The percentage of living bacterial cells related to organic carbon release from senescent oceanic phytoplankton

© 2014 Author(s). Bacteria recycle vast amounts of organic carbon, playing key biogeochemical and ecological roles in the ocean. Bacterioplankton dynamics are expected to be dependent on phytoplankton primary production, but there is a high diversity of processes (e.g., sloppy feeding, cell exudation, viral lysis) involved in the transfer of primary production to dissolved organic carbon available to bacteria. Here, we show the percentage of living heterotrophic bacterioplankton in the subtropical NE Atlantic Ocean in relation to phytoplankton extracellular carbon release (PER). PER represents the fraction of primary production released as dissolved organic carbon. PER variability was explained by phytoplankton cell death, with communities experiencing higher phytoplankton cell mortality showing a larger proportion of phytoplankton extracellular carbon release. Both PER and the percentage of dead phytoplankton cells increased from eutrophic to oligotrophic waters, while abundance of heterotrophic bacteria was highest in the intermediate waters. The percentage of living heterotrophic bacterial cells (range: 60-95%) increased with increasing phytoplankton extracellular carbon release from productive to oligotrophic waters in the subtropical NE Atlantic. The lower PERs, observed at the upwelling waters, have resulted in a decrease in the flux of phytoplankton dissolved organic carbon (DOC) per bacterial cell. The results highlight phytoplankton cell death as a process influencing the flow of dissolved photosynthetic carbon in this region of the subtropical NE Atlantic Ocean, and suggest a close coupling between the fraction of primary production released and heterotrophic bacterial cell survival.This research is a contribution to the project RODA (CTM-2004-06842-CO3-O2) and to the project StressX (CTM2012-32603), funded by the Spanish Ministry of Economy and CompetitivenessPeer Reviewe

Comparison of data-driven building energy use models for retrofit impact evaluation

A change-point (piecewise linear regression) model fitted to the pre-retrofit data as the counterfactual for the savings calculation, is considered to be the best approach to evaluating the energy savings of building retrofits ( ASHRAE Guideline 14). However, when applied to a large portfolio savings analysis with substantial multi-year data, the change-point model does not fit the data well in some cases. The study thus aims to improve the accuracy of the changepoint model by: 1) using more advanced non-linear models, 2) incorporating additional input features, and 3) increasing the time resolution of input variables. We found that random forest regression (RF) models with an array of climate (humidity, wind, solar radiation, etc.), time (day of the week, season, holiday), and energy consumption of the immediate past 1-4 hours (energy lag terms) outperformed the change-point model, shallow neural networks, and support vector machine regression (SVR). Our result implies that high resolution smart meter data should be used in place of monthly utility bills to more accurately evaluate retrofit savings. We further explored the relative contribution of the input variables to the random forest regression model using Shapley Value, a game theoretic variable importance metric. We found that the most important input feature is the energy consumption of the immediate past (or energy lag terms). We also found that solar radiation and weekend day indicators are more important than outdoor temperature. The improved model could provide better insights to portfolio managers in planning future energy retrofits. Policy makers could also use such models to evaluate the average energy saving potential for energy policy changes, such as the requirement of minimum insulation level, and lighting equipment efficiency

Implications of phytoplankton cell death losses forcarbon flux in Oceanic food-webs

En el océano, las condiciones ambientales adversas independientes de la predación tienen como resultado la muerte y lisis celular del fitoplancton que resulta en la liberación de carbono orgánico disuelto (PDOC) a la columna de agua. Las comunidades bacterianas heterotróficas marinas, normalmente dependientes de esta fuente de carbono para su metabolismo, obtienen un beneficio de la liberación de carbono recién sintetizado a la vez que participan en su reciclaje a través de la red trófica microbiana. A pesar de la repercusión que este proceso puede tener en el ciclo del carbono en los océanos, actualmente se desconoce cual es su contribución en ambientes marinos naturales y en el actual escenario de cambio global. El principal objetivo de esta tesis fue analizar las relaciones existentes entre la mortalidad de células del fitoplancton, la proporción de carbono orgánico disuelto (DOC) liberado por el fitoplancton y la supervivencia microbiana bajo diversas condiciones ambientales. La salud de comunidades naturales fitoplanctónicas y bacterianas, la producción primaria total y la liberación fitoplanctónica de DOC fueron determinadas in situ en diferentes regiones oceánicas que comprendieron los mares Mediterráneo, Ártico, Antártico y Atlántico. Los resultados obtenidos en este estudio demostraron la existencia de una relación entre condiciones ambientales tales como la temperatura del agua y la disponibilidad de nutrientes en la muerte celular del fitoplancton. Además, la mortalidad celular del fitoplancton determinada en estos ambientes puede explicar un 41.4% de la PDOC relativa a la producción primaria total, y en regiones oceánicas oligotróficas del noroeste del Océano Atlántico, este proceso sustentó una alta viabilidad bacteriana. Los resultados obtenidos durantes esta tesis resaltan el crucial papel de la lisis celular del fitoplancton en los océanos y ayudan a comprender cuales son las principales vías de transferencia de carbono desde la fotosíntesis hasta el metabolismo heterotrófico bacteriano.Important phytoplankton losses by cell death, independent of grazing are occurring in the ocean. Phytoplankton cells have been described to die upon encountering adverse environmental conditions, and cell death and lysis would result in the release of the carbon incorporated in the photosynthesis by the phytoplankton as dissolved organic carbon (PDOC). The availability of dissolved organic carbon (DOC) is a major constraint for the heterotrophic bacteria, consequently the release by cell mortality of the recently photosynthate carbon is expected to benefit the bacterial community and should be channelled through the microbial food web. All this processes have been poorly documented and the contribution of the phytoplankton cell death to the release of PDOC has not been yet explored in natural communities. The goal of this PhD Thesis is to provide quantitative information on phytoplankton and bacteria cell death in natural communities and to document the fraction of DOC released by phytoplankton (PDOC) under contrasting natural conditions. The exploration of the relationships between the phytoplankton cell mortality, DOC released by phytoplankton (PDOC) and microbial survival would contribute to better understand the path of carbon from photosynthesis to heterotrophic bacteria by cell death processes. Contrasting environmental conditions and communities from different oceanic regions including the Mediterranean Sea, Arctic, Antarctic and Atlantic oceans were studied. Evaluations of the in situ health status of the natural phytoplanktonic communities and bacteria were analyzed by testing the cell membrane permeability; a property that define cell death in cell biology. The total primary production, and the DOC production by phytoplankton were quantified to explore its dynamic with regard to the variability in phytoplankton cell mortality. The bacterial cell survival was also assessed under the same contrasting conditions mediating by the quantification of percentage of living heterotrophic bacteria. The proportion of dead of phytoplankton cells from the diverse phytoplankton populations encountered in the different communities, were related to environmental conditions as water temperature and nutrients availability, and helped to identify their competitive success. Consistent proportions of dead natural phytoplanktonic cells were found during this study that could represent in average about half of the total (40.5 %) phytoplankton abundance. Phytoplankton mortality constitutes a major process implicated in the production of dissolved organic carbon, as the percentage of phytoplankton dead cells explained the 41.4 % of the percentage of released production (PDOC) relative to total primary production. The large production of PDOC observed here, represented in average the half of the total primary production (54.4%) and supported, at the oligotrophic NE Atlantic Ocean, a higher bacterial viabilit

Humans and Nature in the Loop: Integrating occupants & natural conditioning into advanced controls for high performance buildings

Post Occupancy Evaluation plus Measurements (POE+M) has revealed that thermal, visual, acoustic and even air quality standards derived through controlled experimentation alone does not ensure comfort or health in buildings. Introducing human input into environmental standards and into user centric controls is critically needed for a sustainable future. For over a decade, CMU’s Center for Building Performance & Diagnostics has been gathering POE+M data from over 1500 workstations around the world and testing the benefits on innovative environmental control systems. The separation of ambient and task conditioning, the provision of task controls, the introduction of occupant voting and bio-signal inputs into ambient and task set-points, offers major gains in comfort, task performance, energy savings, as well as health and wellness

Die rußländische Sicherheitspolitik um die Jahrtausendwende

13 pages, 3 figures, 6 tablesThe metabolic carbon requirements and excretion rates of three major zooplankton groups in the Southern Ocean were studied in the vicinity of the Antarctic Peninsula in February 2009. The research was conducted in the framework of the ATOS project (POL2006-00550/CTM), as part of the Spanish contribution to the International Polar Year. Our objective was to ascertain the possible consequences of changes on size spectrum and community structure of the Southern Ocean zooplankton for the cycling of biogenic carbon and the stoichiometry of dissolved inorganic nutrients. The carbon respiratory demands and NH4-N and PO4-P excretion rates of < 5 mm size copepods, krill (represented by furcilia spp. and adult Euphausia superba) and salps (blastozoids of Salpa thompsoni) were estimated by incubation experiments. The respiration rates and N:P metabolic quotients of salps were more than twice those of krill (furcilia spp. and adults) and copepods. The possible community shift from krill to salps in the Southern Ocean would therefore encompass not only the substitution of a pivotal zooplankton group (krill) by one with an apparently indifferent role in Antarctic food webs and with higher specific metabolic carbon demands (salps), but the changes in the proportion of zooplankton-recycled N and P would modify the N:P stoichiometry of the dissolved nutrient pool, thus inducing changes in the functional and structural properties of phytoplankton that would translate to the whole Southern Ocean ecosystemThis work was supported by the Spanish funded projects ATOS (POL 2006-0550/CTM) to Carlos M. Duarte, PERFIL (CTM 2006-12344-C01) to Miquel Alcaraz, and the UE funded project ATP (www.eu-atp.org) contract # 226248 to P. WassmannPeer Reviewe

Metatranscriptomes reveal functional variation in diatom communities from the Antarctic Peninsula

Functional genomics of diatom-dominated communities from the Antarctic Peninsula was studied using comparative metatranscriptomics. Samples obtained from diatom-rich communities in the Bransfield Strait, the western Weddell Sea and sea ice in the Bellingshausen Sea/Wilkins Ice Shelf yielded more than 500K pyrosequencing reads that were combined to produce a global metatranscriptome assembly. Multi-gene phylogenies recovered three distinct communities, and diatom-assigned contigs further indicated little read-sharing between communities, validating an assembly-based annotation and analysis approach. Although functional analysis recovered a core of abundant shared annotations that were expressed across the three diatom communities, over 40% of annotations (but accounting for <10% of sequences) were community-specific. The two pelagic communities differed in their expression of N-metabolism and acquisition genes, which was almost absent in post-bloom conditions in the Weddell Sea community, while enrichment of transporters for ammonia and urea in Bransfield Strait diatoms suggests a physiological stance towards acquisition of reduced N-sources. The depletion of carbohydrate and energy metabolism pathways in sea ice relative to pelagic communities, together with increased light energy dissipation (via LHCSR proteins), photorespiration, and NO3 uptake and utilization all pointed to irradiance stress and/or inorganic carbon limitation within sea ice. Ice-binding proteins and cold-shock transcription factors were also enriched in sea ice diatoms. Surprisingly, the abundance of gene transcripts for the translational machinery tracked decreasing environmental temperature across only a 4 degrees C range, possibly reflecting constraints on translational efficiency and protein production in cold environments.Portuguese Science Foundation (FCT) [PTDC/MAR/72630]; Spanish Ministry of Economy and Competitiveness (under the scope of the International Polar Year (IPY)) [POL2006-00550/CTM]info:eu-repo/semantics/publishedVersio

Comparing marine primary production estimates through different methods and development of conversion equations

Numerous studies have compared the rates of primary production using various techniques at specific locations and times. However, these comparisons are local and cannot be used to compare or scale rates of primary production using different methods across ocean basins or seasonal time scales. Here, we quantify the range in rates of primary production derived using different techniques and provide equations that allow conversions of estimates between different methods. We do so on the basis of a compilation of data on volumetric estimates of primary production rates concurrently estimated with at least two different methods. We observed that the comparison of estimates of marine phytoplankton primary production derived from different methods reveals very large variations between methods. The highest primary production estimates are derived using the 18O method, which may provide the best and more generally applicable estimate of gross primary production (GPP). The regression equations presented in this work provide the best available approach to convert data across methods and therefore integrate and synthesize available and future data derived using different methods

Implications of Phytoplankton cell death losses for carbon flux in oceanic food-webs

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Phytoplankton community structure during the record Arctic ice-melting of summer 2007

In the summer of 2007, the Arctic Ocean experienced the largest loss of ice cover yet observed. We examined the phytoplankton community composition at several stations in the NE Arctic Sector during the ATOS-Arctic cruise in July 2007, specifically in the Fram Strait and along the permanent ice edge up to 81°N. The prymnesiophyte Phaeocystis pouchetti, present exclusively in its colonial form, dominated the whole phytoplankton community, representing 82.1 ± 3.1% (mean ± SE) of the phytoplankton biovolume in the region. Diatoms, small flagellates and dinoflagellates, expected to dominate the ice-melt waters in this sector of the Arctic Ocean, were practically insignificant, representing 7.3 ± 2.4%, 6.8 ± 1.4% and 4.4 ± 1.2% of phytoplankton biovolume, respectively. The fraction of the phytoplankton biomass that comprised diatoms increased with increasing water temperature and salinity, and was, therefore, negatively associated with the increased load of ice-melt waters. In contrast, the fraction of the biomass that comprised P. pouchetii was not as clearly related to temperature and had a weak tendency to decrease with increasing temperature. This pattern was likely the result of different populations stress, as the percentage of living cells of P. pouchetii increased with increasing salinity and temperature. The exceptional dominance of the colonial form of P. pouchetii during the massive ice losses of summer 2007 provides indication of major changes in phytoplankton community structure and carbon flow with climate change in the Arctic Ocean. © 2010 Springer-Verlag.This research is a contribution to the ATOS project, a Spanish contribution to the International Polar Year, funded by the Spanish Ministry of Science and Innovation (ref. POL2006-00550/CTM). We thank the crew of R/V Hespérides for support. We are also grateful to Johnna Holding for her kind re-lecture. S. L. was supported by a EUR-OCEANS fellowshipPeer Reviewe