Nitrate limitation and ocean acidification interact with UV-B to reduce photosynthetic performance in the diatom

It has been proposed that ocean acidification (OA) will interact with other environmental factors to influence the overall impact of global change on biological systems. Accordingly we investigated the influence of nitrogen limitation and OA on the physiology of diatoms by growing the diatom Phaeodactylum tricornutum Bohlin under elevated (1000 µatm; high CO2- HC) or ambient (390 µatm; low CO2-LC) levels of CO2 with replete (110 µmol/L; high nitrate-HN) or reduced (10 ?mol/L; low nitrate-LN) levels of NO3- and subjecting the cells to solar radiation with or without UV irradiance to determine their susceptibility to UV radiation (UVR, 280-400 nm). Our results indicate that OA and UVB induced significantly higher inhibition of both the photosynthetic rate and quantum yield under LN than under HN conditions. UVA or/and UVB increased the cells' non-photochemical quenching (NPQ) regardless of the CO2 levels. Under LN and OA conditions, activity of superoxide dismutase and catalase activities were enhanced, along with the highest sensitivity to UVB and the lowest ratio of repair to damage of PSII. HC-grown cells showed a faster recovery rate of yield under HN but not under LN conditions. We conclude therefore that nutrient limitation makes cells more prone to the deleterious effects of UV radiation and that HC conditions (ocean acidification) exacerbate this effect. The finding that nitrate limitation and ocean acidification interact with UV-B to reduce photosynthetic performance of the diatom P. tricornutum implies that ocean primary production and the marine biological C pump will be affected by OA under multiple stressors.

Iron limitation modulates ocean acidification effects on southern ocean phytoplankton communities

The potential interactive effects of iron (Fe) limitation and Ocean Acidification in the Southern Ocean (SO) are largely unknown. Here we present results of a long-term incubation experiment investigating the combined effects of CO2 and Fe availability on natural phytoplankton assemblages from the Weddell Sea, Antarctica. Active Chl a fluorescence measurements revealed that we successfully cultured phytoplankton under both Fe-depleted and Fe-enriched conditions. Fe treatments had significant effects on photosynthetic efficiency (Fv/Fm; 0.3 for Fe-depleted and 0.5 for Fe-enriched conditions), non-photochemical quenching (NPQ), and relative electron transport rates (rETR). pCO2 treatments significantly affected NPQ and rETR, but had no effect on Fv/Fm. Under Fe limitation, increased pCO2 had no influence on C fixation whereas under Fe enrichment, primary production increased with increasing pCO2 levels. These CO2-dependent changes in productivity under Fe-enriched conditions were accompanied by a pronounced taxonomic shift from weakly to heavily silicified diatoms (i.e. from Pseudo-nitzschia sp. to Fragilariopsis sp.). Under Fe-depleted conditions, this functional shift was absent and thinly silicified species dominated all pCO2 treatments (Pseudo-nitzschia sp. and Synedropsis sp. for low and high pCO2, respectively). Our results suggest that Ocean Acidification could increase primary productivity and the abundance of heavily silicified, fast sinking diatoms in Fe-enriched areas, both potentially leading to a stimulation of the biological pump. Over much of the SO, however, Fe limitation could restrict this possible CO2 fertilization effect.

Vanishing coccolith vital effects with alleviated carbon limitation

By recreating a range of geologically relevant concentrations of dissolved inorganic carbon (DIC) in the laboratory, we demonstrate that the magnitude of the vital effects in both carbon and oxygen isotopes of coccolith calcite of multiple species relates to ambient DIC concentration. Under high DIC levels, all the examined coccoliths exhibit significantly reduced isotopic offsets from inorganic calcite compared to the substantial vital effects expressed at low (preindustrial and present-day) DIC concentrations. The supply of carbon to the cell exerts a primary control on biological fractionation in coccolith calcite via the modulation of coccolithophore growth rate, cell size and carbon utilisation by photosynthesis and calcification, altogether accounting for the observed interspecific differences between coccolith species. These laboratory observations support the recent hypothesis from field observations that the appearance of interspecific vital effect in coccolithophores coincides with the long-term Neogene decline of atmospheric CO2 concentrations and bring further valuable constraints by demonstrating a convergence of all examined species towards inorganic values at high pCO2 regimes. This study provides palaeoceanographers with a biogeochemical framework that can be utilised to further develop the use of calcareous nannofossils in palaeoceanography to derive sea surface temperature and pCO2 levels, especially during periods of relatively elevated pCO2 concentrations, as they prevailed during most of the Meso-Cenozoic.

Trichodesmium's strategies to alleviate phosphorus limitation in the future acidified oceans

Global warming may exacerbate inorganic nutrient limitation, including phosphorus (P), in the surface-waters of tropical oceans that are home to extensive blooms of the marine diazotrophic cyanobacterium, Trichodesmium. We examined the combined effects of P limitation and pCO2, forecast under ocean acidification scenarios, on Trichodesmium erythraeum IMS101 cultures. We measured nitrogen acquisition, glutamine synthetase activity, C uptake rates, intracellular Adenosine Triphosphate (ATP) concentration and the pool sizes of related key proteins. Here, we present data supporting the idea that cellular energy re-allocation enables the higher growth and N2 fixation rates detected in Trichodesmium cultured under high pCO2. This is reflected in altered protein abundance and metabolic pools. Also modified are particulate organic carbon and nitrogen production rates, enzymatic activities, and cellular ATP concentrations. We suggest that adjusting these cellular pathways to changing environmental conditions enables Trichodesmium to compensate for low P availability and to thrive in acidified oceans. Moreover, elevated pCO2 could provide Trichodesmium with a competitive dominance that would extend its niche, particularly in P-limited regions of the tropical and subtropical oceans.

LED Jitter-Induced Limitation Effects in the Baud Rate of VLC

In this paper we show that the effect of jitter due to driver and LED is the limiting factor in the baud rate in L-PPM formats for VLC systems.

Implementation and management of private traffic limitation in urban areas: experiences and methodologies.

This paper shows the results of a research aimed to formulate a general model for supporting the implementation and management of an urban road pricing scheme. After a preliminary work, to define the state of the art in the field of sustainable urban mobility strategies, the problem has been theoretically set up in terms of transport economy, introducing the external costs’ concept duly translated into the principle of pricing for the use of public infrastructures. The research is based on the definition of a set of direct and indirect indicators to qualify the urban areas by land use, mobility, environmental and economic conditions. These indicators have been calculated for a selected set of typical urban areas in Europe on the basis of the results of a survey carried out by means of a specific questionnaire. Once identified the most typical and interesting applications of the road pricing concept in cities such as London (Congestion Charging), Milan (Ecopass), Stockholm (Congestion Tax) and Rome (ZTL), a large benchmarking exercise and the cross analysis of direct and indirect indicators, has allowed to define a simple general model, guidelines and key requirements for the implementation of a pricing scheme based traffic restriction in a generic urban area. The model has been finally applied to the design of a road pricing scheme for a particular area in Madrid, and to the quantification of the expected results of its implementation from a land use, mobility, environmental and economic perspective.

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

Several attempts have been carried out to manufacture intermediate band solar cells (IBSC) by means of quantum dot (QD) superlattices. This novel photovoltaic concept allows the collection of a wider range of the sunlight spectrum in order to provide higher cell photocurrent while maintaining the open-circuit voltage (VOC) of the cell. In this work, we analyze InAs/GaAsN QD-IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (JL) versus VOC was measured under varied concentrated light intensity and temperature. We found that the VOC of the cell at 20 K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.

Genomic evolution during a 10,000-generation experiment with bacteria

Molecular methods are used widely to measure genetic diversity within populations and determine relationships among species. However, it is difficult to observe genomic evolution in action because these dynamics are too slow in most organisms. To overcome this limitation, we sampled genomes from populations of Escherichia coli evolving in the laboratory for 10,000 generations. We analyzed the genomes for restriction fragment length polymorphisms (RFLP) using seven insertion sequences (IS) as probes; most polymorphisms detected by this approach reflect rearrangements (including transpositions) rather than point mutations. The evolving genomes became increasingly different from their ancestor over time. Moreover, tremendous diversity accumulated within each population, such that almost every individual had a different genetic fingerprint after 10,000 generations. As has been often suggested, but not previously shown by experiment, the rates of phenotypic and genomic change were discordant, both across replicate populations and over time within a population. Certain pivotal mutations were shared by all descendants in a population, and these are candidates for beneficial mutations, which are rare and difficult to find. More generally, these data show that the genome is highly dynamic even over a time scale that is, from an evolutionary perspective, very brief.

Brownian dynamics simulations of protein folding: Access to milliseconds time scale and beyond

Protein folding occurs on a time scale ranging from milliseconds to minutes for a majority of proteins. Computer simulation of protein folding, from a random configuration to the native structure, is nontrivial owing to the large disparity between the simulation and folding time scales. As an effort to overcome this limitation, simple models with idealized protein subdomains, e.g., the diffusion–collision model of Karplus and Weaver, have gained some popularity. We present here new results for the folding of a four-helix bundle within the framework of the diffusion–collision model. Even with such simplifying assumptions, a direct application of standard Brownian dynamics methods would consume 10,000 processor-years on current supercomputers. We circumvent this difficulty by invoking a special Brownian dynamics simulation. The method features the calculation of the mean passage time of an event from the flux overpopulation method and the sampling of events that lead to productive collisions even if their probability is extremely small (because of large free-energy barriers that separate them from the higher probability events). Using these developments, we demonstrate that a coarse-grained model of the four-helix bundle can be simulated in several days on current supercomputers. Furthermore, such simulations yield folding times that are in the range of time scales observed in experiments.

Estimating the relative roles of top-down and bottom-up forces on insect herbivore populations: A classic study revisited

Although most ecologists agree that both top-down and bottom-up forces (predation and resource limitation, respectively) act in concert to influence populations of herbivores, it has proven difficult to estimate the relative contributions of such forces in terrestrial systems. Using a combination of time–series analysis of population counts recorded over 16 years and experimental data, we present the first estimates of the relative roles of top-down and bottom-up forces on the population dynamics of two terrestrial insect herbivores on the English oak (Quercus robur). Data suggest that temporal variation in winter moth, Operophtera brumata, density is dominated by time-lagged effects of pupal predators. By comparison, spatial variation in O. brumata density is dominated by host–plant quality. Overall, top-down forces explain 34.2% of population variance, bottom-up forces explain 17.2% of population variance, and 48.6% remains unexplained. In contrast, populations of the green oak tortrix, Tortrix viridana, appear dominated by bottom-up forces. Resource limitation, expressed as intraspecific competition among larvae for oak leaves, explains 29.4% of population variance. Host quality effects explain an additional 5.7% of population variance. We detected no major top-down effects on T. viridana populations. An unknown factor causing a linear decline in T. viridana populations over the 16-year study period accounts for most of the remaining unexplained variance. We discuss the observed differences between the insect species and the utility of time–series analysis as a tool in assessing the relative importance of top-down and bottom-up forces on herbivore populations.

Missing Emigrants : Gleanings from Petitions Presented under the Presumption of Life Limitation (Scotland) Acts

Peer reviewed

Exome-wide analysis of rare coding variation identifies novel associations with COPD and airflow limitation in MOCS3, IFIT3 and SERPINA12

Funding: British Women’s Heart and Health Study is funded by the Department of Health grant no. 90049 and the British Heart Foundation grant no. PG/09/022. British Regional Heart Study is supported by the British Heart Foundation (grant RG/ 13/16/30528). CB (COPDBEAT) received funding from the Medical Research Council UK (grant no. G0601369), CB (COPDBEAT) and AJW (UKCOPD) were supported by the National Institute for Health Research (NIHR Leicester Biomedical Research Unit). MB (COPDBEAT) received funding from the NIHR (grant no. PDF-2013-06-052). Hertfordshire Cohort Study received support from the Medical Research Council, Arthritis Research UK, the International Osteoporosis Foundation and the British Heart Foundation; NIHR Biomedical Research Centre in Nutrition, University of Southampton; NIHR Musculoskeletal Biomedical Research Unit, University of Oxford. Generation Scotland: Scottish Family Health Study is funded by the Chief Scientist Office, Scottish Government Health Directorates, grant number CZD/16/6 and the Scottish Funding Council grant HR03006. EU COPD Gene Scan is funded by the European Union, grant no. QLG1-CT-2001-01012. English Longitudinal Study of Aging is funded by the Institute of Aging, NIH grant No. AG1764406S1. GoDARTs is funded by the Wellcome Trust grants 072960, 084726 and 104970. MDT has been supported by MRC fellowship G0902313. UK Biobank Lung Exome Variant Evaluation study was funded by a Medical Research Council strategic award to MDT, IPH, DPS and LVW (MC_PC_12010)

Ape-like or hominid-like? The positional behavior of Oreopithecus bambolii reconsidered

Comparative morphological and functional analyses of the skeletal remains of Oreopithecus bambolii, a hominoid from the Miocene Mediterranean island of Tuscany–Sardinia (Italy), provides evidence that bipedal activities made up a significant part of the positional behavior of this primate. The mosaic pattern of its postcranial morphology is to some degree convergent with that of Australopithecus and functionally intermediate between apes and early hominids. Some unique traits could have been selected only under insular conditions where the absence of predators and the limitation of trophic resources play a crucial role in mammalian evolution.

Identification of an ATP-binding cassette transporter involved in bicarbonate uptake in the cyanobacterium Synechococcus sp. strain PCC 7942

Exposure of cells of cyanobacteria (blue–green algae) grown under high-CO2 conditions to inorganic C-limitation induces transcription of particular genes and expression of high-affinity CO2 and HCO3− transport systems. Among the low-CO2-inducible transcription units of Synechococcus sp. strain PCC 7942 is the cmpABCD operon, encoding an ATP-binding cassette transporter similar to the nitrate/nitrite transporter of the same cyanobacterium. A nitrogen-regulated promoter was used to selectively induce expression of the cmpABCD genes by growth of transgenic cells on nitrate under high CO2 conditions. Measurements of the initial rate of HCO3− uptake after onset of light, and of the steady-state rate of HCO3− uptake in the light, showed that the controlled induction of the cmp genes resulted in selective expression of high-affinity HCO3− transport activity. The forced expression of cmpABCD did not significantly increase the CO2 uptake capabilities of the cells. These findings demonstrated that the cmpABCD genes encode a high-affinity HCO3− transporter. A deletion mutant of cmpAB (M42) retained low CO2-inducible activity of HCO3− transport, indicating the occurrence of HCO3− transporter(s) distinct from the one encoded by cmpABCD. HCO3− uptake by low-CO2-induced M42 cells showed lower affinity for external HCO3− than for wild-type cells under the same conditions, showing that the HCO3− transporter encoded by cmpABCD has the highest affinity for HCO3− among the HCO3− transporters present in the cyanobacterium. This appears to be the first unambiguous identification and description of a primary active HCO3− transporter.

Relationships of dehydroepiandrosterone sulfate in the elderly with functional, psychological, and mental status, and short-term mortality: A French community-based study

In human beings of both sexes, dehydroepiandrosterone sulfate (DHEAS) circulating in blood is mostly an adrenally secreted steroid whose serum concentration (in the micromolar range and 30–50% higher in men than in women) decreases with age, toward ≈20–10% of its value in young adults during the 8th and 9th decades. The mechanism of action of DHEA and DHEAS is poorly known and may include partial transformation into sex steroids, increase of bioavailable insulin-like growth factor I, and effects on neurotransmitter receptors. Whether there is a cause-to-effect relationship between the decreasing levels of DHEAS with age and physiological and pathological manifestations of aging is still undecided, but this is of obvious theoretical and practical interest in view of the easy restoration by DHEA administration. Here we report on 622 subjects over 65 years of age, studied for the 4 years since DHEAS baseline values had been obtained, in the frame of the PAQUID program, analyzing the functional, psychological, and mental status of a community-based population in the south-west of France. We confirm the continuing decrease of DHEAS serum concentration with age, more in men than in women, even if men retain higher levels. Significantly lower values of baseline DHEAS were recorded in women in cases of functional limitation (Instrumental Activities of Daily Living), confinement, dyspnea, depressive symptomatology, poor subjective perception of health and life satisfaction, and usage of various medications. In men, there was a trend for the same correlations, even though not statistically significant in most categories. No differences in DHEAS levels were found in cases of incident dementia in the following 4 years. In men (but not in women), lower DHEAS was significantly associated with increased short-term mortality at 2 and 4 years after baseline measurement. These results, statistically established by taking into account corrections for age, sex, and health indicators, suggest the need for further careful trials of the administration of replacement doses of DHEA in aging humans. Indeed, the first noted results of such “treatment” are consistent with correlations observed here between functional and psychological status and endogenous steroid serum concentrations.