Production and turnover of organic matter in three southern European Fagus sylvatica L. Stands

17 pages, 5 figures, 7 tables.[EN] Above-ground biomass, litterfall and litter accumulation and decomposition at the soil surface were studied within three Mediterranean beech forests from Italy, France and Spain in order to better understand the recycling of elements associated with the turnover organic matter Above-ground tree biomass amounted to 131.9 Mg ha'^ at Etna (Italy), 134.2 Mg ha'' at Sierra de la Demanda (Spain) and 223.9 Mg ha'' at Mont Lozère (France). The highest amount of total litterfall was observed at Sierra de la Demanda (4.7 Mg ha-' year'), followed by the Mont Lozère (4.4 Mg ha' year' ) and Etna (3.9 Mg ha' year'). Total organic matter accumulated on the soil surface in the three beech forests amounted to 25.8 Mg ha'' at Mont Lozère, 14.4 Mg ha'' at Sierra de la Demanda and 12.6 Mg ha'' at Etna. The relative proportions of leaf litter versus total litter were nearly the same in the Etna and Sierra de la Demanda forests (72 - 70%), and close to these values for Mont Lozère (65%). All the studied Mediterranean Fagus sylvatica stands appeared very similar concerning the organic matter distribution and fluxes, even if local climate and soil differences can be noticed.[FR] Les biomasses aériennes, les retombées de litières, leur accumulation à la surface du sol et leur décomposition, ont été étudiées dans trois hêtraies méditerranéennes d'Italie, de France et d'Espagne, pour mieux connaître la restitution au sol des bioéléments par l'intermédiaire de la matière organique. Les biomasses aériennes s'élevaient respectivement à 131.9 Mg ha-1 dans la hêtraie de l'Etna (Italie), 134.2 Mg ha-1 dans celle de Sierra de la Demanda (Espagne) et à 223.9 Mg ha-1 au Mont Lozère (France). Les retombées de litière les plus fortes sont observées dans la hêtraie de la Sierra de la Demanda (4.7 Mg ha-1 an-1), suivie de celles du Mont Lozère (4.4 Mg ha-1 an-1) et de l'Etna (3.9 Mg ha-1 an-1). L'ensemble de la matière organique accumulée à la surface du sol des trois hêtraies était de 25.8 Mg ha-1 au Mont Lozère, 14.4 Mg ha-1 à Sierra de la Demanda et 12.6 Mg ha-1 dans l'Etna. Les proportions respectives de la fraction feuilles par rapport à la litière totale étaient proches dans les stations de l'Etna et de la Sierra de la Demanda (72 - 70%) et voisines de celle du Mont Lozère (65%). Toutes les forêts de Fagus sylvatica dans le climat Méditerranéen sont très similaires par rapport à la distribution et aux flux, malgré que les conditions de climat et de sol soient différentes.[ES] Se han estudiado la biomasa aérea, la caída, acumulación y descomposición de la hojarasca en tres ecosistemas forestales de hayedo en Italia, Francia y España en orden a conocer mejor el reciclado de elementos- biógenos asociados al reciclaje de materia orgánica. La biomasa aérea estimada es de 131.0 Mg ha-1 en Etna (Italia), 134.2 Mg ha-1 en la Sierra de la Demanda (España) y 223.9 Mg ha-1 en Mont Lozère (Francia). La mayor cantidad de caída de hojarasca se ha observado en la Sierra de la Demanda (4.7 Mg ha-1 año-1) seguida de Mont Lozère (4.4 Mg ha-1 año-1). La materia orgánica acumulada en la superficie del suelo en los tres ecosistemas forestales estudiados fue de 25.8 Mg ha-1 en Mont Lozère, 14.4 Mg ha-1 en la Sierra de la Demanda y 12.6 Mg ha-1 en Etna. El porcentaje relativo de las hojas con relación a la hojarasca total fue similar en las parcelas de Etna y Sierra de la Demanda (72-70%) y algo más bajo en Mont Lozère (65%). Los bosques de Fagus sylvatica estudiados reflejaron valores similares respecto a la distribución y flujos de materia orgánica, aunque se han evidenciado diferencias en cuanto a condiciones locales de clima y suelo.This project has been financed by C. E. and I. N. I. A. We thank the facilities given to us by the Environmental Service of J. C. L. in Burgos, Montpellier and Catania and in the same way to the ground staff who have collaborated in it.Peer reviewe

Warm and fertile sub-humid conditions enhance litterfall to sustain high soil respiration fluxes in a mediterranean cork oak forest

Soil respiration is a major component of the global carbon budget and Mediterranean ecosystems have usually been studied in locations with shallow soils, mild temperatures, and a prolonged dry season. This study investigates seasonal soil respiration rates and underlying mechanisms under wetter, warmer, and more fertile conditions in a Mediterranean cork oak forest of Northern Tunisia (Africa), acknowledged as one of the most productive forests in the Mediterranean basin. We applied a soil respiration model based on soil temperature and relative water content and investigated how ecosystem functioning under these favorable conditions affected soil carbon storage through carbon inputs to the soil litter. Annual soil respiration rates varied between 1774 gC m(-2) year(-1) and 2227 gC m(-2) year(-1), which is on the highest range of observations under Mediterranean climate conditions. We attributed this high soil carbon flux as a response to favorable temperatures and soil water content, but this could be sustained only by a small carbon allocation to roots (root/shoot ratio = 0.31-0.41) leading to a large allocation to leaves with a multiannual leaf production, enhanced annual twig elongation (11.5-28.5 cm) with a reduced leaf life span (<1 year) maintaining a low LAI (1.68-1.88) and generating a high litterfall (386-636 gC m(-2) year(-1)). Thus, the favorable climatic and edaphic conditions experienced by these Mediterranean cork oak forests drove high soil respiration fluxes which balanced the high carbon assimilation leading to a relatively small overall contribution (10.96-14.79 kgC m(-2)) to soil carbon storage

Biological monitoring of occupational exposure to metals in electric steel foundry workers and its contribution to 8-oxo-7,8-dihydro-2&#8242;-deoxyguanosine levels

In this study, the urinary concentrations of selected metals in workers from an electric steel foundry in Tunisia were assessed and compared with existing biological limit values and general population reference values. Moreover, the association between oxidative DNA damage, measured as urinary 8-oxo-7,8-dihydro-2\u2019deoxyguanosine (8-oxodG) and co-exposure to metals and polycyclic aromatic hydrocarbons (PAHs) was evaluated. Urinary levels of 12 metals were determined by inductively coupled plasma-mass spectrometry (ICP-MS) in end-shift spot samples from 89 workers. The urinary levels of phenanthrene (U-PHE), as marker of exposure to PAHs, and 8-oxodG were also available. Median levels ranged from 0.4 \ub5g/L (cobalt, Co, and thallium, Tl) to 895 \ub5g/L (zinc, Zn). Only 1% of samples was above the biological limit values for Co, and up to 13.5% of samples were above limit values for Cd. From 3.4% (Co) to 72% (lead, Pb) of samples were above the reference values for the general population. Multiple linear regression models, showed that manganese (Mn), Zn, arsenic (As), barium (Ba), Tl, and Pb were significant predictors of 8-oxodG (0.012 64 p 64 0.048); U-PHE was also a significant predictor (0.003 64 p 64 0.059). The variance explained by models was low (0.11 64 R2 64 0.17, p &lt; 0.005), showing that metals and PAHs were minor contributors to 8-oxodG. Overall, the comparison with biological limit values showed that the study subjects were occupationally exposed to metals, with levels exceeding biological limit values only for Cd

Production and turnover of organic matter in three southern European Fagus sylvatica L. Stands

17 pages, 5 figures, 7 tables.[EN] Above-ground biomass, litterfall and litter accumulation and decomposition at the soil surface were studied within three Mediterranean beech forests from Italy, France and Spain in order to better understand the recycling of elements associated with the turnover organic matter Above-ground tree biomass amounted to 131.9 Mg ha'^ at Etna (Italy), 134.2 Mg ha'' at Sierra de la Demanda (Spain) and 223.9 Mg ha'' at Mont Lozère (France). The highest amount of total litterfall was observed at Sierra de la Demanda (4.7 Mg ha-' year'), followed by the Mont Lozère (4.4 Mg ha' year' ) and Etna (3.9 Mg ha' year'). Total organic matter accumulated on the soil surface in the three beech forests amounted to 25.8 Mg ha'' at Mont Lozère, 14.4 Mg ha'' at Sierra de la Demanda and 12.6 Mg ha'' at Etna. The relative proportions of leaf litter versus total litter were nearly the same in the Etna and Sierra de la Demanda forests (72 - 70%), and close to these values for Mont Lozère (65%). All the studied Mediterranean Fagus sylvatica stands appeared very similar concerning the organic matter distribution and fluxes, even if local climate and soil differences can be noticed.[FR] Les biomasses aériennes, les retombées de litières, leur accumulation à la surface du sol et leur décomposition, ont été étudiées dans trois hêtraies méditerranéennes d'Italie, de France et d'Espagne, pour mieux connaître la restitution au sol des bioéléments par l'intermédiaire de la matière organique. Les biomasses aériennes s'élevaient respectivement à 131.9 Mg ha-1 dans la hêtraie de l'Etna (Italie), 134.2 Mg ha-1 dans celle de Sierra de la Demanda (Espagne) et à 223.9 Mg ha-1 au Mont Lozère (France). Les retombées de litière les plus fortes sont observées dans la hêtraie de la Sierra de la Demanda (4.7 Mg ha-1 an-1), suivie de celles du Mont Lozère (4.4 Mg ha-1 an-1) et de l'Etna (3.9 Mg ha-1 an-1). L'ensemble de la matière organique accumulée à la surface du sol des trois hêtraies était de 25.8 Mg ha-1 au Mont Lozère, 14.4 Mg ha-1 à Sierra de la Demanda et 12.6 Mg ha-1 dans l'Etna. Les proportions respectives de la fraction feuilles par rapport à la litière totale étaient proches dans les stations de l'Etna et de la Sierra de la Demanda (72 - 70%) et voisines de celle du Mont Lozère (65%). Toutes les forêts de Fagus sylvatica dans le climat Méditerranéen sont très similaires par rapport à la distribution et aux flux, malgré que les conditions de climat et de sol soient différentes.[ES] Se han estudiado la biomasa aérea, la caída, acumulación y descomposición de la hojarasca en tres ecosistemas forestales de hayedo en Italia, Francia y España en orden a conocer mejor el reciclado de elementos- biógenos asociados al reciclaje de materia orgánica. La biomasa aérea estimada es de 131.0 Mg ha-1 en Etna (Italia), 134.2 Mg ha-1 en la Sierra de la Demanda (España) y 223.9 Mg ha-1 en Mont Lozère (Francia). La mayor cantidad de caída de hojarasca se ha observado en la Sierra de la Demanda (4.7 Mg ha-1 año-1) seguida de Mont Lozère (4.4 Mg ha-1 año-1). La materia orgánica acumulada en la superficie del suelo en los tres ecosistemas forestales estudiados fue de 25.8 Mg ha-1 en Mont Lozère, 14.4 Mg ha-1 en la Sierra de la Demanda y 12.6 Mg ha-1 en Etna. El porcentaje relativo de las hojas con relación a la hojarasca total fue similar en las parcelas de Etna y Sierra de la Demanda (72-70%) y algo más bajo en Mont Lozère (65%). Los bosques de Fagus sylvatica estudiados reflejaron valores similares respecto a la distribución y flujos de materia orgánica, aunque se han evidenciado diferencias en cuanto a condiciones locales de clima y suelo.This project has been financed by C. E. and I. N. I. A. We thank the facilities given to us by the Environmental Service of J. C. L. in Burgos, Montpellier and Catania and in the same way to the ground staff who have collaborated in it.Peer reviewe

Forced convection and thermocapillarity in silicon Czochraslki crystal growth in hemispherical crucible

International audienceIn order to understand the influence of a semispherical crucible geometry combined with different convection modes as a thermocapillary convection, natural convection and forced convection, induced by crystal rotation, on melt flow pattern in silicon Czochralski crystal growth process, a set of numerical simulations are conducted using Fluent Software. We solve the system of equations of heat and momentum transfer in classical geometry as cylindrical and modified crystal growth process geometry as cylindro-spherical. In addition, we adopt hypothesis adapted to boundary conditions near the interface and calculations are executed to determine temperature, pressure and velocity fields versus Grashof and Reynolds numbers. The analysis of the obtained results led to conclude that there is advantage to modify geometry in comparison with the traditional one. The absence of the stagnation regions of fluid in the hemispherical crucible corner and the possibility to control the melt flow using the crystal rotation enhances the quality of the process comparatively to the cylindrical one. The pressure field is strongly related to the swirl velocity

Analytical study of modified Czochralski crystal growth problem

International audienceAn analytical study of Czochralski crystal growth problem is presented, therefore, we propose a model based on a three-dimensional axisymmetric approach using the Galerkin method for solving the system of equations of heat and momentum in a modified crystal growth process geometry as cylindrical-spherical. To facilitate the procedure of resolution related to the considered problem, we impose some approximation; the molten silicon is assumed to be a viscous, Newtonian and incompressible fluid satisfying the Boussinesq assumption. The thermophysical properties of the fluid are constant except for the density variation in the buoyancy force term. The flow is symmetric in the axial direction. Fixed temperatures are imposed at the walls of the melt crucible and the crystal melt interface. Thus we determine analytically the expressions of temperature and velocity field in the melt, and discuss the temperature properties for different values of the Grashof number

Combined effects of crucible geometry and Marangoni convection on silicon Czochralski crystal growth.

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