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Dynamics of microbial communities during decomposition of litter from pioneering plants in initial soil ecosystems
J. Esperschütz,C. Zimmermann,A. Dümig,G. Welzl
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-14981-2012
Abstract: In initial ecosystems concentrations of all macro- and micronutrients can be considered as extremely low. Plant litter therefore strongly influences the development of a degraders' food web and is an important source for C and N input into soil in such ecosystems. In the present study, a 13C litter decomposition field experiment was performed for 30 weeks in initial soils from a post-mining area near the city of Cottbus (Germany). Two of this regions' dominant but contrasting pioneering plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were chosen to investigate the effects of litter quality on the litter decomposing microbial food web in initially nutrient-poor substrates. The results clearly indicate the importance of litter quality, mainly the amount of N stored in the litter material and its bioavailability for the degradation process and the development of microbial communities in the detritusphere and bulk soil. Whereas the degradation process of the L. corniculatus litter which had a low C/N ratio was fast and most pronounced changes in the microbial community structure were observed 1–4 weeks after litter addition, the degradation of the C. epigejos litter material was slow and microbial community changes mainly occurred at between 4 and 30 weeks after litter addition to the soil. However for both litter materials a clear indication for the importance of fungi for the degradation process was observed both on the abundance level as well as on the level of 13C incorporation (activity).
Passing Corrupt Data Across Network Layers: An Overview of Recent Developments and Issues
Welzl Michael
EURASIP Journal on Advances in Signal Processing , 2005,
Abstract: Recent Internet developments seem to make a point for passing corrupt data from the link to the network layer and above instead of ensuring data integrity with a checksum and ARQ. We give an overview of these efforts (the UDP Lite and DCCP protocols) and explain which circumstances would justify delivery of erroneous data; clearly, the missing piece in the puzzle is efficient and meaningful interlayer communication.
Diversity pattern of nitrogen fixing microbes in nodules of Trifolium arvense (L.) at different initial stages of ecosystem development
S. Schulz, M. Engel, D. Fischer, F. Buegger, M. Elmer, G. Welzl,M. Schloter
Biogeosciences (BG) & Discussions (BGD) , 2013,
Abstract: Legumes can be considered as pioneer plants during ecosystem development, as they form a symbiosis with different nitrogen fixing rhizobia species, which enable the plants to grow on soils with low available nitrogen content. In this study we compared the abundance and diversity of nitrogen fixing microbes based on the functional marker gene nifH, which codes for a subunit of the Fe-protein of the dinitrogenase reductase, in nodules of different size classes of Trifolium arvense (L.). Additionally, carbon and nitrogen contents of the bulk soil and plant material were measured. Plants were harvested from different sites, reflecting 2 (2a) and 5 (5a) yr of ecosystem development, of an opencast lignite mining area in the south of Cottbus, Lower Lusatia (Germany) where the artificial catchment "Chicken Creek" was constructed to study the development of terrestrial ecosystems. Plants from the 5a site revealed higher amounts of carbon and nitrogen, although nifH gene abundances in the nodules and carbon and nitrogen contents between the two soils did not differ significantly. Analysis of the nifH clone libraries showed a significant effect of the nodule size on the community composition of nitrogen fixing microbes. Medium sized nodules (2–5 mm) contained a uniform community composed of Rhizobium leguminosarum bv. trifolii, whereas the small nodules (<2 mm) consisted of a diverse community including clones with non-Rhizobium nifH gene sequences. Regarding the impact of the soil age on the community composition a clear distinction between the small and the medium nodules can be made. While clone libraries from the medium nodules were pretty similar at both soil ages, soil age had a significant effect on the community compositions of the small nodules, where the proportion of R. leguminosarum bv. trifolii increased with soil age.
Microbial food web dynamics along a soil chronosequence of a glacier forefield
J. Esperschütz,A. Pérez-de-Mora,K. Schreiner,G. Welzl
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-1275-2011
Abstract: Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web development at differently developed soils. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland). 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L.) Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL). Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PUFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria and actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain.
Microbial food web dynamics along a soil chronosequence of a glacier forefield
J. Esperschütz, A. Pérez-de-Mora, K. Schreiner, G. Welzl, F. Buegger, J. Zeyer, F. Hagedorn, J. C. Munch,M. Schloter
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web dynamics in soils at different developmental stages. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland). 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L.) Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL). Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PLFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria, especially actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain.
Permutation-validated principal components analysis of microarray data
Jobst Landgrebe, Wolfgang Wurst, Gerhard Welzl
Genome Biology , 2002, DOI: 10.1186/gb-2002-3-4-research0019
Abstract: We used PCA to detect the major sources of variance underlying the hybridization conditions followed by gene selection based on PCA-derived and permutation-based test statistics. We validated our method by applying it to well characterized yeast cell-cycle data and to two datasets from our laboratory. We could describe the major sources of variance, select informative genes and visualize the relationship of genes and arrays. We observed differences in the level of the explained variance and the interpretability of the selected genes.Combining data visualization and permutation-based gene selection, permutation-validated PCA enables one to illustrate gene-expression variance between several conditions and to select genes by taking into account the relationship of between-group to within-group variance of genes. The method can be used to extract the leading sources of variance from microarray data, to visualize relationships between genes and hybridizations and to select informative genes in a statistically reliable manner. This selection accounts for the level of reproducibility of replicates or group structure as well as gene-specific scatter. Visualization of the data can support a straightforward biological interpretation.Microarrays have become standard tools for gene expression analysis as the messenger RNA levels of thousands of genes can be measured in one assay. In a standard microarray experiment, total RNA or mRNA is extracted from cells or tissue, labeled by reverse transcription with radioactive or fluorescent-tag-labeled nucleotides and hybridized to the arrays. After hybridization and washing, the arrays are scanned and the hybridization intensities at each spot are determined by image-analysis software. Two-channel microarrays open up the possibility of carrying out many hybridizations in parallel using a common reference RNA. In such experiments, different experimental conditions can be compared to each other. In many cases, different conditions are a
Counting Plane Graphs: Perfect Matchings, Spanning Cycles, and Kasteleyn's Technique
Micha Sharir,Adam Sheffer,Emo Welzl
Computer Science , 2011,
Abstract: We derive improved upper bounds on the number of crossing-free straight-edge spanning cycles (also known as Hamiltonian tours and simple polygonizations) that can be embedded over any specific set of $N$ points in the plane. More specifically, we bound the ratio between the number of spanning cycles (or perfect matchings) that can be embedded over a point set and the number of triangulations that can be embedded over it. The respective bounds are $O(1.8181^N)$ for cycles and $O(1.1067^N)$ for matchings. These imply a new upper bound of $O(54.543^N)$ on the number of crossing-free straight-edge spanning cycles that can be embedded over any specific set of $N$ points in the plane (improving upon the previous best upper bound $O(68.664^N)$). Our analysis is based on Kasteleyn's linear algebra technique.
The Effect of Network and Infrastructural Variables on SPDY's Performance
Yehia Elkhatib,Gareth Tyson,Michael Welzl
Computer Science , 2014,
Abstract: HTTP is a successful Internet technology on top of which a lot of the web resides. However, limitations with its current specification, i.e. HTTP/1.1, have encouraged some to look for the next generation of HTTP. In SPDY, Google has come up with such a proposal that has growing community acceptance, especially after being adopted by the IETF HTTPbis-WG as the basis for HTTP/2.0. SPDY has the potential to greatly improve web experience with little deployment overhead. However, we still lack an understanding of its true potential in different environments. This paper seeks to resolve these issues, offering a comprehensive evaluation of SPDY's performance using extensive experiments. We identify the impact of network characteristics and website infrastructure on SPDY's potential page loading benefits, finding that these factors are decisive for SPDY and its optimal deployment strategy. Through this, we feed into the wider debate regarding HTTP/2.0, exploring the key aspects that impact the performance of this future protocol.
Entrainment, annual circulation and groundwater inflow in a chain of lakes as inferred by stable 18O isotopic signatures in the water column
Emanuel BRAIG,Gerhard WELZL,Willibald STICHLER,Uta RAEDER
Journal of Limnology , 2010, DOI: 10.4081/jlimnol.2010.278
Abstract: The stable oxygen isotopic signature δ18O of water has been proved to be a useful marker in hydrological lake studies. However, it is applied only sporadically to determine the extent of mixis and stratification, which is vital for all hydrological and limnological studies. We present a study of the changes in δ18O, temperature and Schmidt stability in the water column of three adjacent lakes of very different mixis types (polymictic to meromictic) over almost one year (May 2008 to April 2009). The response of δ18O to important hydrologic processes (entrainment, stratification, circulation, groundwater inflow) and weather influences (cooling period, ice cover and melt water inflow) is discussed. The lakes are part of the Osterseen chain of lakes south of Munich, Germany. Although hydrologically connected, these lakes show various mixis types (polymictic to meromictic) due to large differences in size, groundwater inflow and water renewal time. Polymixis and the strong subsurface inflow of groundwater in Lake Waschsee (25.6 × 103 m3) were indicated by the same trends in the δ18O signature throughout all water layers and by the mean overall signature (-9.94‰) being very close to δ18O of local groundwater (-10.01‰ ± 0.06). δ18O signatures of the larger dimictic Lake Fohnsee (2298.3 × 103 m3) revealed a highly significant trend towards lower values of δ18O in its hypolimnion, indicating inflow of groundwater. A cooling period during the summer stratification characterised by high wind speeds resulted in a considerable drop of lake surface temperatures and Schmidt stability (up to 25%) in lakes Fohnsee and Eishaussee and was followed by a deepening of the mixed upper water layer and entrainment of hypolimnetic water layers. This was clearly shown by a signal change in deeper water layers formerly constant in δ18O. The permanent meromixis present in Lake Eishaussee (297.0 × 103 m3) could also be confirmed by isotopic signatures, as bottom water layers remained significantly isolated in δ18O from the remaining water column over the whole study period. We summarize that the oxygen isotopic signature of water is an easy to interpret, excellent indicator of important hydrologic processes in a lake and can readily be integrated into routine sampling. The present findings will further contribute to the analysis of hydrological data as well as to the interpretation of paleoclimatic reconstructions using proxies of lake water δ18O.
Systemic inflammatory response syndrome and multiple-organ damage / dysfunction in complicated canine babesiosis
C. Welzl,A.L. Leisewitz,L.S. Jacobson,T. Vaughan-Scott
Journal of the South African Veterinary Association , 2012, DOI: 10.4102/jsava.v72i3.640
Abstract: This study was designed to document the systemic inflammatory response syndrome (SIRS) and multiple-organ dysfunction syndrome (MODS) in dogs with complicated babesiosis, and to assess their impact on outcome. Ninety-one cases were evaluated retro-spectively for SIRS and 56 for MODS. The liver, kidneys, lungs, central nervous system and musculature were assessed. Eighty-seven percent of cases were SIRS-positive. Fifty-two percent of the cases assessed for organ damage had single-organ damage and 48 % had MODS. Outcome was not significantly affected by either SIRS or MODS, but involvement of specific organs had a profound effect. Central nervous system involvement resulted in a 57 times greater chance of death and renal involvement in a 5-fold increased risk compared to all other complications. Lung involvement could not be statistically evaluated owing to co-linearity with other organs, but was associated with high mortality. Liver and muscle damage were common, but did not significantly affect outcome. There are manysimilarities between the observations in this study and previous human and animal studies in related fields, lending additional support to the body of evidence for shared underlying pathophysiological mechanisms in systemic inflammatory states.
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