References of "Aubinet, Marc"
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See detailLatitudinal patterns of magnitude and interannual variability in net ecosystem exchange regulated by biological and environmental variables
Yuan, Wenping; Luo, Yiqi; Richardson, Andrew D et al

in Global Change Biology (2009), 15(12), 2905-2920

Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the ... [more ▼]

Over the last two and half decades, strong evidence showed that the terrestrial ecosystems are acting as a net sink for atmospheric carbon. However the spatial and temporal patterns of variation in the sink are not well known. In this study, we examined latitudinal patterns of interannual variability (IAV) in net ecosystem exchange (NEE) of CO2 based on 163 site-years of eddy covariance data, from 39 northern-hemisphere research sites located at latitudes ranging from similar to 29 degrees N to similar to 64 degrees N. We computed the standard deviation of annual NEE integrals at individual sites to represent absolute interannual variability (AIAV), and the corresponding coefficient of variation as a measure of relative interannual variability (RIAV). Our results showed decreased trends of annual NEE with increasing latitude for both deciduous broadleaf forests and evergreen needleleaf forests. Gross primary production (GPP) explained a significant proportion of the spatial variation of NEE across evergreen needleleaf forests, whereas, across deciduous broadleaf forests, it is ecosystem respiration (Re). In addition, AIAV in GPP and Re increased significantly with latitude in deciduous broadleaf forests, but AIAV in GPP decreased significantly with latitude in evergreen needleleaf forests. Furthermore, RIAV in NEE, GPP, and Re appeared to increase significantly with latitude in deciduous broadleaf forests, but not in evergreen needleleaf forests. Correlation analyses showed air temperature was the primary environmental factor that determined RIAV of NEE in deciduous broadleaf forest across the North American sites, and none of the chosen climatic factors could explain RIAV of NEE in evergreen needleleaf forests. Mean annual NEE significantly increased with latitude in grasslands. Precipitation was dominant environmental factor for the spatial variation of magnitude and IAV in GPP and Re in grasslands. [less ▲]

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See detailModelling soil heterotrophic respiration in an agricultural soil: Model structure and first comparison with experimental data.
Buysse, Pauline ULg; Le Dantec, Valérie; Sagnier, Charlotte et al

Poster (2008, November 17)

Ce travail visait à adapter un modèle de respiration hétérotrophe du sol à un site agricole situé en Hesbaye (Belgique) et cultivé avec une rotation betterave sucrière / blé d’hiver / pomme de terre / blé ... [more ▼]

Ce travail visait à adapter un modèle de respiration hétérotrophe du sol à un site agricole situé en Hesbaye (Belgique) et cultivé avec une rotation betterave sucrière / blé d’hiver / pomme de terre / blé d’hiver. A long terme, ce modèle fera partie intégrante d’un modèle plus important qui décrira la respiration totale du sol et l’évolution du contenu en carbone du sol dans les cultures. Le modèle utilisé dans ce travail est dérivé du modèle Century, possède un pas de temps journalier et couvre une échelle spatiale de l’ordre de l’écosystème. La paramétrisation du modèle a été réalisée sur base d’une recherche bibliographique et de données collectées sur le site Carbo-Europe de Lonzée. Les caractéristiques du sol sont issues d’analyses réalisées sur des sols limoneux, typiques de la région de Hesbaye. Les variables conductrices (variables météorologiques et apports de litière) furent obtenues suite à une campagne de mesures de 4 ans réalisée sur le site expérimental de Lonzée. Les paramètres biochimiques du blé, de la pomme de terre et de la betterave furent tirés de la littérature. Une analyse de sensibilité fut réalisée en vue de classer les différents paramètres par rapport à leur impact sur le taux de respiration et les contenus en carbone de chaque pool. Les paramètres les plus importants étaient ceux contrôlant la réponse à la température, l’apport de litière et les teneurs en lignine et en azote. Des différences d’impact à court et long terme ont aussi été mises en évidence, notamment à cause de la dynamique de stabilisation des pools et des types de résidus de culture. Finalement, cette analyse nous a permis de définir de futures expériences qui seraient nécessaires pour améliorer l’ajustement du modèle sur des données expérimentales. [less ▲]

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See detailImpact of climatic conditions on a winter wheat (Triticum aestivum Sp.) crop : interannual variability of CO2 fluxes, plant growth and crop yield
Dufranne, Delphine ULg; Vancutsem, Françoise ULg; Moureaux, Christine ULg et al

Poster (2008, September)

This study analyses the interannual variability of carbon dioxide fluxes, growth and productivity of a winter wheat (Triticum aestivum L.) crop. Two growing seasons (2004-2005 and 2006-2007) were compared ... [more ▼]

This study analyses the interannual variability of carbon dioxide fluxes, growth and productivity of a winter wheat (Triticum aestivum L.) crop. Two growing seasons (2004-2005 and 2006-2007) were compared. Continuous eddy covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the two vegetation seasons until harvest at the Lonzée (Belgium) experimental site. The winter wheat was sown and harvested at similar dates (about mid-October and in early August); crop management by the farmer was similar and corresponded at standard. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C against 9.4 °C) and lower than normal rainfalls (595.1 mm and 675.1 mm against 772 mm). In addition, 2006-2007 was characterised by exceptionally mild and dry winter and spring. This induced not only earlier growth stages but also a larger Gross Primary Productivity. On the contrary, lower Net Primary Productivity and crop productivity were observed on this year. This could be explained, on one hand by the drought in April 2007 and on the other hand to cloudy and humid conditions from end May to harvest. The first induced a stress in wheat plant which produced an unusually small flag leaf. The second induced an assimilation reduction due to low radiation and favoured disease development. The higher GPP and the lower productivity in 2006-2007 raise the question of carbon allocation. We supposed that, as the excess of carbon assimilated in 2006-2007 was not stored in grain or straw, it should have been stored in the roots. However, our biomass measurements did not allow confirming this hypothesis [less ▲]

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See detailAdaptation of a soil heterotrophic respiration model to an agricultural soil.
Buysse, Pauline ULg; Le Dantec, Valérie; Sagnier, Charlotte et al

Poster (2008, September)

This work aimed at adapting a model of soil heterotrophic respiration to an agricultural soil situated in the Hesbaye region (Belgium) and cultivated with a sugar beet / winter wheat / potato/ winter ... [more ▼]

This work aimed at adapting a model of soil heterotrophic respiration to an agricultural soil situated in the Hesbaye region (Belgium) and cultivated with a sugar beet / winter wheat / potato/ winter wheat rotation. This model would be integrated as a sub routine in a larger model describing soil respiration and soil carbon content evolution in crops and that will include autotrophic respiration and CO2 diffusion in soil. The present model is run at a daily time step and at the ecosystem spatial scale and is derived from the CENTURY model. Model parameterisation was performed on the basis of literature survey and of data collected at the Carboeurope agricultural site of Lonzée. Soil characteristics were determined on the basis of analyses performed on loamy soils, typical of the Hesbaye region. Driving variables (meteorological variables and litter input) were obtained during a 4 year measurement campaign performed at the Lonzée experimental site. Biochemical parameters for wheat, potato and sugar beet crops were collected from literature. However, a large parameter variability was noticed as well as a lack of information concerning sugar beet and potato. A sensitivity analysis was performed in order to classify the different parameters in terms of their impact on the respiration rate and carbon contents of each pool. It showed that the most important parameters were those controlling the temperature response, the litter input and its nitrogen and lignin content. The sensitivity analysis also showed differences in parameter impact between short and long term, notably because of pool stabilisation dynamics and crop residue types. This analysis allowed defining the further experiments that need to be developed in order to improve model adjustment on experimental data. [less ▲]

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See detailCarbon balance assessment of a Belgian winter wheat crop
Moureaux, Christine ULg; Debacq, Alain ULg; Hoyaux, Julien et al

in Global Change Biology (2008), 14(6), 1353-1366

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See detailFINAL REPORT PHASE I "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems” «IMPECVOC»
Steppe, Kathy; Šimpraga, Maja; Verbeeck, Hans et al

Report (2008)

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See detailAdvection mechanism and their impact on CO2 net ecosystem exchange at three Carboeurope forest sites
Feigenwinter, Christian; ADVEX team; Heinesch, Bernard ULg et al

Poster (2008)

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See detailEddy flux measurements in difficult conditions.
Schimel, David; Aubinet, Marc ULg; Finnigan, John

in Ecological applications : a publication of the Ecological Society of America (2008), 18(6),

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See detailComparison of horizontal and vertical advective CO2 fluxes at three forest sites
Feigenwinter, Christian; Bernhofer, Christian; Eichelmann, Uwe et al

in Agricultural and Forest Meteorology (2008), 148(1), 12-24

Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda ... [more ▼]

Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda, Uppland, Sweden) to evaluate the relevant terms of the carbon balance by measuring CO2 concentrations [CO2] and the wind field in a 3D multi-tower cube setup. The same experimental setup (geometry and instrumentation) and the same methodology were applied to all the three experiments. It is shown that all sites are affected by advection in different ways and strengths. Everywhere, vertical advection (F-VA) occurred only at night. During the day, F-VA disappeared because of turbulent mixing, leading to a uniform vertical profile of [CO2]. Mean F-VA was nearly zero at the hilly site (wetzstein) and at the flat site (Norunda). However, large, momentary positive or negative contributions occurred at the flat site, whereas vertical non-turbulent fluxes were generally very small at the hilly site. At the slope site (Renon), F-VA was always positive at night because of the permanently negative mean vertical wind component resulting from downslope winds. Horizontal advection also occurred mainly at night. It was positive at the slope site and negative at the flat site in the mean diurnal course. The size of the averaged non-turbulent advective fluxes was of the same order of magnitude as the turbulent flux measured by eddy-covariance technique, but the scatter was very high. This implies that it is not advisable to use directly measured quantities of the non-turbulent advective fluxes for the estimation of net ecosystem exchange (NEE) on e.g. an hourly basis. However, situations with and without advection were closely related to local or synoptic meteorological conditions. Thus, it is possible to separate advection affected NEE estimates from fluxes which are representative of the source term. However, the development of a robust correction scheme for advection requires a more detailed site-specific analysis of single events for the identification of the relevant processes. This paper presents mean characteristics of the advective CO2 fluxes in a first site-to-site comparison and evaluates the main problems for future research. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailDependence of CO2 advection patterns on wind direction on a gentle forested slope
Heinesch, Bernard ULg; Yernaux, Michel ULg; Aubinet, Marc ULg

in Biogeosciences (2008), 5(3), 657-668

Gravitational flows generated on a gentle slope in stable conditions were analysed at a forested site at Vielsalm in Belgium. There were two distinct situations at the site, one corresponding to vertical ... [more ▼]

Gravitational flows generated on a gentle slope in stable conditions were analysed at a forested site at Vielsalm in Belgium. There were two distinct situations at the site, one corresponding to vertical convergence, characterised by a negative vertical velocity at the canopy top and horizontal velocity divergence below the canopy, the other corresponding to an equilibrium situation without any vertical movement. The causes of these two distinct flow patterns were analysed. These measurements combined with those of the horizontal CO2 concentration gradient below the canopy supported the dilution hypothesis suggested by Aubinet et al. (2003): the horizontal CO2 concentration gradient is negative in convergence situations but slightly positive in equilibrium conditions. The existence of such patterns allows us to confirm the coherence of advection observations made at the site. However, the sum of turbulent CO2 flux, changes in CO2 storage and advective terms were shown to greatly overestimate the expected net ecosystem exchange in the convergence conditions. The most probable cause was identified as being a poor estimate of the vertical profile of the vertical velocity component. [less ▲]

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See detailUse of the daily differencing approach to evaluate uncertainties affecting eddy covariance measurements
Laffineur, Quentin ULg; Aubinet, Marc ULg

Poster (2008)

The eddy covariance technique is recognised to be the most adapted micrometeorological method to study the exchange processes between terrestrial ecosystems and the atmosphere. Like all other methods, it ... [more ▼]

The eddy covariance technique is recognised to be the most adapted micrometeorological method to study the exchange processes between terrestrial ecosystems and the atmosphere. Like all other methods, it is submitted to systematic and random measurement errors. A thorough analysis of these errors is necessary in order to set the limits of validity of the method and to quantify the uncertainty that affects net carbon exchange computed with this method. In this presentation, we’ll concentrate on the random errors using the dailydifferencing approach (DDA) developed by Hollinger and Richardson (2005). The interest of this approach is that it requests only single tower measurements and is thus applicable to all flux tower sites. In this approach, uncertainties are estimated by comparing flux values taken at two successive days at the same hour and under similar meteorological conditions. The analysis may be applied to sensible heat, latent heat and CO2 flux densities. It was applied here to the eddy-covariance data from the Vielsalm mixed forest site (10 years of data) and from the Lonzée agricultural site (4 years of data). Both sites are situated in Belgium and are part of the Carboeurope IP network. The study is developed in the frame of the European IMECC project. The absolute and relative random error was quantified for both sites. Their daily evolution and their dependencies on different climate conditions (magnitude of the flux, PPFD, Rnet, wind velocity, wind direction, clarity index) were analysed. For both sites, the absolute random error increases linearly with the absolute value of flux. This is the principal factor controlling the random error. More particularly the response of the random error to wind velocity was analysed. For the CO2 flux, the absolute random error decreases with increasing wind speed. This effect is more important for the agricultural site than for the forest site. The behaviour of the relative random error with wind speed is more contrasted: it generally decreases with increasing wind speed at low velocities but, for some directions may increase with wind speed at high velocities. In addition, the random error was found very dependent on wind direction at the forest site probably as a result of site heterogeneity. [less ▲]

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See detailDescription of cropland CO2 exchange : a comparison of empirical and physiologically based estimates of Reco, GPP and NEE
Tenhunen, J.; Li, Y.-L.; Dinh, N. Q. et al

in CarboEurope-IP meeting 2008 (2008)

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See detailMesure des flux de CO2 et bilan carboné de grandes cultures : Etat de la question et méthodologie
Moureaux, Christine ULg; Bodson, Bernard ULg; Aubinet, Marc ULg

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2008), 12(3), 303-315

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See detailExtrapolating the gross primary productivity from leaf to canopy scale in a winter wheat crop
Hoyaux, Julien; Moureaux, Christine ULg; Tourneur, Denis et al

in Agricultural and Forest Meteorology (2008), 148(4), 668-679

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See detailEddy Covariance Co2 Flux Measurements In Nocturnal Conditions: An Analysis Of The Problem
Aubinet, Marc ULg

in Ecological Applications (2008), 18(6),

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See detailNos grandes cultures captent aussi le CO2
Bodson, Bernard ULg; Moureaux, Christine ULg; Aubinet, Marc ULg

in Nouvelles du Printemps (Les) (2007), (2ème trimestre 2007), 30-31

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See detailLinking flux network measurements to continental scale simulations: Ecosystem carbon dioxide exchange capacity under non-water-stressed conditions
Owen, Katherine; Tenhunen, John; Reichstein, Markus et al

in Global Change Biology (2007), 13

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