References of "Goffin, Stéphanie"
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See detailAnalyse multicouche des flux de CO2 et de leur signature isotopique sur un sol forestier
Goffin, Stéphanie ULg

Doctoral thesis (2014)

Dans cette thèse, nous avons étudié le flux de dioxyde de carbone (CO2) provenant d’un sol forestier (Fs) à des échelles de temps relativement courtes allant de la seconde à quelques jours avec l’objectif ... [more ▼]

Dans cette thèse, nous avons étudié le flux de dioxyde de carbone (CO2) provenant d’un sol forestier (Fs) à des échelles de temps relativement courtes allant de la seconde à quelques jours avec l’objectif général de mieux en comprendre les mécanismes. Le flux de CO2 résulte de deux composantes principales, à savoir la production du CO2 au sein du sol et son transport jusqu’à la surface. Ces deux composantes ont systématiquement été distinguées et analysées afin de mettre en évidence les variables qui les régissent. Cette manière de procéder nous a permis d’investiguer, en plus de leur dynamique, la distribution verticale des sources de CO2. En outre, nous avons étudié la signature isotopique en carbone (C) de ces sources afin d’apporter des éléments nouveaux dans la compréhension du processus de production de CO2, notamment nous avons estimé le temps de transfert d’une molécule fraichement photoassimilée de la canopée vers la rhizosphère. Dans une étude effectuée sur un sol forestier (Haplic Regosol; FAO, 2006) à Hartheim (Allemagne), nous avons montré que les sources de CO2 étaient clairement stratifiées dans le sol et nous avons évalué à 11.5%, 64.7%, 15.8% et 8% la contribution respective des horizons OL, Ah, AhC et C à la production totale de CO2. Cette répartition coïncide avec la distribution des racines et du carbone organique sur ce site. Par contre, nous n’avons pas mis en évidence de différence significative dans la composition isotopique des sources associée aux différents horizons en raison de la large incertitude imputée à ces termes. Pour le processus de production, nous avons mis en évidence des variabilités inter et intra-journalières significatives. Toutes ces variabilités sont correctement expliquées par les variations de température à l’exception de la variabilité intra-journalière des sources dans Ah. Pour expliquer celle-ci, l’hypothèse de l’influence d’une onde de pression à travers le phloème qui présenterait un cycle intra-journalier a été avancée. Cette hypothèse, récemment avancée dans la littérature, suppose un lien étroit entre l’assimilation photosynthétique et l’approvisionnement en substrat de la rhizosphère, laquelle est très importante dans l’horizon Ah. Enfin, nous avons rapporté des variations inter-journalières significatives de la composition isotopique des sources dans l’horizon Ah. Plus précisément, un enrichissement en 13C des termes de production est mis en évidence lors de l’assèchement du sol. En outre, ces variations nous ont permis d’estimer à 3 jours le temps de transfert des photoassimilats dans la rhizosphère de Ah. Pour le processus de transport, nous avons souligné que la diffusion convenait à la description du transport dans toutes les couches de sol à l’exception de la litière. Dans cette dernière, il y a lieu d’inclure un mode de transport induit par la turbulence se produisant à la surface du sol. Parmi les transports résultant de la turbulence, on retrouve l’advection et la dispersion. Nous montrons que l’advection n’est à considérer que sur des échelles de temps extrêmement courtes (< seconde) alors que la dispersion, menant à une augmentation des quantités de C transférées par diffusion, devrait faire l’objet d’une attention particulière sur des échelles de temps moins courtes (heures). [less ▲]

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See detailShort-term temperature impact on soil heterotrophic respiration in limed agricultural soil samples
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

in Biogeochemistry (2013), 112(1-3), 441-455

This study sought to investigate the hourly and daily timescale responses of soil CO2 fluxes to temperature in a limed agricultural soil. Observations from different incubation experiments were compared ... [more ▼]

This study sought to investigate the hourly and daily timescale responses of soil CO2 fluxes to temperature in a limed agricultural soil. Observations from different incubation experiments were compared with the results of a model combining biotic (heterotrophic respiration) and abiotic (carbonate weathering) components. Several samples were pre-incubated for 8-9 days at three temperatures (5, 15 and 25°C) and then submitted to short-term temperature cycles (where the temperature was increased from 5 to 35°C in 10°C stages, with each stage being 3 h long). During the temperature cycles (hourly timescale), the soil CO2 fluxes increased significantly with temperature under all pre-incubation temperature treatments. A hysteresis effect and negative fluxes during cooling phases were also systematically observed. At a given hourly timescale temperature, there was a negative relationship of the CO2 fluxes with the pre-incubation temperature. Using the combined model allowed the experimental results to be clearly described, including the negative fluxes and the hysteresis effect, showing the potentially large contribution of abiotic fluxes to total fluxes in limed soils, after short-term temperature changes. The fairly good agreement between the measured and simulated flux results also suggested that the biotic flux temperature sensitivity was probably unaffected by timescale (hourly or daily) or pre-incubation temperature. The negative relationship of the CO2 fluxes with the pre-incubation temperature probably derived from very labile soil carbon depletion, as shown in the simulations. This was not, however, confirmed by soil carbon measurements, which leaves open the possibility of adaptation within the microbial community. [less ▲]

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See detailHorizon Partitioning of soil CO2 sources and their Isotopic Composition (13C) in a Pinus Sylvestris
Goffin, Stéphanie ULg; Parent, Florian; Plain, Caroline et al

Poster (2012, December 07)

The overall aim of this study is to contribute to a better understanding of mechanisms behind soil CO2 efflux using carbon stable isotopes. Given (i) the interest of conducting in situ studies with soil ... [more ▼]

The overall aim of this study is to contribute to a better understanding of mechanisms behind soil CO2 efflux using carbon stable isotopes. Given (i) the interest of conducting in situ studies with soil multilayer analysis and (ii) the benefits of isotopic tool to improve mechanistic understanding, these two approaches are combined. Quantifying the origin and the determinism of 13CO2 and 12CO2 production processes in the different soil layers using the gradient-efflux approach is the main goal of this work. To meet this one, the work includes an experimental setup and a modeling approach. The experimental set up (see also communication of Parent et al., session B008) comprised a combination of different systems, which were installed in a Scot Pine temperate forest at the Hartheim site (Southwestern Germany). Measurements include (i) half hourly vertical profiles of soil CO2 concentration (using soil CO2 probes), soil water content and temperature; (ii) half hourly soil surface CO2 effluxes (automatic chambers); (iii) half hourly isotopic composition of surface CO2 efflux and soil CO2 concentration profile and (iv) estimation of soil diffusivity through laboratory measurements conducted on soil samples taken at several depths. Using the data collected in the experimental part, we developed and used a diffusive transport model to simulate CO2 (13CO2 and 12CO2) flows inside and out of the soil based on Fick’s law. Given the horizontal homogeneity of soil physical parameters in Hartheim, we treated the soil as a structure consisting of distinctive layers of 5 cm thick and expressed the fick’s first law in a discrete formalism. The diffusion coefficient used in each layer was derived from (i) horizon specific relationships, obtained from laboratory measurements, between soil relative diffusivity and its water content and (ii) the soil water content values measured in situ. The concentration profile was obtained from in situ measurements. So, the main model inputs are the profiles of (i) CO2 (13CO2 and 12CO2) concentration, (ii) soil diffusion coefficient and (iii) soil water content. Once the diffusive fluxes deduced at each layer interface, the CO2 (13CO2 and 12CO2) production profile was calculated using the (discretized) mass balance equation in each layer. The results of the Hartheim measurement campaign will be presented. The CO2 source vertical profile and its link with the root and the Carbon organic content distribution will be showed. The dynamic of CO2 sources and their isotopic signature will be linked to climatic variables such soil temperature and soil water content. For example, we will show that the dynamics of CO2 sources was mainly related to temperature while changing of isotopic signature was more correlated to soil moisture. [less ▲]

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See detailSoil Respiration in forest Ecosystems: Combination of a multilayer Approach and an Isotopic Signal Analysis
Goffin, Stéphanie ULg; Longdoz, Bernard; Maier, Martin et al

in Communications in Agricultural and Applied Biological Sciences (2012, February 10)

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See detailApport de l'approche multicouche et du signal isotopique pour la compréhension de la respiration du sol en écosystème forestier
Goffin, Stéphanie ULg; Longdoz, Bernard; Aubinet, Marc ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2011), 15(4), 575-584

Le flux de dioxyde de carbone émanant du sol participe de manière prépondérante au cycle du carbone. On estime son amplitude à 68 ± 4 Pg C/an. En forêt tempérée, il représente approximativement 60-80% des ... [more ▼]

Le flux de dioxyde de carbone émanant du sol participe de manière prépondérante au cycle du carbone. On estime son amplitude à 68 ± 4 Pg C/an. En forêt tempérée, il représente approximativement 60-80% des émissions totales de CO2 de l’écosystème (respiration de l’écosystème). Compte tenu de l’ampleur de ce flux et des conséquences qu’aurait une quelconque modification de son amplitude sur le chargement en dioxyde de carbone de l’atmosphère, il est primordial d’améliorer la connaissance des mécanismes qui le régissent et de connaître précisément l’influence des variables du milieu (édaphiques et climatiques). Cet article vise à montrer l’intérêt d’effectuer des analyses multicouches des mécanismes à l’origine de ce flux (transport et production) plutôt que de restreindre les études à la surface du sol. De plus, cet article souligne le bénéfice apporté par l’outil isotopique pour améliorer la compréhension mécaniste de ce flux. [less ▲]

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See detailMultilayer Analysis of Soil Respiration and its Isotopic Signature in Forest Ecosystem
Goffin, Stéphanie ULg; Longdoz, Bernard; Maier, Martin et al

in Geophysical Research Abstracts (2011, April 06), 13

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See detailInput of 12CO2 and 13CO2 soil concentration measurements to understand trends in soil carbon production and emission.
Longdoz, Bernard; Plain, Caroline; Parent, Florian et al

Poster (2011, April 05)

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See detailCombination of different techniques and multi-scale approach to understand CO2 budget in a temperate beech forest
Longdoz, Bernard; Epron, Daniel; Goffin, Stéphanie ULg et al

Conference (2010, November)

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See detailSensitivity of soil heterotrophic respiration to temperature: short-term impacts.
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

Poster (2009, September)

Soil respiration is mostly affected by temperature variations but there is still much debate regarding its temperature sensitivity. Especially the difference between short- and long-term responses driven ... [more ▼]

Soil respiration is mostly affected by temperature variations but there is still much debate regarding its temperature sensitivity. Especially the difference between short- and long-term responses driven by changes in microbial activity and population respectively is addressed here. To this end, an incubation experiment is set up with soil samples taken from the surface layer (0-25cm) of a bare area at the Carboeurope agricultural site of Lonzée in Belgium. After homogenization, they are placed into incubators at three different temperatures, namely 5, 15 and 25°C for 2 weeks. Temperature is regulated by Peltier systems that warm up or cool down a bath containing jars with soil samples. All jars are continuously aerated to prevent CO2 from accumulating inside. Moisture levels in the jars are regularly checked and adjusted to ensure that the soil moisture is optimal for soil respiration. Twice a week, short term temperature response is tested by changing incubation temperatures in the range 5 - 35°C. During these cycles, CO2 fluxes are measured at each temperature step with a closed dynamic chamber system. Microbial biomass and hot water-extractable carbon are determined two times during a temperature cycle, allowing a follow up of the evolution of these two variables through a cycle. A comparison between the respiration rates, microbial biomasses and extractable carbon will be presented and would allow a better understanding of the dynamics of the heterotrophic respiration response to temperature in agricultural soils. In the future, other experiments could be derived from this one to focus on substrate availability or soil moisture impacts on soil respiration. [less ▲]

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See detailShort-term temperature impacts on soil respiration.
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

Poster (2009, June)

Despite considerable recent work on soil heterotrophic respiration, a mechanistic understanding of this process is still missing. Temperature is one of the most important driving factors. It can influence ... [more ▼]

Despite considerable recent work on soil heterotrophic respiration, a mechanistic understanding of this process is still missing. Temperature is one of the most important driving factors. It can influence the mechanism through multiple ways, whose importance may vary with time. An incubation experiment is set up to study short-term temperature influences on soil microbial respiration and its evolution through time. Soil samples are taken in spring from the surface layer (0-25cm) of a bare agricultural loamy soil situated in Lonzée in Belgium (Hesbaye region) and are homogenized before being placed into incubators at three different temperatures, namely 5, 15 and 25°C. Temperature is regulated by Peltier systems that warm up or cool down a sand bath containing jars with soil samples. Once a week, incubation temperatures are increased and decreased by 5°C-steps, starting from each incubator temperature, to achieve a one-day temperature cycle between 5 and 35°C. CO2 flux measurements are performed at each temperature step by a closed dynamic chamber system, after the temperature has stabilized in the samples. Microbial biomass (C and N) is determined four times during the temperature cycle by the fumigation-extraction technique and soil labile carbon is measured at the beginning of each cycle by the hot-water extraction method. Moisture levels in soil samples are regularly checked and adjusted to keep optimal soil moisture content. Between CO2 flux measurements, jars are left open to ensure that anaerobic conditions do not occur. Further investigations could include an assessment of the importance of substrate availability and depletion on microbial activity, and a model development related to the results provided by this experiment. [less ▲]

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