References of "Longdoz, Bernard"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailShort-term temperature impact on soil heterotrophic respiration in limed agricultural soil samples
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

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

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

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

Detailed reference viewed: 67 (17 ULg)
Full Text
Peer Reviewed
See detailEvaluation of the potential of MODIS satellite data to predict vegetation phenology in different biomes: An investigation using ground-based NDVI measurements
Hmimina, G.; Dufrêne, Eric; Pontailler, J.-Y. et al

in Remote Sensing of Environment (2013), (132), 145-158

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote ... [more ▼]

Vegetation phenology is the st udy of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenologicalmetrics are derived fromtime series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and fromradiometric data obtainedwith high accuracy fromground-basedmeasurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the in uence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the in exion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE<oneweek). Phenologicalmetrics identical to those providedwith theMODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately twoweeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series ismore likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. [less ▲]

Detailed reference viewed: 34 (3 ULg)
Full Text
Peer Reviewed
See detailHorizon Partitioning of soil CO2 sources and their Isotopic Composition (13C) in a Pinus Sylvestris
Goffin, Stéphanie ULg; Parent, Florian; Plain, Caroline et al

Poster (2012, December 07)

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

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

Detailed reference viewed: 44 (3 ULg)
Full Text
See detailSoil Respiration in forest Ecosystems: Combination of a multilayer Approach and an Isotopic Signal Analysis
Goffin, Stéphanie ULg; Longdoz, Bernard; Maier, Martin et al

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

Detailed reference viewed: 109 (6 ULg)
Full Text
Peer Reviewed
See detailApport de l'approche multicouche et du signal isotopique pour la compréhension de la respiration du sol en écosystème forestier
Goffin, Stéphanie ULg; Longdoz, Bernard; Aubinet, Marc ULg

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

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

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

Detailed reference viewed: 58 (9 ULg)
Full Text
Peer Reviewed
See detailModeling soil heterotrophic respiration with an enzyme-based model: first comparison with field data and suggestions of improvements
Buysse, Pauline ULg; Longdoz, Bernard; Debacq, Alain ULg et al

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

Detailed reference viewed: 23 (11 ULg)
Full Text
See detailMultilayer Analysis of Soil Respiration and its Isotopic Signature in Forest Ecosystem
Goffin, Stéphanie ULg; Longdoz, Bernard; Maier, Martin et al

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

Detailed reference viewed: 45 (22 ULg)
See detailInput of 12CO2 and 13CO2 soil concentration measurements to understand trends in soil carbon production and emission.
Longdoz, Bernard; Plain, Caroline; Parent, Florian et al

Poster (2011, April 05)

Detailed reference viewed: 18 (4 ULg)
See detailCombination of different techniques and multi-scale approach to understand CO2 budget in a temperate beech forest
Longdoz, Bernard; Epron, Daniel; Goffin, Stéphanie ULg et al

Conference (2010, November)

Detailed reference viewed: 8 (0 ULg)
Full Text
Peer Reviewed
See detailCross-calibration functions for soil CO2 efflux measurement systems
Ngao, Jerome; Longdoz, Bernard; Perrin, Dominique ULg et al

in Annals of Forest Science : a Multidisciplinary and International Journal (2006), 63(5), 477-484

Different soil CO2 efflux measurement systems and methodologies were used to estimate the annual soil respiration of different forest sites. To allow comparison between these annual values, this study ... [more ▼]

Different soil CO2 efflux measurement systems and methodologies were used to estimate the annual soil respiration of different forest sites. To allow comparison between these annual values, this study aimed to cross-calibrate five soil CO2 efflux (RS) closed dynamic chamber systems, and compare the in situ measurement methodologies. We first assessed the impact of the measurement methodology on RS by studying the effects of three parameters: record duration, time lag before starting to record and the mode of chamber-soil contact (use of collars or insertion of the chambers into the soil). Secondly, we directly compared systems with identical methodology during field measurements on three forest sites. We observed a significant influence of the chamber-soil contact mode (no impact of the record duration and duration before starting to record). Measurements obtained by insertion led to significantly higher estimates of RS than those obtained using collars (up to 28%). Our inter-comparison showed that deviations existing between in situ measurements performed with the different systems were partly systematic and could be corrected using simple linear equations. Measurements of pressure difference between the inside and the outside of soil chambers allowed explaining a part of the observed deviations between systems. Finally, we assessed the influence of the cross-calibration equations on annual respiration of two beech forest soils. [less ▲]

Detailed reference viewed: 41 (3 ULg)
Full Text
Peer Reviewed
See detailAn Analysis of Soil Respiration across Northern Hemisphere Temperate Ecosystems
Hibbard, K. A.; Law, B. E.; Reichstein, M. et al

in Biogeochemistry (2005), 73(1), 29-70

Detailed reference viewed: 14 (1 ULg)
See detailMeasurements of heat, water vapour and CO2 fluxes above a mixed forest
Aubinet, Marc ULg; Longdoz, Bernard; Yernaux, Michel et al

in Shimizu, H. (Ed.) Carbon dioxide and vegetation : Advanced approaches for absorption of CO2 and responses to CO2 (2001)

Detailed reference viewed: 10 (0 ULg)
Full Text
Peer Reviewed
See detailThe faint young sun climatic paradox: Influence of the continental configuration and of the seasonal cycle on the climatic stability
Longdoz, Bernard; François, Louis ULg

in Global and Planetary Change (1997), 14(3-4), 97-112

A quasi-three-dimensional climate model is used to study the early state of the Earth when the solar luminosity was 70% of the present value, Usually, climatic simulations going back to this period lead ... [more ▼]

A quasi-three-dimensional climate model is used to study the early state of the Earth when the solar luminosity was 70% of the present value, Usually, climatic simulations going back to this period lead to a completely frozen planet contrasting with the geologic evidences of sedimentary rock formation and thus of the presence of liquid water at the surface of the continents during the Archean (4.6-2.5 billion years before present). Here, several model simulations are performed for solar luminosities varying between 0.7 and 1 times the present value. Using the present-day continental configuration and taking the seasonal cycle into account, a steady state is found in which glaciation is complete but snow covers only some oceanic coasts, leaving the continents essentially snow-free. As a result, the albedo of the continental area is strongly reduced compared to that of the frozen ocean, Some continental temperatures can almost reach the freezing point of water in summer (-1 degrees C in the center of Eurasia). This result can be explained by the behavior of the detailed hydrologic cycle included in the model. During the decrease of the solar luminosity, the jump to a completely frozen Earth occurs when the solar luminosity reaches 0.86 times its present value. The behavior of the climatic system is substantially different with a global ocean configuration. In the absence of land surfaces, the meridional heat transport, explicitly calculated, is less effective and the glaciation of a model latitude zone does not lead to the glaciation of its equatorward neighbor. The climate instability is relatively local and the jump to the completely frozen state is much more progressive than in the case of the modem continental configuration. The role of the seasonal cycle in the paleoclimatic simulation is also studied. Due to the non-linearity of the model, removing the seasonal cycle drives the system to an increase of the annual mean planetary albedo and to a decrease of the relative value (0.82) of the critical solar luminosity at which the jump to the completely frozen solution occurs. [less ▲]

Detailed reference viewed: 17 (1 ULg)