Process-based modelling of lichens and bryophytes and their role in global biogeochemical cycles

This thesis presents a process-based modelling approach to quantify carbon uptake by lichens and bryophytes at the global scale. Based on the modelled carbon uptake, potential global rates of nitrogen fixation, phosphorus uptake and chemical weathering by the organisms are estimated. In this way, the significance of lichens and bryophytes for global biogeochemical cycles can be assessed. The model uses gridded climate data and key properties of the habitat (e.g. disturbance intervals) to predict processes which control net carbon uptake, namely photosynthesis, respiration, water uptake and evaporation. It relies on equations used in many dynamical vegetation models, which are combined with concepts specific to lichens and bryophytes, such as poikilohydry or the effect of water content on CO2 diffusivity. To incorporate the great functional variation of lichens and bryophytes at the global scale, the model parameters are characterised by broad ranges of possible values instead of a single, globally uniform value. The predicted terrestrial net uptake of 0.34 to 3.3 Gt / yr of carbon and global patterns of productivity are in accordance with empirically-derived estimates. Based on the simulated estimates of net carbon uptake, further impacts of lichens and bryophytes on biogeochemical cycles are quantified at the global scale. Thereby the focus is on three processes, namely nitrogen fixation, phosphorus uptake and chemical weathering. The presented estimates have the form of potential rates, which means that the amount of nitrogen and phosphorus is quantified which is needed by the organisms to build up biomass, also accounting for resorption and leaching of nutrients. Subsequently, the potential phosphorus uptake on bare ground is used to estimate chemical weathering by the organisms, assuming that they release weathering agents to obtain phosphorus. The predicted requirement for nitrogen ranges from 3.5 to 34 Tg / yr and for phosphorus it ranges from 0.46 to 4.6 Tg / yr. Estimates of chemical weathering are between 0.058 and 1.1 km³ / yr of rock. These values seem to have a realistic order of magnitude and they support the notion that lichens and bryophytes have the potential to play an important role for global biogeochemical cycles.

Untersuchungen zu COX/LOX-Inhibitoren mit Hydroxylradikalfängereigenschaften – Synthese, Testung und Modelling

In der vorliegenden Arbeit werden 52 Verbindungen beschrieben, welche auf COX/LOX-Inhibition mit zusätzlichen Hydroxylradikalfängereigenschaften getestet worden sind. rnEs war möglich eine neue Synthesestrategie für noch nicht beschriebene 4,5-Diarylisoselenazole zu entwickeln und eine vorhandene Synthese für Isothiazoliumchloride von zwei Stufen, mit mäßigen Ausbeuten, auf eine Stufe, mit hoher Ausbeute, zu verkürzen.rnEs wurden mehrere COX-Inhibitoren identifiziert. MSD4a, MSD4h, MSD5a und MSD5h konnten als COX-1-, COX-2- und 5-LOX-Hemmer identifiziert werden. Besonders hervorzuheben ist die Verbindung MSD5h, die zusätzlich zur COX-1-, COX-2- und 5-LOX-Inhibition eine leichte Hemmung im Hydroxylradikalfänger-Assay zeigt, für die ein clog P-Wert von 2,65 berechnet wurde und die im XTT-Zytotoxizitätstestsystem, selbst bei einer Konzentration von 100 µM, kaum toxische Eigenschaften besitzt.rnWeiterhin war es möglich zu zeigen, dass Carbonsäuren gute Hydroxylradikalfängereigenschaften in unserem, auf der Fenton-Reaktion basierenden, Testsystem haben. Die Potenz der Carbonsäuren MSD8b und MSD11j im Vergleich zu den unwirksamen korrespondierenden Ester MSD8a und MSD11i führte zu Untersuchungen mit weiteren Carbonsäuren und deren Ester. Um den Wirkungsmechanismus zu erforschen wurde das Testsystem modifiziert, um eine Komplexierung der Eisenionen durch die Carbonsäuren auszuschließen. An Hand der Substanzen MSD8b und MSD11j wurde nachgewiesen, dass diese mit dem Hydroxylradikal reagieren, ohne zu decarboxylieren oder andere Zerfallsreaktionen einzugehen.rnZusätzlich zu den Untersuchungen der Enzym-Inhibition sowie des Hydroxylradikal-Scavenings wurden Molecular Modelling Studien durchgeführt. Die Ergebnisse der Dockingstudien in COX-1- (1eqg), COX-2- (1cx2) und in COX-1 mutierte COX-2-Kristallstrukturen (1cx2) führen zu einer kritischen Bewertung des folgenden Ansatzes: Es ist nicht unbedingt sinnvoll zuerst Strukturen mit dem Computer zu entwerfen und zu modeln und sie erst dann zu synthetisieren und in Enzym- oder Zellassays zu testen. Die Begründung dafür liegt in der Schwierigkeit einschätzen zu können, wie nah das gewählte Modell der Wirklichkeit ist. In den durchgeführten Dockingstudien konnte der sehr große Einfluss des kokristallisierten Liganden in der als Grundlage dienenden Kristallstruktur auf die Dockingergebnisse gezeigt werden. Durch einen zu kleinen kokristallisierten Liganden in der COX-1-Bindungstasche wurden als Ergebnis der Dockingstudie alle Verbindungen als nicht potent eingestuft, obwohl diese zum Teil im Enzymtestsystem wirksam waren. Dies konnte mit den Mutationsversuchen ausgeglichen werden. rnDeshalb kann man aus diesen Ergebnissen als Fazit ziehen, dass eine Strategie, Strukturen zu synthetisieren, in vitro zu testen und dabei die Strukturentwicklung mit Molecular Modelling Studien zu unterstützen, die Methode der Wahl darstellt.rn

Stable isotope composition of atmospheric carbon monoxide : a modelling study

Stable isotope composition of atmospheric carbon monoxide: A modelling study.rnrnThis study aims at an improved understanding of the stable carbon and oxygen isotope composition of the carbon monoxide (CO) in the global atmosphere by means of numerical simulations. At first, a new kinetic chemistry tagging technique for the most complete parameterisation of isotope effects has been introduced into the Modular Earth Submodel System (MESSy) framework. Incorporated into the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model, an explicit treatment of the isotope effects on the global scale is now possible. The expanded model system has been applied to simulate the chemical system containing up to five isotopologues of all carbon- and oxygen-bearing species, which ultimately determine the δ13C, δ18O and Δ17O isotopic signatures of atmospheric CO. As model input, a new stable isotope-inclusive emission inventory for the relevant trace gases has been compiled. The uncertainties of the emission estimates and of the resulting simulated mixing and isotope ratios have been analysed. The simulated CO mixing and stable isotope ratios have been compared to in-situ measurements from ground-based observatories and from the civil-aircraft-mounted CARIBIC−1 measurement platform.rnrnThe systematically underestimated 13CO/12CO ratios of earlier, simplified modelling studies can now be partly explained. The EMAC simulations do not support the inferences of those studies, which suggest for CO a reduced input of the highly depleted in 13C methane oxidation source. In particular, a high average yield of 0.94 CO per reacted methane (CH4) molecule is simulated in the troposphere, to a large extent due to the competition between the deposition and convective transport processes affecting the CH4 to CO reaction chain intermediates. None of the other factors, assumed or disregarded in previous studies, however hypothesised to have the potential in enriching tropospheric CO in 13C, were found significant when explicitly simulated. The inaccurate surface emissions, likely underestimated over East Asia, are responsible for roughly half of the discrepancies between the simulated and observed 13CO in the northern hemisphere (NH), whereas the remote southern hemisphere (SH) compositions suggest an underestimated fractionation during the oxidation of CO by the hydroxyl radical (OH). A reanalysis of the kinetic isotope effect (KIE) in this reaction contrasts the conventional assumption of a mere pressure dependence, and instead suggests an additional temperature dependence of the 13C KIE, which is driven by changes in the partitioning of the reaction exit channels. This result is yet to be confirmed in the laboratory.rnrnApart from 13CO, for the first time the atmospheric distribution of the oxygen mass-independent fractionation (MIF) in CO, Δ17O, has been consistently simulated on the global scale with EMAC. The applicability of Δ17O(CO) observations to unravelling changes in the tropospheric CH4-CO-OH system has been scrutinised, as well as the implications of the ozone (O3) input to the CO isotope oxygen budget. The Δ17O(CO) is confirmed to be the principal signal for the CO photochemical age, thus providing a measure for the OH chiefly involved in the sink of CO. The highly mass-independently fractionated O3 oxygen is estimated to comprise around 2% of the overall tropospheric CO source, which has implications for the δ18O, but less likely for the Δ17O CO budgets. Finally, additional sensitivity simulations with EMAC corroborate the nearly equal net effects of the present-day CH4 and CO burdens in removing tropospheric OH, as well as the large turnover and stability of the abundance of the latter. The simulated CO isotopologues nonetheless hint at a likely insufficient OH regeneration in the NH high latitudes and the upper troposphere / lower stratosphere (UTLS).rn