Tree ring studies in the tropics and subtropics

According to the Intergovernmental Panel on Climate Change the global surface temperature has continuously risen since 1861. Increasing temperatures combined with changing precipitation patterns are strong indications for a more active and more intense hydrological cycle in the coming decades. In this respect, it is undisputed that the tropical regions are important for the global climate system. The reaction of tropical forests to enhanced atmospheric CO2 concentrations plays a pivotal role for the land carbon and the land water cycle. Currently our understanding of the physiological reactions such as growth response of tropical trees to rising atmospheric CO2 concentration, partly related to water-use-efficiency (WUE) and climate change is still rather poor and controversially discussed (Frank et al. 2015). Modifications in their carbon uptake and transpiration rate have inevitably global consequences. It is still unclear if tropical trees assimilate more CO2 with constant or slightly reduced water losses in a CO2 richer world or if the carbon gain remains almost unchanged with reduced transpiration.Tree-rings are well suited for environmental investigations with much potential for verifications of their well-being. Tree rings are mostly annually resolved, contain environmental information, are easily sampled and as such valuable archives. Growth limiting factors control the development of trees allowing the derivation of transfer functions that relate tree growth to tree physiological quantities as well as climatic parameters (Cook and Kairiukstis 1992; Fritts 1976).Up to now hemispheric investigations using tree rings are mainly based on data sets of mid and high latitude sites or Nordic tree-line sites. Investigations based on trees of tropical or subtropical regions are comparatively rare. This has several causes. One reason is the difficulty to identify tree-rings or growth increments of annual resolution. Consequently, it is often demanding to construct reliable data sets, i.e. chronologies of annual time resolution, for extracting climatic signals and/or tree physiological parameters. Therefore, tropical or subtropical trees have only just recently come into focus of environmentalists and climatologists. Subsequently tree-ring widths chronologies of tropical tree ensembles are anything but numerous and chronologies, e.g. regarding stable isotopes are almost non-existent

A remarkable relationship of the stable carbon isotopic compositions of wood and cellulose in tree-rings of the ropical speices Cariniana micrantha (Ducke) from Brazil

The stable isotopes of carbon were analysed in total wood and cellulose from the tree-rings of the tropical wood species Cariniana micrantha (Ducke). The aim was to examine the isotopic relationship between total wood and its cellulose over the last two and a half centuries. Although the correlation for the whole time period is very high (r = 0.96) it is remarkable that different sub-periods deviate strongly from this close relationship. Consequently, a good correlation from the subset of a longer isotopic record cannot necessarily prove its validity for the whole record. The study indicates that changes of the carbon isotopes of cellulose and of total wood show sometimes during short sub-periods different isotope patterns presumably caused by different environmental effects. Thorough calculations indicate that strong variations within the isotopic record especially changes of the isotopic level along a chronology lead to high correlations between δ13Cwood and δ13Ccel. Contrary thereto subsections with low isotopic variability lead to low correlations. The results imply that long term trends provide similar patterns. Therefore, if long term trends are of interest such as e.g. in climate reconstruction then total wood can be analysed in favour of cellulose, thus saving a tremendous amount of work. However, if short term aspects from a longer record are of interest, cellulose and total wood may sometimes provide different information. In addition it is hypothesized that during intervals of low isotopic variability the proportions of the various wood components may change relative to each other, leading for certain time intervals to different isotope patterns

Tagesgang der H2H_{2} 18^{18}O-Anreicherung im Blattwasser von Eiche und Birke

The work presents a detailed day course of the H$_{2}$ $^{18}$O enrichment within the leaf water of an oak and a birch. Three phases can be distinguished. After a rapid increase during the morning the H$_{2}$ $^{18}$O content falls during the afternoon and shows a very small decrease during the time of 100 % relative humidity at night. The two species do not navy significantly

Die Hochtemperaturzelle HTZ : ein neues Verfahren zur Extraktion von Sauerstoffisotopen aus biogenen Silikaten

Biogene Silikate und deren Sauerstoffisotopensignatur haben sowohl für die marine als auch für die terrestrische paläoklimatologische Forschung aufgrund ihres ubiquitären Vorkommens ein sehr großes Potenzial. Bedingt durch methodische Probleme bei ihrem Aufschluss, sind die Sauerstoffisotope biogener Silikate jedoch bisher nur wenig genutzt worden. Zielsetzung war daher die Entwicklung eines neuartigen, keine Fraktionierungseffekte verursachenden Aufschlussverfahrens zur Extraktion der Sauerstoffisotope. Das neu entwickelte Hochtemperatur-Aufschlussverfahren (HTZ) verzichtet auf die bisher übliche Fluorinierung und erlaubt einen relativ hohen Probendurchsatz. Dies wird durch die Abtrennung sauerstoffhaltiger Verunreinigungen" der Probe und anschließendem Aufschluss in einem Schritt erreicht. Dabei wird ein Mittelfrequenzgenerator zur induktiven Aufheizung eines in eine doppelwandige Glasküvette eingebrachten Reaktionsstabes aus Glaskohlenstoff genutzt. Der Reaktionsstab ist oben mit einer Bohrung, die als Probenbehälter dient, versehen, welche ein Gemisch aus Probenmaterial und Graphitpulver aufnehmen kann. Dieser Stab ist selbst von einem dünnwandigen, oben geschlossenen Zylinder aus Glaskohlenstoff umgeben, um einen Austausch des bei der Reaktion freiwerdenden, im CO gebundenen Sauerstoffs mit dem Sauerstoff der Glasküvette zu verhindern. Nach Evakuierung der Küvette, kann das Probenmaterial aufgeschlossen werden. Der Reaktionsstab wird zur Freisetzung des Sauerstoffs aus biogenem Silikat bis auf eine Temperatur von ca. 1550°C erhitzt. Dabei reagiert Graphit mit Siliziumdioxid zu Siliziumcarbid und Kohlenstoffmonoxid (CO). Das entstandene Kohlenstoffmonoxid wird mit Hilfe flüssigen Stickstoffs unter Verwendung eines Molekularsiebes (5$\mathring{A}$) in ein Probenröhrchen einkondensiert und später in einem Isotopenverhältnismassenspektrometer (Doppeleinlasssystem) vermessen. Zur Freisetzung des Sauerstoffs aus anderen Silikaten kann die induktive Heizung bis auf Temperaturen von 2200°C erhöht werden. Die Temperatureichung erfolgte mit Hilfe eines von der Physikalisch-Technischen Bundesanstalt geeichten Quotientenpyrometers. Die Ergebnisse der durchgeführten Versuchsreihen zeigen, dass biogene Silikate mit dem neuen Verfahren vollständig und ohne Fraktionierung der Sauerstoffisotope in COMessgas umgesetzt werden. Für biogene Silikate unterschiedlicher Herkunft sowie einen internationalen anorganischen Standard konnten $\delta^{18}$-Werte mit einem maximalen Messfehler von ±0,3%o (maximale Abweichung vom Mittelwert) reproduziert werden. Dies bedeutet im allgemeinen eine Standardabweichung von $\sigma \le$ ±0,15$^{°}/_{°°}$. Die Eichung des neuen Verfahrens mit einem internationalen Standard lieferte für Materialien, deren $\delta^{18}$-Werte mit den bisherigen Verfahren publiziert vorliegen, eine sehr gute Übereinstimmung. Damit steht ein neuartiges Verfahren zur Bestimmung der Sauerstoffisotopenverhältnisse biogener Silikate zur Verfügung. Es erlaubt einen wesentlich einfacheren Zugang zu deren $\delta^{18}$-Werten und eröffnet damit eine Vielzahl neuer Anwendungsmöglichkeiten

Kontinuierliche Atmungsmessungen bei E. coli

Escherichia coli wild type is grown in a gas tight batch culture. The oxygen partial pressure is measured continuously in the liquid phase during the growth of the bacteria. The system allows the observation of rapid changes of the respiration rate. Thereby we found a diauxic respiration behavior with glucose as the only carbon source in a pure mineral salt medium. The second respiration phase is caused by a substance secreted into the medium during the uptake of glucose. The presence of glucose in the medium stops the metabolic uptake of this secretion product

Late Holocene relative humidity history on the southeastern Tibetan plateau inferred from a tree-ring δ 18^{18} O record: Recent decrease and conditions during the last 1500 years

In recent decades, the Tibetan plateau (TP) experienced a distinctive temperature increase, with fundamental consequences for the hydrological system. As meteorological time-series extending back more than 60 years are scarce, there is a strong need for proxy data providing insight into the regional hydroclimatic history as well as the long-term variability. Within this study, a recently developed annually resolved 1500 year-long tree-ring stable oxygen isotope (δ18O) time from the southeastern TP is presented. Climate–proxy relationships reveal a strong impact of relative humidity (rH) during the summer months (May to September) on tree-ring δ18O, explaining around 45% of its variance. The derived reconstruction of relative humidity reveals a recent trend towards drier conditions on the TP. However, the present low rH level is not unprecedented in regard to the last 1500 years. In comparison to recent climate conditions, the Medieval Warm Period (MWP) was characterized by more stable conditions with higher humidity values. Hydroclimatic conditions during the Little Ice Age (LIA) suggest a contrasting two-phased period, with a clear shift from drier conditions prevailing between 1400 and 1650 AD to more humid conditions since the second half of the 17th century. Comparisons with other local proxies from lake levels and Pollen data from the southern part of the Tibetan plateau indicate a common regional climate forcing during the MWP and the LIA which can be related to changes in summer monsoon activity. However, the strength of the distinct dryness trend during the 20th century seems unique

A Dual Stable Isotope Approach Unravels Common Climate Signals and Species-Specific Responses to Environmental Change Stored in Multi-Century Tree-Ring Series from the Tibetan Plateau

Tree-rings are recorders of environmental signals and are therefore often used to reconstruct past environmental conditions. In this paper, we present four annually resolved, multi-centennial tree-ring isotope series from the southeastern Tibetan plateau. The investigation site, where juniper and spruce trees jointly occur, is one of the highest known tree-stands in the world. Tree ring cellulose oxygen (δ18O) and carbon (δ13C) isotopes were analyzed for a common period of 1685–2007 AD to investigate climate–isotope relationships. Therefore, various climate parameters from a local meteorological station and from the CRU 4.02 dataset were used. Tree-ring δ18O of both species revealed highly significant sensitivities with a high degree of coherence to hydroclimate variables during the growing season. The obtained δ18O–climate relationships can even be retained using a species mean. In contrast, the individual δ13C series indicated a weaker and non-uniform response to the tested variables. Underlying species-specific responses and adaptations to the long-term trend in atmospheric CO2 bias even after a trend correction identified dominant environmental factors triggering the tree-ring δ13C at our site. However, analysis of individual intrinsic water-use efficiency in juniper and spruce trees indicated a species-specific adaptation strategy to climate chang

400 Years of summer hydroclimate from stable isotopes in Iberian trees

Tree rings are natural archives that annually record distinct types of past climate variability depending on the parameters measured. Here, we use ring-width and stable isotopes in cellulose of trees from the northwestern Iberian Peninsula (IP) to understand regional summer hydroclimate over the last 400 years and the associated atmospheric patterns. Correlations between tree rings and climate data demonstrate that isotope signatures in the targeted Iberian pine forests are very sensitive to water availability during the summer period, and are mainly controlled by stomatal conductance. Non-linear methods based on extreme events analysis allow for capturing distinct seasonal climatic variability recorded by tree-ring parameters and asymmetric signals of the associated atmospheric features. Moreover, years with extreme high (low) values in the tree-ring records were characterised by coherent large-scale atmospheric circulation patterns with reduced (enhanced) moisture transport onto the northwestern IP. These analyses of extremes revealed that high/low proxy values do not necessarily correspond to mirror images in the atmospheric anomaly patterns, suggesting different drivers of these patterns and the corresponding signature recorded in the proxies. Regional hydroclimate features across the broader IP and western Europe during extreme wet/dry summers detected by the northwestern IP trees compare favourably to independent multicentury sea level pressure and drought reconstructions for Europe. Historical records also validate our findings that attribute non-linear moisture signals recorded by extreme tree-ring values to distinct large-scale atmospheric patterns and allow for 400-year reconstructions of the frequency of occurrence of extreme conditions in late spring and summer hydroclimate