Décomposeur | EPFL Graph Search

vignette|Cycle de la matière organique : minéralisation et humification. Les décomposeurs sont les êtres vivants participant directement à la décomposition de la matière organique morte (nécromasse) ou des excréments ou excrétats d'êtres vivants. Ils jouent un rôle majeur, nécessaire au recyclage des éléments (minéraux, oligo-éléments...) qui composent la matière organique. Certains d'entre eux contribuent aux grands processus permanents de détoxication de l'environnement, en recyclant (décomposant) des composés organiques toxiques (toxines naturelles) ou perturbateurs pour l'écosystème (certaines phéromones, hormones et perturbateurs endocriniens par exemple) contenus dans les détritus et les sédiments, le sol, etc. Ce sont essentiellement des bactéries et des champignons, mais aussi lato sensu des détritivores, qui se nourrissent de débris animaux, végétaux ou fongiques qui sont des excrétats, excréments ou font partie de la nécromasse. Dans les sols et environnements terrestres, les bactéries et champignons agissent souvent de concert aux pH neutres, mais les champignons sont plus actifs dans les environnements à pH bas (milieu acide) alors que les bactéries sont plus actives aux pH élevés (milieux basiques). Dans les milieux dits extrêmes ces deux troupes de décomposeurs sont néanmoins tous deux inhibés. Par exemple les champignons eux-mêmes disparaissent presque au-dessous d'un pH de 4,5 sans doute en raison d'une libération d'aluminium à des doses toxiques pour eux et/ou parce que la productivité du milieu en matière organique biodisponible pour eux diminue dans les milieux très acides. Les digestats et excrétats des gros décomposeurs (invertébrés) sont riches en nutriments facilement accessibles à la microflore bactérienne et fongique du sol. Ils contribuent aussi à la qualité de l'humus forestier ou prairial. Des « décomposeurs » sont présents dans tous les compartiments des écosystèmes, presque partout dans la biosphère.

Biotic and Abiotic Constraints on the Decomposition of Fagus sylvatica Leaf Litter Along an Altitudinal Gradient in Contrasting Land-Use Types

Alexandre Buttler, Konstantin Svetlozarov Gavazov, Thomas Spiegelberger, Robert Thomas Edmund Mills

Climate change can affect the process of carbon cycling and leaf litter decomposition in multiple ways, both directly and indirectly, though the strength and direction of this relationship is often context dependent. In this experiment, we followed decomposition of a standard litter type-senescent leaves of Fagus sylvatica collected from a single location-along a 1000 m altitudinal gradient of four sites over 2.5 years. To control the edaphic conditions, we transplanted intact turf mesocosms from three different land-use types [densely wooded, sparsely wooded, and unwooded (UW) pastures] from the highest altitude site into UW pastures along the altitudinal gradient from the moist, cool high-elevation site to the dry, warm low-elevation site, using shade cloth to mimic the light conditions in the original habitats. Decomposition in the drier UW pasture mesocosms increased with altitude, likely because of higher moisture at the highest sites. Decomposition in the more mesic mesocosms from sparsely and densely wooded sites was insensitive to altitude, suggesting an overriding moisture, rather than temperature, constraint on decomposition across these sites. The functional composition of decomposer microbial communities (fungal/bacterial ratio) was similarly insensitive to altitude. Our findings bring substantial evidence for the controlling role of soil moisture on litter decomposition, as well as for the indirect effects of climate through changes in the decomposer community.

Springer Verlag2014

An object-oriented model for adaptive high-performance computing on the computational GRID

Tuan Anh Nguyen

The dissertation presents a new parallel programming paradigm for developing high performance (HPC) applications on the Grid. We address the question "How to tailor HPC applications to the Grid?" where the heterogeneity and the large scale of resources are the two main issues. We respond to the question at two different levels: the programming tool level and the parallelization concept level. At the programming tool level, the adaptation of applications to the Grid environment consists of two forms: either the application components should somehow decompose dynamically based on the available resources; or the components should be able to ask the infrastructure to select automatically the suitable resources by providing descriptive information about the resource requirements. These two forms of adaptation lead to the parallel object model on which resource requirements are integrated into shareable distributed objects under the form of object descriptions. We develop a tool called ParoC++ that implements the parallel object model. ParoC++ provides a comprehensive object-oriented infrastructure for developing and integrating HPC applications, for managing the Grid environment and for executing applications on the Grid. At the parallelization concept level, we investigate the parallelization scheme which provides the user a method to express the parallelism to satisfy the user specified time constraints for a class of problems with known (or well-estimated) complexities on the Grid. The parallelization scheme is constructed on the following two principal elements: the decomposition tree which represents the multi-level decomposition and the decomposition dependency graph which defines the partial order of execution within each decomposition. Through the scheme, the parallelism grain will be automatically chosen based on the available resources at run-time. The parallelization scheme framework has been implemented using the ParoC++. This framework provides a high level abstraction which hides all of the complexities of the Grid environment so that users can focus on the "logic" of their problems. The dissertation has been accompanied with a series of benchmarks and two real life applications from image analysis for real-time textile manufacturing and from snow simulation and avalanche warning. The results show the effectiveness of ParoC++ on developing high performance computing applications and in particular for solving the time constraint problems on the Grid.

EPFL2005

An object-oriented model for adaptive high-performance computing on the computational GRID

Tuan Anh Nguyen

EPFL2005