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531.
532.
The following study presents a statistical analysis of 595 relevés gathered during a survey of isolated grasslands and dwarf shrub heaths in the region of Halle, eastern Germany. Relevés were classified with UPGMA clustering based on a Bray-Curtis distance matrix; the resulting classification was compared with a previously published phytosociological classification. Most of the 14 target communities were supported by both approaches, but in the case of communities on heavily disturbed sites cluster analysis corresponded to units on higher phytosociological levels (alliances). DCA ordinations clearly revealed that nutrient and moisture availability controlled the community differentiation. Both factors were, however, highly correlated with the distance to the outcrop edge. Thus the outcrop size also influenced differentiation of communities, making larger outcrops richer in xerophytic and endangered species. This appears to be largely due to edge effects since the relationships diminished sharply when we controlled for progressively increasing distances from the edge in partial ordinations. Thus, microtopography of outcrops was the most important factor for community differentiation. It is therefore suggested that future research and conservation management should concentrate on the consequences of nutrient influx and changing land use on larger outcrops. 相似文献
533.
The monogenean flatworm Gyrodactylus salaris is a serious threat to wild and farmed Atlantic salmon stocks in Norway. Morphologically, the closely related but harmless Gyrodactylus thymalli on grayling can hardly be distinguished from G. salaris. Until now, molecular approaches could not resolve unambiguously whether G. salaris and G. thymalli represent just one polytypic species, two polytypic species or a complex of more than two species. In the first known genome-wide analysis utilizing 37 conserved microRNA loci, the genetic differentiation of seven populations of G. salaris and G. thymalli was assessed. The concatenated alignment spanned 21,742 bp including 62 variable positions. A neighbor-joining cluster analysis did not support any host-based or mitochondrial haplotype-based grouping of strains. We conclude that a two species concept for G. salaris and G. thymalli does not reflect meaningful biological entities. Instead, G. salaris and G. thymalli are just one species comprising several pathogenic and non-pathogenic strains on various primary hosts. Following the International Code for Zoological Nomenclature, G. salaris Malmberg, 1957 is the valid species name with G. thymalli ?itňan, 1960 becoming the junior synonym. Accordingly, the range of G. salaris is significantly increased, given that formerly G. salaris-free countries such as e.g., Great Britain are now within the species’ natural range. The synonymization of G. salaris and G. thymalli implies severe challenges to current disease management routines, which assume that G. salaris and G. thymalli are readily distinguishable. Protocols for reliable identification of pathogenic and non-pathogenic strains of G. salaris need to be developed. 相似文献
534.
535.
Christopher T. Filstrup Helmut Hillebrand Adam J. Heathcote W. Stanley Harpole John A. Downing 《Ecology letters》2014,17(4):464-474
Freshwater biodiversity loss potentially disrupts ecosystem services related to water quality and may negatively impact ecosystem functioning and temporal community turnover. We analysed a data set containing phytoplankton and zooplankton community data from 131 lakes through 9 years in an agricultural region to test predictions that plankton communities with low biodiversity are less efficient in their use of limiting resources and display greater community turnover (measured as community dissimilarity). Phytoplankton resource use efficiency (RUE = biomass per unit resource) was negatively related to phytoplankton evenness (measured as Pielou's evenness), whereas zooplankton RUE was positively related to phytoplankton evenness. Phytoplankton and zooplankton RUE were high and low, respectively, when Cyanobacteria, especially Microcystis sp., dominated. Phytoplankton communities displayed slower community turnover rates when dominated by few genera. Our findings, which counter findings of many terrestrial studies, suggest that Cyanobacteria dominance may play important roles in ecosystem functioning and community turnover in nutrient‐enriched lakes. 相似文献
536.
Neutrophilic Fe(II) oxidizing microorganisms are found in many natural environments. It has been hypothesized that, at low oxygen concentrations, microbial iron oxidation is favored over abiotic oxidation. Here, we compare the kinetics of abiotic Fe(II) oxidation to oxidation in the presence of the bacterium Leptothrix cholodnii Appels isolated from a wetland sediment. Rates of Fe(II) oxidation were determined in batch experiments at 20°C, pH 7 and oxygen concentrations between 3 and 120 μmol/l. The reaction progress in experiments with and without cells exhibited two distinct phases. During the initial phase, the oxygen dependency of microbial Fe(II) oxidation followed a Michaelis-Menten rate expression (KM = 24.5 ± 10 μmol O2/l, vmax = 1.8 ± 0.2 μmol Fe(II)/(l min) for 108 cells/ml). In contrast, abiotic rates increased linearly with increasing oxygen concentrations. At similar oxygen concentrations, initial Fe(II) oxidation rates were faster in the experiments with bacteria. During the second phase, the accumulated iron oxides catalyzed further oxidative iron precipitation in both abiotic and microbial reaction systems. That is, abiotic oxidation also dominated the reaction progress in the presence of bacteria. In fact, in some experiments with bacteria, iron oxidation during the second phase proceeded slower than in the absence of bacteria, possibly due to an inhibitory effect of extracellular polymeric substances on the growth of Fe(III) oxides. Thus, our results suggest that the competitive advantage of microbial iron oxidation in low oxygen environments may be limited by the autocatalytic nature of abiotic Fe(III) oxide precipitation, unless the accumulation of Fe(III) oxides is prevented, for example, through a close coupling of Fe(II) oxidation and Fe(III) reduction. 相似文献
537.
Mirko Trutnau Mike Petzold Lysann Mehlig Martin Eschenhagen Katja Geipel Susann M��ller Thomas Bley Isolde R?ske 《Bioprocess and biosystems engineering》2011,34(3):287-295
Modelling of activated sludge processes is a commonly used technique to design and optimize wastewater treatment processes.
Since wastewater and activated sludge is characterized by chemical oxygen demand (COD) measurements, units of state variables
describing organic matter are expressed as equivalent amounts of COD. However, current procedures for measuring it have several
drawbacks, including the production of hazardous wastes, so the utility of other variables for characterizing the organic
load in modelling, such as total organic carbon (TOC), warrant re-evaluation. Other advantages of TOC over COD are that it
provides matrix-independent analytical results and it can be readily measured online. Proposals for TOC-based models were
made in the 1990s, but they seem to have sunk into obscurity. To re-assess the value of TOC for this purpose, we have recalculated
the EAWAG module for Bio-P removal coupled to the Activated Sludge Model No. 3 on a TOC basis, and tested it against data
acquired in batch experiments with four single carbon sources (acetate, glucose, citrate and casein). The batch test-based
calibrations showed a good match with experimental data, following modifications of the model to account for the anaerobic
volumes and retention times applied in the tests. 相似文献
538.
Ximena Tabares Heike Zimmermann Elisabeth Dietze Gregor Ratzmann Lukas Belz Andrea Vieth‐Hillebrand Lydie Dupont Heinz Wilkes Benjamin Mapani Ulrike Herzschuh 《Ecology and evolution》2020,10(2):962-979
- Shrub encroachment has far‐reaching ecological and economic consequences in many ecosystems worldwide. Yet, compositional changes associated with shrub encroachment are often overlooked despite having important effects on ecosystem functioning.
- We document the compositional change and potential drivers for a northern Namibian Combretum woodland transitioning into a Terminalia shrubland. We use a multiproxy record (pollen, sedimentary ancient DNA, biomarkers, compound‐specific carbon (δ13C) and deuterium (δD) isotopes, bulk carbon isotopes (δ13Corg), grain size, geochemical properties) from Lake Otjikoto at high taxonomical and temporal resolution.
- We provide evidence that state changes in semiarid environments may occur on a scale of one century and that transitions between stable states can span around 80 years and are characterized by a unique vegetation composition. We demonstrate that the current grass/woody ratio is exceptional for the last 170 years, as supported by n‐alkane distributions and the δ13C and δ13Corg records. Comparing vegetation records to environmental proxy data and census data, we infer a complex network of global and local drivers of vegetation change. While our δD record suggests physiological adaptations of woody species to higher atmospheric pCO2 concentration and drought, our vegetation records reflect the impact of broad‐scale logging for the mining industry, and the macrocharcoal record suggests a decrease in fire activity associated with the intensification of farming. Impact of selective grazing is reflected by changes in abundance and taxonomical composition of grasses and by an increase of nonpalatable and trampling‐resistant taxa. In addition, grain‐size and spore records suggest changes in the erodibility of soils because of reduced grass cover.
- Synthesis. We conclude that transitions to an encroached savanna state are supported by gradual environmental changes induced by management strategies, which affected the resilience of savanna ecosystems. In addition, feedback mechanisms that reflect the interplay between management legacies and climate change maintain the encroached state.
539.
S. Luke Mankin D. Steven Hill Paula M. Olhoft Effie Toren Allan R. Wenck Lawrence Nea Liqun Xing Jeffrey A. Brown Huihua Fu Lesley Ireland Hongmei Jia Helke Hillebrand Todd Jones Hee-Sook Song 《In vitro cellular & developmental biology. Plant》2007,43(6):521-535
Agrobacterium rhizogenes strain K599 (pRi2659), a causative agent of hairy root disease, effectively induces hairy root formation in a variety of
plant species, including numerous soybean (Glycine max) cultivars. Because Agrobacterium-mediated transformation of soybean remains challenging and labor intensive, K599 appeared a suitable progenitor for new agrobacteria
strains for plant transformation. In this paper, we report the disarming and sequencing of pRi2659 and the usefulness of the
resulting disarmed strain in plant transformation studies of Arabidopsis thaliana, maize (Zea mays), tomato (Lycopersicon esculentum), and soybean (G. max).
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献