the community-cultured cyanobacteria, but not for the green algae, which maintained a sustained decrease in growth rate. While gross photosynthesis (Pg) increased in both strains exposed in single cultures, dark respiration (R) and net photosynthesis (Pn) decreased in S. armatus and M. aeruginosa, respectively. These effects were mitigated when both strains were exposed under community culture conditions. Similarly, the ROS generation shown by both strains exposed in single-species cultures was mitigated when exposure occurred in community cultures. MC-LR production and release were significantly decreased in both single-species and community exposures. These results can supply helpful information to further investigate the potential risks of AgNPs and ultimately help policymakers make better-informed decisions about their utilization for environmental restoration.

Life in the PFAS lane: The impact of perfluoroalkyl substances on photosynthesis, cellular exudates, nutrient cycling, and composition of a marine microbial community.

Perfluoroalkyl substances (PFAS) are of great ecological concern, however, exploration of their impact on bacteria-phytoplankton consortia is limited. This study employed a bioassay approach to investigate the effect of unary exposures of increasing concentrations of PFAS (perfluorooctane sulfonate (PFOS) and 6:2 fluorotelomer sulfonate (6:2 FTS)) on microbial communities from the northwestern Gulf of Mexico. Each community was examined for changes in growth and photophysiology, exudate production and shifts in community structure (16S and 18S rRNA genes). 6:2 FTS did not alter the growth or health of phytoplankton communities, as there were no changes relative to the controls (no PFOS added). On the other hand, PFOS elicited significant phototoxicity (p < 0.05), altering PSII antennae size, lowering PSII connectivity, and decreasing photosynthetic efficiency over the incubation (four days). PFOS induced a cellular protective response, indicated by significant increases (p < 0.001) in the release of transparent exopolymer particles (TEP) compared to the control. Eukaryotic communities (18S rRNA gene) changed substantially (p < 0.05) and to a greater extent than prokaryotic communities (16S rRNA gene) in PFOS treatments. Community shifts were concentration-dependent for eukaryotes, with the low treatment (5 mg/L PFOS) dominated by Coscinodiscophyceae (40 %), and the high treatment (30 mg/L PFOS) marked by a Trebouxiophyceae (50 %) dominance. Prokaryotic community shifts were not concentration dependent, as both treatment levels became depleted in Cyanobacteriia and were dominated by members of the Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria classes. Further, PFOS significantly decreased (p < 0.05) the Shannon diversity and Pielou's evenness across treatments for eukaryotes, and in the low treatment (5 mg/L PFOS) for prokaryotes. These findings show that photophysiology was not impacted by 6:2 FTS but PFOS elicited toxicity that impacted photosynthesis, exudate release, and community composition. This research is crucial in understanding how PFOS impacts microbial communities.

Ecotoxicological effects of DBPs on freshwater phytoplankton communities in co-culture systems.

Intensive disinfection of wastewater during the COVID-19 pandemic might elevate the generation of toxic disinfection byproducts (DBPs), which has triggered global concerns about their ecological risks to natural aquatic ecosystems. In this study, the toxicity of 17 DBPs typically present in wastewater effluents on three representative microalgae, including Scenedesmus sp. (Chlorophyta), Microcystis aeruginosa (Cyanophyta), and Cyclotella sp. (Bacillariophyta) was investigated. The sensitivities of the three microalgae to DBPs varied greatly from species to species, indicating that DBPs may change the structure of phytoplankton communities. Later, co-cultures of these phytoplankton groups as a proxy of ecological freshwater scenario were conducted to explore the impacts of DBPs on phytoplankton community succession. M. aeruginosa became surprisingly dominant in co-cultures, representing over 50% after dosing with monochloroacetic acid (MCAA, 0.1-10 mg/L). The highest proportion of M. aeruginosa was 70.3% when exposed to 2 mg/L MCAA. Although Scenedesmus sp. dominated in monochloroacetonitrile (MCAN) exposure, M. aeruginosa accounted for no less than 30% even at 40 mg/L MCAN. In this study, DBPs disrupted the original inter-algal relationship in favor of M. aeruginosa, suggesting that DBPs may contribute to the outbreak of cyanobacterial blooms in aquatic ecosystems.

Influence of nutrient status on the response of the diatom Phaeodactylum tricornutum to oil and dispersant.

Phytoplankton play a central role in our ecosystems, they are responsible for nearly 50 percent of the global primary productivity and major drivers of macro-elemental cycles in the ocean. Phytoplankton are constantly subjected to stressors, some natural such as nutrient limitation and some manmade such as oil spills. With increasing oil exploration activities in coastal zones in the Gulf of Mexico and elsewhere, an oil spill during nutrient-limited conditions for phytoplankton growth is highly likely. We performed a multifactorial study exposing the diatom Phaeodactylum tricornutum (UTEX 646) to oil and/or dispersants under nitrogen and silica limitation as well as co-limitation of both nutrients. Our study found that treatments with nitrogen limitation (-N and-N-Si) showed overall lower growth and chlorophyll a, lower photosynthetic antennae size, lower maximum photosynthetic efficiency, lower protein in exopolymeric substance (EPS), but higher connectivity between photosystems compared to non-nitrogen limited treatments (-Si and +N+Si) in almost all the conditions with oil and/or dispersants. However, certain combinations of nutrient limitation and oil and/or dispersant differed from this trend indicating strong interactive effects. When analyzed for significant interactive effects, the-N treatment impact on cellular growth in oil and oil plus dispersant conditions; and oil and oil plus dispersant conditions on cellular growth in-N-Si and-N treatments were found to be significant. Overall, we demonstrate that nitrogen limitation can affect the oil resistant trait of P. tricornutum, and oil with and without dispersants can have interactive effects with nutrient limitation on this diatom.

Changes in Growth, Photosynthesis Performance, Pigments, and Toxin Contents of Bloom-Forming Cyanobacteria after Exposure to Macroalgal Allelochemicals.

Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (Fv/Fm) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and Fv/Fm and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis depends on the target species' identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.

Bisabolane, cadinane, and cyclonerane sesquiterpenes from an algicolous strain of Trichoderma asperelloides.

Ten new bisabolane derivatives, trichobisabolins Q-Z (1-10), one new cadinane derivative, cadin-4-en-11-ol (11), and three new cyclonerane derivatives, cycloner-3-en-7,11-diol (12), isoepicyclonerodiol oxide (13), and norepicyclonerodiol oxide (14), were isolated from the endophytic fungal strain RR-dl-6-11 of Trichoderma asperelloides that was obtained from a marine alga. Their structures along with relative configurations were established mainly by NMR and IR as well as MS techniques, and the absolute configurations of 10 and 11 were assigned by ECD and X-ray diffraction data, respectively. Sesquiterpenes from the fungus T. asperelloides are reported for the first time. It is interesting that half of the bisabolane derivatives are demethylated. Compound 12 represents the first the occurrence of cyclopentenyl-bearing cycloneranes, and 14 seems a cyclopentyl-degrading cyclonerane derivative. Several isolates feature potent inhibition of marine phytoplankton species.

Sesquiterpenoids and a steroid from the algicolous Trichoderma brevicompactum.

Six new sesquiterpenoids including three bisabolane derivatives, trichobisabolins O1, O2, and P (1-3), two nerolidol derivatives, trichonerolins A and B (4 and 5), one acorane, trichoacorin A (6), along with one new steroid, isoergokonin B (7), were isolated from the culture of Trichoderma brevicompactum A-DL-9-2 obtained from the inner tissue of the red alga Chondria tenuissima. Their structures and relative configurations were assigned by interpretation of 1D/2D NMR and MS data. As acyclic sesquiterpenoids, compounds 4 and 5 were discovered from Trichoderma for the first time. Compounds 1-7 were evaluated for the inhibition of some marine-derived organisms, in which, 3 and 4/5 exhibited potent inhibition against Amphidinium carterae and Chattonella marina with IC50 of 1.8 µg/mL and 1.2 µg/mL, respectively. In addition, compound 7 could inhibit the growth of Pseudoalteromonas citrea with an MIC value of 64 µg/mL.

Amino Acid Analog Induces Stress Response in Marine Synechococcus.

Characterizing the cell-level metabolic trade-offs that phytoplankton exhibit in response to changing environmental conditions is important for predicting the impact of these changes on marine food web dynamics and biogeochemical cycling. The time-selective proteome-labeling approach, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to provide insight into differential allocation of resources at the cellular level, especially when coupled with proteomics. However, the application of this technique in marine phytoplankton remains limited. We demonstrate that the marine cyanobacteria Synechococcus sp. and two groups of eukaryotic algae take up the modified amino acid l-homopropargylglycine (HPG), suggesting that BONCAT can be used to detect translationally active phytoplankton. However, the impact of HPG addition on growth dynamics varied between groups of phytoplankton. In addition, proteomic analysis of Synechococcus cells grown with HPG revealed a physiological shift in nitrogen metabolism, general protein stress, and energy production, indicating a potential limitation for the use of BONCAT in understanding the cell-level response of Synechococcus sp. to environmental change. Variability in HPG sensitivity between algal groups and the impact of HPG on Synechococcus physiology indicates that particular considerations should be taken when applying this technique to other marine taxa or mixed marine microbial communities. IMPORTANCE Phytoplankton form the base of the marine food web and substantially impact global energy and nutrient flow. Marine picocyanobacteria of the genus Synechococcus comprise a large portion of phytoplankton biomass in the ocean and therefore are important model organisms. The technical challenges of environmental proteomics in mixed microbial communities have limited our ability to detect the cell-level adaptations of phytoplankton communities to a changing environment. The proteome labeling technique, bioorthogonal noncanonical amino acid tagging (BONCAT), has potential to address some of these challenges by simplifying proteomic analyses. This study explores the ability of marine phytoplankton to take up the modified amino acid, l-homopropargylglycine (HPG), required for BONCAT, and investigates the proteomic response of Synechococcus to HPG. We not only demonstrate that cyanobacteria can take up HPG but also highlight the physiological impact of HPG on Synechococcus, which has implications for future applications of this technique in the marine environment.

Proharziane and Harziane Derivatives from the Marine Algicolous Fungus Trichoderma asperelloides RR-dl-6-11.

One new proharziane and three new harziane derivatives (1-4) together with six known ones (5-10) were isolated from the marine-alga-derived ascomycete Trichoderma asperelloides RR-dl-6-11. Their structures and relative configurations were determined via spectroscopic techniques, and the absolute configurations were ascertained by analysis of ECD curves. This is the first report on the secondary metabolites of T. asperelloides, and the new isolates (1-4), especially seco-harziane 4, greatly add to the structural diversity of harziane diterpenes as well as their precursors and catabolites. Compounds 1-5 inhibited four marine phytoplankton species, and the structure-activity relationship of harziane derivatives is analyzed.

Susceptibility of phytoplankton to the increasing presence of active pharmaceutical ingredients (APIs) in the aquatic environment: A review.

Human and veterinary pharmaceuticals either in the form of un-metabolized, incompletely metabolized, and metabolized drugs are increasingly present in aquatic ecosystems. These active pharmaceutical ingredients from pharmaceutical industries, hospitals, agricultural, and domestic discharges find their way into water systems - where they adversely affect non-target organisms like phytoplankton. Different aspects of phytoplankton life; ranging from growth, reproduction, morphology, physiology, biochemical composition, oxidative response, proteomics, and transcriptomics are altered by pharmaceuticals. This review discusses the currently available information on the susceptibility of phytoplankton to the ever-increasing presence of pharmaceutical products in the aquatic environment by focusing on the effect of APIs on the physiology, metabolome, and proteome profiles of phytoplankton. We also highlight gaps in literature concerning the salient underlining biochemical interactions between phytoplankton communities and pharmaceuticals that require an in-depth investigation. This is all in a bid to understand the imminent dangers of the contamination of water bodies with pharmaceutical products and how this process unfavorably affects aquatic food webs.

Massive Southern Ocean phytoplankton bloom fed by iron of possible hydrothermal origin.

Primary production in the Southern Ocean (SO) is limited by iron availability. Hydrothermal vents have been identified as a potentially important source of iron to SO surface waters. Here we identify a recurring phytoplankton bloom in the high-nutrient, low-chlorophyll waters of the Antarctic Circumpolar Current in the Pacific sector of the SO, that we argue is fed by iron of hydrothermal origin. In January 2014 the bloom covered an area of ~266,000 km2 with depth-integrated chlorophyll a > 300 mg m-2, primary production rates >1 g C m-2 d-1, and a mean CO2 flux of -0.38 g C m-2 d-1. The elevated iron supporting this bloom is likely of hydrothermal origin based on the recurrent position of the bloom relative to two active hydrothermal vent fields along the Australian Antarctic Ridge and the association of the elevated iron with a distinct water mass characteristic of a nonbuoyant hydrothermal vent plume.

Deoxytrichodermaerin, a harziane lactone from the marine algicolous fungus Trichoderma longibrachiatum A-WH-20-2.

Three metabolites deoxytrichodermaerin (a new harziane lactone), harzianol A and harzianone were obtained from Trichoderma longibrachiatum A-WH-20-2, an endophyte from marine red alga Laurencia okamurai. Their structures and relative configurations were unequivocally assigned by spectroscopic techniques, and the absolute configuration of deoxytrichodermaerin was established by analysis of the ECD curve aided by quantum chemical calculations. Deoxytrichodermaerin represents the second harziane lactone with an ester linkage between C-10 and C-11. Harzianol A occurs as a natural product of Trichoderma for the first time. Harzianone has been previously discovered from T. longibrachiatum cf-11. These isolates exhibited potent inhibition of some marine plankton species.

Phenylhydrazone and Quinazoline Derivatives from the Cold-Seep-Derived Fungus Penicillium oxalicum.

Three new phenylhydrazones, penoxahydrazones A-C (compounds 1-3), and two new quinazolines, penoxazolones A (compound 4) and B (compound 5), with unique linkages were isolated from the fungus Penicillium oxalicum obtained from the deep sea cold seep. Their structures and relative configurations were assigned by analysis of 1D/2D NMR and mass spectroscopic data, and the absolute configurations of 1, 4, and 5 were established on the basis of X-ray crystallography or ECD calculations. Compound 1 represents the first natural phenylhydrazone-bearing steroid, while compounds 2 and 3 are rarely occurring phenylhydrazone tautomers. Compounds 4 and 5 are enantiomers that feature quinazoline and cinnamic acid units. Some isolates exhibited inhibition of several marine phytoplankton species and marine-derived bacteria.

Antifungal and Antimicroalgal Trichothecene Sesquiterpenes from the Marine Algicolous Fungus Trichoderma brevicompactum A-DL-9-2.

Eight new trichothecene derivatives, trichodermarins G-N (1-8), and two new cuparene derivatives, trichocuparins A (9) and B (10), as well as six known trichothecenes (11-16) were isolated from the fungal strain Trichoderma brevicompactum A-DL-9-2 obtained from the inner tissue of the marine red alga Chondria tenuissima. The structures and relative configurations of 1-10 were assigned by NMR and MS data, and the absolute configurations of 1, 2, and 9 were established by X-ray diffraction. Compound 8 features an aminosugar unit bond to the trichothecene framework for the first time, while 9 and 10 represent the first occurrence of cuparene sesquiterpenes in Trichoderma. All the isolates were assayed for growth inhibition of five phytopathogenic fungi (Botrytis cinerea, Cochliobolus miyabeanus, Fusarium oxysporum f. sp. cucumerium, Fusarium oxysporum f. sp. niveum, and Phomopsis asparagi) and four marine phytoplankton species (Amphidinium carterae, Heterocapsa circularisquama, Heterosigma akashiwo, and Prorocentrum donghaiense). Several of them exhibited significant inhibitory activities against the fungi and phytoplankton tested of which trichodermin (12) showed the highest antifungal and antimicroalgal activities with MIC and IC50 values being 4.0 and 0.82 µg/mL, respectively.

The molecular response mechanisms of a diatom Thalassiosira pseudonana to the toxicity of BDE-47 based on whole transcriptome analysis.

Polybrominated diphenyl ethers (PBDEs) are ubiquitously distributed persistent organic pollutants (POPs) in marine environments. Phytoplankton are the entrance of PBDEs entering to biotic environments from abiotic environments, while the responding mechanisms of phytoplankton to PBDEs have not been full established. Therefore, we chose the model diatom Thalassiosira pseudonana in this study, by integrating whole transcriptome analysis with physiological-biochemical data, to reveal the molecular responding mechanisms of T. pseudonana to the toxicity of BDE-47. Our results indicated the changes of genes expressions correlated to the physiological-biochemical changes, and there were multiple molecular mechanisms of T. pseudonana responding to the toxicity of BDE-47: Gene expressions evidence explained the suppression of light reaction and proved the occurrence of cellular oxidative stress; In the meanwhile, up-regulations of genes in pathways involving carbon metabolisms happened, including the Calvin cycle, glycolysis, TCA cycle, fatty acid synthesis, and triacylglycerol synthesis; Lastly, DNA damage was found and three outcome including DNA repair, cell cycle arrest and programmed cell death (PCD) happened, which could finally inhibit the cell division and population growth of T. pseudonana. This study presented the most complete molecular responding mechanisms of phytoplankton cells to PBDEs, and provided valuable information of various PBDEs-sensitive genes with multiple functions for further research involving organic pollutants and phytoplankton.

Anthropogenic Asian aerosols provide Fe to the North Pacific Ocean.

Fossil-fuel emissions may impact phytoplankton primary productivity and carbon cycling by supplying bioavailable Fe to remote areas of the ocean via atmospheric aerosols. However, this pathway has not been confirmed by field observations of anthropogenic Fe in seawater. Here we present high-resolution trace-metal concentrations across the North Pacific Ocean (158°W from 25°to 42°N). A dissolved Fe maximum was observed around 35°N, coincident with high dissolved Pb and Pb isotope ratios matching Asian industrial sources and confirming recent aerosol deposition. Iron-stable isotopes reveal in situ evidence of anthropogenic Fe in seawater, with low δ56Fe (-0.23‰ > δ56Fe > -0.65‰) observed in the region that is most influenced by aerosol deposition. An isotope mass balance suggests that anthropogenic Fe contributes 21-59% of dissolved Fe measured between 35° and 40°N. Thus, anthropogenic aerosol Fe is likely to be an important Fe source to the North Pacific Ocean.

Effects of atrazine and its two major derivatives on the photosynthetic physiology and carbon sequestration potential of a marine diatom.

As one of the most commonly used and frequently detected herbicides in the coastal seawater, the ecotoxicity of atrazine to phytoplankton has been well demonstrated. However, little attention has been paid to the ecotoxicity of its two major hydrolysates (desisopropylatrazine (DIA) and desethylatrazine (DEA)), which are also widely distributed in natural seawater. Here we present a comprehensive analysis of the photosynthetic physiology and chromophoric dissolved organic matter (CDOM) characteristics of the diatom Phaeodactylum tricornutum Pt-1 (CCMP 2561) under atrazine, DIA and DEA stress, respectively. The results showed that both atrazine and the two derivatives had significant negative effects on the concentration of chlorophyll a, maximum quantum efficiency (Fv/Fm) and relative electron transport rates (rETR) of P. tricornutum Pt-1. Furthermore, the CDOM pattern released by P. tricornutum Pt-1 cells also changed significantly after 7-day exposure. Compared with the control group, the fluorescence intensity (3D-EEM spectra) of protein-like components was obviously lower, while that of the humic acid-like components was higher. The findings of this study indicate that the ecotoxicity of atrazine might have been underestimated in previous investigations: both atrazine and its two major derivatives are not only phototoxic to microalgae but also influence the carbon sequestration potential in the coastal seawater.