References of "Heinesch, Bernard"
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See detailClear link between drought stress, photosynthesis and biogenic volatile organic compounds in Fagus sylvatica L.
Šimpraga, M.; Verbeeck, H.; Demarcke, M. et al

in Atmospheric Environment (2011), 45(30), 5254-5259

Direct plant stress sensing is the key for a quantitative understanding of drought stress effects on biogenic volatile organic compound (BVOC) emissions. A given level of drought stress might have a ... [more ▼]

Direct plant stress sensing is the key for a quantitative understanding of drought stress effects on biogenic volatile organic compound (BVOC) emissions. A given level of drought stress might have a fundamentally different effect on the BVOC emissions of different plants. For the first time, we continuously quantified the level of drought stress in a young potted beech (Fagus sylvatica L.) with a linear variable displacement transducer (LVDT) installed at stem level in combination with simultaneous measurements of BVOC emissions and photosynthesis rates at leaf level. This continuous set of measurements allowed us to examine how beech alters its pattern of photosynthesis and carbon allocation to BVOC emissions (mainly monoterpenes, MTs) and radial stem growth during the development of drought stress. We observed an increasing-decreasing trend in the MT emissions as well as in the fraction of assimilated carbon re-emitted back into the atmosphere (ranging between 0.14 and 0.01%). We were able to link these dynamics to pronounced changes in radial stem growth, which served as a direct plant stress indicator. Interestingly, we detected a sudden burst in emission of a non-identified, non-MT BVOC species when drought stress was acute (i.e. pronounced negative stem growth). This burst might have been caused by a certain stress-related green leaf volatile, which disappeared immediately upon re-watering and thus the alleviation of drought stress. These results highlight that direct plant stress sensing creates opportunities to understand the overall complexity of stress-related BVOC emissions. [less ▲]

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See detailComparing monoterpenoid emissions and net photosynthesis of beech (Fagus sylvatica L.) in controlled and natural conditions
Šimpraga; Verbeeck, H.; Demarcke, M. et al

in Atmospheric Environment (2011), 45(17), 2922-2928

Although biogenic volatile organic compounds (BVOCs) only represent a very limited fraction of the plant's carbon (C) budget, they play an important role in atmospheric chemistry for example as a ... [more ▼]

Although biogenic volatile organic compounds (BVOCs) only represent a very limited fraction of the plant's carbon (C) budget, they play an important role in atmospheric chemistry for example as a precursor of tropospheric ozone. We performed a study comparing BVOC emissions of European beech (Fagus sylvatica L.) in controlled and natural environmental conditions. A young and adult beech tree was exposed to short-term temperature variations in growth room conditions and in an experimental forest, respectively. This study attempts to clarify how short-term temperature variations between days influenced the ratio between monoterpenoid (MT) emissions and net photosynthesis (Pn). Within a temperature range of 17-27 °C and 13-23 °C, the MT/Pn carbon ratio increased 10-30 fold for the growth room and forest, respectively. An exponential increasing trend between MT/Pn C ratio and air temperature was observed in both conditions. Beech trees re-emitted a low fraction of the assimilated C back into the atmosphere as MT: 0.01-0.12% and 0.01-0.30% with a temperature rise from 17 to 27 °C and 13-23 °C in growth room and forest conditions, respectively. However, the data showed that the MT/Pn C ratio of young and adult beech trees responded significantly to changes in temperature. [less ▲]

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See detailO2/Ar and CH4 measurements in sea ice : clues for the key status of sea ice in the climate system
Zhou, Jiayun; Tison, Jean-Louis; Eicken, Hajo et al

in Geophysical Research Abstracts (2011, April 08), 13

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See detailIsoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Amelynck, Crist et al

Poster (2011, April 07)

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See detailMeasurement and modeling of methanol deposition/emission in a mixed forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Amelynck, Crist et al

in Geophysical Research Abstracts (2011, April 07), 13

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See detailTemporal evolution of biogeochemical properties of landfast sea ice at Barrow (Alaska)
Zhou, Jiayun ULg; Tison, Jean-Louis; Eicken, Hajo et al

Poster (2011, March)

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See detailA multidisciplinary approach to understanding the sea ice system: implications on gas. Gordon Research Seminars
Zhou, Jiayun ULg; Tison, Jean-Louis; Eicken, Hajo et al

Conference (2011, March)

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See detailFINAL REPORT PHASE II "Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems" "IMPECVOC"
Dewulf, Jo; Joó, Eva; Van Langenhove, Herman et al

Report (2011)

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See detailEffect of seasonality and short-term light and temperature history on monoterpene emissions from European beech (Fagus sylvatica L.)
Demarcke, M.; Amelynck, Crist; Schoon, N. et al

in Hansel, Armin; Dunkl, Jürgen (Eds.) 5th International PTR-MS Conference on Proton Transfer Reaction Mass Spectrometry and its Applications (2011, January)

Branch enclosure measurements of monoterpene emision rates have been performed at different positions in the canopy of a European beech tree in natural environmental conditions. Strong and position ... [more ▼]

Branch enclosure measurements of monoterpene emision rates have been performed at different positions in the canopy of a European beech tree in natural environmental conditions. Strong and position-dependent standard emission rate variations were observed in the course of the growth season. By using the obtained dataset and a modified vesrion of the MEGAN algorithm, the response of the emissions to short-term light and temperature history was investigated [less ▲]

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See detailWhat can we learn from year-round BVOC disjunct eddycovariance measurements? A case example from a temperate forest
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Schoon, N. et al

in Hansel, Armin; Dunkl, Jürgen (Eds.) 5th International PTR-MS Conference on Proton Transfer Reaction Mass Spectrometry and its Applications (2011, January)

Long term ecosystem-scale biogenic volatile organic compounds (BVOC) flux measurements by disjunct eddy-covariance are needed to determine and characterize the BVOC emissions/depositions from episodic ... [more ▼]

Long term ecosystem-scale biogenic volatile organic compounds (BVOC) flux measurements by disjunct eddy-covariance are needed to determine and characterize the BVOC emissions/depositions from episodic events (budburst, stress) as well as the continuous emission/deposition during vegetation growth and its seasonal evolution in interaction with climate and environment. If the data coverage is sufficient, this technique has the potential to provide a dataset covering the whole spectrum of meteorological and phenological conditions encountered by the studied ecosystem ending in a statistically more robust dataset than what can be provided by other BVOC measurement techniques. In addition, long term measurements allow in Oxygenated VOCs (OVOCs) depositions to be estimated in a realistic manner with is not the case with the enclosure technique. Here we present a year-round campaign of disjunct eddy-covariance BVOC fluxes above a mixed temperate forest performed in the frame of the IMPECVOC (Impact of Phenology and Environmental Conditions on BVOC Emissions from Forest Ecosystems) project. We will analyse the three main BVOC species (isoprene/monoterpenes and methanol) in order to illustrate the interest of long-term flux measurements by investigating the main driving variables and the underlying mechanisms of emission/deposition, how de novo carbon allocation to the isoprene/monoterpenes skeleton structure is altered through the time. For methanol, we will show the importance of deposition on a long-term basis and use an empirical model to discriminate the physical and physiological components of the exchange. [less ▲]

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See detailOverview of CO2 dynamics within sea ice
Delille, Bruno ULg; Geilfus, Nicolas-Xavier ULg; Vancoppenolle, M. et al

Conference (2011)

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See detailRespiration of three Belgian crops: Partitioning of total ecosystem respiration in its heterotrophic, above- and below-ground autotrophic components
Suleau, Marie ULg; Moureaux, Christine ULg; Dufranne, Delphine ULg et al

in Agricultural and Forest Meteorology (2011), (151), 633-643

An experimental system combining an eddy covariance system, a micrometeorological station and soil chambers placed in planted areas and in root exclusion zones was installed during three successive years ... [more ▼]

An experimental system combining an eddy covariance system, a micrometeorological station and soil chambers placed in planted areas and in root exclusion zones was installed during three successive years in a production crop managed in a traditional way at the Lonzée experimental site (Belgium). Measurements were made successively on seed potato, winter wheat and sugar beet. The general objectives of the study were, first to evaluate the relative contributions to total ecosystem respiration (TER) of heterotrophic, above ground autotrophic and below ground autotrophic respiration over a succession of three agricultural crops (seed potato, winter wheat and sugar beet) cultivated on successive years at the same location and, secondly, to identify the driving variables of these contributions. Results showed that, during the observation periods, TER was dominated by autotrophic respiration (AR) (60–90%) and that AR was dominated by its above ground component (60–80%). HR was found to increase with temperature and to be independent of Gross Primary Production (GPP), whereas AR was driven by GPP and was mostly independent of temperature. The AR response to GPP was specific to the crop: not only AR intensity but also AR distribution between its above- (ARa) and below- (ARb) ground components were found to differ from one crop to another and, in the winter wheat, from one development stage to another. Generally, ARb contribution to AR was found larger when carbon allocation towards roots was more important. An uncertainty analysis was made and showed that the main sources of uncertainties on the estimates were the spatial variability for soil chamber measurements and uncertainties linked to the data gap filling method for eddy covariance measurements. [less ▲]

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See detailFirst space-based derivation of the global atmospheric methanol emission fluxes
Stavrakou, T.; Guenther, A.; Razavi, A. et al

in Atmospheric Chemistry and Physics (2011), 11

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See detailIsoprene and monoterpene emissions from a mixed temperate forest
Laffineur, Quentin ULg; Aubinet, Marc ULg; Schoon, N. et al

in Atmospheric Environment (2011), 45

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See detailDynamic processes in sea ice captured by the temporal evolution of its biogeochemical
Zhou, Jiayun; Tison, Jean-Louis; Eicken, Hajo et al

in VLIZ Special Publication (2011), 48

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See detailNight-time airflow in a forest canopy near a mountain crest
Sedlak, Pavel; Aubinet, Marc ULg; Heinesch, Bernard ULg et al

in Agricultural and Forest Meteorology (2010), 150(5), 736-744

Night-time airflow within a deep and dense canopy near the top of a mountain ridge is investigated based on measurements at Bily Kriz, Czech Republic. The site is characterized by a young Norway spruce ... [more ▼]

Night-time airflow within a deep and dense canopy near the top of a mountain ridge is investigated based on measurements at Bily Kriz, Czech Republic. The site is characterized by a young Norway spruce forest on a 13 degrees slope and the occurrence of almost exclusively upslope or downslope flows. The forest canopy reaches the ground surface. A decoupled two-layer structure of canopy flow typically develops at night. While the above-canopy flow is most frequently an upslope-directed larger-scale flow over the ridge, the lower-canopy flow is downslope (katabatic). However, the lower-canopy flow can be forced upslope when the wind speed above the canopy exceeds a well-defined limit. Less frequently, on the lee slope to the larger-scale flow, both the above-canopy and the lower-canopy flow are usually downslope, although a flow reversal in the lower canopy is also observed, accompanied with a large shear stress (friction velocity) above the canopy. The occurrence of opposing flows is not limited to sunset/sunrise transition periods. In a simplified modelling approach to the dynamics of the nocturnal lower-canopy flow decoupled from above, local equilibrium is assumed of solely two opposing driving forces - one induced by the negative buoyancy (due to radiative cooling of the canopy) and the other by the hydrodynamic pressure gradient (resulting from the larger-scale flow over the ridge) - and the canopy drag as a retarding force. The diagnostic model gives realistic values of the major driving terms for Bily Kriz, and the downslope or upslope direction and speed of the lower-canopy flow that agree well with the measurements. The model contributes to better interpretation of the experimental results, which are in accordance with recent publications on the flow patterns on forested hills. Knowledge of the lower-canopy flow behaviour and of the degree of its decoupling from the flow aloft is necessary for assessing the contribution of advection to the CO2 budget at sloping forest sites, and for analysis of the flux footprint. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailDirect advection measurements do not help to solve the night-time CO2 closure problem: Evidence from three different forests
Aubinet, Marc ULg; Feigenwinter, Christian; Heinesch, Bernard ULg et al

in Agricultural and Forest Meteorology (2010), 150(5), 655-664

The ADVEX project involved conducting extensive advection measurements at three sites, each with a different topography. One goal of the project was to measure the [CO2] balance under night-time ... [more ▼]

The ADVEX project involved conducting extensive advection measurements at three sites, each with a different topography. One goal of the project was to measure the [CO2] balance under night-time conditions, in an attempt to improve NEE estimates. Four towers were arranged in a square around a main tower, with the sides of the square about 100 m long. Equipped with 16 sonic anemometers and [CO2] sampling points, the towers were installed to measure vertical and horizontal advection of [CO2]. Vertical turbulent fluxes were measured by an eddy covariance system at the top of the main tower. The results showed that horizontal advection varied greatly from site to site and from one wind sector to another, the highest values being reached when there were large friction velocities and fairly unstable conditions. There was less variation in vertical advection, the highest values being reached when there were low friction velocities and stable conditions. The night-time NEE estimates deduced from the mass balance were found to be incompatible with biologically driven fluxes because (i) they varied strongly from one wind sector to another and this variation could not be explained in terms of a response of the biologic flux to climate, (ii) their order of magnitude was not realistic and (iii) they still showed a trend vs. friction velocity. From a critical analysis of the measurement and data treatment we concluded that the causes of the problem are related to the representativeness of the measurement (control volume size, sampling resolution) or the hypotheses underlying the derivation of the [CO2] mass balance (ignoring the horizontal turbulent flux divergence). This suggests that the improvement of eddy flux measurements by developing an advection completed [CO2] mass balance at night would be practically difficult. (C) 2010 Elsevier B.V. All rights reserved. [less ▲]

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See detailLong term carbon dioxide exchange above a mixed forest in the Belgian Ardennes: evaluation of different approaches to deduce total ecosystem respiration from Eddy covariance measurements
Jerome, Elisabeth ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg

Poster (2010, May 05)

The general aim of this research is to analyze inter annual variability of carbon dioxide (CO2) fluxes exchanged by a mixed forest located at the Vielsalm experimental site in Belgium. At this site, CO2 ... [more ▼]

The general aim of this research is to analyze inter annual variability of carbon dioxide (CO2) fluxes exchanged by a mixed forest located at the Vielsalm experimental site in Belgium. At this site, CO2 flux measurements started in 1996 and are still going on. Thirteen complete years of measurements are thus available. Net Ecosystem Exchange (NEE) inter annual variability may be driven by gross primary productivity (GPP) or Total Ecosystem Respiration (TER), which should thus be both quantified. Using flux partitioning methods, TER is deduced from NEE measurements. GPP is then obtained by subtracting TER from NEE. Initially, a robust estimation of TER is required. This work seeks to compare two independent approaches to assess TER in order to quantify the implications on inter-annual variability. The comparison was performed on twelve complete years. TER estimates can be deduced by extrapolating to the whole day NEE measurements taken during selected night or day periods. In both case, the extrapolation is performed by using a respiration response to temperature. The first approach, referred as the night-time approach, consisted in calculating TER using a temperature response function derived from night-time data sets (Reichstein et al., 2005). The second approach, referred as the daytime approach, consisted in assessing TER from the intercept of the NEE/Photosynthetically Photon Flux Density (PPFD) response (Wohlfahrt et al., 2005). For each approach, different modalities were compared: the use of long term (annual) or short term (15 days) data sets for the night-time approach and the use of different types of regression for the daytime approach. In addition, the impact of the temperature choice was studied for each of the approaches. For the night-time approach, main results showed that air temperature sensitivity of ecosystem respiration derived from annual data did not reflect the short-term air temperature sensitivity. Vielsalm is a summer active ecosystem (annual temperature sensitivity larger than short-term temperature sensitivity). Results suggested also that, for both approaches, regressions based on soil temperature gave more robust results than those based on air temperature. Furthermore, the comparison showed that the night-time and the daytime approaches give disagreeing pictures of TER inter annual variability which suggested that the choice of the approach is critical in order to correctly depict TER inter annual variability. Finally, at this stage, TER inter annual variability cannot be explained by variability of climatic conditions. [less ▲]

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See detailVOC emissions from a temperate mixed forest in Belgium measured by eddy-covariance
Laffineur, Quentin ULg; Heinesch, Bernard ULg; Aubinet, Marc ULg et al

Poster (2010, May)

Forest ecosystems are known to be important emitters of Biogenic Volatile Organic Compounds (BVOC). They play an important role in the atmospheric chemistry and may contribute to the formation of ozone ... [more ▼]

Forest ecosystems are known to be important emitters of Biogenic Volatile Organic Compounds (BVOC). They play an important role in the atmospheric chemistry and may contribute to the formation of ozone and aerosols with consequences on air quality and on climate. In order to better understand the effects of environmental parameters on the emissions, micrometeorological flux measurements were carried out above a mixed forest (Fagus sylvatica, Pseudotsuga menziesii, Abies alba, Picea abies) at the Vielsalm experimental site (Belgium) from July to November 2009. The flux measurements were obtained by the eddy-covariance technique using proton transfer reaction mass spectrometry. In our first measurement campaign, among other VOC compounds, isoprene (m/z 69) and monoterpenoid compounds (m/z 137) have been measured continuously with a data coverage of 75 and 58 % respectively, allowing robust statistical analysis. In our analysis, we focused on these two main emissions. A footprint analysis showed that Fagus sylvatica seems to be the main emitter of m/z 137 and Abies alba seems to be the main emitter of m/z 69. BVOCs fluxes present an exponential response to temperature. This response is more pronounced for m/z 69 while it shows the strongest seasonal evolution for m/z 137. A light dependence of m/z 69 and m/z 137 fluxes was observed but the relationship did not exhibit the same behaviour before (hyperbolic relation) and after midday (linear relation). This behaviour difference induced a hysteresis effect on the daily evolution of averaged fluxes. A robust local minimum was also observed just before midday for m/z 69 (less obvious for m/z 137) during July-August period. This minimum is not observed in the CO2 fluxes which are also measured in Vielsalm. The light dependence of BVOC emissions suggests that m/z 69 and m/z 137 emissions are directly linked to the photosynthetic cycle but the presence of the midday local minimum suggests that other processes influence the measured BVOC fluxes. As for the relation with air temperature, a seasonal evolution of flux-light dependence was far more evident for m/z 137 than for m/z 69. This seasonal variation could be explained by a phenological effect. As Fagus sylvatica is the main m/z 137 emitter, its flux is probably influenced by leaves ageing while m/z 69, as mainly emitted by Abies alba, is less influenced by needles ageing. A wind speed dependence of BVOCs fluxes was also observed, the flux increasing linearly with wind speed. This surprising result will be discussed. [less ▲]

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