Co-limitation by iron, silicate, and light of three Southern Ocean diatom species

International audienceThe effect of combined iron, silicate, and light co-limitation was investigated in two Southern Ocean diatom species, Chaetoceros dichaeta and Actinocyclus sp. and one cosmopolitan species, Chaetoceros debilis, all isolated in the Southern Ocean (SO). We found species specific differences in the level of nutrient limitation and its effect on physiological and morphological parameters. Growth of all species tested was clearly co-limited by iron and silicate, reflected in a 4 to 40 times higher increase in cell numbers in the high iron, high silicate treatments compared with the controls. However, the effect of iron and silicate availability on chain length and frustules structures was species specific. Most drastic frustule malformation was found under iron and silicate co-limitation in C. dichaeta while Si limitation caused a strong cell elongation in both Chaetoceros species. Additional a significant increase in chain length was observed in these species under high iron conditions. Therefore, species composition in the SO is likely also indirectly affected by these nutrients via different effects on diatom grazing protection. These morphological changes reflect a potential as biological markers in sediments for the growth history of chain forming species. High light conditions, comparable with light intensities found in the upper 28 m of the SO, showed a negative impact on growth of the endemic species C. dichaeta and Actinocyclus sp. This is in contrast to the assumed light limitation of SO diatoms and indicates an adaptation strategy to the deep mixing and resulting low light conditions in the SO. In contrast to that, the cosmopolitan species C. debilis was not negatively affected by increased light intensity, indicating adaptation to a broader light environment. These results suggest that light limitation of SO phytoplankton due to deep wind mixed layers may play a minor role than hitherto assumed

Spatial Distributions of Multiple Dust Components in the PPN/PN Dust Shells

We investigate spatial distributions of specific dust components in the circumstellar shells of a proto-planetary nebula candidate, HD 179821, and a planetary nebula, BD$+30^{\circ}$3639, by means of spectral imaging. With high-resolution ground-based images and ISO spectra in the mid-infrared, we can derive ``dust feature only'' maps by subtracting synthesized continuum maps from the observed images at the feature wavelength. Such spatially detailed information will help to develop models for the evolution of dust grains around evolved stars.Comment: 4 pages + 7 figures, to appear in the proceedings of the conference, "Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution", Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny. Figures have been degraded to minimize the total file siz

Lavbundsarealerne ved Fussingø

På engene ved Fussingø Hovedgård blev der i 1997-2001 gennemført en tværfaglig undersøgelse af forskellige græsmarksstrategier, som afgræsning, slæt eller driftsophør, ud fra ønsket om at kunne øge naturkvaliteten under miljøvenlig græsmarksdrift og samtidig forbedre landbrugsproduktionen under sådanne forhold. Med henblik på at få en generel beskrivelse af engarealerne er der indsamlet nøgledata vedrørende geologi, afstrømningsforhold, arealernes driftshistorie, klima, hydrologi og vegetationen på arealerne. Der er benyttet en kombination af ældre beskrivelser og nye registreringer. Engområdet er beliggende i en tunneldal, som stort set følger Skals å forløbet. Der er tørveaflejringer med mindre lag af ler og kalkgytje indlejret lokalt. I den øverste meter af jordlaget er humusindholdet ca. 60%. Der var et højt N-indhold i jorden, men med stor variation indenfor området (1,8-2,7%). Den potentielle netto kvælstof mineralisering var betydeligt højere end det niveau man normalt finder på mineraljord. Afstrømningsoplandet ved Fussingø er på 1948 ha, og det består af fire del-oplande, der afvander til Skals å systemet. Lavbundsarealet på 411 ha udgør 21% af det samlede oplandsareal. Lavbundsarealet består bl.a. af 44% vådområder, som ikke udnyttes landbrugsmæssigt, og af 20% vedvarende græsningsarealer. Engarealerne, som indgik i forsøget, blev i perioden før 1955 og i perioden efter 1987 drevet med græsmarksdrift. I den mellemliggende periode var der mere eller mindre intensiv drift af arealerne med både græsmarksdrift og salgsafgrøder. Klimaet i forsøgsperioden var specielt ved at nedbøren i forårsperioden var stigende gennem de år forsøget varede, og arealerne blev mere og mere fugtige i vækstperioden. Med hensyn til fugtighed var der betydelige forskelle i vandstand fra græsningsfold til græsningsfold. Vegetationen var kulturpræget på østarealet og naturpræget på vestarealet. En forklaring på dette forhold kan være, at der på østarealet var en højere N-mineralisering og et højere indhold af plantetilgængeligt K. Danske lavbundsarealer kan variere meget, og der er ikke grundige beskrivelser af alle lavbundsarealer som af arealerne på Fussingø. Man kan derfor ikke sige, hvor stor en del af de danske lavbundsarealer, der har samme forhold som arealerne, der indgik i undersøgelsen. Ud fra gamle kortoptegnelser er det tidligere vurderet, at en tredjedel af Danmarks lavbundsarealer har humusjord og dermed tilsvarende jordtype som engene ved Fussingø

Chromatin status and transcription factor binding to gonadotropin promoters in gonadotrope cell lines.

BackgroundProper expression of key reproductive hormones from gonadotrope cells of the pituitary is required for pubertal onset and reproduction. To further our understanding of the molecular events taking place during embryonic development, leading to expression of the glycoproteins luteinizing hormone (LH) and follicle-stimulating hormone (FSH), we characterized chromatin structure changes, imparted mainly by histone modifications, in model gonadotrope cell lines.MethodsWe evaluated chromatin status and gene expression profiles by chromatin immunoprecipitation assays, DNase sensitivity assay, and RNA sequencing in three developmentally staged gonadotrope cell lines, αT1-1 (progenitor, expressing Cga), αT3-1 (immature, expressing Cga and Gnrhr), and LβT2 (mature, expressing Cga, Gnrhr, Lhb, and Fshb), to assess changes in chromatin status and transcription factor access of gonadotrope-specific genes.ResultsWe found the common mRNA α-subunit of LH and FSH, called Cga, to have an open chromatin conformation in all three cell lines. In contrast, chromatin status of Gnrhr is open only in αT3-1 and LβT2 cells. Lhb begins to open in LβT2 cells and was further opened by activin treatment. Histone H3 modifications associated with active chromatin were high on Gnrhr in αT3-1 and LβT2, and Lhb in LβT2 cells, while H3 modifications associated with repressed chromatin were low on Gnrhr, Lhb, and Fshb in LβT2 cells. Finally, chromatin status correlates with the progressive access of LHX3 to Cga and Gnrhr, followed by PITX1 binding to the Lhb promoter.ConclusionOur data show the gonadotrope-specific genes Cga, Gnrhr, Lhb, and Fshb are not only controlled by developmental transcription factors, but also by epigenetic mechanisms that include the modulation of chromatin structure, and histone modifications

Analytic structure of solutions to multiconfiguration equations

We study the regularity at the positions of the (fixed) nuclei of solutions to (non-relativistic) multiconfiguration equations (including Hartree--Fock) of Coulomb systems. We prove the following: Let {phi_1,...,phi_M} be any solution to the rank--M multiconfiguration equations for a molecule with L fixed nuclei at R_1,...,R_L in R^3. Then, for any j in {1,...,M} and k in {1,...,L}, there exists a neighbourhood U_{j,k} in R^3 of R_k, and functions phi^{(1)}_{j,k}, phi^{(2)}_{j,k}, real analytic in U_{j,k}, such that phi_j(x) = phi^{(1)}_{j,k}(x) + |x - R_k| phi^{(2)}_{j,k}(x), x in U_{j,k} A similar result holds for the corresponding electron density. The proof uses the Kustaanheimo--Stiefel transformation, as applied earlier by the authors to the study of the eigenfunctions of the Schr"odinger operator of atoms and molecules near two-particle coalescence points.Comment: 15 page

Aging of poled ferroelectric ceramics due to relaxation of random depolarization fields by space-charge accumulation near grain boundaries

Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the energy of the local depolarization field caused by mismatch of the polarizations of neighbor grains. The kinetics of charge migration assumes presence of mobile oxygen vacancies in the material due to the intentional or unintentional acceptor doping. Satisfactory agreement of the theory with experiment on the Fe-doped lead zirconate titanate is demonstrated.Comment: theory and experiment, 22 pages, 3 figure

Efficiency of a thermodynamic motor at maximum power

Several recent theories address the efficiency of a macroscopic thermodynamic motor at maximum power and question the so-called "Curzon-Ahlborn (CA) efficiency." Considering the entropy exchanges and productions in an n-sources motor, we study the maximization of its power and show that the controversies are partly due to some imprecision in the maximization variables. When power is maximized with respect to the system temperatures, these temperatures are proportional to the square root of the corresponding source temperatures, which leads to the CA formula for a bi-thermal motor. On the other hand, when power is maximized with respect to the transitions durations, the Carnot efficiency of a bi-thermal motor admits the CA efficiency as a lower bound, which is attained if the duration of the adiabatic transitions can be neglected. Additionally, we compute the energetic efficiency, or "sustainable efficiency," which can be defined for n sources, and we show that it has no other universal upper bound than 1, but that in certain situations, favorable for power production, it does not exceed 1/2