References of "Aubinet, Marc"
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See detailLes grandes cultures et le cycle du carbone
Moureaux, Christine ULg; Aubinet, Marc ULg; Dufranne, Delphine ULg et al

in Livre Blanc Céréales (2010, February 24)

Le cycle du carbone et les flux de carbone dans une culture - Perspectives

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See detailModelling total soil respiration in agricultural soils.
Buysse, Pauline ULg; Goffin, Stéphanie; Carnol, Monique ULg et al

Poster (2010, January 12)

Soil respiration is a process which results in CO2 release from the soil to the atmosphere. It comprises two main components. The first one is heterotrophic respiration: CO2 is produced by soil ... [more ▼]

Soil respiration is a process which results in CO2 release from the soil to the atmosphere. It comprises two main components. The first one is heterotrophic respiration: CO2 is produced by soil microorganisms while decomposing the substrate. The second one is autotrophic respiration in which CO2 originates from roots and rhizospheric organisms. All the CO2 is then transported to the surface by diffusion (see Goffin et al., this session). Many biotic and abiotic factors play a role in soil respiration, making this process complex to analyze and understand. Temperature often appears as the most important driving variable. Besides that, interest in the future CO2 emissions from agricultural soils has been growing. Indeed, these ecosystems are a major concern from environmental, economic and social points of view. In particular, the choice of cultural practices and residue management techniques has a strong influence on CO2 emissions from agricultural systems. This work aims at getting to a better understanding of soil respiration in agricultural soils. To reach this goal, many semi-mechanistic models have been previously developed at very different spatio-temporal scales. We intend to adapt such an existing model to crop soils, within a spatial scale of a cultivated field and an annual temporal scale. The model will be validated by using flux measurements carried out at three different crop sites situated in the Hesbaye region in Belgium (Lonzée) and in the South West of France (Lamasquère, Auradé). The study was focused first on soil heterotrophic respiration. Within this part, short term sensitivity of this component to temperature was studied by means of a laboratory incubation experiment. This one was performed with soil samples taken at the Lonzée site. Among the many interesting results we got, it showed a clear sensitivity of soil heterotrophic respiration to short term temperature changes. In parallel, the soil heterotrophic model was calibrated on soil chamber measurements taken at the Lonzée site (Belgium). Next steps in this part of the work will be to calibrate the model using the data from the French sites, and finally to validate the model on the three sites. Afterwards, an autotrophic respiration submodel will be implemented and the results compared to field measurements carried out at the three sites. A further development could consist in simulating agricultural practices to take their impacts on CO2 emissions from crops into account. [less ▲]

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See detailNew Transfer Functions for Correcting Turbulent Water Vapour Fluxes
De Ligne, Anne ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

in Boundary-Layer Meteorology (2010), 137(2), 205-221

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and ... [more ▼]

We address the problem of the high-frequency correction of water vapour fluxes measured by eddy covariance with a closed-path infrared gas analyser (IRGA). Different transfer functions are compared and evaluated at a forested (Vielsalm, Belgium) and an agricultural (Lonz,e, Belgium) site. Classical functions, usually applied to correct CO2 fluxes (Gaussian, Lorentzian), are found to be unsuited to water vapour cospectral corrections, being characterised by too sharp a decrease at high frequency. Two other functions characterised by a lower decreasing slope are found to better fit experimental transfer functions. They were calibrated and validated on experimental transfer functions and their dependency on air humidity is parameterised. On this basis, new correction coefficients are estimated. The coefficients are found to be larger than those based on the classical functions, even when the dependency of the latter on air humidity is taken into account. The difference amounts to 10 at the forested site and to 5 larger at the crop site. The study highlights the necessity of characterising the water transfer function shape and taking it into account in the correction factor at each site equipped with a closed path IRGA. [less ▲]

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See detailAssessment of the effects of tree species diversity on forest biodiversity and ecosystem functioning (FORBIO) - Final Report
Verheyen, Kris; Carnol, Monique ULg; Branquart, Etienne et al

Report (2010)

Forests are biodiversity hotspots worldwide with 70% of terrestrial biodiversity being included in forested landscapes. However, deforestation, forest degradation and fragmentation lead to an increasing ... [more ▼]

Forests are biodiversity hotspots worldwide with 70% of terrestrial biodiversity being included in forested landscapes. However, deforestation, forest degradation and fragmentation lead to an increasing rate of species extinctions. Hence, predicting the consequences of changes in species numbers, in distribution patterns of taxa, and of shifts in dominance, has become a major challenge for community and ecosystem ecology. However, until now the relationships between biodiversity and ecosystem functioning in forests have been largely underexplored Therefore, the overall aims of the BELSPO cluster project FORBIO are: to review, synthesize and disseminate existing knowledge about the benefits and drawbacks of mixed stands vs monocultures (WP1); and to establish a highly innovative, large-scaled forest biodiversity experiment to evaluate the impact of increasing tree diversity on forest ecosystem functioning (WP2). To achieve the first objective, a so-called ‘white paper’ has been compiled by the FORBIO team members which has been published in Dutch as a special issue of the BosRevue and in French as a special issue of Forêt Wallone. Among stakeholders, many different opinions exist about the functioning of mixed forests and therefore the scientific evidence was confronted with stakeholder perceptions on ecosystem services in mixed forests compared to monocultures. The principal outcome was that stakeholders appear to have quite strong opinions on the functioning of mixed vs monoculture stands, whereas the review of the scientific literature highlighted the lack of specific information on forest ecosystem services in mixed forests compared to monocultures, in particular from studies where confounding factors can be eliminated or accounted for. The second objective was met by establishing two large-scaled tree diversity experiments in Zedelgem (Flanders) and Gedinne (Wallonia). Based on a state-of-the-art experimental design, 32 810 and 33 304 trees of five different species were planted in 42 and 44 experimental plots in Zedelgem and Gedinne, respectively. A third experiment with a similar design will be established in Hecthel-Eksel (Flanders) in 2011. FORBIO’s short-term contributions to sustainable development are mainly related to the fact that the project has introduced the state-of-the-art concepts and empirical support on the various relationships between biodiversity and ecosystem functioning to a large audience of forest owners, managers, users and scientists in Belgium. In the long-run, FORBIO will significantly contribute to a better understanding of the importance of tree species diversity for the functioning of forest ecosystems and the ecosystem services that they provide thanks to the establishment of the two (and soon three) large-scaled tree diversity experiments. Furthermore, the experiments, embedded in the worldwide TreeDivNetwork, will most likely continue to act as an attractor for researchers from Belgium and abroad. [less ▲]

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See detailSpecies effect on the water use efficiency of a mixed forest of beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and silver fir (Abies alba Mill.) in Belgium Ardennes
Soubie, Rémy; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

Poster (2010)

Induced by climate change, intensity and frequency of droughts should be more important for the next century. How does water availability affect the physiology of woody plants at the species and stand ... [more ▼]

Induced by climate change, intensity and frequency of droughts should be more important for the next century. How does water availability affect the physiology of woody plants at the species and stand scale? Carbon and water vapour fluxes measurements of a mixed forest (deciduous and coniferous) were performed for over ten years by the eddy covariance method in Belgian Ardennes (Aubinet et al, 2001) as a part of the CarboEurope project. Whereas carbon fluxes have been analyzed in detailed and good estimations of the Net Ecosystem Exchange (NEE) and Gross Primary Production (GPP) were obtained, a thorough analysis of water vapour fluxes remains to be done. Improving analysis of water vapour fluxes and monitoring species transpiration will contribute to the estimation of the water use efficiency, WUE, at both the species and stand scale. The WUE well characterizes the vegetation productivity and ecosystem response to environmental factors. It also allows evaluating the sensitivity of temperate woody species to drought. The species concerned are beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and silver fir (Abies alba Mill.). Since summer 2009 we monitor and analyze each species water use by measuring sap flow with the thermal dissipation method (Granier, 1987). Results at the species level will then be upscaled and compared to stand water vapour fluxes measurements obtained by the eddy covariance methodology. Transpiration of each species will be analyzed in relation with their own phenological and ecophysiological attributes, ecosystem soil and atmospheric conditions, to clarify among others their behaviour in case of water deficit. Data are actually analysed, the presented results will concern the 2009, and a part of 2010 growing season. [less ▲]

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See detailComparison of two drainage flow situations on a gentle forested slope
Heinesch, Bernard ULg; Yernaux, Michel ULg; Aubinet, Marc ULg

Poster (2010)

Drainage flows generated on a gentle slope in stable conditions were analysed at the forested site of Vielsalm (Belgium). Two distinct situations were encountered, one corresponding to vertical ... [more ▼]

Drainage flows generated on a gentle slope in stable conditions were analysed at the forested site of Vielsalm (Belgium). Two distinct situations were encountered, one corresponding to vertical convergence, characterised by a negative vertical velocity at the canopy top, the other corresponding to an equilibrium situation without any vertical movement. The causes of these two distinct flow patterns were analysed. Moreover, combined measurements of vertical velocity above the canopy and horizontal velocity divergence below the canopy were found to comply with the continuity equation: an acceleration of the horizontal flow was indeed observed in the trunk-space in convergence situations while not in equilibrium conditions. These measurements combined with those of the horizontal [CO2] gradient below the canopy were found to met the dilution hypothesis suggested by Aubinet et al.(2003): the horizontal [CO2] gradient was negative in convergence situations while slightly positive in equilibrium conditions. The existence of such patterns allows us to confirm the coherence of advection observations made at the site and help to better understand the mechanisms responsible of night flux exchanges at work in stable conditions in complex terrains. Nevertheless, difficulties were met when trying to obtain reliable estimates of the advection transport terms. The estimation of the vertical velocity in the trunk-space obtained by using the divergence measurements refuted the hypothesis of linearity of the vertical profile of vertical velocity, assumption usually used when computing vertical advection. This problem resulted in a great uncertainty on vertical advection which did not allowed to improve the night-flux estimation by adding advection terms to the turbulent flux and the storage. [less ▲]

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See detailClimate control of terrestrial carbon exchange across biomes and continents
Yi, Chuixiang; Ricciuto, Daniel; Li, Runze et al

in Environmental Research Letters (2010), 5(3),

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating ... [more ▼]

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. [less ▲]

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See detailHistory effect of light and temperature on monoterpenoid emissions from Fagus sylvatica L.
Demarcke, M.; Schoon, N.; Van Langenhove, H. et al

in Atmospheric Environment (2010), 44(27), 3261-3268

Monoterpenoid emissions from Fagus sylvatica L trees have been measured at light- and temperature-controlled conditions in a growth chamber, using Proton Transfer Reaction Mass Spectrometry (PTR-MS) and ... [more ▼]

Monoterpenoid emissions from Fagus sylvatica L trees have been measured at light- and temperature-controlled conditions in a growth chamber, using Proton Transfer Reaction Mass Spectrometry (PTR-MS) and the dynamic branch enclosure technique. De novo synthesized monoterpenoid Standard Emission Factors, obtained by applying the G97 algorithm (Guenther, 1997), varied between 2 and 32 mu g g(-1)DW h(-1) and showed a strong decline in late August and September, probably due to senescence. The response of monoterpenoid emissions to temperature variations at a constant daily light pattern could be well reproduced with a modified version of the MEGAN algorithm (Guenther et al., 2006), with a typical dependence on the average temperature over the past five days. The diurnal emissions at constant temperature showed a typical hysteretic behaviour, which could also be adequately described with the modified MEGAN algorithm by taking into account a dependence on the average light levels experienced by the trees during the past 10-13 h. The impact of the past light and temperature conditions on the monoterpenoid emissions from E sylvatica L was found to be much stronger than assumed in previous algorithms. Since our experiments were conducted under low light intensity, future studies should aim at confirming and completing the proposed algorithm updates in sunny conditions and natural environments. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

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See detailManagement effects on European cropland respiration
Eugster, W.; Moffat, A. M.; Ceschia, E. et al

in Agriculture, Ecosystems & Environment (2010), 139

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See detailManagement effects on net ecosystem carbon and GHG budgets at European crop sites
Ceschia, E.; Beziat, P.; Dejoux, J. F. et al

in Agriculture, Ecosystems & Environment (2010), 139

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See detailThe net biome production of full crop rotations in Europe
Kutsch, W. L.; Aubinet, Marc ULg; Buchmann, N. et al

in Agriculture, Ecosystems & Environment (2010), 139

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See detailANNUAL SCIENTIFIC REPORT PHASE II "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems" "IMPECVOC"
Dewulf, Jo; Joó, Eva; Steppe, Kathy et al

Report (2009)

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See detailEvaluation of the suitability of the land surface model JULES for climate impact studies in Belgian ecosystem
Van Den Hoof, Catherine; Aubinet, Marc ULg; Heinesch, Bernard ULg et al

Conference (2009, October)

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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 detailParameterization and initialization of a soil organic matter decomposition model in an agricultural soil.
Buysse, Pauline ULg; Le Dantec, Valérie; Mordelet, Patrick et al

Poster (2009, September)

Organic matter decomposition and associated heterotrophic respiration fluxes are widely studied, as these processes could be modified under global warming. Many models have been built at different ... [more ▼]

Organic matter decomposition and associated heterotrophic respiration fluxes are widely studied, as these processes could be modified under global warming. Many models have been built at different temporal and spatial scales to contribute to a better understanding of the mechanisms involved and to quantify soil carbon fluxes. Yet, agroecosystems have been less investigated so far, despite their considerable importance. In this study, a daily-time step ecosystem model derived from CENTURY is described, parameterized and initialized for the Carboeurope agricultural site of Lonzée in Belgium. At this stage, the model aims at describing soil heterotrophic respiration and carbon dynamics in the soil. Model parameterization was performed on the basis of a literature survey (biochemical parameters) and of data collected at the site itself (soil carbon content and soil texture). In order to set up the carbon repartition between the different pools of the model, an initialization phase was run until equilibrium was reached. For this phase, mean daily climatic data were used and the soil was cultivated with winter wheat, considering that all residues were brought to the soil at harvest. At the end, the repartition was found to be independent from the simulated soil carbon content. Simulations showed a very high sensitivity of the model to the amount of incorporated residues and allowed an estimation of the amount of residues that lead the soil to a stable state. It was compatible with field observations. The model was then run with 2007 climatic data and the above-mentioned carbon repartition to simulate heterotrophic respiration. A comparison between these simulated fluxes and automatic measurements of soil respiration, performed during a 3-month period in spring 2007 on a bare zone of the field, showed a reasonable good agreement. Most of the discrepancies between measured and simulated fluxes corresponded to dry events, attesting of a need to reconsider the relationship between soil heterotrophic respiration and soil moisture in the model. To go further with the assessment of the model reliability, a calibration on data from the French Carboeurope site of Lamasquère will be achieved. Other sites may also be used. This heterotrophic soil respiration model is intended to be part of a more complete soil respiration model focused on agroecosystems and developed at the annual and ecosystem scales. In the end, autotrophic respiration, nitrogen mineralization and crop management would also be included. [less ▲]

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See detailMeasuring air-ice CO2 fluxes in the Arctic
Heinesch, Bernard ULg; Yernaux, Michel; Aubinet, Marc ULg et al

in FluxLetter: the Newsletter of FLUXNET (2009), 2(2), 9-10

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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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See detailInterannual variability of CO2 fluxes and yield by a winter wheat crop (Triticum aestivum L.)
Dufranne, Delphine ULg; Vancutsem, Françoise ULg; Moureaux, Christine ULg et al

Poster (2009, April 20)

In this study, two winter wheat (Triticum aestivum L.) cropping seasons were compared at the Lonzée (Belgium) experimental site. The site, crop management, sowing and harvest dates were similar on the two ... [more ▼]

In this study, two winter wheat (Triticum aestivum L.) cropping seasons were compared at the Lonzée (Belgium) experimental site. The site, crop management, sowing and harvest dates were similar on the two years. The main difference between the seasons was due to to climate conditions. Continuous eddy-covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the whole vegetation periods. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C respectively against 9.4 °C for standard) and lower than normal rainfalls (595.1 mm and 675.1 mm respectively against 772 mm for standard). In addition, the second season (2006-2007) was characterised by an exceptionally mild winter, dry and hot conditions in April and by humid and cloudy conditions during the last vegetation phases. These particular conditions induced earlier growth stages and the comparison of global fluxes gives contrasting results: gross primary productivity (GPP) was larger in 2007 but, on the contrary, net primary productivity (NPP) and crop productivity were lower on this year. The bad yields could be explained, on one hand by the drought in April 2007 that induced abnormally small flag leaves, on the other hand by cloudy and humid conditions from end May to harvest, that induced an assimilation reduction due to low radiation and favoured disease development. The simultaneous higher GPP and lower NPP and productivity in 2006-2007 raise the question of carbon allocation. It suggests that the excess carbon assimilated in 2006-2007 was not stored in grain or straw and thus that it would have been stored in the roots or in vegetation parts that decompose before the harvest. Further biomass measurements (and especially root biomass) are necessary to confirm this hypothesis. [less ▲]

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