Biosphere-atmosphere interactions of ammonia with grasslands: Experimental strategy and results from a new European initiative

A new study to address the biosphere-atmosphere exchange of ammonia (NH₃) with grasslands is applying a European transect to interpret NH₃ fluxes in relation to atmospheric conditions, grassland management and soil chemistry. Micrometeorological measurements using the aerodynamic gradient method (AGM) with continuous NH₃ detectors are supported by bioassays of the NH₃ `stomatal compensation point' (<sub>s</sub>). Relaxed eddy accumulation (REA) is also applied to enable flux measurements at one height; this is relevant to help address flux divergence due to gas-particle inter-conversion or the presence of local sources in a landscape.Continuous measurements that contrast intensively managed grasslands with semi-natural grasslands allow a scaling up from 15 min values to seasonal means. The measurements demonstrate the bi-directional nature of NH<sub>3</sub> fluxes, with typically daytime emission and small nocturnal deposition. They confirm the existence of enhanced NH<sub>3</sub> emissions (e.g. 30 g N ha<sup>–1</sup> d<sup>–1</sup>) following cutting of intensively managed swards. Further increased emissions follow fertilization with NH<sub>4</sub>NO<sub>3</sub> (typically 70 g N ha<sup>–1</sup> d<sup>–1</sup>). Measurements using REA support these patterns, but require a greater analytical precision than with the AGM.The results are being used to develop models of NH<sub>3</sub> exchange. `Canopy compensation point' resistance models reproduce bi-directional diurnal patterns, but currently lack a mechanistic basis to predict changes in relation to grassland phenology. An advance proposal here is the coupling of _s to dynamic models of grassland C–N cycling, and a relationship with modelled plant substrate-N is shown. Applications of the work include incorporation of the resistance models in NH₃ dispersion modelling and assessment of global change scenarios.     

Prolactinoma causing secondary amenorrhea in a woman with Ullrich-Turner syndrome

This is the case report of a girl who was diagnosed as having Ullrich-Turner mosaic at the age of 12 years. She had normal pubertal development and menarche at the age of 15 years. The patient had regular menstrual cycles for 12 months before developing secondary amenorrhea. She was started on estrogen/gestagen replacement therapy by her gynecologist. Several months later a prolactinoma was diagnosed by laboratory and imaging techiques. A second-generation dopamine agonist led to almost regular cycles. Therefore, even in patients with susceptibility to ovarian failure secondary amenorrhea necessitates thorough diagnostic investigation. Copyrightz1999S.KargerAG,Basel     

Vaccine-induced immunopathology during bovine respiratory syncytial virus infection: exploring the parameters of pathogenesis

The bovine and human respiratory syncytial viruses cause severe lower respiratory tract infections. Effective vaccines against the respiratory syncytial viruses have been lacking since vaccine failures in the 1960s and 1970s. In this report, we describe a bovine respiratory syncytial virus (bRSV) challenge model in which both classical bRSV respiratory infection and vaccine-enhanced immune pathology were reproduced. The classical, formalin-inactivated (FI) bRSV vaccine that has been associated with vaccine failure was efficient in inducing high antibody titers and reducing viral loads but also primed calves for a far more serious enhanced respiratory disease after a bRSV challenge, thereby mimicking the enhanced clinical situation in FI human RSV (hRSV)-immunized and hRSV-infected infants in the 1960s. We show that immunization with FI-bRSV mainly primes a Th2-like inflammatory response that is characterized by a significant eosinophilic influx in the bronchial alveolar lung fluid and lung tissues and high levels of immunoglobulin E serum antibodies. The current model may be useful in the evaluation of new bRSV candidate vaccines for potency and safety.     

Elevation,Topography, and Edge Effects Drive Functional Composition of Woody Plant Species in Tropical Montane Forests

Tropical montane forests comprise heterogeneous environments along natural gradients of topography and elevation. Human‐induced edge effects further increase the environmental heterogeneity in these forests. The simultaneous effects of natural and human‐induced gradients on the functional diversity of plant leaf traits are poorly understood. In a tropical montane forest in Bolivia, we studied environmental gradients associated with elevation (from 1900 m to 2500 m asl), topography (ridge and gorge), and edge effects (forest edge vs. forest interior), and their relationship with leaf traits and resource‐use strategies. First, we investigated associations of environmental conditions (soil properties and microclimate) with six leaf traits, measured on 119 woody plant species. Second, we evaluated changes in functional composition with community‐weighted means and functional structure with multidimensional functional diversity indices (FRic, FEve and FDiv). We found significant associations between leaf traits and soil properties in accordance with the trade‐off between acquisition and conservation of resources. Functional composition of leaf traits shifted from the dominance of acquisitive species in habitats at low altitudes, gorges, and forest interior to the dominance of conservative species in habitats at high altitudes, ridges, and forest edges. Functional structure was only weakly associated with the environmental gradients. Natural and human‐induced environmental gradients, especially soil properties, are important for driving leaf traits and resource‐use strategies of woody plants. Nevertheless, weak associations between functional structure and environmental gradients suggest a high redundancy of functional leaf traits in this tropical montane forest.     

Dynamic Allostery of the Catabolite Activator Protein Revealed by Interatomic Forces

The Catabolite Activator Protein (CAP) is a showcase example for entropic allostery. For full activation and DNA binding, the homodimeric protein requires the binding of two cyclic AMP (cAMP) molecules in an anti-cooperative manner, the source of which appears to be largely of entropic nature according to previous experimental studies. We here study at atomic detail the allosteric regulation of CAP with Molecular dynamics (MD) simulations. We recover the experimentally observed entropic penalty for the second cAMP binding event with our recently developed force covariance entropy estimator and reveal allosteric communication pathways with Force Distribution Analyses (FDA). Our observations show that CAP binding results in characteristic changes in the interaction pathways connecting the two cAMP allosteric binding sites with each other, as well as with the DNA binding domains. We identified crucial relays in the mostly symmetric allosteric activation network, and suggest point mutants to test this mechanism. Our study suggests inter-residue forces, as opposed to coordinates, as a highly sensitive measure for structural adaptations that, even though minute, can very effectively propagate allosteric signals.     

Estimating Absolute Configurational Entropies of Macromolecules: The Minimally Coupled Subspace Approach

We develop a general minimally coupled subspace approach (MCSA) to compute absolute entropies of macromolecules, such as proteins, from computer generated canonical ensembles. Our approach overcomes limitations of current estimates such as the quasi-harmonic approximation which neglects non-linear and higher-order correlations as well as multi-minima characteristics of protein energy landscapes. Here, Full Correlation Analysis, adaptive kernel density estimation, and mutual information expansions are combined and high accuracy is demonstrated for a number of test systems ranging from alkanes to a 14 residue peptide. We further computed the configurational entropy for the full 67-residue cofactor of the TATA box binding protein illustrating that MCSA yields improved results also for large macromolecular systems.     

Clamping,bending, and twisting inter-domain motions in the misfold-recognizing portion of UDP-glucose: Glycoprotein glucosyltransferase

1. Download : Download high-res image (119KB)
2. Download : Download full-size image

     

Do <Emphasis Type="Italic">Polylepis australis</Emphasis> trees tolerate herbivory? Seasonal patterns of shoot growth and its consumption by livestock

Browsing is one of the main factors determining survival, growth rate, woodland structure, and distribution of the high mountain tree Polylepis australis. This species has a substantial regrowth capacity, which may function as a mechanism to tolerate herbivory, but it is unknown to what extent it may compensate for the impact of herbivory. In 15 low-density tree stands subject to exclusion, moderate, and heavy livestock pressure, we selected 12 P. australis individuals <2 m tall, tagged four new shoots per tree and measured shoot length every month during a year. At the stand and at the tree level, we analyzed monthly dynamics of growth and browsing, and the annual output in terms of total browsing and total gross and net growth (not discounting and discounting consumption, respectively). In addition, we assessed the influence of stand, tree and microsite characteristics on growth and browsing patterns. Polylepis australis fully compensated for herbivory in terms of shoot gross growth at moderate, but not at heavy livestock pressure. In terms of net growth, this species did not fully compensate for herbivory at any stocking rate. We found a strong coupling between browsing and growth along the year, suggesting that regrowth attracts browsing, and browsing promotes regrowth. At the stand level, annual gross growth was not affected by habitat characteristics, while at the tree level, annual gross growth decreased on more rocky microsites for browsed but not for unbrowsed trees. We concluded that stocking densities should be limited to allow for a reasonable annual net growth, as its nitrogen rich leaves are a valuable food resource and P. australis forests provide important ecosystem services.     

Genetic structure of coastal and inland populations of <Emphasis Type="Italic">Spergularia media</Emphasis> (L.) C. Presl (Caryophyllaceae) in Central Europe

In Central Europe, salt-influenced habitats are restricted mainly to the coastlines of the North Sea and the Baltic Sea. The few natural inland salt sites suffer from size reduction and loss in biodiversity, while anthropogenic salt sites around potash mining dumps experienced recent and massive de novo colonization by numerous halophytes. Our study aimed to elucidate the general patterns of gene flow among coastal and inland salt habitats. We used amplified fragment length polymorphisms to assess the genetic diversity and genetic structure of 18 European populations of the halophyte Spergularia media (Caryophyllaceae), sampled from inland and coastal salt sites of Germany, the Netherlands, Denmark, Austria, France and Italy. Estimates of genetic diversity on the population level were generally low, especially within inland salt habitats. Analyses of molecular variance showed comparatively strong differentiation among populations. Multivariate ordination (principal coordinate analysis) and a NeighborNet analysis revealed four distinct groups of populations that showed good correspondence to their geographic origins. A Bayesian analysis performed with the program Structure as well as high pairwise Φ _ST values supported the results of the phenetic analyses. The observed patterns of diversity and differentiation among inland populations of S. media are best explained by the isolated nature of suitable salt habitats, with concomitant reduction of gene flow to and among these sites. Our data support the hypothesis that the colonization of anthropogenic salt sites by S. media originated from natural inland habitats.     

Genetic structure of Galitzkya macrocarpa and G. potaninii, two closely related endemics of central Asian mountain ranges

BACKGROUND AND AIMS Habitats in mountains are often isolated. Plants growing in these sites face severe dispersal limitations, but also difficulties for recruitment. The focus was laid on the magnitude of genetic differences among populations but also on the size of potentially occurring clones. METHODS: RAPD fingerprints were obtained from 23 populations in southern Mongolia. Sampling covered the entire distribution range of Galitzkya macrocarpa; samples of G. potaninii represented only the Mongolian part of its mainly northern Chinese range. KEY RESULTS: The Mongolian endemic G. macrocarpa showed moderately strong population differentiation (Phi ST = 0.251), and limited evidence for isolation by distance. Local genetic diversity was not positively correlated to habitat size, and not reduced in peripheral populations. Clonal growth is possible, but most plants originate from sexual reproduction. In contrast, populations of G. potaninii were highly differentiated (Phi ST = 0.550); and the most remote outposts had reduced genetic diversity. In these areas, isolation is expected to date back to glacial times. CONCLUSIONS: Effects of natural fragmentation differ among species. Both are rare, but G. macrocarpa appears to be able to maintain genetic diversity over its range. Clonal growth is an option in its mixed reproduction strategy and allows survival under harsh conditions. In contrast, genetic structure in G. potaninii gives reason for concern, and further studies on population dynamics are needed.