Martin Luther University of Halle-Wittenberg

About: Martin Luther University of Halle-Wittenberg is a education organization based out in Halle, Germany. It is known for research contribution in the topics: Population & Liquid crystal. The organization has 20232 authors who have published 38773 publications receiving 965004 citations. The organization is also known as: MLU & University of Wittenberg.

Biodiversity change is uncoupled from species richness trends: Consequences for conservation and monitoring

Abstract: Global concern about human impact on biological diversity has triggered an intense research agenda on drivers and consequences of biodiversity change in parallel with international policy seeking to conserve biodiversity and associated ecosystem functions. Quantifying the trends in biodiversity is far from trivial, however, as recently documented by meta-analyses, which report little if any net change in local species richness through time. Here, we summarise several limitations of species richness as a metric of biodiversity change and show that the expectation of directional species richness trends under changing conditions is invalid. Instead, we illustrate how a set of species turnover indices provide more information content regarding temporal trends in biodiversity, as they reflect how dominance and identity shift in communities over time. We apply these metrics to three monitoring datasets representing different ecosystem types. In all datasets, nearly complete species turnover occurred, but this was disconnected from any species richness trends. Instead, turnover was strongly influenced by changes in species presence (identities) and dominance (abundances). We further show that these metrics can detect phases of strong compositional shifts in monitoring data and thus identify a different aspect of biodiversity change decoupled from species richness. Synthesis and applications: Temporal trends in species richness are insufficient to capture key changes in biodiversity in changing environments. In fact, reductions in environmental quality can lead to transient increases in species richness if immigration or extinction has different temporal dynamics. Thus, biodiversity monitoring programmes need to go beyond analyses of trends in richness in favour of more meaningful assessments of biodiversity change.

Colossal dielectric constants in transition-metal oxides

Abstract: Many transition-metal oxides show very large (“colossal”) magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today’s most investigated material with colossal dielectric constant Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2−xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant

Plant rhizodeposition — an important source for carbon turnover in soils

Abstract: The soil organic matter plays a key role in ecological soil functions, and has to be considered as an important CO2 sink on a global scale. Apart from crop residues (shoots and roots), left over on the field after harvest, carbon and nitrogen compounds are also released by plant roots into the soil during vegetation, and undergo several transformation processes. Up to now the knowledge about amount, composition, and turnover of these root-borne compounds is still very limited. So far it could be demonstrated with different plant species, that up to 20 % of photosynthetically fixed C are released into the soil during vegetation period. These C amounts are ecological relevant. Depending on assimilate sink strength during ontogenesis, the C release varies with plant age. A large percentage of these root-borne substances were rapidly respired by microorganisms (64—86 %). About 2—5 % of net C assimilation was kept in soil. The root exudates of maize were mainly water-soluble (79 %), and in this fraction about 64 % carbohydrates, 22 % amino acids/amides and 14 % organic acids could be identified. Plant species and in some cases also plant cultivars varied strongly in their root exudation pattern. Under non-sterile conditions the exuded compounds were rapidly stabilized in water-insoluble forms and bound preferably to the soil clay fraction. The binding of root exudates to soil particles also improved soil structure by increasing aggregate stability. Future research should focus on quantification and characterization of root-borne C compounds during the whole plant ontogenesis. Apart from pot experiments with 14CO2 labeling, it is necessary to conduct model field experiments with 13CO2 labeling in order to be able to distinguish between CO2 originating from the soil C pool and rhizosphere respiration, originating from plant assimilates. Such a separation is necessary to assess if soils are sources or sinks of CO2. The incorporation of root-borne C (14C, 13C) into soil organic matter of different stability is also of particular interest. Pflanzliche Rhizodeposition — eine wichtige Quelle fur den Kohlenstoffumsatz in Boden Die organische Bodensubstanz (OBS) nimmt eine Schlusselrolle bei den okologischen Bodenfunktionen ein und stellt global betrachtet eine wichtige CO2-Senke dar. Neben den auf dem Feld verbleibenden Ernte- und Wurzelruckstanden werden C- und N-Verbindungen auch wahrend des Pflanzenwachstums in den Boden abgegeben und unterliegen dort vielfaltigen Umsetzungsprozessen. Der Kenntnisstand uber die Menge, Zusammensetzung und den Umsatz dieser wurzelburtigen Verbindungen im Boden ist noch sehr begrenzt. Daher beschaftigt sich die vorliegende Publikation mit der Rhizodeposition als wichtiger Quelle des C-Umsatzes in Boden, insbesondere mit den mobilen Wurzelabscheidungen. Bisher konnte anhand verschiedener Pflanzenarten gezeigt werden, dass bis zu 20 % des photosynthetisch fixierten C wahrend der Vegetation durch die Wurzeln freigesetzt werden. Es handelt sich dabei um okologisch relevante C-Mengen. In Abhangigkeit von der Starke des Assimilatsinks wahrend der Ontogenese variiert die C-Freisetzung mit dem Pflanzenalter. Ein hoher Anteil dieser wurzelburtigen Verbindungen (64—86 %) wurde schnell durch Mikroorganismen veratmet. 2—5 % der Netto-C-Fixierung blieben im Boden zuruck. Dieser Bodenruckstand war bei Wurzelabscheidungen von Mais hauptsachlich wasserloslich (79 %), und in dieser Fraktion wurden 64 % Kohlenhydrate, 22 % Aminosauren/Amide und 14 % organische Sauren identifiziert. Pflanzenarten und teilweise auch -sorten variierten stark in der Zusammensetzung ihrer Wurzelexsudate. Unter insterilen Bedingungen wurden die exsudierten Verbindungen schnell in nichtwasserloslicher Form stabilisiert und vor allem an die Tonfraktion des Bodens gebunden. Die Bindung an Bodenpartikel verbesserte die Bodenstruktur durch erhohte Aggregatstabilitat. Zukunftige Forschungsarbeiten sollten sich auf die Quantifizierung und Charakterisierung wurzelburtiger C-Verbindungen wahrend der gesamten pflanzlichen Ontogenese konzentrieren. Abgesehen von Gefasversuchen mit 14CO2-Applikation ist es erforderlich, Feldmodellversuche mit 13CO2-Applikation durchzufuhren, um zwischen der CO2-Emission aus dem Boden-C-Pool und derjenigen aus der Rhizospharenatmung (Ursprung sind Pflanzenassimilate) unterscheiden zu konnen. Eine solche Trennung ist zur Beurteilung, ob Boden eine Quelle oder Senke fur CO2 darstellen, zwingend erforderlich. Von besonderem Interesse ist auch der Einbau des wurzelburtigen C (14C, 13C) in OBS-Fraktionen unterschiedlicher Stabilitat.