Universitatsstr 30

Bayreuth, Germany

Universitatsstr 30

Bayreuth, Germany

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Kallarackal J.,University of Bayreuth | Kallarackal J.,Kerala Forest Research Institute | Otieno D.O.,University of Bayreuth | Reineking B.,Universitatsstr 30 | And 4 more authors.
Trees - Structure and Function | Year: 2013

Functional convergence in water use of trees across species from diverse geographic locations was examined using data on tree water use parameters, with the intention of gaining an understanding on the capacity for water transport for trees with varying structural and functional traits. Wood density (ρw), which is reported to have a negative exponential relation with sap flow density (SFD), showed a bell-shaped curve when the daily SFD data from 101 tree species belonging to 35 angiosperm and gymnosperm families were plotted. The species came from 23 different geographical locations representing all continents. Trees were most efficient in water transport when the ρw was between 0.51 and 0.65 g cm-3. When the ρw increased or decreased from this range, there was a gradual fall in their water transport rate as indicated by lower daily SFD. The unexpected reduction in SFD with decreasing ρw is explained in terms of reduced conductance in the transport pathway, which is a precaution taken by the tree for avoiding cavitation or implosion in larger conducting tubes, which is characteristic of low density wood. The development of severe leaf water potential variations, which is frequently reported in such trees, supports this notion. The SFD versus ρw relation has a potentially wide applicability in predicting water use by forest stands with varying ρw. In addition, the occurrence of a high number of tree species with ρw values in the range of 0.51-0.65 g cm-3 across all continents examined points towards the importance of ρw in the evolutionary process as related to efficient functioning of the water transport mechanism. © 2013 Springer-Verlag Berlin Heidelberg.


Pedashenko H.,Bulgarian Academy of Science | Apostolova I.,Bulgarian Academy of Science | Boch S.,University of Bern | Ganeva A.,Bulgarian Academy of Science | And 8 more authors.
Tuexenia | Year: 2013

We present the data of the 3rd research expedition of the European Dry Grasslands Group (EDGG), which was conducted in 2011 in two contrasting areas in NW Bulgarian mountains. The aim was to collect plot data for comparing Bulgarian dry grasslands with those of other parts of Europe in terms of syntaxonomy and biodiversity. We sampled 15 nested-plot series (0.0001-100 m2) and 68 normal plots (10 m2) covering the full variety of dry grassland types occurring in the Vratsa area (Balkan Mts.) and the Koprivshtitsa area (Sredna Gora Mt.). In the plots all vascular plants, terricolous non-vascular plants and a set of soil and other environmental parameters were determined. By applying modified TWIN-SPAN, we distinguished 10 floristically well characterised vegetation types at the association level. After comparison with the regional and European literature, we propose to place them within three classes and five orders: Festuco-Brometea with the orders Stipo pulcherrimae-Festucetalia pallentis (xerophilous dry grasslands of base-rich rocks; alliance Saturejion montanae), Brachypodietalia pinnati (meso-xeric, basiphilous grasslands; alliances Cirsio-Brachypodion pinnati and Chyrsopogono grylli-Danthonion calycinae), Calluno-Ulicetea with the order Nardetalia stricae (lowland to montane Nar-dus swards; alliance Violion caninae), and Koelerio-Corynephoretea with the orders Sedo-Scleranthetalia (open communities of skeleton-rich, acidic soils; alliance unclear) and Trifolio arvensis-Festucetalia ovinae (closed, meso-xeric, acidophilous grasslands; alliance Armerio rumelicae-Potentillion). The Violion caninae with the association Festuco rubrae-Genistelletum sagittalis is reported from Bulgaria for the first time, while the two occurring Koelerio-Corynephoretea communi-ties are described as new associations (Cetrario aculeatae-Plantaginetum radicatae, Plantagini radica-tae-Agrostietum capillaris). According to DCA the main floristic gradient was largely determined by soil conditions, differentiating the Festuco-Brometea communities on soils with high pH and high humus content from the Koelerio-Corynephoretea communities on acidic, humus-poor soils, while the Calluno-Ulicetea stands are the connecting link. At 10 m2 Festuco-Brometea and Calluno-Ulicetea stands were richer in species across all investigated taxa and in vascular plants than Koelerio-Corynephoretea stands; the latter were richest in lichen species, while bryophyte richness did not differ significantly among syntaxa. Among the Bulgarian classes, the species-area relationships tended to be steepest in the Festuco-Brometea (i.e. highest beta diversity), but both alpha and beta diversity clearly fell behind the Festuco-Brometea communities in the Transylvanian Plateau, Romania, located less than 500 km north of the study region. Overall, our study contributes to a more adequate placement of the Bulgarian dry grasslands in the European syntaxonomic system and provides valuable data for large-scale analyses of biodiversity patterns.


Fishchuk I.I.,Ukrainian Academy of Sciences | Kadashchuk A.,Ukrainian Academy of Sciences | Kadashchuk A.,IMEC | Novikov S.V.,RAS Frumkin Institute of Physical Chemistry and Electrochemistry | And 5 more authors.
Molecular Crystals and Liquid Crystals | Year: 2014

We report on the influence of the lateral electric field on the charge mobility in organic field-effect transistors (OFET) based on C60 films with multigrain morphology. The experimental data were quantitatively described using a recent analytical model by accounting for the strong local electric fields in a multigrain transistor channel and for the energy correlation effects. To rationalize the presence of a correlated disorder in a non-polar C60 material, we show that randomly oriented permanent dipoles in organic gate dielectric layers can generate a significant dipolar disorder in an adjacent nonpolar semiconductor layer. © 2014 Copyright Taylor & Francis Group, LLC.


Fishchuk I.I.,Ukrainian Academy of Sciences | Kadashchuk A.,IMEC | Kadashchuk A.,Ukrainian Academy of Sciences | Hoffmann S.T.,Universitatsstr 30 | And 4 more authors.
AIP Conference Proceedings | Year: 2014

We developed an analytical model to describe hopping conductivity and mobility in organic semiconductors including both energetic disorder and polaronic contributions. The model is based on the Marcus jump rates with a Gaussian energetic disorder, and it is premised upon a generalized Effective Medium approach yet avoids shortcoming involved in the effective transport energy or percolation concepts. The carrier concentration dependence becomes considerably weaker when the polaron energy increases relative to the disorder energy, indicating the absence of universality that is at variance with recent publications. © 2014 AIP Publishing LLC.


Gocke M.,University of Bayreuth | Gocke M.,Universitatsstr 30 | Kuzyakov Y.,University of Gottingen
Geoderma | Year: 2011

In soils of arid and semiarid climates, dissolution of primary (lithogenic) carbonate and recrystallization with CO2 from soil air leads to precipitation of pedogenic carbonates and formation of calcic horizons. Thus, their carbon isotope composition represents the conditions prevailing during their formation. However, the widespread use of the isotopic signature (δ13C, δ18O, δ14C) of pedogenic carbonates for reconstruction of local paleovegetation, paleoprecipitation and other environmental conditions lacks knowledge of the time frame of pedogenic carbonate formation, which depends on climatic factors. We hypothesized that temperature-dependent biotic processes like plant growth and root and rhizomicrobial respiration have stronger influence on soil CaCO3 recrystallization than abiotic temperature-dependent solubility of CO2 and CaCO3.To assess the effect of temperature on initial CaCO3 recrystallization rates, loess with primary CaCO3 was exposed to 14CO2 from root and rhizomicrobial respiration of plants labeled in 14CO2 atmosphere at 10, 20 or 30°C. 14C recovered in recrystallized CaCO3 was quantified to calculate amounts of secondary CaCO3 and corresponding recrystallization rates, which were in the range of 10-6-10-4day-1, meaning that 10-4-10-2% of total loess CaCO3 were recrystallized per day. Increasing rates with increasing temperature showed the major role of biological activities like enhanced water uptake by roots and respiration. The abiotic effect of lower solubility of CO2 in water by increasing temperature was completely overcompensated by biotic processes. Based on initial recrystallization rates, periods necessary for complete recrystallization were estimated for different temperatures, presuming that CaCO3 recrystallization in soil takes place mainly during the growing season. Taking into account the shortening effect of increasing temperature on the length of growing season, the contrast between low and high temperature was diminished, yielding recrystallization periods of 5740years, 4330years and 1060years at 10, 20 and 30°C, respectively. In summary, increasing CaCO3 recrystallization rates with increasing temperature demonstrated the important role of vegetation for pedogenic CaCO3 formation and the predominantly biotic effects of growing season temperature.Considering the long periods of pedogenic carbonate formation lasting to some millennia, we conclude that methodological resolution of paleoenvironmental studies based on isotope composition of pedogenic carbonates is limited not by instrumental precision but by the time frame of pedogenic carbonate formation and hence cannot be better than thousands of years. © 2011 Elsevier B.V.


Wenzel S.,University of Bayreuth | Wenzel S.,Universitatsstr 30 | Martins B.M.,University of Bayreuth | Rosch P.,University of Bayreuth | And 3 more authors.
Biochemical Journal | Year: 2010

The eukaryotic transcription elongation factor DSIF [DRB (5,6-dichloro-1-β-D-ribofuranosylbenzimidazole) sensitivity-inducing factor] is composed of two subunits, hSpt4 and hSpt5, which are homologous to the yeast factors Spt4 and Spt5. DSIF is involved in regulating the processivity of RNA polymerase II and plays an essential role in transcriptional activation of eukaryotes. At several eukaryotic promoters, DSIF, together with NELF (negative elongation factor), leads to promoter-proximal pausing of RNA polymerase II. In the present paper we describe the crystal structure of hSpt4 in complex with the dimerization region of hSpt5 (amino acids 176-273) at a resolution of 1.55 Å (1 Å=0.1 nm). The heterodimer shows high structural similarity to its homologue from Saccharomyces cerevisiae. Furthermore, hSpt5-NGN is structurally similar to the NTD (N-terminal domain) of the bacterial transcription factor NusG. A homologue for hSpt4 has not yet been found in bacteria. However, the archaeal transcription factor RpoE" appears to be distantly related. Although a comparison of the NusG-NTD of Escherichia coli with hSpt5 revealed a similarity of the three-dimensional structures, interaction of E. coli NusG-NTD with hSpt4 could not be observed by NMR titration experiments. A conserved glutamate residue, which was shown to be crucial for dimerization in yeast, is also involved in the human heterodimer, but is substituted for a glutamine residue in Escherichia coli NusG. However, exchanging the glutamine for glutamate proved not to be sufficient to induce hSpt4 binding. © The Authors Journal compilation.

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