Étude de l’influence de la densité de peuplement sur le fonctionnement du sol dans des chênaies par la mesuredes rapports isotopiques du carbone (13C/12C) et de l’azote (15N/14N) en EA-IRMS

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Functional Assemblages of Collembola Determine Soil Microbial Communities and Associated Functions

Soil processes such as decomposition are mainly performed by soil biota. Although soils worldwide are extremely biodiverse, the relationship between decomposers (fauna and microorganisms), and ecosystem function is poorly understood. Collembola are abundant and ubiquitous microarthropods that are found in terrestrial ecosystems. They can affect the amount of biomass and the activity of microbial communities, either directly through selectively feeding on fungi and bacteria, or indirectly by dissemination of microbial propagules, and the alteration of nutrient availability. However, despite the functional role they play in belowground food webs, the interactions between natural assemblages of soil microbes and Collembola receive little attention. This study, conducted in microcosm conditions, examines the effects of two distinct natural assemblages of functional groups of Collembola (ep- and euedaphic) upon microbial communities using PLFA markers and their associated soil functions (e.g., enzymatic activities and C mineralization rate) over a 2-month period. Our principal objective was to determine whether different functional groups of Collembola had varying effects on microbial soil community abundance, structure and activity, resulting in potentially important effects on ecosystem processes. Our findings show that the interactions of the functional groups of Collembola with microbial communities vary significantly whether they are alone or combined. A distinct response in the composition of the microbial communities was found at the end of the 2-month period. The communities were significantly different from each other in terms of PLFA marker composition. We found that the epedaphic species were related to and promoted Gram+ bacteria whereas euedaphic species were related to Gram- bacterial markers. This had further repercussions on soil function, such as nutrient recycling. Combining both functional groups did not lead to a complementary effect on soil microbial properties, with a drastically different outcome between the first and the second month of the experiment. Additional research dealing with the interactions between decomposers using natural assemblages will help to predict the functional outcomes of soil biota structure and composition

Beech leaf degradation in laboratory experiments: Effects of eight detritivorous invertebrate species

This work addresses the impact of eight detritivorous species of soil macro-invertebrates (three millipedes, two woodlice and three earthworms) on short-term carbon mineralization and mechanical breakdown of beech leaves. The production rate, size class distribution and OM content of invertebrate faeces were also measured. Hierarchical clustering (HC) and multivariate analysis were performed to find relevant functional groups among the species studied.Our results identified three groups of macro-invertebrates on the basis of their impacts on beach leaf degradation (hierarchical clustering): (1) invertebrates that produce fresh faeces with high N contents compared with other species (i.e. polydesmidae and a single species of lumbricidae); (2) other lumbricidae that fragment litter into fine particles in their faeces and actively stimulate CO2 release; (3) other arthropods that fragment litter into coarse particles and have weak impacts on OM mineralization. These groups over-ride taxonomy, and are proposed as a tentative functional classification of litter dwelling invertebrates. On the other hand, an idiosyncratic impact of species was observed in each group, highlighting how much empirical data are still needed to propose a robust functional classification of litter invertebrates

Comprendre et maîtriser les risques techniques et environnementaux : aller au-delà du risque ?

Comprendre et maîtriser les risques techniques et environnementaux : aller au-delà du risque ? Rédacteurs associés : Frédérick Lemarchand, Dominique Bourg, Pierre-Benoît Joly, Alain Kaufmann, Marc Mormont et Dominique Pécaud. VertigO, vol. 12, n° 1, 2012 http://vertigo.revues.org/11899 L’émergence des « nouveaux risques », collectifs, d’origine technologique et naturels s'articulant avec le risque technique (Fukushima), dont les conditions d’apparition étaient préparées depuis fort longtemps,..

Evolution des activités enzymatiques microbiennes sous l’effet de contraintes anthropiques

Evolution des activités enzymatiques microbiennes sous l’effet de contraintes anthropiques. 3ème édition du colloque d’Ecologie Microbienne de l’Association Francophone d’Ecologie Microbienn

Evolution des activités enzymatiques microbiennes sous l’effet de contraintes anthropiques

Evolution des activités enzymatiques microbiennes sous l’effet de contraintes anthropiques. 3ème édition du colloque d’Ecologie Microbienne de l’Association Francophone d’Ecologie Microbienn

Enzymatic activities in crop and grassland soils and the impact of copper addition

Enzymatic activities in crop and grassland soils and the impact of copper addition . Third International Conference on Enzymes in the Environmen

Activités enzymatiques et qualité des sols agricoles

Activités enzymatiques et qualité des sols agricoles. 9èmes Journées Nationales de l’Etude des Sol

Fungal, bacterial and plant dsDNA contributions to soil total DNA extracted from silty soils under different farming practices: Relationships with chloroform-labile carbon

Twelve differently-managed silty soils from North-Western France were chosen to compare two common methods of quantifying soil microbial biomass: Chloroform fumigation and extraction-labile carbon (CL_C) and microbial double stranded DNA (dsDNA). We also determined the contributions of each of the fungal, bacterial, and plant kingdoms to the total community dsDNA using real-time Polymerase Chain Reaction with kingdom-specific ribosomal primer sets. Regardless of the method, the highest microbial biomasses were associated with long-term untilled plots. Site (locations) specificities could also be detected, especially in conventionally cultivated lands. Regardless of site, a strong linear relationship could be drawn between CL_C and dsDNA in tilled lands (r = 0.91, n = 15, P = 0.01) and in grasslands (r = 0.78, n = 21, P = 0.01). Moreover, we propose a logarithmic model describing all of our silty soils, irrespective of management. In order to explain the non-linearity (log) of this relationship, we tested the hypothesis of a weak plant dsDNA contribution in total dsDNA in comparison with the well-documented root cell contribution to CL_C quantifications. Plant dsDNA never exceeded 2.6% of total dsDNA content for all of the soils studied. Among groups examined, the bacterial dsDNA contribution to the community dsDNA pool was the most site- and/or pedoclimatic-dependent. Fungi constituted a major component of total microbial biomass in grassland or in land with permanent plant cover where their proportion reached almost 50% of total dsDNA. More precisely, fungal dsDNA concentration was highly related to tillage. Our study demonstrated the expediency of the total microbial dsDNA quantification in agricultural silty soils rather than the time-consuming quantification of CL_C. Quantifying the relative contribution of bacterial or fungal biomass in total dsDNA by real-time PCR allows to access to a new level of knowledge of the soil microbial biomass and to reveal the balances between those two kingdoms according to soils or farming practices

Response of collembolan assemblages to plant species successional gradient

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