Hyphomycètes aquatiques : importance dans la décomposition des litières

Les auteurs comparent les communautés d'hyphomycètes aquatiques récoltés dans l'écume de 7 cours d'eau du Béarn et des Landes. L'abondance de spores observées dans les deux régions diffère considérablement (174-1175 spores/µl en Béarn et 2-57 spores/µl dans les Landes) tandis que les variations de richesse spécifique apparaissent faibles. L'influence de la végétation riveraine et du pH de l'eau est discutée.Des expériences de dégradation in vitro montrent que des souches isolées de Tetracladium marchalianum, Heliscus lugdunensis et dans une moindre mesure Anguillospora longissima présentent une activité cellulolytique. T. marchalianum et H. lugdunensis, participent activement à la décomposition de litière de saule blanc, avec respectivement 21,7 et 18,2 % de dégradation après 5 semaines à 18°C.Aquatic hyphomycete communities from the foam of seven streams in the Bearn and Landes regions of France were compared at four different dates. The total number of species was similar in the two regions, but common species (> 5 spores/µl) in the Bearn were twice as abundant as in the Landes. Mean spore concentrations in the Bearn and Landes streams were in a ratio of 10 : 1. In the Bearn, spore concentration and the number of fungal species increased considerably in autumn, subsequent to the fall of leaf litter into the streams. Analysis of variance of spore concentrations (original or transformed data) in the two regions showed that date, station and the interaction of these two factors were highly significant parameters (P ANOVA < 0.0001). Alatospora acuminate was the commonest species both in the Bearn (77 % annual mean) and in the Landes (41 %). After A. acuminata, Clavatospora stellata (7 %) and Tetracladium marchalianum (4 %,) in the Bearn, Flagellospora curvula (28 %) and Clavastospora longibrachiata (20 %) in the Landes were the dominant species of the mycoflora. Five species new to France were noted : Actinospora megalospora Ingold, Camposporium pellucidum (Grave) Hugues, Diplocladiella scalaroides Arnaud, Flabellospora acuminata Descals and Triscelophorus monosporus Ingold. The difference in fungal richness between the two regions was suggested to be due to the composition of the riparian vegetation, the phenology of the litter fall, the presence (or absence) of plant matter accumulation in the stream, and the pH of the stream water. Litter deposits in the Landes streams were rare and made up exclusivey of pine needles, the few deciduous leaves which fall being exported to surrounding lakes and to the ocean. Water pH was always low (5.0-5.5). The riparian vegetation of the Bearn streams, on the contrary, was abundant and varied Cash, common locust-tree, alder, willow, oak, chestnut, poplar). Moreover the neutral or weakly acid pH of the Bearn streams (6.3-7.0) seemed to favour fungal diversity (cf. BÄRLOCHER and ROSSET, 1981; WOOD-EGGENSCHWILLER and BARLOCHER, 1983).Single spore isolates of Anguillospora langissima (de Wild.) Ingold, Heliscus lugdunensis Saccardo et Therry and Tetraclacium marchalianum De Wild were obtained from decomposing leaf litter in the Bearn streams. In laboratory experiments, the degradation activity of each species was tested both on sterilized paper cellulose and white willow leaf litter. The cellutolytic activity of fungal cultures was significant when compared with controls (t test). After 5 weeks at 18 °C, mass loss was 8.6 % for A.longissima and 10.0 % for H.lugdunensis and T.marchalianum. Aeration stimulated cellulose degradation for T.marchalianum (16.6 %) only. With willow leaves as substrate, degradation was greater for T.marchalianum (22.7 %) than for N. lugdunensis (11.8 %) and A. longissima (6.2 %, non-significant)

Evolutionary Stability of Ecological Hierarchy

A self-similar hierarchical solution that is both dynamically and evolutionarily stable is found to the multi dimensional Lotka-Volterra equation with a single chain of prey-predator relations. This gives a simple and natural explanation to the key features of hierarchical ecosystems, such as its ubiquity, pyramidal population distribution, and higher aggressiveness among higher trophic levels. pacs{87.23.Kg, 89.75.Da, 05.45.-a} keywords{Lotka-Volterra equation, Trophic pyramid, Self-similarity}Comment: 4 Pages RevTeX4, 1 Fig, 1 Table, shortened by publishers reques

Isotropization of Bianchi-Type Cosmological Solutions in Brans-Dicke Theory

The cosmic, general analitic solutions of the Brans--Dicke Theory for the flat space of homogeneous and isotropic models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions --which includes cosmological models with the open and the closed spaces of the Friedmann--Robertson--Walker metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi--Type metric clasification-- when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scalar field, $\phi$, times a function of the mean scale factor or ``volume element'', $a^3 = a_1 a_2 a_3$, which depends on time and on the barotropic index of the equation of state used, can be written as a function of a ``cosmic time'' reduced in terms of another function of the mean scale factor depending itself again on the barotropic index but independent of the metrics here employed. This reduction procedure permites one to analyze if explicitly given anisotropic cosmological solutions ``isotropize'' in the course of their time evolution. For if so can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations.Comment: 15 pages, Late

Leaf litter breakdown budgets in streams of various trophic status: effects of dissolved inorganic nutrients on microorganisms and invertebrates

1. We investigated the effect of trophic status on the organic matter budget in freshwater ecosystems. During leaf litter breakdown, the relative contribution of the functional groups and the quantity/quality of organic matter available to higher trophic levels are expected to be modified by the anthropogenic release of nutrients. 2. Carbon budgets were established during the breakdown of alder leaves enclosed in coarse mesh bags and submerged in six streams: two oligotrophic, one mesotrophic, two eutrophic and one hypertrophic streams. Nitrate concentrations were 4.5–6.7 mg L−1 and the trophic status of each stream was defined by the soluble reactive phosphorus concentration ranging from 3.4 (oligotrophic) to 89 μg L−1 (hypertrophic). An ammonium gradient paralleled the phosphate gradient with mean concentrations ranging from 1.4 to 560 μg L−1 NH4-N. The corresponding unionised ammonia concentrations ranged from 0.08 to 19 μg L−1 NH3-N over the six streams. 3. The dominant shredder taxa were different in the oligo-, meso- and eutrophic streams. No shredders were observed in the hypertrophic stream. These changes may be accounted for by the gradual increase in the concentration of ammonia over the six streams. The shredder biomass dramatically decreased in eu- and hypertrophic streams compared with oligo- and mesotrophic. 4. Fungal biomass increased threefold from the most oligotrophic to the less eutrophic stream and decreased in the most eutrophic and the hypertrophic. Bacterial biomass increased twofold from the most oligotrophic to the hypertrophic stream. Along the trophic gradient, the microbial CO2 production followed that of microbial biomass whereas the microbial fine particulate organic matter and net dissolved organic carbon (DOC) did not consistently vary. These results indicate that the microorganisms utilised the substrate and the DOC differently in streams of various trophic statuses. 5. In streams receiving various anthropogenic inputs, the relative contribution of the functional groups to leaf mass loss varied extensively as a result of stimulation and the deleterious effects of dissolved inorganic compounds. The quality/quantity of the organic matter produced by microorganisms slightly varied, as they use DOC from stream water instead of the substrate they decompose in streams of higher trophic status

Isotropization of Bianchi type models and a new FRW solution in Brans-Dicke theory

Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans-Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curve ($k\neq0$) Friedmann-Robertson-Walker (FRW) cosmologies in Brans-Dicke theory is analyzed.Comment: 15 pages, 4 postscript figures, to appear in Gen. Rel. Grav., special issue dedicated in honour of Prof. H. Dehne

A new method to determine arterial distensibility in small arteries

Several methods allow to measure arterial distensibilty. One of them consists in estimating the direct distensibility (D) from diameter and distending blood pressure. Herein, we propose a new method to assess the distensibility in small arteries which is based on spectral analysis of time motion mode ultrasound images of radial arteries. A Fourier transform was performed on intensity of upper and lower walls. Spectral amplitude at heart frequency from both wall spectra was estimated and summed (SumAmp). SumAmp was then compared with direct distensibility. A significant correlation was found between SumAmp and D (r = 0.7, p = 0.02)

Heterodyne non-demolition measurements on cold atomic samples: towards the preparation of non-classical states for atom interferometry

We report on a novel experiment to generate non-classical atomic states via quantum non-demolition (QND) measurements on cold atomic samples prepared in a high finesse ring cavity. The heterodyne technique developed for the QND detection exhibits an optical shot-noise limited behavior for local oscillator optical power of a few hundred \muW, and a detection bandwidth of several GHz. This detection tool is used in single pass to follow non destructively the internal state evolution of an atomic sample when subjected to Rabi oscillations or a spin-echo interferometric sequence.Comment: 23 page

Competitive interaction between two aquatic hyphomycete species and increase in leaf litter breakdown

Aquatic hyphomycete species produce large numbers of conidia which rapidly colonize the leaf litter that falls into rivers during autumn. Our objective was to understand how a species which produces many fewer conidia than another in laboratory conditions can nevertheless be codominant in a natural setting. In microcosm studies with two pioneer dominant species, Flagellospora curvula and Tetrachaetum elegans, inoculated on alder leaves, we first verified that the ratio of the conidium production of both species (6 to 7:1) was inverse to that of individual conidial masses (1:7) as previously described. Calculating the percentage of leaf mass loss that corresponds to 1 mg of conidial mass produced, the combination of the two species produced 2.9-fold more loss than the mean of each species. By contrast, the reproductive biomasses of F. curvula and T. elegans were 5.2- and 2.6-fold lower, respectively. As a result, the conidium production of F. curvula in the combination was only 3.2-fold that of T. elegans instead of 6- to 7-fold in pure culture. In a mixed culture of the two species, T. elegans conidia had a high germination potential (>90%) whereas the proportion of germinated F. curvula conidia was only 50%. Moreover, T. elegans reduced the area on which F. curvula could grow on poor and rich solid media. These results indicate that the dominance of F. curvula conidia in the river may be partly controlled by T. elegans and suggest that a negative interaction between microfungi may have a positive effect on the ecosystem functioning

Innovación tecnológica en una empresa fruti-hortícola

El sector fruti-hortícola se caracteriza por la temporalidad de producción, lo que genera una serie de problemas por los tiempos de vacancia y la dificultad de fidelizar un plantel de personal competente tan necesario en los integrantes de la cadena alimentaria. Por tal motivo, se ha estudiado un empaque de frutilla de la provincia de Tucumán, destinada a su producción como su congelado, así como el de arándanos y durazno. La producción de frutillas es propia y se realiza en los meses de julio a noviembre. Mediante la compra de fruta ha incorporado el congelado de arándano, para los meses de noviembre a diciembre y de durazno desde enero hasta marzo. Los productores de frutillas congelados disponen de tecnologías, como son los túneles de congelado dinámico, lo que les confiere una potencialidad para brindar una producción continua y de calidad en el congelado. El objetivo de este trabajo es buscar alternativas para aprovechar las instalaciones en el congelado de productos fruti-hortícolas de Tucumán con destino principalmente para exportación. Para seleccionar la alternativa se tuvo en cuenta la producción fruti-hortícola que puede ser congelado y se cultiva en Tucumán y los periodos de vacancia del empaque. Por otro lado, se ha efectuado el análisis de la situación del mercado de producto basado en: producto, producción, destino de la producción, calendario de la papa, canales de distribución y precio. Para determinar los potenciales mercados se ha trabajado con la evolución de las exportaciones de Argentina del producto y se seleccionaron los principales destinados. A éstos se efectuó un estudio de la importación del producto y mediante un análisis de tendencias se ha calculado la demanda insatisfecha, a fin de compararse con la capacidad de congelado para determinar el nivel de producción de papas prefritas congeladas. Como conclusión final de este trabajo, se ha detectado que las papas pre-fritas congeladas le permitirán lograr la producción de frutillas, arándanos y durazno congelado, lo que podrían mejorar la rentabilidad y contar con un grupo humano fijo, competente y hasta fidelizarlo al disponer de una fuente de trabajo continua, cuyo principal cliente es Brasil y después Chile.publishedVersio