1,700 research outputs found
Response of mature Norway spruce (Picea abies) to elevated atmospheric CO²
No full textThe aim of this thesis was to identify pathways and rates of C allocation in tall forest trees, and to identify effects of elevated CO2 on respiratory processes and root growth. Correspondingly, this thesis is divided into three separate parts:
Chapter 2)
Long-term 13C labeling provides evidence for temporal and spatial carbon allocation patterns in mature Picea abies (published in Oecologia)
Chapter 3)
Respiratory fluxes and fine root responses in mature Picea abies trees exposed to elevated atmospheric CO2 concentrations (published in Biogeochemistry)
Chapter 4)
Photosynthetic enhancement and diurnal stem and soil carbon fluxes in a mature Norway spruce stand under elevated CO2 (published in Environmental and Experimental Botany)
The work was conducted at the Swiss canopy crane (SCC) research site in Hofstetten near Basel, Switzerland, and explored signals produced by free air CO2 enrichment (FACE) in 110-year-old, ca. 37m tall P. abies trees. Chapter 2 capitalizes on the isotopic signal carried by the CO2 gas used for CO2 enrichment, yet does not address effects of elevated CO2 as such, but rather deals with basic questions of C transfer in tall trees. Chapter 3 explores the longer-term CO2 effects on mature P. abies (i.e. 2.5 years), whereas chapter 4 reports short-term (diurnal) responses to elevated CO2. In the following, I will provide a summary of the results of the three chapters of my thesis, extended by a conclusion that links these chapters.
Chapter 2) Long-term 13C labeling of Picea abies
As a side effect, the FACE technique provided the unique opportunity to study C translocation within the tree body using the stable isotope 13C signal the FACE gas carries. Since control trees are not (can not) be similarly labeled with 13C the tree responses to elevated CO2 were not the subject of this chapter. Yet, FACE resembles a continuous 13C labeling of new assimilates. Tracking the fate of these assimilates over a period of 2.5 years in tall trees offers new insights in tree C relations under steady state conditions. We tracked 13C signals in mature P. abies trees at a high spatial and temporal resolution, i.e. from the canopy (needles and branchlets), down to the tree trunk (year rings and stem CO2 efflux), and into the soil compartment (fine roots, fungi, soil CO2 efflux). The following key questions were answered:
1. How long does it take for new C to arrive at a certain tissue type or respiratory flux?
2. What is the proportional contribution of newly assimilated C to concurrent tree tissue production and maintenance?
3. How long does it take until old C is replaced by new C in various tissues?
Generally, we observed a reduction of new assimilate investment with distance from the canopy, which can be explained by a progressive dilution of new C into the existing C storage pools in the tree. New sunlit needles (and adjacent branchlets) exhibited a nearly 100% share of new C, whereas shaded needles also used some older C. Stem wood isotope signals evidenced a complete exchange of old C by new C within 2 years. Fine roots contained only 49-56% new C, hence are using older C pools for a longer period of time. A surprisingly low fraction of novel C (26-43%) was recovered from fungal sporocarps, presumably related to the influence of neighboring trees that were not CO2 enriched. The first appearance of new C in soil and stem CO2 release occurred after 12 days, reflecting a lag due to the long transport distances in these 37m tall trees. The CO2 released by stems was composed of 50% new C already in the first year of FACE. In contrast, only ca. 15% new C contributed to soil CO2 efflux, reflecting the use of older substrates, and the influence of older roots and litter from neighboring trees blown in by wind.
These findings indicate a rapid contribution of new assimilates to tissue formation, and thus, a fast replacement of mobile C reserves with new C, and a progressive signal dilution from treetop to the bottom. The two-year replacement time in stem xylem shows that the storage pool is contributing substantially to tree ring formation. We speculate that the turnover of mobile C pools might be enhanced by elevated CO2, and the metabolic costs of this turnover might compensate for some of the extra C taken up at elevated CO2 concentrations, and thus, may explain the ‘missing C’ at the whole tree level. These metabolic costs are unlikely to produce measurable signals at tissue level, given the large heterotrophic volume of such trees.
Chapter 3) Responses of Picea abies to elevated CO2
Most FACE experiments revealed strong initial growth responses to elevated CO2 that diminished over the first 3 years (Körner 2006). Since growth in natural undisturbed systems is commonly not showing a continued stimulation under altered CO2 for reasons of nutrient supply, a step increase in CO2 concentration should induce overflow responses in terms of enhanced respiration and fine root expansion, the latter in order to forage for nutrients to balance the additional C input. In this web-FACE experiment, established in a natural Central European forest, we investigated mature ca. 110-year-old P. abies trees in their steady state of growth (C cycle coupled to the nutrient cycle; Körner 2006). In this publication we were particularly interested in:
1. Seasonal shifts in assimilate allocation;
2. Locations of C-investment;
3. Residence times (turnover) of mobile C pools.
We tracked the respiratory and fine root growth responses of these trees before and directly after the start of FACE, and for further 2.5 years. The CO2 concentration in the canopy (e.g. 540 ppm) was about twice the pre-industrial level. We anticipated a stimulation of CO2 release, and faster root expansion into root-free soil space (in-growth core method), but we also expected a weaker signal in these mature trees compared to young trees. Seasonal stem CO2 efflux did not show any sign of increase during the 2.5 years under elevated CO2. This result lines up with the lack of any stem radial growth response (ongoing work). Fine roots (<0.5-2 mm) did not accumulate more dry matter in the course of 2.5 years of CO2 fertilization. Interestingly, we observed a slight but significant reduction of CO2 release from the soil despite clear evidence by isotopic signals that novel assimilates arrived in the soil.
These data suggest that such mature trees do not even show a transient stimulation of respiration to a step increase of CO2, as was observed in other FACE experiments using much younger trees (Norby et al. 2010). Other growth-limiting factors appear to prevent more vigorous tree growth and thus, metabolism at high CO2 (Norby & Zak 2011). N limitation can be excluded at our site because of high N-deposition. A part of the extra C taken up by needles at elevated CO2 might have been allocated belowground, however, not to fine roots. Conversely, slightly reduced rather than increased rates of soil CO2 efflux implies that respiration of roots and/or soil organisms declined under elevated CO2, implying an overall reduced C allocation into the rhizosphere. We assume that extra C absorbed by foliage is either retained within the tree body (stored carbohydrates), recycled by respiration rates below detection limit across all heterotrophic plant tissues, or lost through enhanced leaching of dissolved organic or inorganic carbon (DIC/DOC).
In summary, we conclude that mature P. abies trees at our site are roughly C saturated at current CO2 concentrations. We find no indication of stimulated belowground metabolic activity (fine roots and soil CO2 efflux).
Chapter 5) Diurnal courses in P. abies under elevated CO2
Leaf-level photosynthetic stimulation in trees following a step increase of atmospheric CO2 was commonly observed in CO2 enrichment experiments, however, mostly without corresponding growth stimulation. Hence, the fate of this additional C input in tree still is not fully resolved, but C overflow mechanisms such as respiratory C losses might account for this C surplus. Since these potential variations in C fluxes might not be detectable on a daily basis, a response may emerge on shorter timescales (i.e. on a diurnal basis). This chapter (co-authorship) explored the diurnal variations in C fluxes (i.e. net photosynthesis, and CO2 efflux from the forest floor and the from stem) in mature P. abies trees exposed to elevated CO2 in the SCC web-FACE experiment. We tracked the diurnal variations of these fluxes on a summer day shortly before the onset of FACE, and twice during the FACE periods in summer 2009 and 2010.
Results from this study confirmed a CO2-induced photosynthetic stimulation shortly after the onset of FACE, and a change in magnitude throughout the day. Intriguingly, this stimulation of Anet diminished in the second year under FACE, indicating photosynthetic downregulation in these trees. The respiratory fluxes from P. abies stems, as observed on a seasonal basis (chapter 4), were not affected by high levels of CO2 whereas soil CO2 efflux decreased slightly with prolonged exposure to elevated CO2. Further, the diurnal patterns of CO2 release (stems and soil) were not altered by CO2 enrichment.
In conclusion, despite larger C input into the tree system in the first year of FACE, respiratory overflow mechanisms could not be observed even on a diurnal basis, corroborating our results obtained in chapter 4. Additionally, the photosynthetic downregulation observed at high CO2 confirms the assumption that these trees are C saturated.
Final conclusions
Stimulatory effects of elevated CO2 on tree growth are constrained by several growth-limiting factors, mainly availability of nutrients and other resources, and the developmental stage (age) of a tree. This thesis for the first time illuminates the current (chapter 2) and future (chapters 3 and 4) C balance of mature evergreen conifers subjected to prospective CO2 levels of 540 ppm in a near-natural forest in Switzerland. Isotopic labeling of fresh assimilates successfully depicted the pathways of C in these trees, thus provided basic insights into how P. abies trees handle the distribution of assimilates. We observed remarkable tree-specific variations in all pre-treatment measurements, emphasizing the importance of recording baseline conditions prior to any experiment. At current CO2 levels, all investigated tissues (except for needles in the sun), and respiratory fluxes depended only partly on new assimilates. The further away from the upper tree canopy, the greater the role of old C stores for new tissue formation and respiration. Since no aboveground growth stimulation was observed (ongoing works) despite higher but transient rates of photosynthesis, and since stem CO2 efflux remained unaffected by elevated CO2, we assume that the extra C assimilated in the first year is dissipated via respiration associated with C turnover (phloem) at rates below detection limit. These processes seem to be too small to be detectable but their accumulated rate along the entire phloem system might account for the unresolved ‘missing C’ at elevated CO2. We found no evidence for increased C investment belowground at elevated CO2 that might also account for some of the higher leaf-level C input at elevated CO2.
References
Körner C (2006) Plant CO2 responses: An issue of definition, time and resource supply. New Phytologist 172:393-411
Norby RJ, Warren JM, Iversen CM, Medlyn BE, McMurtie RE (2010) CO2 enhancement of forest productivity constrained by limited nitrogen availability. Proceedings of the National Academy of Sciences of the United States of America 107:19368-19373.
Norby RJ, Zak DR (2011) Ecological lessons from free-air CO2 enrichment (FACE) experiments. Annual Review of Ecology, Evolution, and Systematics 42:181-20
Retinotopic activation in response to subjective contours in primary visual cortex.
No full textObjects in our visual environment are arranged in depth and hence there is a considerable amount of overlap and occlusion in the image they generate on the retina. In order to properly segment the image into figure and background, boundary interpolation is required even across large distances. Here we study the cortical mechanisms involved in collinear contour interpolation using fMRI. Human observers were asked to discriminate the curvature of interpolated boundaries in Kanizsa figures and in control configurations, which contained identical physical information but did not generated subjective shapes. We measured a spatially precise spin-echo BOLD signal and found stronger responses to subjective shapes than non-shapes at the subjective boundary locations, but not at the inducer locations. The responses to subjective contours within primary visual cortex were retinotopically specific and analogous to that to real contours, which is intriguing given that subjective and luminance-defined contours are physically fundamentally different. We suggest that in the absence of retinal stimulation, the observed activation changes in primary visual cortex are driven by intracortical interactions and feedback, which are revealed in the absence of a physical stimulus
Globale Ordnungspolitik am Scheideweg: eine Analyse der aktuellen Finanzmarktkrise
No full text'Die Finanzmarktkrise hat mittlerweile die virtuellen Finanzmärkte verlassen und ist in einen konjunkturellen Abschwung gemündet. Nach den Erfahrungen vergangener Finanzkrisen steht eine tiefe und lang anhaltende Rezession bevor. Weltweit steht die ökonomische und politische Bewältigung dieser Krise an der Spitze der politischen Prioritäten. Zusätzlich dürfte der Verzicht auf langfristig ausgerichtete Investitionen in Forschung und Entwicklung, Infrastruktur, Klimaschutz, Energie- und Nahrungsmittelsicherheit eine fatale Wirkung haben. Angesichts des internationalen Zusammenhangs von Märkten und Politiken werden nationale Alleingänge jedoch nicht zum Ziel führen. Das gilt für die Fiskal- und Geldpolitik zur unmittelbaren Krisenbewältigung ebenso wie für alle längerfristig ausgerichtete Maßnahmen im Bereich der internationalen Politik. Vor diesem Hintergrund analysiert die Studie die Situation in den wichtigsten Schlüsselmärkten und zentralen Politikfeldern. Leitend sind folgende Fragen: 1. Welche Konsequenzen hat die Finanzmarktkrise für die USA, die EU, China, Indien, Russland, Brasilien, Mexiko, die Staaten des Golfkooperationsrats und Südafrika? Welche Gegenmaßnahmen haben diese Länder bislang ergriffen? Und welche Vorstellungen zur Reform der 'Global Economic Governance' dominieren in ihnen? 2. Welche Implikationen hat die Finanzmarktkrise für die Finanzpolitik, die Handelspolitik, die Energiemärkte, die Nahrungsmittelversorgung, den Klimaschutz und die Europäische Integration?' (Autorenreferat). Inhaltsverzeichnis: Stormy Mildner: USA - pragmatisches Krisenmanagement verstärkt Zielkonflikte (15-20); Jutta Frasch: Die Finanzkrise: ein Weckruf für die EU (21-26); Hanns Günther Hilpert: China - Domino oder Rettungsanker der Weltwirtschaft? (27-31); Hanns Günther Hilpert, Christian Wagner: Indien - zurück zur Hindu-Wachstumsrate? (32-36); Ognian N. Hishow: Russland - Segen und Fluch des Ressourcenreichtums (37-41); Caroline Silva-Garbade, Claudia Zilla: Brasilien - Jazz auf hohem Niveau (42-46); Günther Maihold: Mexiko - Erkältung oder Lungenentzündung? (47-51); Eckart Woertz: Golf-Kooperationsrat - mit Ölpolster in die Krise (52-56); Gero Erdmann: Südafrika - Fels in der Krisenflut? (57-64); Heribert Dieter: Die künftige Gestaltung der internationalen Finanzbeziehungen (65-71); Christina Langhorst, Stormy Mildner: Finanzkrise und Welthandel: der Abschluss der Doha-Runde könnte einen wichtigen Impuls geben (72-79); Kirsten Westphal: Von der Finanzkrise in die Energiekrise? (80-85); Bettina Rudloff: Wie die Finanzkrise aus der Ernährungskrise eine Hungerkrise macht (86-92); Susanne Dröge: Klimapolitik in Zeiten der Wirtschaftskrise (93-98); Daniela Schwarzer: Auswirkungen der Krise auf die Eurozone (99-106)
The synthesis of ortho-condensed polyaromatic compounds and their physico-chemical properties
No full textThis Bachelor Thesis deals with the preparation of laterally/axially extended polyaromatic compounds with helically shaped structure ("long/wide" helicenes) with major focus on optimizing key steps in the synthesis of tetrabenzo[9]helicene and its derivatives. In Theoretical Background the author summarises the physico- chemical properties of helicenes and methods of their preparation describing approaches that can be used for the preparation of extended helicenes. In chapter Results and Discussion the synthesis of tetrabenzo[9]helicene and its derivatives is presented including their preparation in a nonracemic form, resolution of racemates into enantiomers and study on their properties. The Experimental Part provides the reader with practical information on experimental procedures and characterization of the prepared compounds
Type 1 interferon receptor (IFNAR)-dependent modulation of myeloid cell activation determines the course of experimental autoimmune encephalomyelitis
No full textType 1 interferon receptor (IFNAR)-dependent modulation of myeloid cell activation determines the course of experimental autoimmune encephalomyelitis
No full textBythinella angelitae
No full textBythinella angelitae nom. nov. Synonymy: Paludinella opaca Ziegler — Frauenfeld, 1857: 576, fig. 6, non Gallenstein, 1848: 18–19. Type material: Lectotype of Paludinella opaca Frauenfeld, 1857, here designated, and holotype of Bythinella angelitae: NHMW (Naturhistorisches Museum Wien) 103753 (Veldes See = Lake Bled, Slovenia); paralectotypes of P. opaca Frauenfeld, 1857 and paratypes of B. angelitae: NHMW 103754 (4, Veldes See = Lake Bled, Slovenia); NHMW 103758 (three specimens, no locality data); NHMW 103759 (three specimens, no locality data). Type locality: Through our designation of the lectotype from the Slovenian sample, the type locality is restricted to Veldes See = Lake Bled, which, since the species is not lacustrine (Radoman, 1976), must be conceived as “the area around Lake Bled”. Additional material: spring in Tscheppaschlucht, southern Carinthia, 46.4837 °N, 14.2632 °E, 680 m asl., leg. P. Mildner, 30 March 2006. Etymology: This species is dedicated to the first author’s wife Angela “Angelita” Schmitz-Ornés. Description: Shell (Figs 2, 3; Table 2) conical to subcylindrical with typical blunt apex, holotype 3.18 mm high and 1.71 mm wide, with 4 whorls, shells from the Tscheppaschlucht 2.61 ± 0.08 mm (range 2.48– 2.76 mm) high and 1.67 ± 0.06 mm (range 1.56–1.80 mm) wide, with 3 3 / 8 – 3 7 / 8 convex whorls of which protoconch comprises 1.1–1.2 whorls with delicately pitted spiral lines, teleoconch without structure apart from growth lines; aperture ovate with typically pronounced angle posteriorly; umbilicus largely covered; operculum corneous, yellow, thin, ellipsoidal, paucispiral, nucleus submarginal. Tentacles without conspicuous ciliation; epidermis black except mantle edge; ctenidium with 21–26 gill filaments, connected to pericardium with short vessel, osphradium under or slightly behind middle of ctenidium, elongate, about 1 / 3 or somewhat less of gill length, kidney may penetrate slightly into the mantle roof; radula formula R: 4–5 1 4–5 / 1-2 1–2, L: 3 1 4, M 1: 17–23, M 2: 27–31. Stomach without appendix, rectum with shallow loop along pallial genital glands; ovary small sac with wide lobes comprising 0.25 whorls, starting about 1 whorl below apex, distal end close to but not reaching posterior end of stomach, albumen gland comprising three fifth length of pallial oviduct, renal oviduct describing wide loop of 270 °, seminal receptacle small, tubular, arising close to junction with bursal duct, receptacle and bursal duct may be embedded into albumen gland tissue, bursa copulatrix a long sac arching around posterior end of albumen gland, bursal duct entering ventrally (Fig. 6); testis lobate, comprising about 1 whorl, starting about 0.5 whorls below apex, covering posterior chamber of stomach, seminal vesicle comprising 0.25 whorls, proximal vas deferens entering kidney-shaped prostate just in front of posterior wall of mantle cavity, distal vas deferens emerging at distal tip of prostate becoming muscular ductus ejaculatorius coiling in proximal third of resting penis, penis longer than tubular accessory gland, anterior third of penis with black pigment. Habitat and distribution: It is only known from springs in the area of Lake Bled in Slovenia and in the Tscheppaschlucht just across the Austrian border in Carinthia. Remarks: Morphologically and anatomically, B. angelitae nom. nov. falls well into the range of variation of its immediate sister species, B. opaca, which is also stem species of B. robiciana characterized by a globular, derived shell shape (see below). The only distinguishing feature of the new species is the denticulation of the marginal teeth of the radula, with the fewest number of denticles on the inner marginal and the highest number on the outer one. Although there is some overlap with the remaining populations — hardly though in case of the outer marginal —, the shift towards the extreme ends of the overall distribution in opposite directions must be considered distinctive. There are reports of phenotypic plasticity of radula tooth shape depending on diet (Padilla 1998; Andrade & Solferini 2006), but we are not aware of any case of phenotypical plasticity in numbers of denticles. The numbers representing the extreme ends of the total variation observed among the populations investigated suggest that probably more than one controlling genetic locus is involved. In addition, B. angelitae nom. nov. turned out to be sister species of B. opaca and B. robiciana with HKY + I + Γ distances> 0.048 in the phylogenetic analysis based on the 638 bp long fragment of COI. The combination of these facts justifies recognition as separate species. According to paragraph 72.7 of the ICZN the types of the species whose name is to be replaced are also types of the new name regardless of any restriction of the applicability of that name as in the present case. Therefore, the samples from Italy preserved their status as types although they most likely represent a different species (see Introduction). Frauenfeld’s (1857) Lake Bled-sample apparently consisted of representatives of two populations judging from the color of the periostracum and the different ways of original treatment. The three lighter shells had been glued onto black cardboard (see Fig. 2), whereas the two darker shells were removed from white cardboard.Published as part of Haase, Martin, Wilke, Thomas & Mildner, Paul, 2007, Identifying species of Bythinella (Caenogastropoda: Rissooidea): A plea for an integrative approach, pp. 1-16 in Zootaxa 1563 on pages 9-11, DOI: 10.5281/zenodo.17838
Type 1 interferon receptor (IFNAR)-dependent modulation of myeloid cell activation determines the course of experimental autoimmune encephalomyelitis
No full textType 1 interferon receptor (IFNAR)-dependent modulation of myeloid cell activation determines the course of experimental autoimmune encephalomyelitis
No full textType 1 interferon receptor (IFNAR)-dependent modulation of myeloid cell activation determines the course of experimental autoimmune encephalomyelitis
No full text- …
