References of "Aubinet, Marc"
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See detailLes grandes cultures et le CO2
Bodson, Bernard ULg; Vancutsem, Françoise ULg; Dufranne, Delphine ULg et al

in Livre Blanc Céréales (2009, February 18)

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See detailSurvey of air-ice ocean carbon dioxyde exchange over arctic sea-ice
Heinesch, Bernard ULg; Aubinet, Marc ULg; Carnat, Gauthier et al

Conference (2009)

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See detailExceptional Carbon Uptake In European Forests During The Warm Spring Of 2007: A Data-Model Analysis
Delpierre, N.; Soudani, K.; Kostner, B. et al

in Global Change Biology (2009), 15(6), 1455-1474

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature ... [more ▼]

Temperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006-winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44 degrees to 62 degrees N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m(-2) anomaly compared with the decadal mean over the January-May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m(-2) anomaly over 5 months), leading to higher net uptake than the long-term mean at all sites (+12 to +79 gC m(-2) anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process-based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation. [less ▲]

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See detailAvailable energy and energy balance closure at four coniferous forest sites across Europe
Moderow, Uta; Aubinet, Marc ULg; Feigenwinter, Christian et al

in Theoretical & Applied Climatology (2009), 98(3-4), 397-412

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany ... [more ▼]

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J (H), latent heat J (E), heat storage of biomass J (veg) and heat storage due to photosynthesis J (C) were of minor importance during day but of some importance during night, where J (veg) turned out to be the most important one. Comparisons of calculated storage terms (J (E), J (H)) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m(-2) (10-11 W m(-2) for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m(-2) (approximately 6 W m(-2) for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone. [less ▲]

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See detailCarbon sequestration by a crop during a four year rotational cycle
Aubinet, Marc ULg; Moureaux, Christine ULg; Bodson, Bernard ULg et al

in Agricultural and Forest Meteorology (2009), 149

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See detailWind velocity perturbation of soil respiration measurements using closed dynamic chambers
Suleau, Marie ULg; Debacq, Alain ULg; Dehaes, V. et al

in European Journal of Soil Science (2009), 60(4), 515-524

P>Soil respiration measurements performed with closed dynamic chambers are very sensitive to pressure differences inside and outside the chamber: differences as small as 1 Pa can induce errors that are of ... [more ▼]

P>Soil respiration measurements performed with closed dynamic chambers are very sensitive to pressure differences inside and outside the chamber: differences as small as 1 Pa can induce errors that are of the same magnitude as the flux itself. The problem is usually solved by adding a vent to the experimental set-up. However, although this may give acceptable results in most cases, it is not effective at sites that are very exposed to wind. At the CarboEurope-IP agricultural site of Lonzee (Belgium), on bare soil, we used a vent composed of a vertical tube whose upper end was placed between two horizontal plates. Whilst this system worked properly in low-wind conditions, it led to a significant flux over-estimation (up to 300%) under strong wind conditions. We analysed the causes of this error and attributed it to a dynamic pressure effect at the vent, leading to air aspiration from within the chamber. We suggest that this is because the wind at the vent level was not the same as that experienced in the chamber, because of the large vertical wind speed gradient close to the soil. Another vent geometry was then proposed that positioned the vent at the chamber level. This new design was tested on both manual and automatically operated chambers. It was found to be efficient in windy conditions as most of the artificial correlation between soil respiration measurements and wind speed had disappeared. [less ▲]

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See detailEstimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2
van Gorsel, Eva; Delpierre, Nicolas; Leuning, Ray et al

in Agricultural and Forest Meteorology (2009), 149(11), 1919-1930

Micrometeorological measurements of night time ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and ... [more ▼]

Micrometeorological measurements of night time ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397-403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (F-C) and change in storage (F-S) of CO2 in the few hours after sundown. The sum of F-C and F-S reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration R-Rmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of F-c + F-s extrapolated to zero light, R-LRC, and (3) with a detailed process-based forest ecosystem model, R-cast. At most sites respiration rates estimated using the u*-filter, R-ust, were smaller than R-Rmax, and R-LRC. Agreement of our approach with independent measurements indicates that R-Rmax, provides an excellent estimate of nighttime ecosystem respiration. (C) 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailUncertainty of carbon dioxide fluxes introduced by different high-pass filtering methods
Ibrom, Andreas; Geißler, Simon; Laffineur, Quentin ULg et al

Conference (2009)

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See detailAn analysis of the random error affecting CO2 fluxes measured by eddy covariance
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2009)

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with ... [more ▼]

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with increasing wind speed. As random errors accumulate in quadrature, they are less critical than systematic errors as far as flux sums are concerned. On the other hand it may affect significantly half-hour data and pose problem for modelling or analysis of flux response to environmental parameters. It is therefore useful to characterize the site and the specific conditions under which the random error is the most important. The random error on CO2 flux was computed at two sites, one cropland and one forested site, by using the daily differencing approach (DDA, Hollinger and Richardson 2005). Relationships with flux and wind speed were compared between different periods (day vs. night, growing season vs. rest of the year) and for different flux computation methods. First, an increase of random error with decreasing wind speed was observed at low speed. This effect was not observed during the rest period at the cropland site and disappears when a high-pass filtering is applied to the data. It may be explained by two processes: on one hand, the below canopy air layer is less efficiently mixed which can create large flux variations when CO2 sources and sinks are separated. On the other hand, mesoscale motions may exceed small-scale turbulence at low wind speed. At similar wind speeds, the random error was lower at the cropland than at the forested site, which can be due to either process: indeed, at the cropland site, the distance between CO2 sources and sinks is smaller which reduce the low mixing effect but the site is also more flat and homogeneous which reduce the impact of mesoscale movements. The possibility of mesoscale movement impact is supported by the fact that the effect disappears when applying a high pass filtering. The random error was also found sensitive to the computational method: in particular it is larger when the flux is computed using the block average rather than the running mean, it increases when storage is taken into account and decreases when data are filtered by applying stationarity screening or u* filtering. [less ▲]

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See detailAn analysis of the random error affecting CO2 fluxes measured by eddy covariance.
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2009)

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with ... [more ▼]

This study focuses on random errors associated with eddy covariance flux measurements. This error is heteroscedastic, increases linearly with the flux magnitude and the error on CO2 flux decreases with increasing wind speed. As random errors accumulate in quadrature, they are less critical than systematic errors as far as flux sums are concerned. On the other hand it may affect significantly half-hour data and pose problem for modelling or analysis of flux response to environmental parameters. It is therefore useful to characterize the site and the specific conditions under which the random error is the most important. The random error on CO2 flux was computed at two sites, one cropland and one forested site, by using the daily differencing approach (DDA, Hollinger and Richardson 2005). Relationships with flux and wind speed were compared between different periods (day vs. night, growing season vs. rest of the year) and for different flux computation methods. First, an increase of random error with decreasing wind speed was observed at low speed. This effect was not observed during the rest period at the cropland site and disappears when a high-pass filtering is applied to the data. It may be explained by two processes: on one hand, the below canopy air layer is less efficiently mixed which can create large flux variations when CO2 sources and sinks are separated. On the other hand, mesoscale motions may exceed small-scale turbulence at low wind speed. At similar wind speeds, the random error was lower at the cropland than at the forested site, which can be due to either process: indeed, at the cropland site, the distance between CO2 sources and sinks is smaller which reduce the low mixing effect but the site is also more flat and homogeneous which reduce the impact of mesoscale movements. The possibility of mesoscale movement impact is supported by the fact that the effect disappears when applying a high pass filtering. The random error was also found sensitive to the computational method: in particular it is larger when the flux is computed using the block average rather than the running mean, it increases when storage is taken into account and decreases when data are filtered by applying stationarity screening or u* filtering. [less ▲]

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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)

Detailed reference viewed: 11 (1 ULg)